Molecular mapping of Asian soybean rust resistance in Chinese and Japanese soybean lines, Xiao Jing Huang, Himeshirazu, and Iyodaizu B

Abstract

Asian soybean rust (ASR), caused by the fungus Phakopsora pachyrhizi, is one of the most serious soybean diseases in South America and other tropical and sub-tropical areas. The soybean lines, ‘Xiao Jing Huang,’ ‘Himeshirazu,’ and ‘Iyodaizu B’ were previously identified for their resistance to ASR fungus, while the genetic basis of the resistance has yet to be known. In this study, we mapped the ASR resistance loci in these three lines using three independent mapping populations derived from crosses with an ASR susceptible variety, BRS184. In each population, resistance to ASR appeared to be primarily controlled by a single major gene. The resistance genes with largest effect from Xiao Jing Huang and Himeshirazu were genetically mapped on chromosome 18 corresponding to the same location of known resistant locus, Rpp1. On the other hand, quantitative trait locus analysis mapped the major ASR resistance locus of Iyodaizu B to the region of chromosome 16 where Rpp2 was previously mapped. Genetic mapping with DNA markers and disease reactions of seven candidates carrying Rpp1 to four Brazilian ASR isolates revealed a significant variation in their ASR resistance reaction, indicating that they share different resistance genes tightly linked to each other or different resistant alleles of a single Rpp1 gene. Therefore, these seven soybean lines could be clearly separated into at least two functional groups.