Persian melon (Inodorus Group)

Botanical Description

According to Naudin’s 1882 classification of melons, described in detail by Robinson and Decker-Walters (1997), most Persian melons do not meet the criteria described for Cucumis melo var. inodorous (Javanmardi, 2010). The definition of the inodorous group, or winter melons, is that the fruits are usually larger, mature later, and store longer than fruits of the cantalupensis group. They also have a smooth or wrinkled rind surface, but not a netted one, usually white or green flesh, and no musky aroma, hence the name inodorus. The fruits do not separate from the peduncle at maturity, and the plants are usually andromonoecious (Robinson and Decker-Walters, 1997; Pitrat, 2008). The reticulatus group includes fruits that are round to oval, with a typical netted skin, with or without ribs. The flesh is usually orange, aromatic, and sweet (Pitrat, 2008). In fact, Persian melons are not smooth; they have a netted skin with or without ribs. The rind color can be white, yellow, gray, dark green, and even black, uniform or spotted. These are round, oval, or elongated fruits with a musky aroma. The flesh is usually white to cream, light green, or orange. The fruits of most cultivars do not separate from the peduncle at maturity (Javanmardi, 2010). According to the definition of a cultigroup (cultivar group) given by Pitrat (2008), Persian melons may be defined as a cultigroup within the above-mentioned botanical groups.

Cross-pollination between different Persian melon cultivars can occur freely. Therefore, there is a great diversity of intermediate-type cultivars. Each cultivar has adapted to local environmental conditions. They are selected on site, cultivated, and named over generations according to fruit type and quality, resistance to environmental stresses, pests and diseases, and ease of cultivation. It should be noted that there is a decrease in the number of cultural groups (such as ‘Doody Sabz’ and ‘Ghandi Zard’) and an increase in the number of cultivars (such as ‘Susky Sabz’ and ‘Susky Zard’) in some cultural groups. Some common cultivars in Iran are: Abatar, Abbas Shuri, Akbar Abadi, Alam Gargar, Atashin, Bahar Hamedan, Bakharman, Balkhi, Ebrahimkhani, Eivanaki, Garmsari, Ghalamghash, Gorgab, Haj-Mashallahi, Jabbari, Jafar abadi, Jafari, Jarju, Kadkhoda Hosseini, Khaghani or Shakhteh Mashad, Kharcheh Zanjan, Khatuni, Majidi, Marand, Mashhadi, Mohajeran Hamedan, Mohamad Abadi, Rostagh, Sabuni, Shafi Abadi, Shah abadi, Shahsavari, Shirazi, Shomal, Suski Sabz, Susky Zard, Tashkandi, Tokhm Mohamad, Zarand Saveh, Zarcheh Esfahan, Zard Garmsari or Aliabadi, Zard Jalal, and Zard Tabriz. It is possible that some similar cultivars are known under different names in different regions (Javanmardi, 2010).

Description of some cultivars:

• Abbas Shuri: Vigorous, late-season (120–150 days), suitable for semi-arid hot and dry and semi-arid conditions, oval fruits (20–45 cm long, 12–25 cm wide), greenish-gray rind with fine netting, firm and suitable for transport and storage, white-greenish flesh with 10%–15% sugar. This cultivar was widely grown in Garmsar, Varamin, Eivanaki, Tehran, and the northwest of Iran’s central desert. Before the appearance of Suski Sabz and Suski Zard cultivars, this cultivar was best suited for dryland farming.
• Khaghani Mashad: Vigorous, semi-early (90–130 days), cylindrical fruits, greenish-yellow thin rind, netted with deep smooth ribs, flesh green to orange, 10%–15% sugar, large fruits (40–45 cm long and 15–18 cm wide) with an average weight of 3.5–4 kg. This is the most cultivated cultivar in northeastern Iran, and it is distributed in other parts of Iran as well.
• Zard Karaj: mid-season (100–120 days), oval fruits (20–30 cm L, 17–25 cm W), 1.5–2 kg, dark yellow netted rind, greenish-white firm flesh, 8%–12% sugar.
• Tashkandi (Dar Gazi): Vigorous plant, semi-early (90–100 days), cylindrical fruits (20–40 cm L, 12–17 cm W), average weight 4–5 kg, when ripe fully slip (separate from the peduncle), creamy to yellowish with brown stripes on the rind, white and soft flesh with 10%–14% sugar, poor transportability and storability.
• Jabbari: Vigorous, mid-season (100–110 days), oval fruits, netted with 8–9 ribs, yellow-gray rind, sugar 11%–14.5%, suitable for semi-arid regions and saline soils.
• Khatuni: Vigorous, early (90–100 days), several fruits per plant, oval fruits, netted with 6–8 yellow ribs, yellow-greenish rind, 11%–14.5% sugar, suitable for semi-arid regions and saline soils (Kashi, 2000).

Growing Conditions

Persian melons require a long growing season (90–180 days), depending on the cultivar and climatic conditions. They prefer sunlight and hot, dry climatic conditions to achieve the best quality (sugar and flavor). Although the plant grows well in warm and humid regions, leaf diseases are especially serious, and the fruits do not develop the best quality. In Iran, most of this crop is grown in arid and semi-arid regions under irrigation; however, in some areas it is grown under dryland farming.

Soils

Melons are grown on many soil classes—from sands and sandy loams to silt loams and clay loams. Where earliness or a short growing season is important, sandy loam is considered superior. In fact, this soil class is almost ideal in most growing regions. Any loose, well-drained soil is satisfactory if other conditions are favorable for melon growing. In any soil, organic matter and water-holding capacity are important for production. For dryland farming, high water-holding capacity and soil structure determine success in production.

Melons grow on neutral or alkaline soils, but when grown on acid soils, flowers may drop. The soil should be well prepared, as for other cultivated crops. In some areas, land for planting is prepared on ridges or beds to ensure good surface drainage. Where the crop is grown under irrigation, the land is prepared according to the irrigation practice.

Land preparation begins in autumn with plowing to a depth of 30 cm to improve rainfall absorption, reduce disease inoculum, and allow residues of previous crops to decompose. This is important, especially if heavy soils are used. At this time, application of manure and chemical phosphorus and potassium fertilizers is recommended (based on soil analysis). Fertilizers are broadcast before bed formation or applied in beds between seed rows and the irrigation furrow, or added to the irrigation water. Before spring planting, disking and leveling of the surface are carried out.

On most irrigated plots, the soil is formed into furrows (50 cm deep) and beds (2–4 m wide), depending on soil type, available water, and cultivar vigor. Raised beds improve drainage, modify temperature, and increase the depth of the rooting zone. This also helps plants resist root, crown, stem, leaf, and fruit rots caused by Phytophthora. Before laser land leveling became widespread in agriculture, farmers placed small barriers (called “patekh”) along furrows every few meters, depending on land slope and furrow length, to raise the water level during irrigation. This holds water in the furrows for a longer time and improves water infiltration into the lateral beds where plant roots grow. The height of the patekh is determined so that water does not overflow the ridge. The top of the patekh is usually covered with plastic to prevent erosion.

Installing the patekh in the furrow.

The first irrigation is carried out before sowing the seeds, to determine the final water mark level and adjust the height of the patekhs (if necessary). Irrigation is continued until the water reaches the seed placement site (figure).

Land preparation for dryland farming of Persian melons is different. Usually, at the end of winter, a heavy, deep soil with high water-holding capacity is selected, and after large basins are created, it is heavily irrigated. After the soil reaches field capacity, it is plowed, disked, and carefully leveled. Leveling helps reduce water losses from evaporation. Chemical fertilization is not common, as the land should already be fertile. Choosing a suitable cultivar adapted to dryland farming, the correct sowing date, and methods that reduce water loss during growth are initial necessities. Currently, due to the possibility of using groundwater for irrigation, a method of semi-dry farming with supplemental irrigation at the fruit-setting stage and during subsequent growth is used. This method is very useful for increasing fruit size and total yield; however, sugar content and fruit flavor decrease (Kashi, 2000).

Planting

Film coverings in furrows.

Persian melon plants are very tender, and seeds do not germinate at temperatures below 15 °C; therefore, field planting should be delayed until the danger of cold weather or frost has passed and the soil has become warm. In the central regions of Iran, unheated plastic tunnels have become popular for commercial production of Persian melons in order to stimulate earlier ripening. Polyethylene plastic is usually suspended with wire hoops (every 1.5 m) over the beds, covering the seed rows on both sides. The cover is secured with soil to hold it in place. Tunnels raise the temperature during the day, protect young plants from wind, and exclude harmful insects and insect-borne diseases, if present, since at this time the field is still cold and insects have not begun their activity. Such cover provides only slight frost protection. In any case, covers must be removed as soon as the female flowers open, otherwise the flowers cannot be pollinated (figure).

A significant part of the commercial crop is grown by direct sowing in the field using hill sowing on flat ground, on beds, or on raised beds. The choice of system usually follows local customs that have developed according to the irrigation systems used and the soil drainage characteristics. Although transplanting is not common due to the susceptibility of seedlings to transplant shock, 3–4-week-old seedlings can be used if they have been grown in a plug system (Javanmardi, 2009).

Before planting, seeds are usually soaked for several days at 20 °C–25 °C until the radicle tip appears. Traditionally, several seeds are hand-sown in each hole to help them break through the soil (Postchi, 1965). The hills where seeds are sown are usually 10 cm from the water mark on the beds to prevent seedling dampening.

Cutting out excess seedlings with a long-handled knife from outside the plastic tunnel.

Plant spacing depends on cultivar vigor and the irrigation system. Seeds are sown in rows 50–75 cm apart under irrigated farming and 100 cm apart under dryland farming. Row spacing is usually 1.25–2 m. At this row spacing, 3–4 kg/ha of seed is required. Plants are carefully thinned to one or two when they have two or three leaves and are well rooted. The remaining plants should not be disturbed during thinning. When tunnels are used, a small, sharp, long-handled knife is used to thin excess seedlings. This is done by piercing the plastic cover without tearing it (Figure).

When plastic tunnels are used, care must be taken not to damage the plants on warm sunny days. Excess heat can accumulate under the plastic, and high temperatures can damage plants if ventilation is not provided. For this, farmers cut the plastic on the sides of the tunnel. Some farmers simply open the ends of the tunnel on warm days. After the danger of cold weather has passed, the cover is gradually removed over a month. After that, the plastic tunnels are collected. At this time, the plants are turned toward the top of the ridges and secured with dry soil to prevent wind twisting and falling into the furrows. Care must be taken not to break the stem.

Irrigation

Although Persian melons are adapted to a dry and hot climate and need less water compared with other cucurbit crops, they require a large amount of water because of the high temperatures during the long growing season.

The field is irrigated immediately after sowing. The second irrigation is delayed until the seedlings show temporary wilting. This helps the seedlings develop roots deeper and more distributed in the subsoil than at the soil surface, and increases resistance to drought and harsh conditions. Previously, traditional farmers used a 14-day interval between irrigations. They also deliberately skipped another irrigation, usually after pruning the plants and/or early fruit flowers, to induce fruit set. During fruit growth and before harvest, the interval between irrigations is shortened to 6–8 days. Excess water during fruit ripening reduces sweetness and storage life.

Pruning

Pruning of plants, flowers, lateral branches, and fruits is an important practice in Persian melon cultivation. Plant pruning is carried out after the seedlings reach the five- to six-leaf stage, when the first lateral branches reach a length of 5 cm. It consists of removing the apical meristem of the main stem while retaining two lateral branches. These branches will form the final structure of the plant. The main reason for such pruning is that the main stem bears male flowers and delays the development of lateral branches, which bear male and female flowers. In the dryland farming method, the two lateral branches spread in opposite directions to cover the ground, reducing water evaporation and weed growth. In traditional farming, the two lateral branches are directed over the bed.

The more the plant branches, the more female flowers are formed. But not every flower produces the desired fruit, because there is strong competition among young fruits. Therefore, pruning of lateral branches and early fruit-flowers (local name “Tarash”) is carried out when the lateral branches grow to at least 50 cm in length. Then secondary lateral branches, all male and female flowers, and fruits that exist before the sixth and after the eighth leaf are removed. Fruits on the sixth to eighth leaves are retained and constitute the final crop. The final number of fruits per plant depends on its vigor. Usually, two fruits are retained on each plant. Fruits before the sixth leaf and fruits at the distal ends of the branches in most Persian melons are usually smaller than fruits in the middle part of the branch. On undamaged plants, lateral branches and fruits are formed. All fruits, especially those that appeared earlier, will be small. In fact, Tarash synchronizes the vegetative and reproductive development of plants to obtain large and high-quality fruits. This is more important for large-fruited cultivars than for small-fruited cultivars. Tarash is not necessary for small-fruited cultivars (Kashi, 2000).

Flower pruning is another cultural practice for Persian melons, which consists of selecting and retaining one or two healthy, pest-free fruits and removing all other flowers and fruits. Meanwhile, there was a local practice (before the widespread use of chemical pesticides) to protect selected fruits from the melon fruit fly (Myiopardalis pardalina). Fruits about 2 cm long were wrapped in a leaf of the same plant and buried in the ground. An alternative method on small farms was to moisten the fruits with saliva and cover them with soil. As the melon grew, the soil covering was repeated until the rind became thicker, preventing the melon fly from inserting its ovipositor into the fruit and laying eggs (Amiri-Ardakani and Emadi, 2006).

Turning Fruits

Fruits on a plant do not develop equally quickly. During fruit growth and development, their growth, health, defects, infections, etc., are carefully monitored. Turning the fruits during growth is done to prevent uneven coloration of the rind or soil infections on the part of the fruit touching the ground. Meanwhile, unnecessary lateral branches, fruits, flowers, and weeds are removed.

Harvesting

Persian melons should be left on the vine until fully ripe, of high quality, and with the greatest sugar content, but they are still firm. If left on the vine, the sugar will not increase, but the flesh will become soft and lose its tenderness. Fruits on the same plant do not ripen simultaneously.

Certain changes occur that can be used as an index, but they should be correlated with the internal state, including texture, taste, and sweetness. As the fruits approach maturity, the net becomes fully rounded and its color dulls. Immature fruits have a flattened netted shell and a small fold along the top. As ripening progresses, small cracks appear around the peduncle at the base of the fruit. The peduncle end of the fruit at this moment becomes soft, and its aroma intensifies. In Persian melons, except for some cultivars such as Tashkandi, an abscission layer called “full slip” does not develop at maturity. The sugar content (soluble solids) in the juice of the edible part is one of the most important factors, determined using a refractometer (Javanmardi, 2010). After harvest, the fruits are sorted by size, shape, color, and general appearance.

Transport and Storage

Persian melons are transported to local and distant markets usually by trucks. When loading trucks, some wheat straw is usually placed around the fruits. This prevents bruising of the fruits and keeps them dry. Persian melons are usually not stored, except for late cultivars, which are usually consumed in midwinter. They can be stored at 7–10 °C and 85%–90% relative humidity (Javanmardi, 2010).

Seed Production

Different melon groups within Cucumis melo are compatible with each other. They are insect-pollinated; therefore, the minimum isolation distance for commercial hybrid seed production should be 1000 m, although some seed regulatory agencies specify a distance of only 500 m (Raymond, 2009). Heterosis is not of great importance when the parents belong to the same cultigroup; however, it is clearly observed in F₁ hybrids between two different parental lines (Pitrat, 2008).

The conditions for producing high-quality melon seed are usually the same as those for producing high-quality fruits. Although the most important selection criteria for cucurbit growers are fruit size and fruit quality, including sugar content, aroma, flesh texture, and color (Javanmardi, 2010), selection for seed production is carried out during the production processes, starting before flowering (vegetative habit, foliage and immature fruit traits), after flowering (fruit type and morphology), during fruiting (fruit type, morphology, and external traits), and at harvest (fruit type, morphology, external traits, and fruit quality factors) (Raymond, 2009).

In Iran, melon seeds are usually extracted manually. Fully ripe melons are cut in half, and the seeds with placentas are scraped into a container. The mixture is left for several days to ferment in water before washing. Good seeds sink to the bottom of the container, while placentas and empty seeds float. Then the seeds are washed in running water. Some small producers do not follow the fermentation process. They wash the mixture in appropriately sized sieves to extract the seeds. Then the seeds are usually sun-dried. Storing dry seeds in the dark at 5 °C and low humidity will maintain their viability for 10 years or more.

Besides using seeds for planting the next year, some seeds are eaten as roasted nuts (Javanmardi, 2010), since they are rich in lipids and proteins, representing a large amount of energy (Pitrat, 2008).

References

1. Wehner, T.C., Naegele, R.P., Myers, J.R., Dhillon, N.P.S., Crosby, K. (2020). Cucurbits. 2nd ed. USA.
2. Pessarakli, M. (2016). Handbook of Cucurbits. Growth, Cultural Practices, and Physiology. The University of Arizona. School of Plant Sciences. Tucson, Arizona, USA.