Introgression of blast and bacterial blight disease resistance genes in a rice genotype ADT43 through marker assisted back cross breeding.

Bacterial Leaf Blight (Xanthomonas oryzae pv. oryzae) and blast (Magnaporthe oryzae) are the major biotic stresses around the rice-growing zones of the world. The development of resistant varieties through Marker Assisted Backcross Breeding is the utmost economical and eco-friendly method for achieving stable yield. Amongst the resistance genes recognized, Xa21 and Pi54 possess broad-spectrum resistance to many Xoo and blast strains around the world. In the present study, we have effectively introgressed a Bacterial Blight resistance gene (Xa21) and a blast resistance gene (Pi54) into susceptible variety ADT43 from RP-Bio-Patho-2 coupled with phenotypic selection for agronomic, cooking quality and grain traits through MABC. MABC was sustained till BC2F2 generation with specific markers pTA248 for Xa21 and Pi54MAS for Pi54 resistance genes. A set of SSR markers for parental polymorphism were utilized for maximum regaining of recurrent parent genome in each backcrossing. "Positive plants" from BC2F1 were selfed to generate BC2F2 and the homozygous lines for bacterial leaf blight and blast resistance genes were identified for further assessment.

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.

Molecular cloning, characterization, expression and chromosomal location of OsGAPDH, a submergence responsive gene in rice ( Oryza sativa L.).

Differential clones from submergence stress and control treatment from rice seedlings were isolated by the differential screening method. One of the clones, OsGAPDH, represented a gene that was expressed at high level during 12-h submergence. A homology search of GenBank databases showed that OsGAPDH had significant sequence homology with maize non-reversible glyceraldehyde-3-Phosphate dehydrogenase. The OsGAPDH sequence consists of 1,772 bp with the longest open reading frame encoding 499 amino acids with a calculated relative mass of 54.2 kDa. Genomic Southern analysis indicated that one or two copies of the OsGAPDH gene occur in the Yukihikari genome. The chromosomal location of the OsGAPDH gene was identified by RFLP analysis indicating that OsGAPDH was located on chromosome 8. Tissue-specific expression of OsGAPDH indicated that the high level of mRNA was detected in the panicle. Plants exposed to drought, submergence and ABA treatment showed an increased accumulation of OsGAPDH transcripts. The induction of Escherichia coli cells containing the pGST-OsGAPDH plasmid resulted in the accumulation of a large amount of the 83.2-kDa recombinant protein. The purified GAPDH enzyme showed an optimum activity at pH 8.5 and 50 degrees C, and was strongly inhibited by ATP and ADP.