Effect of cobalt-60 gamma irradiation on viability of soybean (glycine max. l) seed

Thumbnail Image
Journal Title
Journal ISSN
Volume Title
The rapid rate of deterioration and low viability of soybean seeds particularly in storage is a major constraint to its production in the subtropical and tropical areas. Various approaches have been made to solve this problem but they have centred mainly on the control of the environment. Experimental mutagenesis is one of the ways by which genetic variability could be created to serve as basis for selection. In this study, induced mutations were used to create genetic variation and mutants with improved storability selected to provide a more lasting solution to this problem. Seeds of three soybean varieties - Gmx 92-6-10, Gmx 92-5-4E and TGX 87D- 1303 were subjected to four (4) months ambient storage and three accelerated ageing tests. The germination percentages computed 7days after planting showed that 20% ethanol solution better mimicked ambient storage than 20% methanol solution and the 75°C hot water. In the radiation dosage response studies, dry seeds containing 10% moisture from the three varieties were subjected to 0, 50, 100, 150, 200 and 250 Gy doses of 60Co gamma rays at Ghana Atomic Energy Commission, Kwabenya and sown. The 250 Gy dose reduced both germination percentage and plant height by about 50% relative to the control and was used as the dosage appropriate for induced mutations for the varieties. Five thousand M2 plants were harvested and screened individually for improve storability using 20% ethanol solution, storing threshed seeds at ambient condition and storing seeds in pods also at ambient conditions. The 20% ethanol solution was less effective in selecting putative in mutants compared to the two ambient storage screening methods, but could be used as an initial screening method. The variety Gmx 92-6-10 was generally considered to give the greatest response to irradiation because it produce the largest proportion of putative mutant improved storability in two out of the three screening methods used at the M2 generation. Since TGX 87D_1303 produced the smallest proportion of putative mutants with improved storability at the M2 generation was considered the meat unresponsive. Only mutants with 80% germination and above were selected in the M2 to produce the M3 generation. The amount of improvement gained depended on the variety and the screening method In Gmx 92-6-10, the improvements from selection of M2 and M3 over the control were 25.7 % and 60.3% respectively. The improvement of M3 over M2 was 45.3%. In Grnx 92-5-4E, the improvements from selection of M2 and M3 over the control were 17.0% and 63.7% respectively whilst the improvement of M3 over M2 was 42.3%. For TGX 87D 1303, the improvements from selection of M2 and M3 over the control were 24.7% and 32.7% whilst the improvement of M3 over M2 was 65.0%. Even though TGX 87D-1303 gave the smallest proportion of improved mutants, it produced the highest gain in selection at the M3 generation
A Thesis Submitted to the School of Graduate Studies, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana, in partial fulfilment of the requirements for the award of Master of Science (M.Sc.) Degree in Plant Breeding, 2001