Knowledge of genetic resources is essential for breeders to create new crop varieties with improved characteristics. In this respect, mutant populations may conveniently provide a powerful tool for identifying new functional genes. Therefore, we used the Micro-Tom tomato variety, which has a reduced size and a relatively short life-cycle compared to other commercial tomato cultivars, to construct a mutant population using gamma-ray radiation as a mutagen. To determine the optimal mutagenic intensity of gamma rays for tomato, dry seeds of Micro-Tom were irradiated with gamma-ray intensities from 0 to 1000 gray (Gy) with increments of 100 Gy. The germination rate of mutagenized seeds (M1 seeds) on MS media was not affected by the tested gamma-ray intensity range. However, seedling growth was severely reduced with increasing irradiation. Seedling growth rate at eight days after germination showed that the median gamma-ray doses for hypocotyl and root elongation were 600 and 300-400 Gy, respectively. The survival test for 300, 400, and 500 Gy-treated M1 seeds showed that survival rates significantly decreased with increasing irradiation. The survival rate of 400 Gy-radiated seeds was 48%, while that of 500 Gy-radiated seeds was only 25%, compared with the control treatment. Therefore, we concluded that gamma-ray irradiation at 300-400 Gy is best for tomato mutagenesis. To find new mutants, M2 seeds produced by M1 plants were grown. We found several mutants, including plants with varying cotyledon number, variegated or red leaves, and green hypocotyls.
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Mutation is an effective strategy not only for creating novel variation into crop genome but also for direct releasing adapted and high-yielding genotypes. The current work explores inducing genetic variability in bread wheat using physical and chemical mutagens. Three wheat cultivars were treated by three mutagens; gamma irradiation (five doses; 250, 300, 350, 400 and 450 Gray); laser ray (three treatments; 1, 1.5, and 2 hour exposure) and EMS (three concentrations; 0.2, 0.3 and 0.4%). Besides, a combination of physical (laser) and chemical (EMS) mutagens using middle range of each treatment (1.5 hour laser and 0.3% EMS) was attempted to be applied. The treated seeds were sown in the first season and 4050 M1 plants were harvested. The harvested seeds were sown in the second season, and 78750 M2 plants were obtained. The selection was performed in second season (M2) based on morpho-physiological and yield traits; flag leaf area, flag leaf chlorophyll content, plant height, spike length, grain yield per plant and its components. Based on evaluated traits fourteen mutants were selected to be evaluated in the third generation (M3). The results indicated that the used mutagens had direct impact and significantly improved agronomic traits in derivative mutants compared to their parent cultivars. Moreover, the maximum increment in yield related traits were obtained by 0.4% EMS, 1 and 2 hour-laser, 350-Gy, 1.5 hour × 0.3% EMS and 250-Gy. The obtained results highlighted the importance of these doses of applied mutagens to induce useful genetic variability in bread wheat for improving grain yield and contributing traits.
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