Abstract
With a view to improve bulb and seed yield potentials of summer onion, seeds of BARI Piaz-2 were irradiated with 75 Gy, 100 Gy and 125 Gy doses of gamma rays from a 60Co source in 2006.Fifty four days old seedlings were transplanted on 20 January 2007.Thirteen, 12 and 9 M1 plants, respectively, from 75 Gy, 100 Gy and 125 Gy dosesproduced fertile seeds which were kept separately dose wise. In M2 generation, seedlings of 13 progenies from 75 Gy, 10 from 100 Gy and 7 from 125 Gy were transplanted on 15 December 2008 in plant- progeny- rows and 11, 7 and 6, respectively, were selected based on higher percentage of seed producing plants compare to parent BARI Piaz-2.In M3and M4 generations, 13 progenies, 6 each from 75 Gy and 100 Gy and the other from 125 Gy were further selected based on higher seed yield than the parent. Additionally, in M3 generation, observation trial with the above 13 mutant lines for bulb yield potential in Kharif-I seasonin 2011 revealed the mutant lines BP2/75/5 and BP2/100/2 had significantly higher fresh and dry bulb yield than BARI Piaz-2 and that of BP2/75/2 had not differed significantly. Shelf life expressed here as rate of weight loss on storage for 2.0 months under ambient condition exhibited all the 13 mutants had longer shelf life than the parent and the check variety. The mutant BP2/100/2 had the longest shelf life followed by BP2/125/1 and BP2/100/12 and BP2/75/13. Preliminary yield trial for seed yield potential in M4 generation in winter season of 2011-2012 showed all the 13 mutant lines could produce seed from seed in the same season but the parent BARI Piaz-2 failed. In advance yield trial for bulb yield potential in Kharif-II season of 2012, the mutants BP2/75/2, BP2/75/5 and BP2/100/2 produced significantly higher bulb yields atIshurdi and Magura than the check variety BARI Piaz-3.Unlike Kharif-I season the shelf life of the bulbs of mutants and the check variety did not differ significantly in Kharif-II although yield was almost double. Advance yield trial for seed yield potentialsin 2012-13 of five selected mutants showed all the mutant lines produced sufficient seeds from seed in the same season like preliminary yield trial. Seed production of the mutants ranged from 798-1193 kg/ha with the highest being in BP2/75/3 followed by BP2/75/2 while the parent BARI Piaz-2 produced the lowest seed yield of all.
Highlights
Onion (Allium cepa L.) is one of the most important and major spices crop here in Bangladesh
On the other hand the parent variety BARI Piaz-2 could not produce any seed or negligible amount of seeds (Fig.1). This might be due to the predicted segmental homology of the chromosomes of mutants due to duplication by irradiation which might ensure regular meiosis and regular seed production (Chakraborty, 2011 and Hoque, 2011) observed longer chromosome length of the mutants than the parent BARI Piaz-2 apart from increased DNA contents by 1.5 to 3.0 fold
The effective mutations for higher bulb and seed yields along with longer shelf life could be induced in summer onion by gamma irradiation dose range of 75Gy-125 Gy
Summary
Onion (Allium cepa L.) is one of the most important and major spices crop here in Bangladesh. Of the total production 0.4-0.5 million tons become spoiled due to short storage ability of the existing varieties This means to meet the demand we have to produce 0.5-0.6million tons or more onion. Onion seed is produced from bulb by planting in the month of October, which requires nearly 1.5 to 2.0 tons of bulbs to plant a hectare of land. This big amount of bulb is sufficient to meet the annual requirement of 42-56 families of Bangladesh. Production of seed from seed will require only 8-10 kg of seed for the same area of land
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