Bean

Common bean (Phaseolus vulgaris)

Common bean (Phaseolus vulgaris L., syn. Phaseolus vulgaris Savi) belongs to the genus Phaseolus, family Fabaceae (Fabaceae). Less commonly, other names may be used: French, garden, snap, stick, haricot, bush, field and green bean.

It is represented by bush (dwarf determinate), semi-climbing and climbing (indeterminate) forms. Modern determinate bush cultivars differ from earlier indeterminate climbing cultivars by lower apical dominance and little or no response to short-day photoperiod. Indeterminate climbing cultivars and vertical cultivars branch more and, due to the presence of more flowering nodes, have greater yield potential.

Common bean is an annual warm-season plant with a herbaceous stem, woody at the base. The height of bush forms reaches 25–60 cm with a small number of nodes and terminal inflorescences. Climbing forms can reach 2–3 m in length and have up to 25 flowering nodes. Climbing forms lodge heavily, so they are usually supported on poles or a trellis.

The root system is taprooted. Usually the root system of many bean cultivars is small and not extensive, and lateral branches are shallow. The main root is usually short, but on deep loose soils it can reach about 1 m. In the presence of Rhizobium bacteria, nodules develop on lateral roots. A root system that firmly anchors the plant is an important characteristic for mechanical harvesting.

Leaves are pinnately trifoliate (trifoliate), often pubescent. Shape ranges from rhombic to broadly ovate. Modern cultivars have small leaves, which improves light penetration into the canopy, especially at high sowing density. Although this characteristic tends to increase total yield, small leaf size is associated with small bean size. Leaf colour varies from yellow-green to blue-green.

Inflorescence is a raceme with 2–8 flowers, located in leaf axils. The flower is large, perfect, papilionaceous, white, pink or purple. There are 10 stamens, 9 of which are united into a tube enclosing the long ovary; one upper stamen is free from the others. Bean is a self-pollinating plant, sometimes cross-pollination by insects is noted.

The fruit is a 3–10-seeded pod. The number of seeds is one of the characteristics of a cultivar; most bean cultivars contain from three to five seeds. Depending on the cultivar, the pod can have a varied shape, from straight to sabre-shaped, with a straight or curved beak. Pod length is almost always significantly greater than width; length varies from 8 to 20 cm and more, and width from less than 1 to several cm. The colour of immature pods is yellow, green, but in some cultivars (borlotti bean, also known as cranberry bean) it can be white with contrasting marbled red spots on the surface. Other species or cultivars may be purple or almost black. In mature pods grown for dry harvest, for example navy bean, the pod colour is usually tan. Depending on the cultivar, the cross-section shape varies from round to elongated-oval, and some are heart-shaped.

The dehiscence characteristic of the bean pod as a means of seed dispersal is due to the presence of lignin along the pod suture line; this, along with the fact that ripening seeds are enclosed in a parchment-like inner wall, is a desirable characteristic for crops harvested dry, but not for crops harvested as fresh pods for the vegetable market.

The amount of pod fibre and the rate of its development also vary. Through breeding, the amount of fibre has been significantly reduced. The stringless cultivar was developed more than 100 years ago. Currently only reproductive and other old bean cultivars possess strong, string-like suture fibre. Calvin Keeney, a seed grower from Le Roy, New York, is considered the author of the first stringless cultivar, developed around 1800. Stringlessness is a recessive trait and is present in most currently grown cultivars. Stringless cultivars also contain fewer wall fibres. The word “string” was used because of the strong string-like fibres on the dorsal and ventral sutures of the pod, with the dorsal being the strongest. When the seeds fully ripened, the pod burst. The term “snap” probably arose from the sound produced when fresh pods are broken. Most common bean pods are glabrous, some have pubescence. Pods do not have a tough calyx like peas.

Pods are attached low on the stem and ripen unevenly, which greatly complicates harvesting.

The size and weight of mature seeds vary greatly: seed length ranges from 5 to 20 mm, and the weight of individual seeds of some cultivars varies from 0.15 to more than 0.80 g. Seed shape is round, rounded, ovate, oblong and kidney-shaped. The colour of the seed coat depends on the cultivar and can have many colours and combinations, which is of certain importance. Interestingly, in different countries of Latin America a certain seed coat colour is preferred: black coat — Brazil, El Salvador, Mexico and Venezuela; red — Colombia and Honduras; yellow — Peru; white — Chile. Cultivars grown for processing usually have white or light-coloured seeds. Other important characteristics of mature seeds are the thickness and adherence of the seed coat and the resistance of the cotyledon to cracking; cracking resistance is genetically linked to seed coat colour.

According to use, common bean (Phaseolus vulgaris) is divided into the following groups:

• French bean: green, yellow or purple fleshy pods containing underdeveloped seeds are eaten. Pods have no string or parchment layer.
• Haricot filet bean (Haricot filet bean): pods contain strings, but fleshy immature pods are eaten.
• Haricot (Haricot): fresh seeds are eaten, pods contain strings and fibres and are usually not eaten.
• Dry (field) bean: dry shelled seeds are eaten, pods contain strings, fibres, a tough parchment layer and are not eaten.

In domestic practice, bean cultivars depending on the presence of a parchment layer and fibres in the pod valves are divided into vegetable (asparagus, snap) and grain (shelling). In vegetable cultivars, pods are fleshy due to strong development of parenchyma and weak development of the parchment layer. In addition, the sclerenchyma of vascular bundles in some of them is not developed, so pods of asparagus cultivars are tender and suitable for food until seeds are formed. Pods of these cultivars do not split, but thresh poorly.

In shelling cultivars, the parchment layer develops early, and its thickness is significant — from 1/10 to 1/20 of the pod valve thickness. Therefore they are not used for food as green pods. The presence of the parchment layer is determined by breaking the pod, and to determine the presence of fibre, the tip of the pod is torn off. If a string stretches along the pod suture, then fibre is present.

Seeds of various colours, sometimes mosaic. 1000-seed weight 200–500 g.

Multiflora bean (Phaseolus multiflorus)

Multiflora bean (Phaseolus multiflorus Wild). It has a long climbing stem, large white and red flowers, and large flattened-elliptical seeds. 1000-seed weight 700–1200 g. Pods are short, wide with a beak. During germination it does not carry cotyledons above the soil surface. It came to Russia in the 18th century under the name “Turkish beans”.

Golden bean (Phaseolus aureus)

Golden bean, or mung bean (Phaseolus aureus Piper). A climbing or semi-climbing pubescent plant. It has long thin narrow many-seeded pods without a beak. Seeds are small, yellow or green, 1000-seed weight 30–60 g. In Central Asia and Transcaucasia it is used for food, and straw for fodder. It is more demanding for heat and moisture than common bean. It is cultivated in Asia, with small areas in the Far East.

Temperature requirements

Common bean is a heat-loving plant. The minimum temperature for germination of bean seeds is +8…+12 °C; seedlings appear at 12–13 °C. At temperatures below +8–10 °C germination slows, and many seeds rot. Temperatures above 35 °C also do not favour germination. The optimum temperature for seed germination is from 25 to 30 °C. Under good conditions seedlings appear within 7–12 days.

Effect of temperature on germination of common bean (National Garden Bureau, Inc. Downers Grove, IL.):

• at 10 °C germination was absent;
• at 15 °C germination occurred after 16.1 days;
• at 20 °C — after 11.4 days;
• at 25 °C — after 8.1 days;
• at 30 °C — after 6.4 days;
• at 35 °C — after 6.2 days;
• at 40 °C germination was absent.

Frosts down to -0.1…-1 °C are lethal to seedlings; according to other data, short-term frosts of -0.5…-1.5 °C are lethal to seedlings. Older seedlings can withstand light frosts.

Some cultivars (usually dark-coloured) can germinate at temperatures of 7–8 °C, and cultivars have also been bred that tolerate frosts down to -2 °C.

At the seedling stage, bean does not tolerate even short-term frosts and dies at temperatures of -0.5…-1.5 °C; at the flowering stage bean is damaged at temperatures of -0.5…-1.0 °C, and during the milk-ripe stage at -2.0 °C. A temperature of 0…+5 °C causes disruption of physiological processes, retardation of growth and development, lengthening the growing season by 10–27 days and reducing productivity by 10–70%.

An average air temperature of 20–25 °C is optimal for growth and high yield. Field bean grows better at lower temperatures and is more sensitive to high temperatures during flowering than bush cultivars. Heat stress negatively affects pod set, and some cultivars are more resistant to it than others. The favourable soil temperature range is 18–30 °C.

During budding and flowering, bean is also sensitive to elevated temperatures. At night temperatures from +17 °C to +27 °C or daytime temperatures from +22 °C to +32 °C, bud formation stops, and buds, flowers and ovaries up to 3 cm are shed. Ovaries larger than 3 cm stop growing and wilt under the action of high night temperatures. This is noted both under drought and under continuous irrigation and misting.

Bean develops and grows normally at an average daily air temperature not below +15 °C. The optimum temperature for growth and development depending on the phase of bean development is in the range +18…+30 °C.

Golden bean (mung bean) is the most demanding form for high temperatures. It is heat-tolerant.

Moisture requirements

Bean is considered a less moisture-demanding grain legume crop than peas, lentil or faba beans. However, during germination bean needs moisture.

For seed swelling, 104.5% (100–120%) water of their mass is required. A high water requirement is also noted in the flowering and pod-setting phases. Soil moisture during this period should be not lower than capillary moisture.

Bean is sensitive to drought and waterlogging. Ideally moisture should be evenly distributed throughout the growth period; usually 250–450 mm is sufficient. To obtain high yields, proper moisture management is necessary. Soil moisture should be close to field capacity, especially during flowering. According to other recommendations, the optimal soil moisture for bean is 50–85% of full water-holding capacity depending on soil and climatic conditions, plant development phase, application of fertilizers and biological characteristics of the cultivar.

After emergence, bean tolerates short-term drought until the budding phase. However, excessive air dryness causes wilting of leaves. Under severe prolonged drought, bean plants remain viable, but there is a significant reduction in productivity. With moisture deficiency, bean has an interruption in flowering, and growth processes stop. After normalisation of the water regime, flowering and pod filling resume, but the lag in plant development is not compensated.

During budding, flowering and pod formation, bean is especially sensitive to lack of moisture. If drought occurs during this period, wilting of leaves, reduction of pods and deterioration of their quality (thickening of the parchment layer in the valves) are observed, and shedding of buds, flowers and young pods may also occur. Vegetable bean is more moisture-loving than grain bean, therefore even in hot weather it significantly reduces yield.

Drought leads to a decrease in biomass, seed and pod yield, number and size of seeds, and also worsens colour, fibre content and elasticity. Under drought, ripening occurs, as under normal moisture, but can be shortened by 1–6 days. The average seed yield decreases by 27–62%.

Dry winds can cause flower shedding.

Excess moisture and waterlogging cause anoxia, to which bean is very sensitive, and lead to increased incidence of root rot.

Light requirements

Bean is a light-loving plant. Most modern bean cultivars are insensitive to photoperiod. Nevertheless, some cultivars are still used that develop flower buds only under short days.

The crop is especially sensitive to light in youth, less so during flowering. Under strong shading its seedlings become etiolated and weak, which negatively affects yield formation.

Bean passes the light stage of vernalization under a short light day, but there are cultivars that are neutral and also positively responsive to day length. These are mainly cultivars grown in northern latitudes. Under a short day, bean accelerates development and reduces growth, which is manifested in a decrease in plant height and other economically valuable traits.

Bean realises its light requirement by the ability to change the angle of leaf inclination relative to the sun's rays. This ability increases photosynthesis efficiency and is also used to prevent overheating of plants and excessive transpiration, but weakens the crop's ability to compete with weeds. Bean leaves face the sun and follow it, but during periods of excessive heat and low soil moisture the leaves turn parallel to the sun's rays.

Yield decreases when plants are shaded.

Soil requirements

Optimal soils for growing bean are light chernozems, sod-podzolic, sandy loam, light loam, loamy fertile soils, rich in lime, structured (medium-structured), medium-textured, not too wet, well drained, friable.

Optimal agrochemical parameters of the arable layer for bean:

• pH 6.5–7.5 (pHKCl — 6.0–7.0) (according to other recommendations, slightly acid soils with pH 6.0–6.5 are preferred, Rubatzky; also 6.0–8.0, Biddle);
• humus content (by I. V. Tyurin) — not less than 2%;
• content of mobile phosphorus and exchangeable potassium (by A. T. Kirsanov) — not less than 150 mg/kg soil.

Bean grows best on neutral soils. For example, most soils of South America and Africa are acidic, with high aluminium and manganese content and low phosphate content, so correction of pH by liming is usually practised, since bean is susceptible to aluminium toxicity.

In northern regions, light, well-warmed soils are considered best for bean. On cold soils with a close groundwater level, this crop reduces yield, and water stagnation on such soils for 2–5 days leads to complete death of plants.

Among bean species, tepary, lima and mung bean are less sensitive to soil salinity.

Unfavourable for cultivation are compacted, heavy, clayey, poorly warmed soils, with a high groundwater level, dense solonetzic and very light sandy soils. On wet peat soils bean yield is greatly reduced.

To obtain an early harvest, seedlings are planted on southern slopes protected from cold northern winds.

Germination

Germination of seeds of common bean and other species is epigeal, since the cotyledons of the seeds emerge from the soil together with the shoot. The first embryonic leaves develop from the shoot as one pair of opposite and (as a rule) ovate leaves. Then the remains of the embryo shrivel and fall off the stem, leaving two small scars. The shoot continues to develop, forming pinnate and mainly trifoliate true leaves.

Vegetative development

The stem continues to elongate, more leaves appear on lateral axes, their length can vary, and some branching may occur. Stems are round in cross-section; the lower part of the stem is usually erect without twining, while the upper part of the stem may begin to twine, as in some climbing species around a support. However, more determinate bean types tend to remain vertical and develop as bush forms.

Leaves develop oppositely and alternately up the stem, but buds develop in leaf axils, which in turn produce secondary leaf-bearing branches. Leaves are trifoliate, the two lateral leaflets are asymmetric, and the terminal leaflet is symmetric.

Among bean cultivars, two clearly different growth habits can be distinguished: determinate and indeterminate. The difference is that in the first case the main stem and lateral branches terminate in inflorescences, while in the second case the main stem and lateral branches are crowned with a vegetative meristem capable of continuing to grow and develop more leaves and flowers. In these indeterminate cultivars, flowers are located laterally, directly at the nodes of the main stem and lateral branches.

Determinate types have been described by two main characteristics: with few nodes and with many nodes. Types with few nodes have from three to seven trifoliate leaves on the main stem before the terminal double inflorescence; they have been selected for early maturity and are more suitable for growing in cool temperate climates. Multi-node types include types with 15–25 leaves on the main stem. In determinate types the plant is almost always erect due to short internodes, whereas in indeterminate types, due to long internodes, climbing ability is often observed. In these latter types, some have abundant branching and are spreading, while others have reduced branching and are often grown together with maize in the highland regions of the Andes (Debouck, 1991).

Root development

The bean root system consists of a fine branching system that is relatively shallowly developed. Multiple branching of adventitious roots occurs under non-compacted soil conditions. In the presence of Rhizobium bacteria, nodule development occurs mainly in clusters around the main root, but nodules can develop on any part of the root system and its branches.

While bean benefits from symbiotic relationships with soil Rhizobium, allowing nitrogen fixation, plants grown in non-native regions of the world, especially Europe, North America and Australia, where there are no natural populations of certain Rhizobium strains, require additional sources of organic or inorganic nitrogen. Some crops are grown using commercial Rhizobium inoculant formulations applied either to seeds before planting or as granules to the soil, but this is often less effective, and additional nitrogen is often required.

Flower development

Flowers are formed from axillary buds at the nodes of the main stem. These lateral branches or peduncles can produce several groups of up to three flower buds on bracts located on one or several peduncles. Flowers are typical of legumes (Fabaceae). Several flowers form on an axillary bud, which may end in a terminal inflorescence.

Pod development

Pod setting occurs acropetally from the base upwards, but flowers may drop, and this can occur on any of the inflorescences, with up to 50% flower loss noted during flowering and pod setting. Environmental conditions can influence flower retention, but the full list of causes is unclear.

Although insect pollinators assist in pollination of Phaseolus vulgaris, many flowers are self-sterile. After pollination, pods form, which botanically are dehiscent fruits; each side of the pod represents a carpel. In the natural state, pods split along the sutures to release seeds.

Micronutrients

Bean often suffers from micronutrient deficiency or toxicity.

Sulfur deficiency is manifested by the whole leaf becoming chlorotic in the lower part, and then affecting the upper leaves. This problem is especially relevant when using compound fertilisers that contain little or no additional sulfur.

Zinc deficiency causes interveinal chlorosis of young leaves, and necrotic spots appear on the leaf surface. Zinc is especially deficient on alkaline soils in some countries of America and Australia.

Boron deficiency usually occurs soon after germination, when beans are still small. In severe cases the growing point dies and secondary buds proliferate. Bean is very sensitive to excess boron in the soil.

Manganese toxicity occurs on soils of volcanic origin with pH less than 5.5, and can also be caused by excessive application of ammonium sulfate.

Seed preparation

Bean seeds are very fragile and susceptible to mechanical damage to the seed coat or cotyledons, where damage to the dehydrated embryonic plumule can occur as a fracture on the hypocotyl. Seeds with such damage germinate without a growing point, leading to a condition known as baldhead or snakehead. Improvements in seed harvesting equipment, for example the use of rubber belts for seed separation instead of metal cylinders, significantly reduce damage.

Germination is hypogeal, when the radicle expands, pushing the cotyledons above the soil surface until the cotyledon leaves expand.

Seed germination depends on temperature, and at soil temperatures below 10 °C this process practically does not begin. Bean requires conditions ensuring rapid germination and cotyledon emergence. In some cases, seeds planted early under cool conditions may emerge poorly, so several attempts have been made to develop a laboratory seed viability test. As with peas, the electrical conductivity test showed a relationship between high electrolyte leakage and low field emergence, but establishing a test score was difficult due to large differences in seed size. There appears to be a need for a separate set of results to interpret germination energy of large-seeded types compared with small-seeded ones. Another viability test used as an advisory tool in the UK is based on the use of tetrazolium chloride solution, when the abaxial surfaces of embryos are allowed to soak in the solution after removal of the seed coat, and the number of embryos with areas of unstained or unreacted tissue is recorded. The relationship between a large number of seeds with unstained areas and poor emergence has been shown in the UK and is used to identify seeds with poor potential for early sowing.

Preparation of bean seeds for sowing consists of sorting and air-thermal warming.

It is recommended to treat seeds with bacterial preparations.

When there is a deficiency of micronutrients in the soil, it is recommended to treat seeds with micronutrient fertilizers:

• when the manganese content in the soil is less than 3.0 mg/kg, it is recommended to treat seeds with manganese sulfate solution at the rate of 80–120 g MnSO₄ per 1 t of seeds;
• when the zinc content in the soil is less than 1.0 mg/kg, it is recommended to treat seeds with zinc sulfate solution at the rate of 150–200 g ZnSO₄ per 1 t of seeds.

When treating seeds with micronutrient fertilisers, the adhesive NaCMC (0.2 kg/t) is used; the solution consumption should be 10 l/t. After treatment, seeds should have a moisture content of no more than 14%.

Protective fungicidal seed treatment is useful for minimising rotting. Seeds are often tested for germination in cold soil to determine their viability under adverse conditions. Cultivars with white seed coats often showed poor emergence compared with similar cultivars with dark seed colour. Breeders have corrected this feature in new cultivars with white seed coats.

Sowing dates

Sowing methods

The sowing method is wide-row. Row spacing in the main growing areas and areas of insufficient moisture is 60 cm, in northern areas 45 cm. Sometimes seeds are planted in a shallow furrow, which is then covered during cultivation.

To obtain high yields, many bush forms are grown at a density of about 40 plants/m². High density is achieved by close row arrangement or wide-row sowing. Such growing is not suitable for hand harvesting, but is well suited for mechanical harvesting.

Wide row spacing is used so that the crop can be harvested repeatedly by hand when bean is grown on a trellis. Trellis planting of bean is usually carried out at a distance of about 10 cm from each other in the row with row spacing from 120 to 150 cm. Hill plantings with pole support are placed at equal distances from each other, from 90 to 120 cm. Hill plantings are usually sown with five or six seeds per hill, later thinned to three plants.

Planting density for hand harvesting of bush bean is from 45 to 60 thousand plants per hectare, whereas for mechanised harvesting with high planting density from 250 to 450 thousand plants per hectare are grown. The use of frontal multi-row harvesters has facilitated the practice of narrow-row high-density planting. Although very close plant spacing generally reduces pod colour, this is often an acceptable sacrifice for obtaining high yield. However, high planting density increases the potential for diseases. The widespread use of precision seeders ensures accurate plant spacing and reduces the amount of seed sown; the high cost of seed also leads to a reduction in seeding rate.

In some parts of the tropics and subtropics, bean is grown together with maize or okra (Abelmoschus esculentus) or after them, often using the stems of these crops for support.

In Europe, the USA and other developed regions, large-scale planting operations depend on precision seeders capable of planting beans at uniform depth with uniform spacing both between seeds and between rows. They can be planted in wide beds about 2 m across or with uniform row distribution across the field. Such planting requires a well-formed seedbed with sufficient moisture for uniform and rapid germination and emergence.

Small-seeded forms are sown with grain seeders, large-seeded with maize or cotton seeders.

For processing enterprises using combine harvesting, sowing is carried out with a SPV-6V seeder or other sowing units on a flat surface with row spacing of 45 cm and distance between plants in the row of 8–9 cm. The seeding rate of viable seeds is 240–280 thousand pcs/ha. For conveyor supply of products and uniform loading of the line with products, it is necessary to sow cultivars of different maturity groups in several dates, usually with an interval of 8–12 days.

To obtain fresh bean pods, sowing on narrow-profile beds 10–12 cm high, with bed surface width 25–30 cm, row spacing 70 cm, and distance between plants in the row 7–8 cm can be used. For this, the combined sowing unit AKP-4 can be used. The seeding rate of viable seeds is 170–200 thousand pcs/ha. Seed placement depth: on light soils 4–5 cm, on medium soils 3–4 cm. With insufficient moisture, seed placement depth is increased by 1 cm. For this unit, pre-sowing soil preparation is not required, since it itself immediately forms beds and sows.

In some regions, the sowing method is determined by temperature, the onset of the rainy season and altitude above sea level (Woolley et al., 1991). In tropical and subtropical regions, bean can be sown together with maize or other crops, and therefore different approaches are applied to their sowing. In these regions, bush and climbing bean forms can be grown both alone and in combination with each other.

Seeding rates and plant density

Seeding rate 0.25–0.4 million/ha viable seeds. Weight rate for small-seeded cultivars is 70–80 kg/ha, for large-seeded 100–150 kg/ha.

Snap bean responds strongly to changes in plant density. Mechanical harvesters are capable of harvesting bean from several rows, and although bean can be grown on beds where each bed 1 m wide contains four rows, it can also be planted without beds. Usually row spacing is 50–90 cm, and distance between seeds is about 5–10 cm. Seeds are sown to a depth of 5–10 cm, depending on soil type and moisture. The optimum density is 60 plants/m².

For large-scale commercial dry bean production in Canada and other countries where large-scale production is carried out, sowing is mainly on narrow row spacing (50 cm) or wide rows (75–90 cm). The choice of row spacing depends on the farming system: narrow rows are preferred for cereals or oilseed crops, and wide rows for those growing other row crops such as potato or maize. Plant density is 17–25 plants/m². Inter-row cultivation can be carried out while plants are small. After drilling, the soil is usually rolled to compact soil and stones to reduce soil mass at harvest (Goodwin, 2003).

In small production systems in tropical and subtropical countries, beans can be sown together with maize. Various systems and combinations can be used, depending on land availability and economic conditions. Relay intercropping of bush or semi-bush beans planted immediately after maize maturity is especially common. A second combination is when beans are planted between maize rows at the same time, although in some areas the difference between the two harvest periods is several weeks. Another system is planting beans with other crops such as bananas, cassava, sweet potato, coffee and young sugarcane. Each system is described in detail by Woolley et al. (1991). Intercropping usually gives low yield, but the advantage for small farmers is reduced risk if one crop fails. Different systems require different sowing densities, which were reviewed by Woolley and Davis (1991).

Sowing depth

Since bean carries cotyledons above the soil surface, sowing depth is shallow — 3–5 cm. When the top layer dries out, sowing depth is increased to 6–8 cm.

Mixed crops

Under conditions of sufficient moisture, bean crops can be combined with maize and potato.

Seedling Method

High-moor peat is well suited for preparing the nutrient mixture.

To obtain the optimal nutrient content in the mixture, the following are added to high-moor peat: 0.7-0.8 kg/m³ of ammonium nitrate; 0.9-1.0 of superphosphate; 0.6-0.7 of potassium sulfate; 0.5-0.6 of magnesium sulfate; 5.5-6.0 of chalk; and 5.1-5.5 kg/m³ of dolomite powder. Before preparing the mixture, it is recommended to conduct a chemical analysis and, if necessary, adjust the recommended doses.

Agrochemical parameters of the peat mixture (Autko):

• pH of the water extract — 5.8-6.5;
• NH₄ — 15-20 mg/dm³;
• NO₃ — 130-150 mg/dm³;
• P₂O₅ — 30-40 mg/dm³;
• K₂O — 200-250 mg/dm³;
• CaO — 170-210 mg/dm³;
• MgO — 60-70 mg/dm³.

Plastic plug trays measuring 40 × 40 cm with 64 cells, each 65 cm³ in volume, are suitable for growing seedlings. The trays are filled with substrate and compacted to 3/4 of their volume, then one seed is placed in each cell, the remaining part of the cell is filled, and it is lightly compacted. After sowing, watering is carried out.

Until the seeds germinate, the air temperature is maintained at +20…+25 °C; after germination, at +17…+20 °C; the substrate temperature should not be higher than +15 °C. Because of the small volume of substrate and its rapid drying out, watering is recommended several times a day.

The use of trays simplifies seedling care and field planting. It should be taken into account that beans have large seeds and their roots quickly colonize the volume of soil in the cell. Therefore, no later than 15 days after sowing the seeds into the trays, the seedlings (at the stage of two primordial leaves) must be planted in the field. If planting is delayed, the root system grows beyond the substrate, the root tips dry out, and the base of the stem lignifies. Such seedlings are unable to ensure a high yield.

Transplanting seedlings into the field is carried out when the average daily air temperature reaches +14 °C.

Bean seedlings are grown when weather conditions are sufficiently warm and greenhouses are not required. The trays can be placed in well-warmed areas protected from cold winds on wooden pallets, which can be covered with film. Such structures do not require large expenses, and the cost of production remains relatively low. When the temperature rises sharply during the day, the film is opened slightly for ventilation and watering.

3-4 days before planting, the seedlings are hardened off: during the day the temperature is maintained at +14…+16 °C, at night at +12…+14 °C, with moderate watering. Before planting, the plants are watered abundantly.

The field planting pattern for seedlings depends on the machinery used and the tractor tramline. Row spacing is usually 60-90 cm, and the distance between plants in a row is 10-15 cm. With such patterns, 110,000-130,000 plants are placed per hectare. Watering seedlings at a rate of 0.5 L of water per plant is mandatory.

Cultural Control Methods

When growing beans, which are often grown with wider row spacing than peas, mechanical weed control can be carried out at several stages of crop growth. The critical period for weeding is between 3 and 6 weeks after planting to preserve maximum yield (Burnside et al., 1998). Using the stale seedbed method initially, with irrigation if necessary, will promote early germination of weed seedlings, which can then be lightly worked. Post-planting inter-row cultivations should be carried out with a hoe to a depth that will not disturb the developing bean roots.

Weeds are less of a problem in intercropped or mixed crops. If beans are grown together with maize, these crops fill more than one ecological niche and thus compete effectively with a larger number of weed species. In cases where beans follow maize, producers pay great attention to weed control in maize in order to reduce the number of germinating weed seeds before planting beans (Woolley and Davis, 1991).

Biofumigants

Biofumigants have been used for many years, and significant research is currently continuing into the use of these methods on annual crops. The technique is based on incorporating fresh, mulched plant material into the soil, which releases several substances capable of suppressing soilborne pests or diseases, and in some cases it is claimed that weeds are also suppressed. Plants of the genus Cabbage (Brassica spp.) are particularly active sulfur accumulators and synthesize significant amounts of sulfur-rich glucosinolates. Damaged leaves release myrosinase enzymes, which break down glucosinolates into several products, including isothiocyanates (which are very toxic). Work has shown that these products are active against some soilborne diseases and pests, but there are claims that weed suppression can also be achieved.

Growing a Brassica cover crop for use as a biofumigant involves establishing an autumn sowing of the crop, usually mustard, in particular brown mustard (Brassica juncea), although other members of the cabbage family (Brassicaceae) may be used.

While the use of such cover crops has a number of advantages in agriculture, such as providing a nutrient source for new developing crops, helping to improve soil structure by adding organic matter, and having a certain effect on suppressing pests such as nematodes, there is little reliable information that this technique can become a sustainable means of weed suppression in pea and bean crops. It has been suggested that crucifers may have an allelopathic effect on weeds, and reports from Europe and North America also state that crucifers can be used for integrated weed management (Tollsten and Bergstrom, 1988; Turk et al., 2005). However, there are no reliable data indicating a reduction in weed numbers in the growing crop (Haramoto and Gallandt, 2005a,b). Similarly, there are reports of suppression of black-grass (Alopecurus myosuroides) with a mustard cover crop preceding spring sowings of fodder beans (Jim Scrimshaw), but the effect was not repeated in beans from year to year, although other work on winter cereals has shown significant suppression. This may be partly due to insufficient persistence of glucosinolates in the soil during the weed germination period, or other factors may be involved.

Herbicides

In the UK and Europe, there is a limited range of herbicides for this crop. The contact herbicide diquat, applied pre-emergence, destroys weeds present at the time of spraying. Pre-emergence application of S-metolachlor, linuron and pendimethalin plus clomazone is permitted and can provide useful pre-emergence weed control. However, there is a restriction on the use of S-metolachlor. Bentazone is the only post-emergence herbicide for broadleaf weed control. Under severe weed problems, an adjuvant oil can be added, but this may increase the crop damage effect. Wild oats can usually be controlled by soil cultivation before sowing. Cycloxydim controls annual as well as perennial grasses, but not annual bluegrass (Poa annua).

Before crop emergence, it is recommended to treat crops with soil herbicides: Gesagard, SC or Gesagard, WP or Stomp, 33% SC. Later, when weed seedlings appear, it is recommended to carry out two sprayings of the crops with split doses of the herbicide Basagran: the first in the phase of 2-3 true leaves of the crop; the second as weed seedlings appear, but not earlier than 7-14 days after the first treatment. The working solution consumption rate per treatment is 300 L/ha.

If beans are grown on narrow-profile ridges or in seedling culture, soil herbicides are not applied, and on the 5th-6th day after sowing an inter-row treatment is carried out. When weed seedlings appear, it is necessary to carry out two sprayings (0.4 + 0.4 L/ha) or three sprayings (0.3 + 0.4 + 0.4 L/ha) of the crops with split doses of the herbicide Basagran: the first in the phase of 2-3 true leaves of the crop; subsequent ones as weed seedlings appear with an interval of not less than 7-14 days after the previous treatment.

When using the KOU-4/6 cultivator developed by RUE “Institute of Vegetable Growing”, with correctly selected working parts, it is possible to achieve 95-98% weed destruction in the inter-row spaces. Application of herbicide with the KOU-4/6 cultivator-sprayer with simultaneous inter-row loosening allows reducing the working fluid consumption to 100-150 L/ha. Carrying out 3-4 such treatments eliminates manual labor for weeding bean crops. During flowering, treatments are stopped, since bean leaves and flowers break off easily.

Against weeds in bean crops, the herbicide prometryn, 50% WP, can be used at a rate of 3 kg/ha of the preparation. Spraying is carried out 2-3 days before emergence.

For beans (Vicia) and beans (Phaseolus sp.), bentazone is the only material safe for use as a post-emergence herbicide for controlling broadleaf (dicotyledonous) weeds. The selective action of bentazone may be related to differential retention and uptake, as well as the ability to metabolize bentazone (for more details, see Pea).

Green Beans (Immature Seeds)

The yield of green beans increases rapidly in the early stages of ripening, when the crop can be harvested for freezing, while in the later stages, when the crop can be harvested for canning, the yield increases more slowly.

Although it is not customary to establish a sliding payment scale for farmers depending on the degree of crop maturity, it is usually necessary to have an acceptable method for assessing maturity so that standards can be maintained.

The main stages of bean ripening can be briefly described as follows:

• rapid increase in pod length with relatively slow seed development;
• pod enlargement and more rapid seed enlargement;
• lignification, increased firmness and drying of the pod, as well as drying and hardening of the seed.

Several methods have been developed that measure the physical changes occurring during ripening and, as a rule, they are a more practical means of determining maturity than any chemical assessments.

A common assessment method is based on average seed length. Seed length is measured by measuring the total length of ten seeds, each being the largest seed taken from the largest pod taken from a sample of ten plants. Depending on the variety of bean used, the practical stage of suitability for freezing can be taken between 100 mm and 120 mm of seed length. For canning, seed length is greater.

Harvesting is carried out by a self-propelled bean harvester equipped with longitudinal pick-up drums that rotate along the row, and under the action of spring teeth attached to the drum, the pods are removed from the plant. They are lifted into the machine together with a certain amount of leaves and other debris. The pods are then lifted into the cleaning and sorting sections of the harvester. Light debris (mainly leaves and stems) is blown back onto the field. Pod seed separation devices are capable of handling large numbers of them, and the residues are also blown back onto the field. The beans are then unloaded into boxes and transported to the processing plant.

Freezing and canning operations are similar to those described for peas and beans.

For the Fresh Market (Pods)

The harvesting maturity of snap beans is determined by seed length every 2-3 days from 25 randomly selected plants; for this, pods are picked and the length of the largest seed is measured. Harvesting begins when the average length of the measured seeds reaches 5 mm (when the seeds reach a length of 8-10 mm, harvesting is stopped). Harvested pods are immediately delivered for processing.

To forecast and plan the yield of snap beans in developed countries, degree-days measurement is often used.

Harvesting begins when the pods reach consumer ripeness. During this period, they break off easily from the peduncle, the break point is smooth and juicy, and the dry matter content in the pods is 7-8% (at the end of harvesting, 9-12%).

Bean pods should be young (immature), fresh, clean, whole, healthy, with or without a peduncle. The color, taste and smell of the pods should correspond to the variety. It is necessary that the bean pods be juicy, fleshy, easily broken when bent, without bulges from seeds, at the break without coarse fibrous strings and inner leathery film, with rudimentary seeds. The presence of bean pods that are rotting, wilted, dirty, steamed, wet, with coarse seeds, with foreign odors or tastes caused by growing, transportation and storage conditions is not allowed.

In most countries of the world, manual harvesting of bush and field beans is common, since the use of machinery is impractical in many countries. Pods on poles with an indeterminate flowering period can be harvested over a longer period compared to bush varieties, so yields are usually higher. In addition to greater yield potential, the advantages of producing beans on supports include better adaptation to conditions with more precipitation, reduced humidity inside the leaf canopy and lower disease incidence. In addition, since the pods less often come into contact with the soil, they are clean and grow straight. Nevertheless, production of bush beans continues to grow compared to pole beans because of lower production costs.

For fresh use, they are harvested several times by hand, in the morning hours, with simultaneous sorting and subsequent packing. Beans are packed tightly in wooden boxes or low-density polyethylene boxes, level with the edges. The net weight should be no more than 12 kg. Packaging containers should be strong, dry, clean, without foreign odor and ensure the quality, safety and preservation of the pods during transportation, storage and sale.

Several attempts have been made to use machine harvesting of beans, but the damage caused to the pods is considered unacceptably high for sale on the fresh market. Varieties with very thin pods are known as fine beans, which are imported into Europe usually from African countries, in particular Kenya. Fine beans are harvested very carefully to minimize pod damage during transport. Pod damage usually occurs during harvesting and packing, and after the boxes are covered with plastic film, fungal spoilage can quickly occur at high relative humidity.

For successful machine harvesting, the equipment and plants must be compatible. Modern varieties facilitate mechanization because they are characterized by concentrated flowering and pod set, vertical growth with pod set in the middle or high on the plant, reduced foliage, strong root attachment to the soil, and resistance to some diseases. All these factors increase the efficiency of harvesting machinery, which uses many metal teeth to remove pods by combing through the foliage. The separated pods and leaves are subsequently separated. Initially, machine harvesting was used only for processing crops, since pod damage is usually not a serious product defect if the pods are processed within a short time. However, damage becomes easily noticeable and unacceptable for harvesting fresh market beans. Many modern mechanical harvesters have been modified to significantly reduce pod damage and are capable of harvesting pods for the fresh market.

Bean varieties specifically harvested for fresh seeds (Shelled bean) are harvested when the seeds reach full size and become relatively hard. Seed moisture is very high compared to dry bean seeds. Manual labor and/or machines are used to harvest the pods. The seeds are separated from the pods, and the latter are discarded because they are fibrous and not juicy.

Bean pods have a high respiration rate, so they should be quickly cooled to about 5 °C and maintained at 95% relative humidity. Hydrocooling is the preferred method for achieving rapid cooling and maintaining pod turgor. Temperatures below 3 °C for more than a few days should be avoided, as they promote chilling injury. A storage life of acceptable quality pods for 2-3 weeks is achieved at 5-10 °C and 95% relative humidity.

For Processing (Dry Seeds)

Beans are harvested when the crop is fully mature, that is, when most pods turn yellow and the seeds harden. By this time the leaves have fallen, and pod ripening reaches 70-80%.

Mechanized harvesting of some varieties is difficult due to low pod attachment to the stem below 10 cm. Therefore, two methods of two-phase harvesting are used. The first, more common for varieties with pod attachment not lower than 10 cm from the soil surface, consists of mowing the plants into windrows with a ZhBA-3.5 header. The second method is suitable for bush, short-stemmed varieties and consists of pulling and laying into windrows with an FA-4 bean harvester. Then the mown windrows are picked up and threshed with an SK-4 combine equipped with special attachments.

In most American and Canadian farms, beans are cut, with the root cut off, and the plant laid on the ground. When the beans dry to 20% moisture, the windrows are picked up by a combine.

The combine is adjusted so as to cause minimal damage to the beans. Bean seeds are very fragile, so the crop is harvested early in the day to reduce losses of the seed coat or shelling. Beans can be damaged when handled at moisture below 13%. Often in small-scale production, the crop is harvested by hand, either by pulling up the aboveground part and laying it on the ground for complete drying, or by hanging the vines in stacks for drying. Threshing and sorting are often carried out by hand combing.

Bean Seed Fly (Delia platura)

The bean seed fly (Delia platura), or seedcorn maggot, English Bean seed fly (seedcorn maggot), is a very common pest found in most countries with a temperate climate and affecting a wide range of large-seeded crops, including peas, beans, passion fruit, lupin, maize and soybeans. With severe infestation, a large number of seedlings may die, which seriously affects the plant population. Pea or bean seeds from late sowing dates are attacked by fly larvae during germination. Faba beans (Vicia faba) are rarely damaged, since they are not often sown in early summer, but late-sown beans and peas for freezing or the fresh market are especially susceptible.

Larvae from eggs laid in freshly disturbed soil feed on decomposing plant matter and also penetrate freshly germinated seeds. The larvae feed inside the cotyledons and damage the developing plumule and root. Tunneling may occur in the stem, and the growing point may be damaged, leading to the appearance of the “bald head” or “snake head” symptom, when the stem elongates but terminal leaves are absent. Secondary shoots may develop from seeds in peas and faba beans (Vicia faba), but in beans (Phaseolus sp.) the seedlings do not compensate for the damage. Heavily infested seeds do not emerge and rot before emergence. Damage is often noted as patches in the field, since flies tend to aggregate before oviposition.

In late spring, adults aggregate on fresh disturbed soil in fields containing large amounts of green weeds or fresh crop residues. Later-treated soils on which weed infestation has developed are more likely to be infested by Delia platura. Flies lay eggs on the soil surface, where larvae can feed on plant residues and also penetrate large seeds immediately after germination.

To reduce the risk of infestation, when preparing the seedbed it is necessary to bury all weeds, especially if they have not had time to dry out, and also to avoid soils with a high level of plant residues, such as carrot, sugar beet or bulb crops. In small-scale production, peas or beans can be protected with fleece or plastic film until germination, but in commercial bean crops (Phaseolus sp.) insecticidal seed treatment is often used.

Mexican Bean Beetle (Epilachna varivestis)

Mexican bean beetle (Epilachna varivestis).

The Mexican bean beetle (Epilachna varivestis), English Mexican bean beetle, is perhaps the most serious insect pest of dry beans in the western regions of the USA. It is believed to be native to the plateau region of southern Mexico, but the insect is found in the USA (in most states east of the Rocky Mountains), as well as in Mexico. In the eastern regions of the USA, the pest is present wherever beans are grown, while in the west infestation occurs in isolated areas, depending on local conditions and precipitation. The insect is not a serious pest in Guatemala and Mexico, but is very numerous in some areas in the western USA. The southern limit of the known distribution is Guatemala, and the northern limit is southern Canada and New England.

Adult Mexican bean beetles overwinter in debris in fields and along field edges. Beetles emerge onto bean fields in June and July, and females begin to lay egg masses on plants after they have fed for 1-2 weeks. Larvae and adults feed on the underside of leaves, scraping off the epidermis of the leaf and leaving a skeletonized leaf.

Pest control includes monitoring and searching for egg masses, which allows the grower to make a timely decision on whether treatment is necessary before damage begins (Sanchez-Arroyo, 2015).

Dry Beans

Cultivated varieties arose as a result of many years of domestication of wild species with different seed characteristics. Species with the smallest seed size were associated with wild populations, while species with larger seeds were further domesticated and cultivated. A great deal of work has been done to study the genetic origin of the species using specific traits, including the seed protein phaseolin, to try to determine the origin of specific Phaseolus varieties (Gepts et al., 1986).

Kaplan (1965a,b) conducted many studies of ancient plant remains of four Phaseolus species in Mesoamerica. These studies suggested that Phaseolus vulgaris may have originated in Mexico about 700-400 years ago. It now appears that beans originate from two main sources: Mesoamerican types, which were mainly small-seeded, and Andean types, which were usually large-seeded. Both types were distributed throughout the main growing areas in Central and South America, Africa, Europe and the USA.

Bean breeding has focused on optimizing some specific characteristics, mainly morphological and physiological. The most obvious morphological difference is the climbing growth habit of the wild plant. The climbing growth habit gives an advantage in wild populations of mixed plants, since the climbing stem is able to compete for light among woody plants and trees that provide support for the climbing bean. Once on a support, the climbing bean twines around it and produces branches growing at right angles to gravity. These climbing types also produce abundant branches, long internodes and a large number of nodes. Most climbing forms are also very indeterminate.

Cultivation led to a different set of selection criteria, since a greater degree of determinacy makes harvesting easier. It also led to shortening of internodes to obtain a more compact plant and a plant with sufficient stem strength to stand on its own, with loss of twining without the need for additional support.

A descriptor system for different plant types was developed based on data from the International Center for Tropical Agriculture (CIAT, 1980) and the US PI collection based on seven types (IBPGR, 1982), and was subsequently modified by Leakey (1988).

Proposed description of Phaseolus plant types (Leakey, 1988):

• Indeterminate climbing, long internodes, inflorescences mainly at the top of the plant — ancestors of the primitive Andean type (Phaseolus aborigineus);
• Climbing with well-distributed pods; limited branching, not sensitive to day length — European and American pole beans;
• Indeterminate with short internodes; branches long, little or no branching — numerous strongly branched bush beans, North American Pinto and early European Swiss beans;
• Indeterminate bush; branches short, growth of main stem and terminal guide poorly developed; without twining — a variety common in Near Eastern germplasm;
• Indeterminate bush; stem powerful, curved; short internodes; lateral branches of equal growth — black-seeded American varieties. Early sea bean varieties;
• Erect, indeterminate bush; strong non-twining main stem and branches; weak development of a distinct guide — San Fernando, typical of certain Mesoamerican varieties;
• Determinate growth; reproductive buds terminating the main stem and branches; vigorous and spreading bush — many Spanish and Portuguese varieties;
• Spreading determinate bush; branching of main stem and branches — several Bush Blue Lake types;
• Determinate bush; weak branches, few terminal buds — Masterpiece, Diacol, Nima, etc.;
• Determinate bush; vigorous multi-shoot; erect lateral branches; short lower nodes — Chimbó;
• Determinate bush; open habit; several well-developed branches — Michigan pea bean;
• Determinate bush; narrowed lower internodes; densely branched; concentrated zone of internal flowering — most modern bush varieties of French and Dutch breeding suitable for mechanized harvesting.

Cultivation in northern latitudes, for example in Europe, has led to selection pressure differing from that in the tropics and subtropics. This became possible due to day neutrality, providing a greater degree of determinacy and early maturity. Day neutrality made it possible to shorten internodes to obtain a compact, stiff-stemmed plant type.

Growing conditions also influenced selection criteria in other climatic regimes in different countries, and growth habit ideotypes favor (or hinder) differences such as low precipitation, high temperatures and altitude above sea level. In northern latitudes, day neutrality is important when the growing season is short. Photoperiodism is the influence of day or night length on growth and flowering, and in legumes the inheritance of the response is controlled by at least two major loci expressing dominance or recessiveness, or both (Smartt, 1988).

Leaf size can influence susceptibility to drought stress, and a larger leaf area is an advantage in areas with more diffuse light, at high altitude or in oceanic climatic zones of the world.

Pod dehiscence is an unfavorable characteristic, so preference is given to varieties that have a low frequency of seed shattering. Pod walls with a high fiber content are more prone to splitting, so selection for pods with low fiber content has made it possible to reduce the likelihood of dehiscence and at the same time improve the taste qualities of the pods when they are harvested green and used as a vegetable.

Seed size and color are also important characteristics, and selection according to certain criteria has led to a wide range of varieties used today. Although wild species often had seed colors from black to brown, including mottled seed coats, domestication and subsequent selection led to the appearance of varieties with larger seeds than wild species and a wide range of seed color and pattern, including red, cream and white.

Commercial classes of dry beans in North American literature are usually described in terms of their color and size. Currently, these commercial class names are recognized in international trade.

Red and Garnet-Red Dry Bean Seeds

The recessive red allele leads to the formation of the garnet-red color of dark red, as well as light red kidney beans (Smith, 1939). Other red bean varieties, such as red Mexican and others, carry the dominant red allele. Many of these red beans lose their color during cooking, but a variety Stop has recently been developed — a small garnet-red bean having the same size and shape as Mexican small red and developed on the same genetic background as dark red kidney, which retains its color during cooking (Leakey, 1999).

White-Seeded Beans

In the 1960s, four sea bean varieties developed in a breeding program using X-rays at Michigan State University were introduced and evaluated as a potential canning crop in the UK (Kelly, 2014). Some commercial interest was shown, and one of the varieties, Seafarer, was re-registered as Purley King and tested for production (Scarisbrick et al., 1976; Evans and Davis, 1978). Although this variety was not commercially successful at the time, development of new varieties continues.

Northern Bean

Attempts to introduce the northern bean in France were seriously affected by bacterial scab (Xanthomonas phaseoli), transmitted through seeds.

Since then, disease-resistant germplasm of the northern bean has been developed, and breeding work was then carried out to develop an early-maturing determinate variety with some success within a hybridization program with Leakey’s Horsehead (Leakey, 1999).

Dry Beans with Brown, Yellow and Green Seeds

The color of brown Swedish and brown Dutch beans is due to glucosides of the flavonoid quercetin. Yellow beans, characteristic of the seasonally very dry Pacific coastal regions of South America, do not contain quercetin, but instead contain the flavonoid kaempferol and its monoglucoside. Yellow beans are known under the names Canarios, Mantecas and Mayacoba and are famous for their digestibility because they do not contain tannins. The variety Prim was obtained as a result of wide crossing and received some commercial production (Leakey and Harbach, 1975).

Green seeds, due to stable chlorophyll, were originally selected as French flageolets verts, and many green-seeded flageolets have been developed in France, with some varieties possessing resistance to anthracnose (Colletotrichum lindemuthianum) (Dean, 1968).

The nutritional qualities of seeds are also being studied, and improving protein content and quality has been identified as potential goals. It is also desirable to reduce the amount of antinutritional factors, since the presence of trypsin inhibitors and lectins affects digestibility. These substances are heat-labile, so before consumption beans require a period of complete rehydration followed by thorough cooking to denature these substances. Lectins are retained in undercooked or slowly cooked red kidney beans.

Improving seed yield by increasing seed size, reducing pod shattering, standing ability and early maturity are all main breeding objectives.

Early maturity is an important characteristic, especially if beans are grown in more northern parts of the world with a temperate climate, where frosts can cause serious damage to the crop when it reaches maturity. Cold resistance is necessary for vigorous early germination (soil temperature not below 12 °C is required); cool temperatures in the early stages of growth lead to the appearance of short plants and, consequently, pods that develop close to the ground or on the soil surface, which makes recovery during mechanical harvesting difficult, with a high degree of pod shattering and seed loss. Resistance to heat and drought in the later stages of growth is often desirable in hot summers.

In addition to these morphological and physiological characteristics, breeders strive to develop varieties with increased resistance to a wide range of pests, diseases and disorders. The main pathogens include bean rust (Uromyces appendiculatus), white mold (Sclerotinia sclerotiorum), certain viruses and bacterial blight (Pseudomonas spp.). Breeding for pathogen resistance, especially in the tropics, is very difficult because there are a large number of pathogens; each of them can be seed-borne, and almost all can be present in several racial forms or strains. Wild Phaseolus species are currently being screened for resistance to pests and diseases, and some lines have been identified for future development.

In France and the USA, the problem of disease prevention is largely solved by producing seeds in areas free from diseases due to warm dry weather conditions persisting throughout the growing season. Seed production in Africa follows similar practices.

Green Beans (Dwarf French, Snap Beans)

Stringless pods or “snap” beans are widely grown and used as a frozen product. Pod size and shape vary greatly among varieties. For the processed vegetable market, pod size determines the final product.

Sizes of green French bean and Romano bean pods (data from PGRO, 2013):

• very thin, Kenyan bean — 6-8 mm;
• thin, Bobby beans — 8-9 mm;
• medium, filet beans — 9-10 mm;
• large-podded, French and some fleshy Romano varieties — >10 mm;
• flat-podded, Italian flat bean — often >15 mm.

Varieties

Depending on the presence of a parchment layer and fibers in the pod valves, bean varieties are divided into:

• vegetable (also called asparagus, pod);
• grain (shelling).

Vegetable varieties according to the length of the growing season from emergence to technical ripeness are divided into 6 groups:

• ultra-early — growing season up to 46 days;
• early — 46-50;
• mid-early — 51-55;
• mid-season — 61-70;
• late — 76-80;
• very late — more than 95.

The most common bean varieties: Motolskaya Belaya, Krasnogradskaya 244, Krasnogradskaya 5, Krasnogradskaya 6, Dneprovskaya Bomba, Belosemyannaya Frunzenskaya, Dneprovskaya 8, Kishinevskaya Shtambovaya 1, Pervomaiskaya, Oka, Shchedraya, Oran, Gornal, Nerussa, Biychanka.

Origin and Taxonomy

Remains of large-seeded lima beans found in Peru were determined to be more than 7,000 years old. Remains of small-seeded lima beans found in Central America are about 2,500 years old. Wild species are still found in Mexico, Central America and all Andean regions. Cultivation is widespread: the crop is grown by subsistence farmers in northern Brazil, and it has also become an important staple legume crop in some regions of Africa and Southeast Asia.

Common names identifying small-seeded lima beans are sieva, and sometimes sea bean. Butter bean and Madagascar bean refer to large-seeded types. “Fordhook” is a generally recognized name for the large-seeded “potato lima” group.

Disagreements about the taxonomic classification of lima beans exist regarding the species designation Phaseolus lunatus and Phaseolus limensis. In earlier classification, large-seeded lima beans were assigned to Phaseolus limensis, and the small-seeded form to Phaseolus lunatus; various forms were assigned botanical variety designations, which are often written differently. Separate species status for different lima types is doubtful and probably not justified, since all types are interfertile. Currently, all varieties of lima beans, wild and cultivated, are identified as Phaseolus lunatus.

Botanical Description

Lima bean, or moon bean (Phaseolus lunatus L.), is considered a perennial or annual plant with a long growing season, but is grown as an annual. Both climbing and bush varieties occur. Climbing forms can reach 3-4 m in length, while bush forms are 50-90 cm tall.

Plants have a strongly branched root system of moderate depth, often more than 1 m. Roots are capable of developing nodules containing Rhizobium.

Flowering is indeterminate, flowers are small, self-pollinating, although cross-pollination sometimes occurs.

Seeds vary in color, have a moon-shaped form (kidney-shaped), hence the species name. Weight of 1,000 seeds is 250-1,000 g.

The length of slightly curved oblong pods ranges from 5 to 15 cm, and the width from 2 to 3 cm. Most varieties usually contain from two to four seeds, although other varieties may have up to six seeds in a pod. Pods of some varieties are thick, others relatively thin. Pods dehisce easily. The large, flat, oblong seeds of some plant types reach 3 cm in length. Seeds of other types are also flat, but more rounded and about 1 cm long; seeds of each type are smooth.

Commonly grown varieties have a light green or white seed coat, others may be red, purple, brown or black. The two large seed cotyledons make up most of the seed volume. Seeds of wild species have a high content of cyanogenic glucosides and must be leached before or during cooking. Glucoside content in modern varieties, especially in light-colored seeds, is insignificant or absent. Nevertheless, eating raw lima beans is not recommended.

It is cultivated in America, Africa, Asia, and some European countries. In Russia it is found in vegetable gardens.

Cultivation

Lima beans are more sensitive to the environment than common beans and require warmer weather for growth. The optimal average temperature ranges between 15 and 25 °C. Large-seeded lima beans are usually adapted to lower temperatures and higher humidity than small-seeded ones, especially with regard to pollination. For large-seeded lima beans, temperatures above 30 °C and relative humidity less than 60% during flowering can lead to flower drop. Such sensitivity limits production to fairly specific conditions.

The growth regulator NAA has been used to improve pod set.

Seeds germinate well at temperatures from 15 to 30 °C; above or below this range germination is poor.

Effect of temperature on germination of lima beans (National Garden Bureau, Inc. Downers Grove, IL.):

• at 10 °C there was no germination;
• at 15 °C germination occurred after 30.5 days;
• at 20 °C — after 17.4 days;
• at 25 °C — after 6.5 days;
• at 30 °C — after 6.7 days;
• above 35 °C there was no germination.

Planting depth depends on seed size and can be from 3 to 6 cm, with large-seeded varieties planted deeper. Seedlings emerge most quickly at a temperature of about 25 °C. Seeds are very susceptible to mechanical damage.

Light-textured, warm and well-drained soils give higher yields than the use of fine-textured soils. Slightly acidic soil with pH 6-7 is also preferred. Apart from temperature limitations, cultural practices for lima beans are similar to those used for beans, but the longer growing period requires more moisture and nutrients. Moisture deficiency is most critical during flowering. Additional nutrition is usually provided by fertilizers containing nitrogen, phosphorus and potassium. The response to nitrogen fertilizer application is higher than in beans.

Many of the same diseases and pests that affect common snap beans and other legume species also affect lima beans.

When planting the bush type, the usual row spacing is 60-90 cm with 10-15 cm between plants. Varieties grown on poles are spaced more widely to allow manual harvesting.

Harvesting

Depending on the variety and growing temperature, the period from sowing to harvest can be from 70 to 110 days, and longer at low temperatures. Compared with snap beans, which are usually grown for fleshy pods, lima beans require more time to harvest in order to produce enlarged but immature seeds. As seeds mature, the color of the seed coat changes from green to cream or white. During seed maturation, the pod becomes convex as a result of seed enlargement. At the harvest stage for fresh use, the pods are green and seed moisture is 60-70%. Due to different flowering times, pods mature unevenly, which is less important for fresh use than for processing.

Because of the high labor intensity of manual harvesting, a significant portion of the fresh crop is harvested by machines. The difficult manual removal of immature seeds from pods is an additional incentive for mechanization. Effective mechanization of harvesting requires dwarf plants with a determinate flowering type. The yield of fresh green lima beans in the pod is from 2 to 3 t/ha.

Harvested mechanically and cleaned lima bean seeds have a short postharvest period, so they are processed as soon as possible, usually by freezing or canning. Beans of different degrees of maturity are separated by specific weight using salt solutions. Freshly harvested lima beans in pods can be stored in good condition for several weeks at 5-7 °C and 90% relative humidity. At lower temperatures, chilling injury may occur.