Molecular mapping of Asian soybean rust resistance in soybean landraces PI 594767A, PI 587905 and PI 416764

Asian soybean rust (ASR), caused by Phakopsora pachyrhizi, is one of the most serious diseases of soybean. The soybean landraces PI 594767A, PI 587905 and PI 416764 previously showed high levels of resistance to a wide range of ASR fungus, while the genetic basis of the resistance has yet to be understood. In this study, the ASR resistance loci were mapped using three independent mapping populations, POP‐1, POP‐2 and POP‐3 derived from crosses BRS184 × PI 594767A, BRS184 × PI 587905 and BRS184 × PI 416764, respectively. In each population, the resistance to ASR segregated as a single gene, but the resistance was dominant in PI 594767A and PI 587905 and incompletely dominant in PI 416764. The resistance genes from both PI 594767A and PI 587905 were mapped on chromosome 18 corresponding to the same location as known resistance locus Rpp1. Quantitative trait locus (QTL) analysis performed on POP‐3 identified the putative ASR resistance locus in PI 416764 on the defined region of chromosome 6 where Rpp3 was located. The QTLs detected by the mapping explained about 67–72% of the phenotypic variation in POP‐3. Cluster analysis based on disease reactions to 64 ASR populations demonstrated the presence of at least two types of functional resistant Rpp1 alleles: strong and weak allele(s), e.g. soybean accession PI 594767A and PI 587905 carry the strong resistant Rpp1 allele(s). Introducing or pyramiding strong Rpp1 allele(s) in elite soybean cultivars is expected to be useful against the South American rust population.EEA PergaminoFil: Hossain, Motaher M. Japan International Research Center for Agricultural Sciences (JIRCAS); Japón. Bangabandhu Sheikh Mujibur Rahman Agricultural University; BangladeshFil: Akamatsu, Hajime. Japan International Research Center for Agricultural Sciences (JIRCAS); JapónFil: Morishita, Masami. Japan International Research Center for Agricultural Sciences (JIRCAS); JapónFil: Mori, T. Japan International Research Center for Agricultural Sciences (JIRCAS); JapónFil: Yamaoka, Yuichi. University of Tsukuba. Faculty of Life and Environmental Sciences; JapónFil: Suenaga, Kazuhiro. Japan International Research Center for Agricultural Sciences (JIRCAS); JapónFil: Soares, Rafael Moreira. Empresa Brasileira de Pesquisa Agropecuária (EMBRAPA). National Soybean Research Center (EMBRAPA Soja); BrasilFil: Bogado, Alicia Noelia. Instituto Paraguayo de Tecnología Agraria (IPTA). Research Center of Capitán Miranda (CICM); ParaguayFil: Ivancovich, Antonio Juan. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Pergamino; ArgentinaFil: Yamanaka, Naoki. Japan International Research Center for Agricultural Sciences (JIRCAS); Japó

Pathogenic diversity of soybean rust in Argentina, Brazil, and Paraguay

Phakopsora pachyrhizi, the cause of soybean rust, is an economically important pathogen of soybean in South America. Understanding the pathogenicity of indigenous fungal populations is useful for identifying resistant plant genotypes and targeting effective cultivars against certain populations. Fifty-nine rust populations from Argentina, Brazil, and Paraguay were evaluated for pathogenicity in three cropping seasons, 2007/2008–2009/2010, using 16 soybean differentials. Only two pairs of P. pachyrhizi populations displayed identical pathogenicity profiles, indicating substantial pathogenic variation in the rust populations. Comparative analysis of 59 South American and five Japanese samples revealed that pathogenic differences were not only detected within South America but also distinct between the P. pachyrhizi populations from South America and Japan. In addition, seasonal changes in rust pathogenicity were detected during the sampling period. The differentials containing resistance genes (Rpp: resistance to P. p achyrhizi) Rpp1, Rpp2, Rpp3, and Rpp4, except for Plant Introduction (PI) 587880A, displayed a resistant reaction to only 1.8–14, 24–28, 22, and 36 % of South American P. pachyrhizi populations, respectively. In contrast, PI 587880A (Rpp1), Shiranui (Rpp5), and 3 Rpp-unknown differentials (PI 587855, PI 587905, and PI 594767A) showed a resistant reaction to 78–96 % of all populations. This study demonstrated that P. pachyrhizi populations from South America vary geographically and temporally in pathogenicity and that the known Rpp genes other than Rpp1 in PI 587880A and Rpp5 have been less effective against recent pathogen populations in the countries studied.EEA PergaminoFil: Akamatsu, Hajime. Japan International Research Center for Agricultural Sciences (JIRCAS). Biological Resources and Post-harvest Division; JapónFil: Yamanaka, Naoki. Japan International Research Center for Agricultural Sciences (JIRCAS). Biological Resources and Post-harvest Division; JapónFil: Yamaoka, Yuichi. University of Tsukuba. Faculty of Life and Environmental Sciences; JapónFil: Soares, Rafael Moreira. Empresa Brasileira de Pesquisa Agropecuária (EMBRAPA). National Soybean Research Center (EMBRAPA Soja); BrasilFil: Morel, Wilfrido. Instituto Paraguayo de Tecnología Agraria (IPTA). Research Center of Capitán Miranda (CICM); ParaguayFil: Ivancovich, Antonio Juan. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Pergamino; ArgentinaFil: Bogado, Alicia Noelia. Instituto Paraguayo de Tecnología Agraria (IPTA). Research Center of Capitán Miranda (CICM); ParaguayFil: Kato, Masayasu. Japan International Research Center for Agricultural Sciences (JIRCAS). Biological Resources and Post-harvest Division; Japón. National Agriculture and Food Research Organization (NARO). Agricultural Research Center (NARO/ARC); JapónFil: Yorinori, José Tadashi. Empresa Brasileira de Pesquisa Agropecuária (EMBRAPA). National Soybean Research Center (EMBRAPA Soja); Brasil. Tadashi Agro; BrasilFil: Suenaga, Kazuhiro. Japan International Research Center for Agricultural Sciences (JIRCAS). Biological Resources and Post-harvest Division; Japó