Author : Vilaphone Kanyasone

Summary : Rice blast disease, caused by Pyricularia oryzae is one of the most devastating disease of rice worldwide including Laos. The feasible control for rice blast is the use of resistant cultivars. The objective of this study was to evaluate the reactions of 36 rice varieties to blast and to genetically characterize the blast pathogen. Twenty-eight isolates of P. oryzae were collected from three different rice areas in Luangprangbang province, Laos, and eight isolates of P. oryzae from Thailand. Single conidium isolates were inoculated onto thirty-six commercial rice varieties. The rice varieties TDK21-B24, JHN and IR81431 cultivars had shown a high level of resistance against isolates from Laos and Thailand. When parents were screened against 28 isolates, it was found that TDK21 was resistant to isolates with its RI value of 0.81. Clustering of thirty-six blast isolates using thirty-six cultivars has shown pathotypic similarity index of 40%. In virulence testing of thirty-six blast isolates against 36 test varieties 14 isolates were virulence (39%) and 22 were avirulent. The genetics of to blast (TDK21) donor was crossed with TDK5 susceptible. The F1 seedlings of the cross between TDK5 with TDK21, the most susceptible and resistant checks, respectively, in the LPB3-2 isolate Laos was resistant, indicating dominance of resistance over susceptibility. In the F2 population, the ratio of resistant and susceptible seedling in the cross of TDK5 x TDK21 showed goodness fit to the expected ratio of 3R : 1S (x2=0.04, P=0.090-0.080). In this research the studied population and 5 resistant cultivars might be of interest to breeders from Laos