Abstract
The quality of onion seeds deteriorates rapidly during harvesting, processing and storage at ambient condition. To overcome this situation a series of field and laboratory experiments were conducted at BAU, Mymensingh, Seed Pathology Centre, BAU, Mymensingh and Seed Testing Laboratory, BADC, Dhaka during September 1998 to August 2002 to study the quality of onion seeds as affected by harvesting, threshing, cleaning, drying and storage methods. Quality of onion seeds assessed through determination of purity, seed weight, germination, vigour, seed health and field performance of stored seeds.
A survey was conducted with a questionnaire to find out the existing technology of seed production, processing and storage practices of onion seeds at farmers' level in the major onion seed production areas of Bangladesh. The survey reports showed that high cost of seed production was due to higher cost of mother bulbs are used for seed production. From field and laboratory experiments it was concluded that best quality of seeds were obtained when the crop was harvested at the stage from 20-30% of the capsules dehisced and threshed by hand or by mechanical thresher. The mechanical method of cleaning was the best instead of cleaning by winnowing using kula. Quality seed was also obtained from the seed samples which were dried under shade over cemented floor, under shade over polythene sheet and by mechanical dryer. Experiments to assess the effect of containers, seed moisture levels, storage conditions and storage period showed that seed stored in sealed aluminum foil bag and sealed metal container, at 6-7% seed moisture level, under dehumidified or refrigerated condition gave the best performance followed by jute bag with polythene lining. In ambient condition with low moisture level in sealed aluminum foil bag or metal container may be used. It was found that ten different seed borne fungal pathogens representing five genera were associated with onion seeds of which the pathogens were Aspergillus niger, A. flavus, Fusarium oxysporum, F. culmorum, F. poae, Alternaria porri, Alternaria tenuis, Curvularia lunata, Penicillium atramentosum and P. pinophilum. The results showed that it is useful if the standard germination test is supplemented by a vigour test, particularly by seedling evaluation and length measurement test. Moreover, field performance of the stored seed was done to confirm the germination and vigour test.