Pathogenicity of soybean rust populations in Brazil 4 cropping seasons 2007 - 2011.

Soybean rust caused by Phakopsora pachyrhizi is one of the most serious threats to soybean production in Brazil. In this study, we evaluated pathogenicity of the 7 rust samples collected in Brazil in the 2010/11 season based on infection types produced on 16 differential varieties, and compared them with those in 3 seasons of 2007/08?2009/10. When the data were classified into 3 categories: susceptible, intermediate, and resistant, none of the 7 samples from the 2010/11 season showed identical pathogenicity profile in the differentials. Cluster analysis and principal coordinate analysis revealed that 31 rust samples from the 4 seasons vary geographically and temporally in pathogenicity. The cluster analysis divided the 31 samples into 2 groups (A and B), and the 7 samples from the 2010/11 season were scattered throughout in both groups. The frequencies of susceptible reaction produced in differentials 3?6, 9, 10, and 12 were significantly higher for group A than for group B. The differentials containing resistance genes Rpp1, Rpp2, Rpp3 and Rpp4, except for PI 587880A, displayed resistant reaction to only <13%,