Determination of the optimum dose range of gamma irradiation for mutation induction in maize (zea mays L.)

This study was conducted to determine the optimum dose range of gamma irradiation for mutation induction in maize varieties (Mugtama-45 and Var-113). The effects of gamma irradiation on germination, emergence, root shoot ratio, growth parameters, ear parameters, yield and yield components for the two varieties were studied to select desirable mutants that can be utilized in breeding program to increase maize production and/ or productivity in Sudan, which is constrained by many biotic and abiotic factors. Dry seeds from the two varieties were treated using gamma irradiation derived from 60Co at the irradiator of the Sudan Atomic Energy Center, Khartoum, Sudan. Five doses (0, 50, 100, 150 and 200 Gy) were applied as acute (at short time) treatments. The treated seeds were used in three green house experiments to investigate germination percentage, emergence percentage, root shoot ratio and one field expermint to test the performance at Gezira Research Station Farm (GRF). The field experiments were arranged in a randomized complete block design (RCBD) with three replications, for two successive seasons 2007 and 2008, while in the greenhouse experiments Completely Randomized Design (CRD) was used. Data were collected on germination and emergence percentages, root shoot ratio, growth parameters, ear parameters and grain yield. Results showed that, effects of gamma irradiation on all measured traits increased with increasing gamma irradiation doses. The highest dose (200 Gy) resulted in significant decrease in germination percentage, emergence percentage, growth parameters, ear parameters and grain yield for Mugtama-45. In Var-113 the same trend was also observed, except for germination percentage (was not significantly decreased). Root shoot ratio was significantly increased in Var-I13, but not in Mugtama-45. Chemical analysis showed that, gamma irradiation doses resulted in significant increase in ash, protein and carbohydrates contents, while significant decrease was observed in fat content. The dose 150 Gy had stimulatory effect on protein content for the two varieties, which could be used to select for desirable mutants with high protein content. Grain yield for the two varieties revealed highly significant positive correlation with effective ear length, ear diameter, 100 kernels weight, weight of kernels/ear, dry ear weight, plant height, ear height and number of plants at harvest, with acoefficient of correlation value ranged from 36 to 78%. Mean squares for season x treatment interaction in Var-113 were significant for ear height, ear weight husked, ear weight dehusked, effective ear length, number of kernels/ row and number of rows/ ear, whereas in Mugtama-45 only threshing ability, effective ear length and number of kernels/row revealed significant effects. As the numbers of plants at harvest and grain yield depend mainly on plant survival more than germination % and emergence %, the optimum dose range necessary for mutation induction is highly governed by the survival rate. High number of chlorophyll mutants was observed at doses of 100 and 150 Gy, for Var-l13 and Mugtama- 45, respectively. Accordingly, the optimum dose range of gamma irradiation for mutation induction is 50 -150 and 100 -150 Gy for Var- 113 and Mugtama- 45, respectively