Hybrid Seed Production Technology
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:

i. 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.

ii. 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.

iii. 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.

iv. 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.

v. 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.

Activities	Cucumber	Squash	Muskmelon	Watermelon
Trailing/Pruning	Single Stem	Top cutting	Trail upright	Pinching of lower & upper femal flower
Fruiting node	8th node	-	11-16th node	1-2 fruit middle node (12-15 node)
Duration of pollination	10-15 days	10 days	15 days	-
Harvesting (days after pollination)	35-50 days	40-45 days pollination	full slip stage	55-65 days
Labour (acre/day)	20-25	8	25-30	12-15
Planting ratio	4:1	2:1 to 5:1	5:1 to 8:1	5:1 to 6:1
Plant pop. (ha)	19,000/ha	-	27,600/ha	8,000/ha
Curing of fruit	7-10 days	one month	7-10 days	7-10 days
Seed yield (ha)	300-500 kg.	-	200-300 kg.	100-250 kg.
Seed extraction	fermentation	fermentation	fermentation	fermentation