Pathogenic variation of Asian soybean rust pathogen in Bangladesh

Abstract

Asian soybean rust (ASR) caused by Phakopsora pachyrhizi is estimated to cause massive yield losses in Bangladesh. For understanding its population structure to guide deployment of durable resistance in soybean germplasm against all pathogen populations, 13 P. pachyrhizi strains collected from Lakshmipur, Noakhali and Bhola Districts in Bangladesh in 2016 were evaluated for pathogenicity on 12 soybean differentials. The tested strains had both identical and dissimilar pathogenicity profiles. Eight distinct pathotypes were identified, indicating pathogenic variation among the strains. In comparative analysis of pathogenicity profiles of 149 Latin American and 8 Japanese ASR samples, strains from Bangladesh were genetically distinct from those from the other countries and had highest similarities with Japanese strains. The most effective ASR-resistance genes were Rpp3 (PI 462312 and PI 416764) and Rpp5 (PI 200526) on which all Bangladeshi strains induced resistant lesions with little or no sporulation. The Rpp-pyramided line No6-12-1, carrying Rpp2, Rpp4 and Rpp5, had the strongest resistance; none of the Bangladeshi P. pachyrhizi strains produced uredinia or urediniospores. Therefore, pyramiding of Rpp genes should be useful for soybean breeding programs in Bangladesh.