Floral biology of onion construed as an annual crop for seed production

Abstract

Floral biology of onion was studied employing 14 genotypes grown as annual crop for seed production in which bulbs were produced by transplanting the seedlings during first week of September, harvesting prematurely during last week of December, curing subsequently for 4 days and replanting the bulbs without storage during 29-30 December in open field condition. All the genotypes behaved as short-day tropical type in which flowering stalks were induced even at 25.35o/ 11.74oC day/ night temperature during last week of December to last week of January. All the eleven floral characters varied significantly among the genotypes. Days required from replanting of the bulb to initiation of scape ranged between 33.12 to 41.67 days. Days required from scape initiation to opening of first flower in the umbel ranged between 26.22 to 32.47 days and it took 26.22 to 32.66 days from opening of first to last flower in the umbel. Dichogamous self-pollination control mechanism in the bisexual flowers of onion was manifested by differential maturity of the style and filaments at anthesis, the average length of the style (1.43 mm) being half of that of the filament (3.10 mm) at anthesis. It took on an average 4.75 days for the style to mature and become of the same size as that of filament to reach the vicinity of its own pollens in the anthers. Pollen grains which were small and more or less oblong to oval in shape showed both high viability and germinability with significant variation among the genotypes. The germinating liquid containing 20% sucrose + 0.025% of boric acid was found adequate for in vitro pollen germination.