Efficiency of electron beam over gamma rays to induce desirable grain-type mutation in rice (Oryza sativa L.).

PURPOSE: Rice is the predominant crop of Tamil Nadu state, India that occupies about 30% of the total cropped area. However, grain type and quality are the critical traits that determine the market value and domestic consumption rice variety. Most of the households of Tamil Nadu, India prefer to consume medium slender to fine grain type of rice. Hence, the present study was conducted to induce medium slender grain type in popular rice variety ADT 37 (Aduthurai 37), a short bold rice variety using gamma rays (GR) and electron beam (EB) mutagens. MATERIALS AND METHODS: Healthy, dried seeds (12.0% moisture content) of ADT 37 rice variety were exposed to various doses of GR (100-500 Gy) and EB (200-600 Gy). The irradiated population were maintained up to M4 generation by plant to progeny row basis to identify stable mutants for grain-type variation. The selected grain-type mutants (medium slender- and slender-type mutants) in M4 generation were characterized for phenotypic and grain quality traits. RESULTS: A high frequency of desirable grain-type variation was observed in EB-irradiated population than gamma-irradiated population. A total of 25 grain-type mutants (long slender and medium slender) were obtained in M4 generation of ADT 37 variety. The morphological characterization and cooking quality assessment of the 'grain-type' mutants revealed that six out of 25 mutants viz., M-3 (Mutant-3), M-5, M-9, M-10, M-13 and M-15 recorded single plant yield of more than 30 g. There was non-significant variation in yield per plant (g) among the mutants and control (parent) due to key changes in grain type and thousand grain weight. CONCLUSION: EB showed higher mutation frequency, mutagenic effectiveness and efficiency than the GR in inducing both chlorophyll and viable mutants. This study revealed that the percentage contribution of the EB was 2.57 times higher than that of GR in obtaining desirable slender and medium slender grain-type mutants. The grain-type mutants obtained in the present study can be either directly released as variety or used as parents in hybridization program of rice crop improvement.

Screening tolerance to phosphorus starvation and haplotype analysis using phosphorus uptake 1 (Pup1) QTL linked markers in rice genotypes.

Phosphorus (P) deficiency tolerance is a pivotal trait for plant growth and development. Most of the commercial modern cultivars lack this trait and reported it as a very serious problem limiting crop productivity. This trait is advantageous if present in modern high yielding varieties as it increases the yield under the phosphorus-deficient soil conditions. With the importance of phosphorus deficiency tolerance, the present investigation was carried out with an objective to screen for tolerance to phosphorus deficiency using solution culture and phosphorus uptake 1 (Pup1) locus linked markers in 30 diverse rice genotypes. A wide range of varied responses to P deficiency in rice genotypes for all the traits were observed. Root length and enzyme activity showed increased mean performance under the - P condition when compared to + P condition. Medium to high heritability estimates were obtained for most of the traits. Correlation analysis showed that the traits: root P content, fresh shoot weight, dry shoot weight, and shoot length showed highly significant correlations with each other under - P conditions. Based on the hydroponics and molecular screening, three genotypes viz., ADT (R) 48, Improved Pusa Basmati 1 and UPLRI 5 were classified as tolerant for its response to P deficiency as they possessed significant increase in desirable root and shoot traits, increased acid phosphatase enzyme and these genotypes also possessed the Pup1 allele for all the five markers. The selected genotypes may be useful for the exploration of novel genes conferring phosphorus deficiency tolerance and used as donor parents in the breeding programs. Absence of this allele in the rice genotypes viz., drought tolerant (Anna (R) 4) and submergence tolerant (CR 1009 Sub 1) may warrant the development of multiple abiotic stress tolerance cultivars for upland and submergence cropping systems in future rice breeding program.

Molecular evaluation of genetic diversity and association studies in rice (Oryza sativa L.).

In the present study, we tested rice genotypes that included un(der)exploited landraces of Tamil Nadu along with indica and japonica test cultivars to ascertain their genetic diversity structure. Highly polymorphic microsatellite markers were used for generating marker segregation data. A novel measure, allele discrimination index, was used to determine subpopulation differentiation power of each marker. Phenotypic data were collected for yield and component traits. Pattern of molecular differentiation separated indica and japonica genotypes; indica genotypes had two subpopulations within. Landraces were found to have indica genome, but formed a separate subgroup with low linkage disequilibrium. The landraces further separated into distinct group in both hierarchical clustering analysis using neighbour-joining method as well as in the model based population structure analysis. Japonica and the remaining indica cultivars formed two other distinct groups. Linkage disequilibrium observed in the whole population was considerably reduced in subpopulations. Low linkage disequilibrium of landforms suggests their narrow adaptation in local geographical niche. Many population specific alleles could be identified particularly for japonica cultivars and landraces. Association analysis revealed nine marker-trait associations with three agronomic traits, of which 67% were previously reported. Although the testing landraces together with known cultivars had permitted genomewide association mapping, the experiment offers scope to study more landraces collected from the entire geographical region for drawing more reliable information.