लता या बेल वाली सब्‍जीयों (कुकरबि‍ट) के बीज उत्‍पादन की तकनीक 

1. Varietal Seed Production of cucrbits

Requirement of seed production

The basic requirement of seed production is availability of improved varieties/hybrids and their demand among the farmers. Preferably the variety should be released and notified for certified seed production, however, any kind/variety can be multiplied for Truthfully Labeled Seed (TFL). The status of available varieties are given in table 2 and table 3.

Isolation requirements

The cucurbits are cross pollinated in nature and honeybees are major pollinator, thus for pure seed production an isolation distance all around seed field is necessaryto separate it from fields of other varieties, fields of the same variety not confirming to varietal purity requirement. The isolation distance of 400 m for C.S. and 800 m for F.S. and at least 1000 m isolation is required for breeder seed production.
It is important to mention that muskmelon, longmelon and snapemelon (phoot) can cross with each other. Similarly, species of genus Cucurbita have the risk of crossability among them. The cucumber can cross easily with its wild relative Cucumis hardwickee found in wild form in sub-mountanious regions of Himalayas.

Choice of season and areas of seed production :

Seed crop should be raised in such a seasons which remain dry at the time of seed maturity and seed extraction. Rainy season is preferred over summer season for raising seed crop.
Locations are also important in seed production with reference to seed yield and quality of seed. To harness the advantage of climate, private sector seed companies are organizing their seed production in these areas. The Jalana (Aurangabad) in Maharashtra, Ranibenur and around Bangalore in Karnataka, Nandyal Vlley in A.P., are the main areas of seed production.

Table: Major cucurbits seed production regions in India

Roguing

Seed crop is to be monitored at various stages of crop growth for removal of off-type and obviously should be carried out before flowering to avoid natural cross-pollination. However, fruit set and complete fruit development stages are also important. The crop-wise main features described here under for effective roguing (George, 1985).

Maturity of fruit:

Cucurbits takes fairly long time to attain harvestable maturity. The maximum period is required in crops like pumpkin (Cucurbita moschata), ashgourd and watermelon, however, muskmelon, round melon and bitter gourd take relatively lesstime. The maturity also influenced by the environmental factors and crop management (trailing etc.). The maturity period is shorter in summer season than rainy season. 

Table: Harvestable maturity in cucurbits in India

Besides days to maturity, some other parameters like change in colour also used as crietria of maturity index. 
Cucumber and summer squash: Fruit turn pale yellow to golden yellow and attached with plant. 
Pumpkin: Fruit redena and seeds inside the shell break readily from pulp. 
Muskmelon: Full slip stage. 
Watermelon: Fruits are ready for harvest when they reach edible maturity, fruit colour change from green/white to pale yellow of under side of the fruit. 
Bitter gourd and snake gourd: Fruit turn to bright yellow. 
Bottle gourd: At maturity fruit colour fade to straw green or pale yellow. 
Luffa: Complete drying/fruit turn to gray colour.

Seed Extraction

There are two method of seed extraction employed in cucurbits.

1. Dry method: 

The dried fruits are cut from one side and the seeds comes out from the fruit e.g. sponge gourd, ridge gourd, snake gourd.

2. Wet method: 

This method is employed for seeds extraction of cucumber, muskmelon, watermelon, ash gourd, bitter gourd, round melon and long melon. The fruit of cucumber and bitter gourd, summer squash and long melon are cut longitudinally and seed is scooped out while fruit of muskmelon and pumpkin are cut into two piece and seed is scooped out from cavity. However, in case of watermelon and ash gourd whole central portion are manually scooped out and macerated to separate the seed from pulp. In wet method, the seed extraction done by three ways :

1. Mechanical Extraction: In this method the fruits are cut into pieces and macerated by machine. The seeds are separated out from pulp by floating with water. This method is quick, less expensive and seeds retain good lusture, but require good amount of water. This method is applicable in bottle gourd, watermelon, round melon and ash gourd.

2. Natural Fermentation: The scooped material kept in wooden/plastic or steel veseal for 48 hours at room temperature and stired 2-3 times and then seed is washed thoroughly with water 2-3 times. The main problem with this method are discolouration and poor lusture of seed.

3. Chemical Extraction: 25-30 ml. of HCL or 8-10 ml. of commercial H2SO4 added per 5 kg of pulp and some quantity of water is mixed, stirring of pulp is done to enhance to separation and left for 30 minutes. The impurities will float and seed will sink. The seed should be washed thoroughly with clean water. This is quick method but accuracy of acid and time is important (Agarwal, 1980).

Seed Yield

Seed yield depends upon the crop, variety, location, season and management of the seed crops. 

Seed attributes of selected cucurbits varieties of IARI

2. Hybrid seed production of cucurbits

To exploit the phenomenon of heterosis the basic requirements are presence of hetrotic combination, flower size and colour, pollen production capacity of male plant and longer duration of stigma receiptivity, easiness in emasculation and pollination, attraction to insect as a means of pollen transfer, seed setting and their economic feasibility in production as well as adoption.

Since, most of the cucurbits are having large flower size, separation of male and female part (monoecious sex form), coloured petals (yellow/white), easiness in emsculation and pollition, adequaccy of pollen grain and nectaries support the production of F1, hybrid seed.

Three Steps in F1 Hybrid Seed Production:

Three steps involved in F1 hybrid seed production are

1. Development of inbred line and their production: The inbred lines developed through exploiting inbreeding depression and fixation of the desired traits in them. The seed of the developed lines are produced in isolation or by hand pollination.
2. Testing of combining ability: The combining ability (gca/sca) is tested by line x tester or dialled cross method.
3. Production of F1 hybrid seed: Techniques have been developed and is variable for crop to crop.

Techniques of Hybrid Seed Production:

1. Hand emasculation and hand pollination: 

This technique is applicable for limited scale produciton, since lot of trained labour are required in pinching, pollen collection and hand pollition.

2. Hand emasculation and pollination by insect: 

The male flowers from female lines are pinched off day before of anthesis regularly, which honeybees and other insects (voluntary) uses as a pollinizer. The male and female are grown in alternate rows. The fruit set on female lines are of hybrid and harvested for seed extraction.

The planting ratio varies within the crops e.g. summer squash 3:1 and 4:1 in muskmelon and cucumber but depend upon the population of bees in plot. The technique used in bottlegourd, pumpkin, muskmelon, cucumber, summer squash andbittergourd for hybrid seed production.

3. Use of genetic male sterility system:

 Genetic male sterlity system have been utilized for commercial hybrid production in muskmelon (Punjab Hyb.-1). The genetic male sterlity in muskmelon controlled by single recessive gene (msms). For hybrid seen production, the male sterile line used as female parent. Since genetic male sterile line is maintained in heterozygous forms, 50% fertile plants are to be removed at flowering.

The other 50% having non-dehiscent empty anther are retained in female rows. The female and male are grown in 4:1 ratio. However, to maintain the good plant population in female rows it is suggested that seed parent should be sown with double seed rate. It is also advised that female line seedling should be raised in polythene bags and transplanted at flower appearance in order to avoid the fertile plants in female rows.

The pollination is done by honey bees and 1 to 2 medium sizes hives are good enough to ensure the good pollination and fruit set at female row. 

The male sterile line is maintained in hetrozygous form by crossing with maintainer line under adequate isolation distance or under cover.

4. Use of gynoecious sex form : 

The gynaecious sex form have been commercially exploited in hybrid seed production of cucumber (Pusa Sanyog) at IARI R.S. Katrain and in muskmelon (MH-10) at PAU, Ludhiana.

For hybrid seed sproduction female and male rows are planted in 4:1 ratio. The female (seed parent) bear only female flowers and pollition in done by insect (honeybee). To ensure the good fruit and seed recovery, the sufficient population of honeybee 1 to 1½ colony of midium size has to be kept at the boundry of seed production plot to boost the amount of crossing.

The parental lines i.e. male parent maintained by selfing (mixed pollination) and rouge out undesirable plants before contaimation take place. The female lines i.e. gynoecious lines maintained by inducing the staminate flower through the sprays of silver nitrate 200 ppm at two to four true leaf stage and then selfing is carried out. It was observed that 10-11 male flowers appear per 100 nodes.

The performance of gynaecious lines are unstable under high temperatue and long photo period condtions (Hormuzdi and More, 1989) because of their thermo-sepcific responses for gynaecious stability. That is why the gynaecious cucumber did not receive much attention in the tropical countries. However, few true breeding tropical gynaecious lines in cucumber and muskmelon have been developed at IARI. As a result of development of true breeding line, muskmelon hybrid Pusa Rasraj was developed. These homozygous gynoecious lines are maintained by using GA3, 1500ppm or silver nitrate 200-300 ppm or sodium thio sulphate 400 ppm to induce staminate flowers at two and four true leaf stage. Homozygous lines are planted in strict field isolation. The gynoecious lines are crossed with monocious male parent to produce F1 hybrid.

5. Hybrid seed production through chemical sex expression: 

The hybrid seed can also be produce in cucurbits by the application of chemicals for attaining the sex of cucurbits. Specific chemicals are known to induce femaleness and maleness as desired. The spraying of ethrel (2-choloro-ethyl-phosphonic acid) 200-300 ppm at two and four true leaf stage and another at flowering is useful for inducing the pistilate flower successively in first few nodes on the female in bottlegourd, pumpkin and squash for F1 seed production, Verma et al., 1985.

The row of male parent is grown side by the side of female and natural cross pollination is allowed. In the absence of insect, hand pollination is possible when two sexes are separate. Four to five fruit set at initial nodes are sufficient for hybrid seed. The complete suppression of male flowers in squash can be achieve at higher concentration of (400-500 ppm) of ethrel applied twice and has made hybrid seed production comparatively easier and nearly 56% of toal squash seed produced in USA is of F1 hybrid.

The other chemicals like GA3, (10-25 ppm) in cucumber, MH-(100 ppm), ethephone (600 ppm) in squash induces female flowers.

Hybrid Seed Production Activities

Different activities carried out for F1 hybrid seed production of cucumber, Squash, Muskmelon and Watermelon are given in table.

Authors:

Dr.BS Tomar,

 Sr. Scientist, Seed Production Unit, IARI New Delhi

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