A systematic review on physical mutagens in rice breeding in Southeast Asia

In the 1920s, Lewis Stadler initiated the introduction of permanent improvements to the genetic makeup of irradiated plants. Since then, studies related to breeding mutations have grown, as efforts have been made to expand and improve crop productivity and quality. Stadler's discovery began with x-rays on corn and barley and later extended to the use of gamma-rays, thermal, and fast neutrons in crops. Radiation has since been shown to be an effective and unique method for increasing the genetic variability of species, including rice. Numerous systematic reviews have been conducted on the impact of physical mutagens on the production and grain quality of rice in Southeast Asia. However, the existing literature still lacks information on the type of radiation used, the rice planting materials used, the dosage of physical mutagens, and the differences in mutated characteristics. Therefore, this article aims to review existing literature on the use of physical mutagens in rice crops in Southeast Asian countries. Guided by the PRISMA Statement review method, 28 primary studies were identified through a systematic review of the Scopus, Science Direct, Emerald Insight, Multidisciplinary Digital Publishing, and MDPI journal databases published between 2016 and 2020. The results show that 96% of the articles used seeds as planting materials, and 80% of the articles focused on gamma-rays as a source of physical mutagens. The optimal dosage of gamma-rays applied was around 100 to 250 Gy to improve plant development, abiotic stress, biochemical properties, and nutritional and industrial quality of rice.

Induced variability and assessment of mutagenic effectiveness and efficiency in sorghum genotypes [Sorghum bicolor (L.) Moench]

PURPOSE

Sorghum is an important cereal crop, cultivated for food, fodder and biofuel. Mutation breeding techniques are used to create genetic variability for qualitative and quantitative traits in crop plants. The purpose of this study was to create induced variability and estimate mutagenic effectiveness and efficiency of physical and chemical mutagens in two sorghum cultivars.

MATERIALS AND METHODS

Gamma rays (100, 200, 300 and 400 Gy, Co⁶⁰ source, Bhabha Atomic Research Center, Mumbai, India), ethyl methane sulphonate (0.1%, 0.2%, 0.3%, and 0.4% EMS, Sigma-Aldrich, India) and their combinations were used to mutagenize 296B (rainy season) and Parbhani moti (post-rainy) cultivars. Morphological and yield traits were analyzed for enhanced variability in qualitative and quantitative traits across M₂ and M₃ generations.

RESULTS

Based on the mutagenic sensitivity, lethal dose at 50% survivability (LD₅₀) for both the genotypes was found to be 269-281 Gy in case of gamma rays and 0.32-0.33% for EMS. Based on reduced germination and survivability, mutagenic sensitivity was dose dependent and genotype independent. High frequency of chlorophyll mutations (albino, xantha, viridis, variegated and chlorine) were linearly correlated with dose in both the genotypes. Among the favorable mutants, dwarf and brown midrib were isolated from Parbhani moti population, which could be used in the cross breeding programs. A combined treatment, 100Gy +0.1% EMS showed high mutagenic effectiveness and efficiency. Enhanced genetic variation for quantitative traits as measured by wide range values and coefficient of variation was attributed to the effect of physical and chemical mutagens. Early flowering, high grain yield (24-49% increase over control) were identified in M₂ and validated in M₃ generation in both genotypes.

CONCLUSIONS

This study has revealed wide genetic variability and better effectiveness and efficiency of the physical (300 Gy) and chemical mutagens (0.2%) and their combination (200 Gy+ 0.2%) across two sorghum genotypes. Significant correlations identified between quantitative traits will help in better selection in the segregating generations.