Durable resistance to asian soybean rust by gene pyramiding durable resistance to asian soybean rust by gene pyramiding

Abstract

The objective of this study was to summarize the evolution of scientific research about fungus Phakopsora pachyrhizi affecting soybean; to develop and validate KASP molecular markers in soybean populations for Asian soybean rust (ASR) resistance genes Rpp1 (PI 200492, PI 594538A, PI 587880A, PI 594723), Rpp2 (PI 230970), Rpp3 (PI 506764), Rpp4 (PI 459025A), and Rpp5 (PI 506764, PI 200487), and pyramid Rpp genes in soybean populations. A scientometric analysis was applied in the Thomson Reuters Web of Science database that reported studies of the ASR from 1945 to 2018. Several articles aiming to understand fungal etiology and strategies to control the pathogen were published. There was an increase in the number of publications between 2005 and 2013 related to ASR dissemination in America. Several countries, institutions, and plant scientists are deeply involved in ASR research and have been making efforts to control this disease and ensure food security worldwide. The F2 soybean populations derived from crosses between rust-susceptible (55I57RSF IPRO, 63I64RSF IPRO) x rust-resistant sources (PI 200492, PI 594738A, PI 587880A, PI 594723, PI 230970, PI 506764, PI 459025A, and PI 200487), were individually evaluated in field conditions for ASR phenotypic reactions. SNP markers were developed according to markers associated with Rpp genes available at the SoyBase, using KASP methodology. Based on a slight difference in map position and different phenotypic disease reactions of PI 200492, the PI 594723 carries a resistance gene Rpp1-b mapped in Chr 18 in a 12.4 cM region. A total of 26 KASP markers were significantly associated with ASR. Among these, M1, M5, and M6 (Rpp1), M13 and M14 (Rpp2), M16, M17 and M20 (Rpp3), M25 and M26 (Rpp4), and M27 and M28 (Rpp5) had the potential to be used in marker-assisted selection strategies. From the markers validation, fifteen pyramided populations with different Rpp genes were developed, and the F3 lines were evaluated for phenotypic resistance and yield. The Rpp1-b of different resistant sources (PI 587880A, PI 594723, PI 4538A) have higher resistance and yield performance comparing other genes. The best gene combinations were Rpp1-b + Rpp5, showing neither uredinia formation nor sporulation in more than 70% of the F3 population. Rpp-pyramided lines developed in this study have the potential to be used in backcross programs for improving Asian soybean rust resistance.