Everything you need to learn about the production of quality vegetable seed under protected conditions.
Although cost of seed is only a fraction of the total cost of inputs involved in growing a vegetable crop but timely providing availability of good quality seed is the basic unit in increasing the production and productivity. Raising healthy seedlings through good quality seed, suitable cultural practices and optimum environmental conditions are pre-requisite for success in vegetable growing.
Inadequate availability of quality seed is one of the major causes of low productivity and poor quality of vegetable produce. Thus, in order to enhance the production and productivity of vegetable, it is necessary to increase the production of quality vegetable seeds.
Protected vegetable cultivation has been to increase the production of quality vegetable seeds for off-season and long duration commercial purposes. Raising seed crops of high value vegetable crops under protection can further enhance production and quality of seeds.
The protected structures may be climate controlled greenhouses, semi-climate controlled greenhouses, naturally ventilated greenhouses, insect proof net-houses, walk-in-tunnels, low cost poly-houses and plastic low tunnels etc. Greenhouses, mainly the climate and semi- climate controlled are also used for seed production of high value vegetables as the crops get very short crop season under open field conditions.
The high value vegetables include slicing tomatoes, cherry tomatoes, sweet peppers, parthenocarpic cucumbers etc. The major constraint for using this type of structure is that the basic or initial cost of fabrication and running cost of such greenhouses is very high which increases the seed cost as compared to seed produced under other structures or under open field conditions, but yield and quality of seed under such structures is always very high.
Naturally ventilated greenhouses can be used for seed production of tomato, sweet pepper, cucumber including parthenocarpic cucumber, summer squash, muskmelon etc. but the duration for seed crop and the seed yield are less compared to climate controlled or semi- climate controlled greenhouses.
The insect proof net-houses can be used commercially for seed production of sweet pepper, tomato, brinjal and other vegetables like cucurbits etc. These structures can be used to protect the crops against viruses and other insects like fruit bores during rainy and post rainy season but the seed yield is always less compared to all kind of greenhouses including cost of seed production, which is also very less compared to greenhouses.
Walk-in-tunnels can be used commercially for seed production of cucurbits like muskmelon, watermelon, summer squash, bottle gourd, bitter gourd etc. even during off-season but these structures can only be used during peak winter months to protect the crops against low temperature injury (Dec-mid Feb) in north Indian plains. Walk-in-tunnels, plastic low tunnels and even rain shelters are suitable for raising seed crops of onion, French bean, leek, garden pea etc. especially in hills where their seed maturity coincides with the rains.
Plastic low tunnels can be used commercially for off-season seed production of cucurbits. The basic purpose is to advance the seed crops which is not possible under open field conditions of northern plains of India.
The important points required for to be considered for quality seed production under protected conditions are as follows:
1. Training and Pruning:
Source-sink relationship affects the growth habit, fruit bearing pattern and seed yield in cucurbits and solanaceous vegetables. In tomato, the growth habit can be indeterminate, semi-determinate or determinate. The indeterminate varieties/hybrids are preferred for hybrid seed production inside the greenhouses.
Such plants can be grown over a long period and produce a number of fruit trusses. Indeterminate tomato varieties are staked and trained upright. Pruning of side branches are done to maintain single stem or maximum double stem. Seed production of determinate or semi-determinate varieties is less popular and not preferred under greenhouse conditions.
Usually first to fourth cluster at each branch are selected for emasculation in case of hybrid seed production. In single stem, terminal pinching is carried out after 6 to 10 clusters. Lateral shoots are removed regularly. Defoliation of leaves commences at the time of setting of fourth cluster only. The training and pruning is a very regular process in greenhouse tomato crop hence a careful attention is always helpful in high seed yield.
Pruning in sweet pepper is normally limited to the shoots that grow on the stem below the first branching, or to some of the weak side shoots. Pepper leaves have a rather low level of photosynthetic efficiency and consequently a large area of active leaves is necessary to produce sufficient dry matter.
Pruning is done only in few cases where the growth is luxuriant. Under protected cultivation, the stem structure of pepper is often too weak to take the load of the plant, hence there is a need to train the plant. Pepper plants should be trained upright by allowing two main branches after removal of first terminal bud in a way to expose the leaves to the maximum light, the canopy must always be ventilated.
The sweet pepper seed crop can be grown for a period of 9 to 10 months depending upon the climatic conditions of the area. The eggplant has an upright growth habit, hence horizontal strings fixed on either side of the plant row are enough to support them.
A good pruning system consists of removing the side shoots up to the position of first flower appearance, allowing two branches to develop from the first terminal flower node, followed by periodic removal of shoots from the inner part of the plant and removal of the oldest leaves suffice to allow good air exchange and a balanced framework of plants.
Cucumber requires a supporting system in order to grow vertically by means of its tendrils. Plastic or fibre strings are useful for training. They hang down from wire stretched at height of 1.5 to 2.0 m.
Pruning operations are summarized here under needs regular and careful attention for cucumber seed crop:
A. Long-Fruited Cultivars:
The side shoots and fruits on the main stem are removed up to a height of 60-70 cm. The fruits are then allowed to set on the main stem up to a height of 2 or 3 meter. Side shoots up to 2 m length are not allowed. Above 2 m length, three branches are allowed to develop. The fruits are allowed to set up to first 2-3 nodes. De-shaped fruits and old leaves are removed in order to improve aeration.
B. Short-Fruited Cultivars:
The fruits and side shoots of the main stem are removed up to a height of 40-50 cm. Further pruning is done as follows:
I. The side shoots are pruned to 1 fruit/leaf. The fruits on the main stem are removed.
II. The side shoots are pruned to 1 fruit and 2 leaves. The fruits on the main stem are removed.
III. The side shoots are pruned to 1 fruit and 2 leaves. The fruits on the main stem are allowed to develop.
IV. The side shoots are pruned to 1 fruit and 2 leaves up to 1m., then pruned to 2 fruits and 3 leaves up to 2m. The fruits on the main stem are removed.
Parthenocarpic Varieties:
In gynoecious or parthenocarpic cucumber varieties, one single stem is allowed from the beginning of the plant and fruits are allowed on the main stem only. Three seed crop of such varieties are possible under greenhouse conditions in a period of one year.
Muskmelon:
In muskmelon single stem training is the commonest system. The plants are trained upright. All branches below 6-8 nodes are removed. Female flowers are retained on branches emerging from 9-16 nodes on the main stem. After fruit set the tips of the branches are pinched off retaining 2-3 leaves per branch.
The top of the main stem is pinched off after 25 nodes. In double stem training system, the main stem is pinched off at the second leaf stage and the plants are trained upright with 2 main branches. The secondary branches appearing on each of the 2 main axis may be pinched off after the first fruit-set or two leaves afterwards. Maximum 3 to 4 fruits are allowed per plant for optimum growth.
The tips of the two main branches are pinched off up to 20-25 nodes. The middle portion of the plant should be allowed to retain the fruits. After harvesting first 3 to 4 fruits, further fruits may be allowed to set. In muskmelon, the duration of seed production can be doubled by this way to increase the seed yield.
Watermelon:
In watermelon, the main stem is trained upright along with 3-4 strong branches with the help of plastic strings. The first female flower, if it develops below 8-10 nodes on the main stem, is pinched off. In the middle portion of the plant 2-3 fruits are allowed to develop between 12-25 nodes.
The growing tip of each branch after 2nd or 3rd node is pinched off. For small-fruited varieties, 4 fruits are allowed to develop per plant. The developing fruits are provided a support using nylon net bags if insect pollination has been used in the protected structures.
Summer Squash:
In summer squash, the main stems and branches are short, thus, making the plant bushy. And ad such does not require any training and pruning. The older leaves are, however, removed for proper aeration. The winter squash has long vines and needs upright training. The main stem is pinched off at 4 nodes allowing two strong branches to develop. Two fruits are allowed to set on each branch between 12-16 nodes. The main branches are pinched off at 30 nodes. Each developing fruit is provided with a support using a nylon net bag.
2. Emasculation and Pollination:
Flowering period in male and female parents is synchronized by adjusting the sowing time. In solanaceous vegetables, the emasculation of the perfect flower on the seed parent is done a day prior to anthesis, leaving the petals intact. Such petals turn yellow (in tomato), purple or white (in brinjal) and white (in sweet pepper) on the day of anthesis.
Flowers with under developed inverted stigmas are pinched off. Fresh pollen from several plants of male parents is collected by a vibrator on the day of anthesis. Since only ripen pollen are shed by vibrating the flowers, such pollen have the highest viability.
Pollen is collected in a small cup attached to a finger ring or other container as per need. Pollination is done by dipping the stigma into the pollen mass. Half of the calyx of pollinated flowers is removed to distinguish it from un-pollinated flowers. In eggplant, the stigma is quite receptive a day prior to anthesis.
Hence, emasculation and bud pollination can be done simultaneously, a day prior to anthesis which is quite successful. Since the bees do not visit the emasculated flowers in solanaceous crops, bagging of emasculated flowers is not necessary. Pollen grains can be stored for a long period i.e. 1 to 2 months at 0°C using silica gel for their proper drying.
The sex expression in cucurbits is mainly monoecious, andromonoecious and gynoecious. The perfect flowers on ‘the seed parents’ in muskmelon and cucumber are emasculated a day prior to anthesis which is not required in parthenocarpic varieties. The perfect flowers of watermelon on the other hand are not emasculated, as the anthers do not produce viable pollen. The emasculated flowers are bagged in order to avoid chance self-pollination. In monoecious plants, the female flowers are bagged a day prior to anthesis.
The male flowers are either collected in the evening a day prior to anthesis and are kept in a moist polythene bag or collected early in the morning (5 am) on the day of anthesis. Pollination is done on the day of anthesis by dusting pollen on the stigma of the female flowers. Pollination work commences at 7 am and completed by 9.30 am. Pollinated flowers are re-bagged to avoid contamination by visiting bees.
Pollination work continues up to 15 days in muskmelon and cucumber and up to 10 days in watermelon and squash. Emasculation and pollination work requires 20-25 laborers/day/acre in case of muskmelon and cucumber. Pollination and bagging in watermelon and squash requires 12-15 laborers per day/acre.
Insect pollinators like honey bees (Apis melifera or Apis indica) are largely used in cucurbitaceous vegetables under protected seed production but proper and careful management of the pollinators is required to avoid pollinator’s destruction. Similarly, in case of tomato, ‘bumble bees’ are the best pollinators among insects but they are not available in India. Hence, only option left is to use electric bee or vibrators or hand pollination in open pollinated varieties.
3. Harvesting in Fruit/Vegetable Seed Crops:
The mature fruits in different vegetable crops are harvested at different times after pollination. The stages of harvest in some of the important crops are as under (Table 12.2).
4. Fruit Curing:
The fruits need be cured prior to seed extraction. The duration of curing in different crops are given as under (Table 12.3).
5. Seed Extraction:
In tomato, cucumber, watermelon and muskmelon, the seeds are extracted by fermentation method. Under warm condition, the fermentation process is complete in 24 hours. At 25°C, it requires 2 days for the completion of fermentation process. The pulp is stirred several times in a day to maintain uniform rate of fermentation and to avoid dis-colouration of the seeds.
Fermentation methods of seed extraction also control the seed borne bacterial canker in tomato. The seeds are washed thoroughly with excess of clean water. Tomato seeds are also extracted using 10 cc of 36 percent HCL or 30% of NaOH is added to 4.0 kg of tomato pulp.
The treatment is given for a period of 15 minutes, and then washed with clean water. In eggplant and bell pepper, the ripe fruits are crushed and washed. In squash, the seeds are separated from the placental material using rice bran and then washed. Seed drying is done using dry air at 28-30°C.
Expected Seed Yield in Different Vegetable Crops:
The seed yield, though, varies depending upon the crop or variety, protected structure and crop management in different vegetable crops but with good management 100-700 kg seed can be harvested from one hectare in different vegetables.
Advantages:
i. Off-season seed production is possible in several vegetables, especially in cucurbits.
ii. Seeds of vegetables can be produced all the year round by avoiding the season.
iii. High seed yield can be obtained from small area of a protected structure.
iv. Production of virus free quality seed is possible even during rainy or post rainy season.
v. Provides the best opportunity for organic seed production in vegetables.
vi. Uniform establishment of seed crops leads to quality seed production.
vii. Early fruiting leads to advancement in seed production.
viii. More fruit setting due to congenial climatic conditions under protection provides long duration for fruit setting.
ix. Different cross pollinated crops/varieties belonging to same family/crop can be grown in adjacent greenhouses for seed production without any problem of isolation distance.
x. Handling is very easy during winter season.
xi. Seed production is possible even if soil salinity is high using soil-less media for cultivation.
xii. Seed in case of parthenocarpic varieties of cucumber is only possible under protected conditions.
xiii. Several seed crops are possible under a protected structure in a duration of one year.
xiv. Crop is protected from heavy rains and viral disease transmitted by insect vectors like white flies etc.
xv. The protected area is always kept neat and clean so objectionable weed or diseased plants etc. under check.
Constraints:
i. Normally the cost of seed production is high.
ii. The seed production job is highly labour intensive and technical.
iii. Difficulty in the maintenance of the pollinators under protected conditions.
iv. Soil borne fungus sometimes becomes a severe problem for crop production.