Plantain and Starchy Banana

Uses

Plantains and starchy bananas are an important food for more than 50 million people in many tropical countries. They are one of the cheapest sources of calorie-rich food and are available throughout the year. The compatibility of plantain with intercrops is a decisive advantage for its wide use in subsistence farming.

The distinction between plantain and dessert banana is quite clear, but between plantains and starchy bananas it is less definite, and the names are often interchanged. The best-known distinction is that plantains and starchy bananas are eaten cooked, even when ripe, and therefore they are usually considered together as “cooking bananas.”

The fruits of plantains and starchy bananas are unpalatable if not cooked; when eaten raw, they have a strong and lasting astringent taste. Even after cooking, the fruit pulp usually remains relatively firm. Ripe dessert banana fruits are sugary and are usually eaten without cooking. The main difference in composition between plantains and starchy bananas compared with dessert bananas is the amount and rate of conversion of accumulated starch into sugars as the fruits ripen. Plantains and starchy bananas are eaten when very little starch has been converted in the pulp, whereas dessert bananas are eaten when conversion is already well underway. By comparison, the total solids content in ripe bananas is about 80% sugars and less than 5% starch, while ripe plantains contain about 66% sugars and 17% starch. Unripe dessert bananas contain starch and can be used as a boiled vegetable, like plantains and starchy bananas, but they are usually allowed to ripen, which enables starch to be converted into sugar.

As a staple and subsistence crop, individual consumption of one or two plantain fruits per meal is common. Being an inexpensive source of calories, it has unfortunately become a low-status food in many countries. In addition to being a very good source of easily digestible carbohydrates (about 30% of the edible portion), plantain has high taste appeal and satiety, provides a good level of provitamin A, about 20 mg/100 g fresh weight of vitamin C, and sufficient B-group vitamins. Plantain is a high source of potassium. It is a high source of potassium, although it contains little iron and sodium. Protein and fat contents are about 1% and 0.3% of the edible portion, respectively. Comparison of the nutritional value of plantain with other important starchy vegetables favors the former.

The astringent taste of the fruit pulp is due to tannin compounds, which are removed by cooking. The peel, which is not eaten, constitutes about 40% of fresh weight. Plantain is prepared in various ways: roasted, boiled, baked, or fried as a vegetable, used in soups and porridges. It is also processed into chips, flakes, and flour. In Rwanda, Burundi, and parts of Uganda and Zaire, most starchy bananas are used to produce wine and beer.

Large terminal male flower buds are also used as a vegetable, although preparing them requires changing the boiling water several times to remove astringency. In New Caledonia and other regions, the fleshy rhizomes are eaten as a starchy food; some clones are grown specifically for this purpose. In India, the inner sheaths of the pseudostem are also used as a vegetable. In addition, pseudostems are often used for livestock feed and as mulch in plantations. The foliage is also used for mulching and finds wide use as wrapping and stuffing material.

Origin and Domestication

Indochina and Southeast Asia are the presumed centers of diversity and domestication of wild Musa species, although wild species are distributed from India to Thailand and are also found in New Guinea and Australia. Most botanists consider Malaysia the place of origin of Musa acuminata; peripheral areas of India and the Philippines are considered the place of origin of Musa balbisiana. Geographer Carl Sauer suggested that some Musa species were probably among the first domesticated plants. Various banana species have been cultivated in Southeast Asia for thousands of years. Bananas were reported to have been cultivated in India around 500 BC and in West Africa around AD 500. Musa species were seen by European explorers of the West African coast at the end of the 15th century. The word “banana” may have originated from local languages of Sierra Leone or Nigeria.

European traders visiting these places may have adopted the word “banana” from the similar-sounding “bana.” Movement eastward from Southeast Asia brought bananas to the island territories of the Pacific. Bananas in the Americas are thought to have been introduced by European traders from West Africa.

Probably the rhizome and inner stem tissues of wild plants were first used as food, since the extremely seedy fruits were practically inedible due to the large number of stone-hard seeds and the relatively small amount of pulp. These wild forms evolved toward greater edibility, presumably as a result of human selection of plants producing parthenocarpic fruits.

Production

Although statistics from the Food and Agriculture Organization of the United Nations (FAO) show that recorded banana production was much greater (about 52 million tons versus 28 million tons) than plantain production, it is generally believed that perhaps up to half of total banana production is used as a cooked vegetable. Clearly, plantains and starchy bananas are a crop grown almost exclusively in developing countries. The volume of backyard or home-garden banana production is enormous, especially in many African countries, and this volume is poorly reflected in production statistics. In addition, plantain is often grown in intercrops, and such shared land use makes obtaining and interpreting accurate production statistics difficult. It is estimated that 85% of all plantains and starchy bananas are grown by peasant farmers and in smallholdings for local consumption and trade. Exports have grown from almost zero to about 12 million tons per year. Africa produces more than 70% of the world total of plantains and starchy bananas, with Uganda alone producing about 30%.

A widely recognized main use of bananas is fresh consumption without cooking, and large volumes of fruit are exported worldwide. On the other hand, most production of plantains and starchy bananas is destined for local or regional consumption. Unlike dessert bananas, few plantains and starchy bananas are transported over long distances, not so much because of postharvest handling problems as because of limited demand in regions outside the tropics. However, changing demographics have led to more bananas appearing in international trade. Since the 1960s, exports have increased noticeably in response to demand from ethnic migrants in importing countries.

Taxonomy

The banana family (Musaceae) consists of two genera, enset (Ensete) and banana (Musa). Because of continued use of previously misapplied nomenclature, there is some confusion in their taxonomy.

The genus Ensete (Ensete), comprising six to seven species, originates from Asia but has existed in the wild in Africa for centuries. Ensete ventricosum (synonyms Ensete edule and Musa edule) is widely known as the Abyssinian banana and is cultivated to a limited extent in Ethiopia. Although all parts of the plant are eaten, the starchy root and inner stem tissue are the main parts of the plant used as food.

The genus Banana (Musa) comprises about 40 species, the most important of which are Musa acuminata and Musa balbisiana. All edible bananas derive from two wild species—diploid Musa acuminata and Musa balbisiana with a chromosome composition of 2n = 22. Although all wild Musa species are diploids, not all have the same chromosome number; some have 2n = 14, 2n = 18, or 2n = 20. Almost all cultivated bananas are polyploids, most of them triploids obtained by hybridization within and between Musa acuminata and Musa balbisiana. Geneticists identify the basic genome of Musa acuminata as AA, from which triploids (AAA) originated by natural polyploidization. The AAA group is important for horticulture because two major dessert banana clones, Gros Michel and Cavendish, are derived from this group. Cavendish clones are still widely grown as an export crop.

The genome of Musa balbisiana is identified as BB. No diploid form of Musa balbisiana has edible or parthenocarpic fruits, and BBB triploids are not known. Musa balbisiana occurs in areas of the Indian subcontinent where distinct wet and dry seasons exist, and it is generally considered a more hardy and drought-tolerant species. Wild Musa balbisiana has not been found in the humid tropics.

It is presumed that human transfer of diploid and triploid clones of Musa acuminata to other areas resulted in natural hybridization with diploids of Musa balbisiana. As a result, hybrids with genomic compositions AB, AAB, and ABB were obtained. Hybridization between Musa acuminata and Musa balbisiana occurs easily in nature, and hybrids with different characteristics probably arose at different times and in different places. Parthenocarpy and better edibility of Musa acuminata combined with the hardiness of Musa balbisiana allowed bananas to be grown in many less humid tropical areas. In addition to hardiness, Musa balbisiana also contributed greater disease resistance, fruit starchiness, and acidity.

The plantain subgroup, obtained from crossing Musa acuminata x Musa balbisiana, has genomic identities AAB and ABB. The AAB plantain group is widespread in West Africa, where considerable diversity is found. It is also common in parts of tropical America but is rarely found in Southeast Asia. On the other hand, ABB clones are numerous in India and parts of Southeast Asia, and virtually all of them are starchy bananas, although they are sometimes incorrectly called plantains. Starchy bananas are often preferred to plantains because they grow better and have better cooking characteristics.

Parthenocarpic triploid clones are more productive than diploids, which may be explained by the absence of seeds. These clones have greater vigor and larger fruits, so they are preferred for cultivation over tetraploids and diploid clones. Diploids, often having seeds, are grown least often and have little economic importance. Nevertheless, some seed-bearing diploid clones of Musa acuminata are still grown in Southeast Asia. Tetraploids such as AAAB, AABB, and ABBB also occur, but only a few ABBB clones have any local importance. AAAA plants do not occur in nature but have been developed by breeders.

Botanical Description

Plantains and starchy bananas are large perennial herbaceous monocotyledonous plants, grown mainly for their starchy parthenocarpic fruits. The initial roots of the plant are short-lived and are quickly replaced by numerous adventitious roots that form from the lower part and sides of the underground stem tissues (rhizome). As the rhizome grows, additional adventitious roots and lateral root branches form, so the presence of several hundred adventitious roots is not unusual. Most roots are located in the upper 30 cm of soil. They are relatively small and thin, although some have lateral matted spread of several meters, which improves nutrient uptake and anchorage. Roots are constantly formed, replacing dead ones and also increasing in total number. The lifespan of individual roots is 4 to 6 months.

The rhizome is a compressed underground stem with many closely spaced internodes. The apical part of the rhizome contains meristematic tissues from which leaves, roots, and suckers develop. During growth, the rhizome also enlarges and completes its growth, forming the aerial stem and inflorescence. The width of the rhizome of a mature plant can range from 15 to more than 30 cm. Axillary buds in the upper part or on the sides germinate and develop as suckers, which can be used for propagation. Apical dominance limits the number of buds germinating as suckers, although pruning practices also affect the number of suckers initiated.

Leaves are initiated in a spiral inward from the outer part of the flattened apical meristem, resulting in the formation of a pseudostem, a trunk-like structure consisting of tightly rolled leaf sheaths, which is often mistaken for a stem. The length of the pseudostem is a characteristic of the cultivar, but it is also influenced by the environment.

Each leaf consists of a sheath, petiole, midrib, and leaf blade. The first leaves are almost blade-less, but the size of the leaf blade increases in width and length with subsequent leaves until flowering begins; thereafter leaf formation ceases. Subsequent emerging leaves are smaller. Most leaf development occurs inside the pseudostem. There it forms as a cylinder folded in half. The right half of the leaf blade rolls onto itself, and the left part rolls onto the right half and midrib. It is in this configuration that the leaf moves upward by elongation of the sheath and petiole and emerges vertically at the top of the pseudostem. After emergence, the rolled leaf unfurls within a week, continuing the remainder of its expansion. The position of leaves changes with age, and from an almost vertical position the leaf gradually bends to horizontal and further, and in old age droops.

The veins within the leaf blades are unbranched and parallel to each other but perpendicular to the midrib. The leaf blades have little resistance to transverse tearing, often caused by strong wind; this arrangement allows the vascular connections of the veins with the midrib to remain intact, and leaf function is not substantially impaired. Thus, torn and tattered foliage may not be as damaged as it appears.

The inflorescence appears when the apical meristem elongates and pushes upward through the pseudostem. Depending on the cultivar, the inflorescence usually forms after 30 or more leaves have formed. Usually the flower stalk requires about a month from initiation to emergence from the top of the pseudostem, and its length ranges from several to more than 7 m.

The inflorescence bears both female and male flowers on the aerial stem passing through the pseudostem and largely supported by it. Initially erect, the inflorescence usually becomes pendent due to its own increasing weight. The position of the inflorescence is thought to be influenced by geotropism and the presence or absence of the male flower bud, so some cultivars are not completely pendent.

Flowers are formed in nodal clusters; the first basal nodes produce female flowers. A cluster of female flowers is called a “hand,” and individual flowers are called “fingers.” The entire inflorescence, often called a “bunch,” has from several to 10 or more spirally arranged hands, each containing 5 to 20 fingers. The size of the bunch, the number of hands and fingers, their size and shape are characteristics of the cultivar, and differences among cultivars are significant.

Female and male flowers initially look alike but change with further growth. Female flowers have an elongated ovary consisting of three fused pistillate flowers. Due to the usual sterility of male and female flowers, ovaries do not develop, and the fruit is an unfertilized berry. Flowers secrete nectar and may attract insects, birds, and bats, which are pollinators of wild banana species (Musa).

After several basal clusters (hands) of female flowers form, clusters of hermaphroditic flowers form in the intermediate nodes of the inflorescence, and male flowers form in the distal nodes. Both of the latter flower forms usually degenerate. At the end of the inflorescence is the male terminal bud, which in many cultivars may continue to produce male flowers until the bunch is harvested.

Fruits of the AAB plantain group are long and curved, whereas fruits of the ABB starchy banana group are short, angular, thick, and almost straight. At first the fruits may be green or various shades of red, but as they ripen the color changes, becoming yellow, brown, and/or black; the inner pulp is white or yellow.

Ecological Requirements

Best growth of plantain is observed in humid tropical lowlands, but it is cultivated in many frost-free areas within 30° of the equator, in both humid and dry climates. Optimal growth occurs at 27–28°C. Temperatures significantly below 20°C or above 38°C limit growth, although plants are able to tolerate a wider temperature range. Depending on duration of exposure, a temperature of 10°C can cause chilling injury, and temperatures above 45°C also cause harm. On slopes, plantings are made to use maximum sun exposure. Although plants do not respond to photoperiod, they require high light intensity for maximum growth, although good growth is observed even under partial shade. Dry matter accumulation is most favorable at 24–28°C, while 32–34°C increases the rate of new leaf emergence.

The best soils for production are deep, well-drained loams with high fertility, organic matter content, and water-holding capacity. Soil type is often more important in site selection than climate, although in some subtropical regions climate may be the main factor. To ensure good drainage, land with a gentle slope or hills is often selected. Many tropical areas receive high rainfall, and because banana is sensitive to waterlogging, good drainage is very important; field drains are sometimes installed. For optimal root development, soils with light texture and high organic matter content are preferred. Because most adventitious fibrous roots are located in the upper 50 cm of soil, shallow soils can be and often are used. Having a weak root system, plantain is easily blown over by strong wind; therefore dwarf clones are often grown because they are more resistant to wind damage. In some situations, windbreaks are used to reduce wind force, but their disadvantage is that windbreaks create shade and occupy field space. Plantain is sensitive to salinity. The preferred soil pH ranges from 5.0 to 7.5; pH below 5.0 limits productivity. Lime should be applied to correct increased acidity.

In many tropical areas, especially for subsistence farmers, nutrient supply for the crop depends largely on available soil organic matter. Because banana requires relatively good soils with sufficient organic matter, newly cleared forest land is often used. Because nutrition is most important at the beginning of plant growth, additional organic and/or synthetic fertilizers are usually applied at planting. On nutrient-poor soils, fertilizers must be at a high level and applied frequently. Most fertilizers for the crop growing cycle are usually applied at planting, since subsequent fertilizers are difficult to apply without damaging the fine root system. Usually nitrogen fertilizers are applied several times during the production cycle. Additional nitrogen can be effectively supplied through irrigation. The greatest demand for potassium occurs during flowering.

Mulching is known to significantly increase yield, so it is applied as often as possible. Mulching is beneficial because it limits weed growth and runoff of soil and nutrients, stabilizes soil temperature, and reduces losses from evaporation from the soil surface.

Access to a uniform moisture supply is very important; on average 150–200 mm of rainfall per month is usually sufficient for the crop growing cycle; 25 mm per week is considered the minimum. In most banana production regions, annual rainfall ranges from 1000 to 2000 mm. Dry periods, especially during flowering, reduce productivity; in such situations supplemental irrigation is desirable. Important conditions are good drainage and well-aerated soils, because plantain is easily damaged by flooding. Flood irrigation is widely used, but because of nutrient leaching this practice is being replaced by overhead or low-level sprinkler irrigation; the use of drip irrigation is also growing rapidly.

In subsistence farming, plantings most often have a short productive life, mainly due to minimal cultivation or neglect. The rather large diversity of plantain and starchy banana clones existing in subsistence farming often requires different cultural practices than the more uniform clones used in intensive monoculture. In some areas, a “bush-fallow” system is used, where plantain is grown for several years and then the land is plowed for other crops. Rotation is recommended, especially with crops that improve soil and nutrients. In commercial plantings, the economic productive life is from four to eight crop cycles, each varying from 12 to 18 months. In home gardens, banana is often grown indefinitely, especially where organic waste can be frequently used to replenish soil nutrients. Intercropping is widely practiced by subsistence and commercial growers, especially in Africa. Cassava, yam, maize, okra, aroids, beans, and peanut are crops commonly grown in intercrops.

Weed control is carried out mainly by manual tillage, especially in traditional cultivation. Control is most important in the early stages of growth, when plants are least competitive. Once full canopy is achieved, weeds are suppressed well enough. Mulching with leaves or other organic materials is an effective and widely used practice for weed control. In plantation production, chemical herbicides are more often used.

Sucker removal is a common cultural practice to reduce competition with the mother plant and maintain desired plant density, as well as to provide a source of propagation material. Leaf pruning is done to remove diseased and aging foliage or to prevent foliage from damaging developing fruits. The male flower bud may be removed to reduce the weight of the developing bunch and/or collected for use as a vegetable.

Propagation

Plantain is propagated exclusively vegetatively. Sword, maiden, peeper, and water suckers, which form as shoots from buds on the rhizome, are used as material. Sword suckers, the most preferred for propagation, are large shoots from half a meter to a meter long, formed from the lower axillary buds of the rhizome. They have narrow leaves and are usually planted intact with a large part of the mother rhizome and roots; sometimes the foliage is cut off. Roots of sword and other types of suckers are usually slightly trimmed before planting. Maiden suckers are larger, and older shoots (5–8 months) have tall and broad leaves; they usually already have a fairly large rhizome. Before planting, foliage is cut off to remove diseased, damaged, or insect-infested leaf sheaths. To control nematodes, suckers and corms can be disinfected with hot water (53–55°C). The dipping period is usually about 20 minutes, but may vary depending on the size and volume of plants treated. Peepers are newly emerged shoots with few leaves; because of their small size and lack of food reserves, they are usually discarded for propagation. Water suckers have a narrow pseudostem, broad leaves, and a small attachment to the mother root. They are also avoided because they produce weak plants and low yields.

In addition to obtaining propagation material, pruning is carried out to selectively remove unwanted suckers that would compete with the main plant. Usually plantain is not pruned until 2–3 months after fruit harvest, because, unlike dessert bananas, sucker formation is suppressed until fruit harvest. Propagation material is also obtained from nurseries, where large numbers of sword and maiden suckers are produced. The practice of destroying the apical meristem of the mother plant allows axillary buds to sprout. Usually about 5 usable suckers can be collected from each nursery plant, but under intensive management up to 8–10 can be obtained. Suckers taken from existing plants cause some damage to the rhizome and roots of the mother plant, so it is preferable to obtain suckers from nurseries. Suckers should be planted soon after collection, because they have a short postharvest period and store poorly.

Rhizomes or parts of rhizomes, called “bits,” are also used for propagation. Those containing several viable axillary buds are cut from the aerial growth before planting. Large bits can be divided into two or three parts, depending on the original size and the number and location of axillary buds.

Shoot-tip meristem tissue culture is a useful and expanding alternative for rapidly obtaining large numbers of propagable plants. Its use is more expensive than traditional propagation and is currently possible only on intensively cultivated plantations. The advantage of tissue culture is obtaining disease-free material, and the overall uniformity of propagated plants allows better planting planning than using material from nurseries. Nevertheless, tissue culture propagation has shown an increase in somaclonal variation of about 5%. The use of true seeds is mainly limited to breeding work.

Seedling and sucker planting material is planted in deep holes about 40–60 cm in diameter and depth. Usually a mound of loose fertile soil mixed with a small amount of fertilizer is first placed in the hole before planting. Then the seedling or sucker is placed on the mound and covered with soil so that the neck of the seedling is at or slightly below the surface. In the case of rhizomes, the top layer of soil should be about 15 cm. Sufficient planting depth is very important, because with shallow planting the already shallow root system becomes vulnerable to winds. With poor drainage, planting on raised mounds or beds may be necessary.

Spacing between plants varies depending on clones. Early-maturing small plantains of the “False Horn” type are usually spaced 2 x 2 m apart, large “Medium French” at 2.5 x 2 m, and large “Giant French” at 3 x 2 m. At such spacing, approximately 2500, 2000, and 1500 plants per hectare are obtained, respectively. To ensure an appropriate population in commercial plantations, various configurations are used that allow equipment movement. Planting density is adjusted accordingly if intercropping is practiced. In home gardens, spacing between individual plants is often wider, up to 3–6 m.

The use of dwarf cultivars is likely to continue to increase compared with large-fruited cultivars because of ease of cultivation and lack of negative effect on fruit size. Although higher planting density produces more bunches, fruit development is delayed, and smaller bunches and fruits are obtained. However, yield is comparable to low-density plantings. The minimum fruit size for most commercial production is about 270 g. High-density plantations are more suited to intensive production, require more care, and usually have a shorter productive life.

In the humid tropics, planting can begin at almost any time, but in tropical areas with seasonal rainfall, plantings are planned immediately before the start of the rainy season. Scheduling takes into account avoiding drought during flowering. Irrigation availability is an important factor influencing planting schedule. Planting time is also influenced by market opportunities and climate, and sometimes these factors are incompatible. By using different ages and sizes of propagation material, harvest can be scheduled for continuous production. Production schedules can also be adjusted by using different clones. For example, the plantain cultivar “False Horn” flowers after about 10 months, and the crop is harvested after about 2 months. “Medium French” flowers after 12 months and is harvested after 15 months, and “Giant French” flowers after 15 months and is harvested after 18 months.

After the first production cycle, subsequent cultivation can be continued by ratooning, when suckers emerge from the mother plants of the previous harvest. However, in years after initial planting, flowering becomes less synchronous, so replanting may be required, especially in the presence of weeds, diseases, and other factors contributing to yield decline.

Growth and Development

The rate of leaf emergence and their size depend on specific clones and growing conditions. The number of developing and retained leaves, as well as the size of their surface, are important components of the crop cycle. In mature plants, the maximum number of unfurled leaves at any one time varies from 10 to 15, with a number of developing unopened leaves. Leaf growth is rapid, and elongation of about 10 cm per day is not unusual. A new leaf forms about every 7–10 days, and during this time the oldest leaf usually senesces. The leaf area index (LAI) reaches a maximum around the beginning of flowering, then slowly declines. Plantains tend to be smaller plants and have less leaf surface than dessert bananas. Although their leaf canopy is impressive with a total leaf area exceeding 10 m², it is much smaller than that of many dessert banana cultivars.

The inflorescence usually appears after 30–40 leaves have formed and is fairly well developed before emerging from the pseudostem; in some cultivars up to 50 leaves are formed. At inflorescence initiation, further leaf production ceases, and the size of recently formed leaves decreases. With the appearance of the inflorescence, further leaf emergence stops. The size of the inflorescence is largely determined by the size of the apical meristem at the time of initiation. During flowering and fruit development, propping or tying is usually required to support the inflorescence.

Periods of flowering and fruit development vary among clones; fruits require 2 to 4 months after flowering to mature. Only one inflorescence (bunch) develops on a flower stalk, after which stem senescence occurs; although after harvest the inflorescence continues to develop and grow if not removed. The total lifespan of the pseudostem may be either 12 or 24 months; the duration of this period is influenced by clone characteristics, temperature, and growing conditions.

Harvesting and Postharvest Handling

Visual inspection of fruit fullness and angularity of the fruit cross-section shape are generally accepted criteria for determining harvest time. The peel of unripe fruits has some angularity, which becomes round as they ripen. When harvesting plantain, workers using machetes first cut part of the pseudostem so that the weight of the bunch bends the cut pseudostem downward, making the bunch more accessible and easier to cut from the flower stalk. As a rule, this procedure is not required for dwarf cultivars. Because pseudostem growth has already ceased with inflorescence development, cutting is not a harmful practice, and cleaning “spent” pseudostems is necessary to prepare for the next crop cycle.

In commercial production, harvested bunches are cut into hands and packed in the field. “Dehanding,” the practice of separating the bunch into hands, helps reduce physical damage and repeated handling. To further minimize physical damage, hands may be wrapped or packed in polyethylene film and placed in soft boxes. To prevent latex from cut surfaces from staining the fruits, they can be washed; sometimes fruits are treated with a protective fungicide. The former practice of treating bunches during transport and distribution, whether at transfer stations or directly by consumers, has largely ceased for commercial producers. However, small and subsistence farmers still transport harvested whole bunches from fields to home gardens and local markets.

Overall, the variability in plantain yield is enormous: from less than 5 t/ha for subsistence farmers to 50 t/ha under intensive cultivation. Its yield is much lower than that of bananas. Cultivars of False Horn and French types in West Africa yield from 10 to 30 t/ha under subsistence and intensive production, respectively. Plantain yield varies among clonal types, although it can be quite comparable if calculated as yield per hectare per year.

Uneven fruit development and the ability to accurately predict harvest maturity are important yield variables. Fruits are harvested at the preclimacteric stage, and further ripening continues in the postharvest stage. At the preclimacteric stage, almost all carbohydrates are in the form of starch. During subsequent ripening, carbohydrates gradually convert into reducing and nonreducing sugars. Initially the dominant sugar is sucrose, but later glucose and fructose predominate. In plantain, carbohydrate breakdown is incomplete, whereas in dessert bananas starch breakdown is usually completed during ripening. Plantains do not require and do not receive ethylene treatment for ripening. In contrast, dessert bananas, especially those intended for export, are usually treated with ethylene or acetylene (100 ppm for 12–24 h) to stimulate early and uniform ripening.

The main problems with harvest and postharvest handling are mainly related to the susceptibility of fruits to physical damage and rot from pathogenic fungi. Unfortunately, plantains do not receive the level of attention and postharvest care provided to dessert bananas.

Freshly harvested bananas can be stored in a refrigerator at 13°C to delay natural ripening. Storage life is increased if they are packed in airtight polyethylene, preferably with ethylene-absorbing material. It is very important to avoid low relative humidity, because this shortens the preclimacteric period and increases moisture loss. Various coating materials effectively slow fruit ripening and moisture loss, but are not widely used because of the low economic value of plantain.

Because fruits are sensitive to chilling, they should not be stored below 12°C. Because refrigeration facilities are rare in plantain-producing countries, chilling injuries are uncommon. When stored in controlled atmosphere (O₂ 1–3% and CO₂ 5–10%), lower temperatures are permissible. Hypobaric storage at half atmospheric pressure can also extend storage life. At temperatures above 25–30°C, the proportion of starch converting to sugars increases; this amount varies among clones.

Diseases and Pests

Dessert bananas appear to be much more and more widely susceptible to diseases than plantains. Nevertheless, they have a number of diseases that seriously affect production; some important field and postharvest diseases are as follows:

• Colletotrichum musae (English Anthracnose crown rot);
• Mycosphaerella fijiensis var. diformis (English Black sigatoka, black leaf streak);
• Chloridium musae (Cladosporium musae) (English Chloridium leaf speck);
• Trachysphaera fructigena, Verticillium dahliae (English Cigar end rot);
• Cordana musae (English Cordana leaf spot);
• Deightoniella torulosa (English Deightoniella leaf spot);
• Xanthomonas campestris pv. musacearum (English Enset bacterial wilt);
• Fusarium oxysporum f. sp. cubense (English Fusarium wilt, Panama disease);
• Erwinia chrysanthemi pv. paradisica (English Head rot);
• Pseudomonas solanacearum (English Moko);
• Pyricularia grisea (English Pitting disease);
• Sclerotinia sclerotiorum, Verticillium spp. (English Stalk rot);
• Ceratocystis paradoxa (English Stem end rot);
• Mycosphaerella musicola (English Yellow sigatoka).

Various strains of Pseudomonas solanacearum, in addition to causing Moko disease, are considered responsible for diseases known as blood disease and bugtok disease (tapurog). Bunchy top virus and a strain of cucumber mosaic virus, each transmitted by aphids, are serious diseases affecting plantain. An important physiological disease caused by stress is the failure of heart leaves to unfurl and leaf wilt. This condition, manifested in shortened internodes, prevents bunch development.

Some disease control is achieved by using disease-free propagation material and other crop management methods that avoid and/or limit disease incidence, as well as by chemical pesticides. Pesticides are used quite widely in intensive commercial production and, to some extent, in subsistence farming. Variable efficacy and more frequent appearance of pesticide resistance make it clear that the search for genetic resistance should be expanded.

The banana weevil, Cosmopolites sordidus, is considered the main insect pest. Species of Temnoschoita and other weevils also cause damage or destruction of pseudostem tissues similar to that caused by the banana weevil. Locusts, Zonocerns variegatus, as well as various aphids, thrips, and spider mites are other important pests. The banana aphid, Pentalonia nigronervosa, is responsible for virus transmission. Caterpillars of CfiPlusia chalcites and Sibine apicalis cause serious crop losses. Additional weevil insects are Caligo eurilochus, Ceramidia viridis, and Opsiphanes tamarindi.

Often more serious than insects or diseases is the destructive damage caused by root nematodes. The burrowing nematode Radopholus similis is the main pest causing serious yield losses due to lodging or destruction of pseudostems. Other nematodes damaging roots and corm tissues are Pratylenchus coffeae, Helicotylenchus multicinctus, and species of Meloidogyne, often grouped as burrowing, spiral, and root-knot nematodes, respectively. Nematode control is somewhat limited because the semipermanent nature of the crop limits nematicide treatment. Nematicides are usually used in intensive cultivation, but crop rotation, fallow, and flooding are other methods of cultural control.

In newly cleared forests in humid zones of Africa, plantain yields usually decline in the second or third crop cycle. This is a common phenomenon caused by a number of factors that may include (1) rapid reduction of organic matter, (2) rapid deterioration of soil fertility due to depletion or erosion, (3) increase in nematode population, (4) banana weevil infestation, (5) high sucker growth, and (6) weeds. High sucker growth causes the corm crown to rise above the soil surface, and roots cannot adequately penetrate the soil and use it. Weeds compete with the crop for nutrients and moisture and can significantly reduce yield. These factors limit the ability to sustain production over many cultivation cycles. Yield decline in starchy banana cultivation is somewhat less common than in plantain cultivation.

Crop Improvement

Because of the important food status of plantains and starchy bananas, their production is likely to continue. Research agencies are actively breeding for higher productivity, resistance to diseases, insects, and nematodes, and broader adaptability to location. At international research centers such as the International Institute of Tropical Agriculture (IITA) and the International Network for the Improvement of Banana and Plantain (INIBAP), there is good opportunity for successful hybridization within bananas and between bananas and other bananas. These and other institutions emphasize sustainable production of plantains and starchy bananas for subsistence farmers in the tropics, because this is considered a priority food and an important source of income. Significant germplasm resources have been collected and maintained by institutions in Honduras, Brazil, Burundi, the Philippines, India, and Malaysia.

Progress is being made in resistance to diseases, insect pests, and nematodes, as well as in crop management, which may increase productivity. Increased intensive production may make plantain available not only in local markets. Although this commodity has not gained wide acceptance outside the tropics, postharvest practices are already adequate for distant marketing and export production. This is important for the economies of developing countries.

References

1. Rubatzky, Vincent E., Yamaguchi, Mas. (1997). World vegetables: principles, production, and nutritive values. 2nd ed.