59-05-032 Proceeding

63 Proceedings of the Princess Maha Chakri Sirindhorn Congress 2,700 plant mutant varieties [9]. For sorghum, only 15 mutant varieties have been released [10]. This researchwas taken to obtain new sorghummutants for high yield by usingmutation breeding. II. Materials and Methods Seeds of sorghum (Yezin-7) were obtained from the Department of Agriculture Research, Yezin.Theywere irradiatedwith different doses (100, 200, 300, 400, 500, 600 and 700Gy) of Gamma ray at the Department of Atomic Energy, Yangon. The LD-50% of sorghum (Yezin-7) was 780 Gy. According to IAEA [11], the effective dose for inducing mutations should be lower than that of the LD-50 value. The M1 generation was raised in the field of the Biotechnological Research Department, Kyaukse during 2013 cultivated season. The seeds subjected to Gamma irradiation were sown along with the control following randomized block design (RBD) with 3 replications, at the spacing of 15 cmwithin plants and 45 cm between plants in M1 generation. Harvesting was done by using bulk harvesting method. For each treatment, more than 250 seeds fromM1 generationwere taken randomly to grow in M2 generation. They were planted following (RBD) with 3 replication during 2014 cultivated season. The spacing was 15 cm within plants and 45 cm between plants. All treated plants and control plants were carefully screened for viable mutations and spectrum of mutations. The frequency of mutants was calculated in percentage on the basic of number of mutants identified versus plant population of each treatment. Data were collected for the yield contributing traits viz., plant height, stem width, panicle length, panicle width, number of seeds per plant, 100 seed weight, yield per plant and days to maturity. III. Results and Discussions A. Frequency and spectrum of viable mutations In M2 generation, a total plant population of 1546 surviving plants was harvested. In order to induce variability and utilize useful mutations for efficient plant breeding, the systematic study of induced viablemorphological mutations inM1 andM2 generation is themost dependable index [12]. Morphological changes in leaf structure, plant habit, panicle shape, seed color, seed size, seed shape and day to maturity were scored inM2 generation (Figure 1). These mutants were characterized and named on the basis of specific characters for spectrum of viable mutations. A high frequency and spectrum of viable mutations was observed in M2 generation (Table 1). Leaf type mutation consisted of narrow leaf mutants and broad leaf mutants. Dwarf mutants, tall mutants and twin stem mutants were included in plant type mutation. Panicle and seed type mutation contained twin paniclemutants, compact paniclemutants, spread paniclemutants, pink seed mutants, brown seed mutants, round seed mutants, long seed mutants, small seed mutants and bold seed mutants. The highest frequency of leaf type mutations was found at 500 Gy (0.93). Dose 300 Gy induced the highest frequency of plant type mutations (1.26). The highest frequencies of panicle