Effect of bulb size and duration of vernalization on onion (allium cepa l.) seed yield

Abstract

In Kenya onion seeds are very expensive because they are all imported due to lack of low temperatures for vernalization requirements. A study was conducted in 1992 and 1993 at Kabete to determine the effect of bulb size, vernalization temperature and duration on onion seed yield. It also aimed at comparing artificial and natural vernalization on onion seed production. Three introduced onion cul tivars namely KON2, KON4, KON6 and locally popular Tropicana Hybrid were grown at Kabete for bulb production. Bulbs of three sizes (40, 55 and 80 mm diameter) were vernalized naturally at Njambini (2530 m above sea level) and artificially at 10° in an incubator. The non vernalized bulbs were stored at Kabete at room temperature (17-18°C). The mother bulbs were vernalized for 1, 2, 3 and 4 months and grown at Kabete for two seasons. The experimental design was a split-split- split plot with three replicates. Results indicated that vernalization temperatures, duration and bulb size significantly influenced seed yield of all cultivars. Flower stalk length, number of leaves per plant, days to flowering and seed maturity were inversely related to duration of vernalization. One thousand-seed weight and germination percentage increased with increasing vernalization duration. Percent flowering, number of flower stalks per mother bulb, number of florets per umbel and seed yield significantly increased with storage duration to an optimum of two and half months. Vernalization of mother bulbs significantly reduced the number of leaves per plant, days to flowering, seed maturity and flower stalk length but significantly increased percentage of flowering shoots, number of seed stalks per plant, the number of florets per umbel, 1000-seed weight, seed yield and germination percentage. An increase in bulb size significantly increased the percentage of flowering, number of seed stalks per plant, number of florets per umbel, flower stalk length, number of leaves per plant and seed yield but had no significant effect on days to flowering and seed maturity, 1000-seed weight and germination percentage. The optimal storage duration and bulb size for seed production were 2~ months and large bulb size (80 mm diameter), respectively. Natural vernalization was as effective as artificial vernalization and therefore, can be utilized for commercial onion seed production