Screening of rice blast resistance in Thai upland rice using pathogenicity assays and molecular markers

Abstract

ABSTRACT Rice blast disease caused by the fungus Pyricularia oryzae is one of the most devastating diseases of rice (Oryza sativa L.). Therefore, the use of resistant rice varieties would be the most effective way to control this disease. Based on disease evaluation, upland rice varieties were classified into two groups: resistant (35%) and moderately resistant (65%). Forty upland rice varieties and two lowland rice varieties were genotyped for seven major rice blast resistance genes Pi37, Pid2, Pi9, Pi36(t), Pi5, Pik-m, and Pi54. The gene frequencies of the seven major R genes ranged from 2.38% to 100%. The 42 varieties contained one to five R genes. Two varieties had five blast resistance genes, whereas 21 varieties contained four R genes, 15 varieties contained three R genes, 3 varieties contained two R genes, and only one variety contained one R gene. Furthermore, the relationship between the presence of different R genes and disease reactions was investigated using a multiple stepwise regression model. Three markers, Pi5, Pi54MAS, and Ckm2, for three R genes (Pi5, Pi54, and Pik-m) were moderately correlated with blast disease with partial correlation coefficients of 0.35 to 0.47. These results provide new sources of resistance genes for designing future breeding program to develop leaf blast-resistant rice varieties.