Control of growth cycle of onion for high yield and quality seed production

The present study was stimulated by the problem of onion seed production in Bangladesh and similar regions where seed production is possible only during the short cool winter period after which rapid increase in temperature as well as early shower adversely affect the quality of seed. Experiments were carried out in order to develop suitable production techniques to get high yield and quality of onion seed overcoming the stated adverse situation. The present research was conducted at the Horticulture Farm, Department of Horticulture, Bangladesh Agricultural University, Mymensingh and in the Plant Genetic Laboratory of Bangladesh Institute of Nuclear Agriculture, Mymensingh during the period from 1997-98 to 1999-2000 to manipụlate the control of growth cycle of onion for high yield and production of quality seed. А series of experiments were conducted mainly on planting time, pre-planting cold temperature treatment, duration of pre-planting cold temperature treatment, bulb size, plant spacing and shading condition. The results revealed that the number of days required for 80% emergence of bulb, plant height, number of leaves per hill, days required to bolting, seed set per umbel, seed yield per umbel and germination percentage of harvested seeds were significantly influenced by the treatment of different experiments under study. Results showed that among different planting time, November 1 was the best for seed yield and quality. Early planting gave higher seed quality. Accelerated seed crop development was achieved by pre-planting cold treatments. Onion bulbs treated by 12°C temperature performed best with 45 days duration of pre-planting cold treatment. Also 7°C temperature, as well as 30 days duration gave significant results. Pre-planting cold treated seed crop enhanced bulb emergence and completed vegetative growth earlier, also early initiation of flower stalks, flowering, fruit setting, maturity and consequently quality seed. From preplanting cold treatment, seed crop was harvested at least 11-14 days before the nontreated ones. Bulb size influenced the yield and quality seed production. Medium sized (10-15 g) bulbs produced more effective flowering stalks and showed better performance on seed yield and quality. Whereas, small (5 g) and large (20 g) sized bulbs produced less seed yield due to less flower stalks and less effective flowering stalks, respectively. In case of plant density, maximum seed yield and quality was obtained from medium density (20 x 20 cm). High density (20 x 15 cm) gave high yield by increasing plant population per unit area and low density (20 x 25 cm) reduced higher seed yield per unit area due to less plant population. Seed yield was the highest under 50% shade condition compared to 25% shade and no shade (control), but in respect of seed quality (1000 seed weight and germination) open condition was the best.