Genetic diversity, allelic variation and marker trait associations in gamma irradiated mutants of rice (Oryza sativa L.).

PURPOSE: Rice is a prime staple crop for more than half of the world population. Improved White Ponni (IWP) is a premium quality grain rice variety that is fetching a good price and is increasingly popular among the consumers of Tamil Nadu. Tall plant stature of IWP makes them susceptible to lodging and medium duration are two undesirable traits in the variety increases yield losses in the field and also productivity. In this context, we aimed to generate a large mutant population of IWP irradiated with various doses of gamma irradiation to recover putative mutants for semi-dwarfism and earliness. MATERIALS AND METHODS: Totally, 34 putative mutants (22 early, 11 semi-dwarf and early and 1 Narrow-leaf dwarf mutant) were phenotyped for nine morphological traits and genotyped using 34 microsatellite markers linked to a trait of interest of earliness and semi-dwarfism. Trait variability, allelic variations, genetic structure and marker-trait associations in gamma-irradiated putative mutants of Improved White Ponni (IWP) rice were investigated in this study. RESULTS: The hierarchical clustering of morphological data produced five clusters with a dissimilarity coefficient of 1.39. A minimum dissimilarity coefficient of 0.23 was observed between the mutants IWPM9 and IWPM20 and a maximum dissimilarity coefficient of 2.55 was observed between IWPM1 and IWPM25. In cluster analysis with molecular marker data, five clusters with a similarity coefficient of 0.67 were observed. The mutant IWPM29 exhibited the most divergence from the wild type at the genotype level. The first principal component explained 50.99% of the total variability and the majority of the traits were contributed positively. The single-marker analysis revealed the strong association of SSR marker RM3912 with the traits plant height, panicle length and number of grains per panicle with an R2 value of 0.235, 0.235 and 0.250 respectively. CONCLUSIONS: The study identified semi-dwarf and short-duration rice mutants of IWP that can be utilized as potential breeding stocks. The trait-linked SSR markers can improve selection cycles in advanced breeding programs.

Assessment of efficacy of mutagenesis of gamma-irradiation in plant height and days to maturity through expression analysis in rice.

Introduction of semi-dwarfism and early maturity in rice cultivars is important to achieve improved plant architecture, lodging resistance and high yield. Gamma rays induced mutations are routinely used to achieve these traits. We report the development of a semi-dwarf, early maturing and high-yielding mutant of rice cultivar 'Improved White Ponni', a popular cosmopolitan variety in south India preferred for its superior grain quality traits. Through gamma rays induced mutagenesis, several mutants were developed and subjected to selection up to six generations (M6) until the superior mutants were stabilized. In the M6 generation, significant reduction in days to flowering (up to 11.81% reduction) and plant height (up to 40% reduction) combined with an increase in single plant yield (up to 45.73% increase) was observed in the mutant population. The cooking quality traits viz., linear elongation ratio, breadthwise expansion ratio, gel consistency and gelatinization temperature of the mutants were similar to the parent variety Improved White Ponni. The genetic characterization with SSR markers showed variability between the semi-dwarf-early mutants and the Improved White Ponni. Gibberellin responsiveness study and quantitative real-time PCR showed a faulty gibberellin pathway and epistatic control between the genes such as OsKOL4 and OsBRD2 causing semi-dwarfism in a mutant. These mutants have potential as new rice varieties and can be used as new sources of semi-dwarfism and earliness for improving high grain quality rice varieties.