Pi34-AVRPi34: a new gene-for-gene interaction for partial resistance in rice to blast caused by Magnaporthe grisea

The japonica rice (Oryza sativa) cultivar Chubu 32 has a high level of partial resistance to blast, which is mainly controlled by a dominant resistance gene located on chromosome 11. The partial resistance to the rice blast fungus (Magnaporthe grisea) in Chubu 32 has isolate specificity; isolate IBOS8-1-1 is more aggressive on Chubu 32 than are other isolates. We hypothesized that the gene-for-gene relationship fits this case of a partial resistance gene in Chubu 32 against the avirulence gene in the pathogen. The partial resistance gene in Chubu 32 was mapped between DNA markers C1172 (and three other co-segregated markers) and E2021 and was designated Pi34. In the 32 F3 lines from the cross between a chromosome segment substitution line (Pi34 −) from Koshihikari/Kasalath and Chubu 32, the lines with high levels of partial resistance to the M. grisea isolate Y93-245c-2 corresponded to the presence of Pi34 estimated by graphic genotyping. This indicated that Pi34 has partial resistance to isolate Y93-245c-2 in compatible interactions. The 69 blast isolates from the F1 progeny produced by the cross between Y93-245c-2 and IBOS8-1-1 were tested for aggressiveness on Chubu 32 and rice cultivar Koshihikari (Pi34 −). The progeny segregated at a 1 : 1 ratio for strong to weak aggressiveness on Chubu 32. The results suggested that Y93-245c-2 has one gene encoding avirulence to Pi34 (AVRPi34), and IBOS8-1-1 is extremely aggressive on Chubu 32 because of the absence of AVRPi34. This is the first report of a gene-for-gene relationship between a fungal disease resistance gene associated with severity of disease and pathogen aggressiveness.