Seed Production of Seedless (Triploid) Watermelon
The credit of production of seedless watermelon goes to Japanese scientists. Kihara (1951) who gave an exceptionally clear account of various steps in production of triploid fruits. The triploids are the resultant of a cross of tetraploid and diploid parent. The steps involved in triploid seed production are:
(i) Production of parental line (Tetraploid and diploid): Application of colehicine 0.2 % to 0.4% to growing points of young seedlings at 1 to 2 true leaf stage for 2 to 3 days sueecssively to induced tetraploids (44 chromosomes). The treatment is given under controlled conditions avoiding direct sunlight. The terminal growth will be slow and promoted carefully. The tetraploid plants are characterised by broad thick leaves and bigger pollen grain and at flowering pollen fertility and pollen size be tested. The seeds will be broad and bigger. Fermentation method of seed extraction to be avoided and tetraploid seed should be soaked ovenight before sowing. The maintenance of tetraploid lines at stable level is important and continous selection for improvement of quality and vigour in tetrapolid lines has to be done for atleast 4-5 generation. The seed of diploid line is produced in isolation.
(ii) Seed Production of Tripliod (3x): Triploid seed are produced by two ways :
(a) Hand pollination in female tetraploid by diploid male and pinching of male of tetrapoloid before anthesis.
(b) Pinching of male of tetraploid line and allow to open or natural cross pollination with diploid.
The planting of tetraploid and diploid is done in 1:1 ratio. Seed yield from 4:5 to 6.8 kg/acre under open pollination.
The cost of triploid is very high, germination is very poor due to hard thick seed coat. Seed germination is to be done in controlled condition which enhance the cost of production. The triploid will not set the fruit alone, therefore stimulation of fruitdevelopment has to be brought about by n pollen through bee pollination. Hence, as polinizer, a diploid cultivar has to be planted in the field with triploid field.