Genetic variation of infection degrees to blast disease among rice genotypes

The blast of rice caused by Pyricularia oryzae is a disease prevalent throughout the world. The pathogen overwintering in rice straw and stubble for many years makes disease mitigation difficult. Among all available methods of managing disease, the use of resistant varieties is an economical approach. The objective of this study was to identify genotypes with slow-blasting that could be used in breeding resistant hybrids. A total of 25 rice genotypes with different combinations of resistance genes were tested in 2013 and 2014 for rice blast resistance. The reactions of genotypes varied from highly resistant to highly susceptible. Of the 25 genotypes tested in 2013, only three were highly resistant to leaf blast (disease score: 1), while Rasi and RamanadStr3 were resistant (disease score: 2). Genotypes Co39 and HR12 were highly susceptible recording a disease score of 8 and the remaining genotypes were classified as susceptible with scores ranging from 5 to 7. In 2014, only Tetep genotype was found highly resistant to leaf blast with disease score '1', and genotypes NILA57, RamanadStr3, Shia-tia-tsao, IR64, Rasi, and Tadukan were resistant with disease scores ranging from 2 to 3. The remaining genotypes were susceptible to leaf blast with disease scores of 4-7 and two genotypes Co39 and HR12 were highly susceptible to leaf blast (disease scores: 8-9). For neck blast, all genotypes were resistant (disease scores: 0-3) in both years except for CO39 and HR12, which were recorded as moderately resistant in 2013 and resistant in 2014. Based on 2 years of data on the apparent rate of infection, area under the disease progress curve, and components of slow-blasting, the genotypes viz., IR64, Tadukan, Rasi, Tetep, and RamanadStr3 were identified as slow-blasting types. Hence, these genotypes can be harnessed to develop blast-resistant varieties in rice breeding programmes.