Pathogenic Races and Virulence Gene Structure of Magnaporthe oryzae Population and Breeding Strategy for Blast Resistance in Heilongjiang Province

Abstract

Rice blast, caused by Magnaporthe oryzae, became more severe in Heilongjiang Province, China during the past few years. The objectives of this study were to understand the race and virulence gene compositions of local M. oryzae populations, and purposefully select blast resistance genes for efficient development and deployment of resistant rice cultivars. A total of 173 isolates, collected from different rice-cropping districts of the province in 2006, were tested for their pathogenicity against 9 Japanese and 7 Chinese differential varieties (DVs) together with 31 rice monogenic lines (MLs) with different blast resistance genes and 12 local leading cultivars. Out of these 173 isolates, 55 Japanese pathotypes were identified using the Japanese DVs, and the predominant races were 017, 077, 037, 377, and 047, which accounted for 38.15% of all isolates tested. The comparison of differential ability between Japanese and Chinese DVs testified that the former one was much more suitable for M. oryzae pathotyping in Heilongjiang Province. Among the 12 leading cultivars tested, only Longjing 14 and Longdun 104 still kept good resistance to blast disease. The resistance gene Pi9 showed the broadest resistance spectrum (on average 94.80%) to all the blast isolates tested, and was of the highest utilization value in rice blast resistance breeding. The resistance genes Pi-z5(CA), Pi-z5(R), Pi-ta2(R), Pi-ta2(P), Pi-12(t), and Pi20(t) also showed high utilization values due to their resistance spectra of around 70%. The most effective breeding strategy for blast resistance should be as follows: 1) to use rationally Longjing 14, Longdun 104, and Pi9 as resistance donors, and pyramid one to several broad-spectrum resistance genes into elite leading cultivars by means of marker-assisted selection; 2) to strengthen monitoring of predominant virulent races and their temporal and spatial variation; and 3) to explore new resistance resources extensively and transfer the new broad-spectrum resistance genes into leading cultivars purposefully.