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Variation of the avirulence gene AvirPib among a worldwide collection of isolates of Magnaporthe oryzae

Chunda Feng: University of Arkansas

<div>Blast disease, caused by the fungus <em>Magnaporthe oryzae </em>(<em>Mo</em>), is one of the most destructive diseases of rice. Deploying resistant cultivars, based on the understanding of race population structure, is the most economical and effective way to manage this disease. The <em>Pib</em> gene, which confers high resistance to a wide range of races of <em>Mo</em>, has been used in global rice breeding programs for over 30 years. The objectives of this study were to investigate the <em>AvrPib</em>-based race structure in Africa, Asia, and North and South American populations of <em>Mo</em>, and then dissect molecular mechanisms underlying variation in <em>AvrPib</em>. The phenotype of all isolates from the four populations was tested on the <em>Pib</em>-monogenic line IRBLb-B. The genotype of each isolate was characterized by triple cycles of PCR assays targeted the whole gene, coding, and upstream regions of <em>AvrPib</em>. High resistance frequencies among isolates in some populations indicated that <em>Pib</em> is still effective in such populations. Various combinations of phenotype/genotype were identified, indicating that genetic diversity of <em>AvrPib</em> was different in some populations. A total of 15 isolates, selected from each population, were subjected to re-sequencing of <em>AvrPib</em>. Functionality of novel <em>AvrPib</em> variants, which were not previously detected, were validated by a mutagenesis assay. The results can provide insights on the effectiveness of deploying rice cultivars containing the <em>Pib</em> resistance gene.</div>