Abstract
BackgroundRice blast is a destructive disease caused by Magnaporthe oryzae, and it has a large impact on rice production worldwide. Compared with leaf blast resistance, our understanding of panicle blast resistance is limited, with only one panicle blast resistance gene, Pb1, isolated so far. The japonica cultivar Miyazakimochi shows resistance to panicle blast, yet the genetic components accounting for this resistance remain to be determined.ResultsIn this study, we evaluated the panicle blast resistance of populations derived from a cross between Miyazakimochi and the Bikei 22 cultivar, which is susceptible to both leaf and panicle blast. The phenotypic analyses revealed no correlation between panicle blast resistance and leaf blast resistance. Quantitative trait locus (QTL) analysis of 158 recombinant inbred lines using 112 developed genome-wide and 35 previously reported polymerase chain reaction (PCR) markers revealed the presence of two QTLs conferring panicle blast resistance in Miyazakimochi: a major QTL, qPbm11, on chromosome 11; and a minor QTL, qPbm9, on chromosome 9. To clarify the contribution of these QTLs to panicle blast resistance, 24 lines homozygous for each QTL were selected from 2,818 progeny of a BC2F7 backcrossed population, and characterized for disease phenotypes. The panicle blast resistance of the lines harboring qPbm11 was very similar to the resistant donor parental cultivar Miyazakimochi, whereas the contribution of qPbm9 to the resistance was small. Genotyping of the BC2F7 individuals highlighted the overlap between the qPbm11 region and a locus of the panicle blast resistance gene, Pb1. Reverse transcriptase PCR analysis revealed that the Pb1 transcript was absent in the panicles of Miyazakimochi, demonstrating that qPbm11 is a novel genetic component of panicle blast resistance.ConclusionsThis study revealed that Miyazakimochi harbors a novel panicle blast resistance controlled mainly by the major QTL qPbm11. qPbm11 is distinct from Pb1 and could be a genetic source for breeding panicle blast resistance, and will improve understanding of the molecular basis of host resistance to panicle blast.
Highlights
Rice blast is a destructive disease caused by Magnaporthe oryzae, and it has a large impact on rice production worldwide
Compared with leaf blast resistance, less is known about the genetic components for panicle blast resistance, which is indispensable for stable rice production
This study used three experimental fields under different pressure from rice blast to demonstrate that the rice cultivar Miyazakimochi harbors panicle blast resistance without correlation with leaf blast resistance
Summary
Rice blast is a destructive disease caused by Magnaporthe oryzae, and it has a large impact on rice production worldwide. Variations in heading date among individual plants further complicate the evaluation of resistance levels These technical problems are obstacles to the exploration of new gene resources and the progress of genetic analysis of rice panicle blast resistance. Both QTL analyses indicated the presence of a major QTL on the long arm of chromosome 11, and the location of the QTL corresponded to the qPbm region, suggested from the information of the marker sequences. An assay under gentler conditions for panicle blast disease might be required to evaluate the effect of minor QTLs. because of the difficulty and complexity of evaluating panicle blast resistance, the QTL analyses were influenced by many factors. We conclude that the major QTL qPbm is responsible for resistance to panicle blast in Miyazakimochi
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