Chemical- and irradiation-induced mutants of indica rice IR64 for forward and reverse genetics

IR64, the most widely grown indica rice in South and Southeast Asia, possesses many positive agronomic characteristics (e.g., wide adaptability, high yield potential, tolerance to multiple diseases and pests, and good eating quality,) that make it an ideal genotype for identifying mutational changes in traits of agronomic importance. We have produced a large collection of chemical and irradiation-induced IR64 mutants with different genetic lesions that are amenable to both forward and reverse genetics. About 60,000 IR64 mutants have been generated by mutagenesis using chemicals (diepoxybutane and ethylmethanesulfonate) and irradiation (fast neutron and gamma ray). More than 38,000 independent lines have been advanced to M4 generation enabling evaluation of quantitative traits by replicated trials. Morphological variations at vegetative and reproductive stages, including plant architecture, growth habit, pigmentation and various physiological characters, are commonly observed in the four mutagenized populations. Conditional mutants such as gain or loss of resistance to blast, bacterial blight, and tungro disease have been identified at frequencies ranging from 0.01% to 0.1%. Results from pilot experiments indicate that the mutant collections are suitable for reverse genetics through PCR-detection of deletions and TILLING. Furthermore, deletions can be detected using oligomer chips suggesting a general technique to pinpoint deletions when genome-wide oligomer chips are broadly available. M4 mutant seeds are available for users for screening of altered response to multiple stresses. So far, more than 15,000 mutant lines have been distributed. To facilitate broad usage of the mutants, a mutant database has been constructed in the International Rice Information System (IRIS; http: //www.iris.irri.org) to document the phenotypes and gene function discovered by users

Effects and possible causes of an unprecedented rice blast epidemic on the traditional farming system of Bhutan

Abstract In 1995, an unprecedented rice blast epidemic (caused by Pyricularia grisea) occurred in Bhutan in mostly traditional cultivars in the high (1800-2600 m) and some parts of mid altitude (1200-1800 m) agroecological zones. Possible causes of the outbreak such as introduction of a new pathogen race, unusual weather patterns and changes in agricultural practices were investigated and yield losses analysed. Weather data were examined for unusual patterns and farmers from the affected areas were interviewed to determine possible changes of cultural practices. Blast isolates were collected from various affected rice areas and analysed for variability of the pathogen population by MGR (Magnaporthe grisea repeat 586) fingerprinting. Rice yields declined parabolically with increasing disease with losses for some farmers being nearly 100%. Restriction fragment length polymorphism analysis using MGR fingerprints of 71 isolates resulted in 58 haplotypes that grouped into 13 lineages. Lineage BhR1 and BhR4 were represented by 22 and 13 isolates, respectively, whereas the other lineages were represented by only one to six isolates each. Haplotypic diversity both in the early and late season's collections was very high suggesting that the blast epidemic was not caused by a new introduction or race change of the pathogen. There was no drastic shift in agricultural practices or rice cultivars which could explain the blast outbreak. However, the weather data indicated that the climatic conditions in 1995 favoured blast and these unusual conditions, in combination with the ubiquitous presence of the pathogen, probably account for the epidemic