Characterization of three soybean landraces resistant to Asian soybean rust disease

Luciano Nobuhiro Aoyagi,Yukie Muraki,Naoki Yamanaka

doi:10.1007/s11032-020-01132-w

Abstract

Phakopsora pachyrhizi is an obligatory biotrophic fungus that causes Asian soybean rust (ASR) disease. ASR control primarily involves chemical control and the use of resistant soybean cultivars carrying an Rpp (resistance to P. pachyrhizi) gene. This study aimed to characterize the ASR resistance of three soybean Asian landraces. By screening the world core collection (WC) of soybean, which consists of 80 varieties, three landraces were identified in Southeast Asia as resistant to ASR. Genetic mapping using the F2 population derived from a cross with an ASR-susceptible variety, BRS 184, indicated that KS 1034 (WC2) has ASR resistance conferred by a single dominant resistance gene, mapped on chromosome 18, in the same region where Rpp1 was mapped previously. The BRS 184 × WC61 (COL/THAI/1986/THAI-80) F2 population, on the other hand, showed an ASR resistance locus mapped by quantitative trait locus analysis on chromosome 6, in the region where the resistance conferred by PI 416764 Rpp3 resides, with a logarithm of the odds score peak at the same position as the marker, Satt079, while the BRS 184 × WC51 (HM 39) population showed the resistance to ASR allocated between Satt079 and Sat_263 markers, also in the region where Rpp3 was mapped previously. Both WC51 and WC61 have the same infection profile as FT-2 and PI 462312 when tested against the same ASR isolate panel. These three WCs can be used in MAS programs for introgression of Rpp1 and Rpp3 and the development of ASR-resistant cultivars in the breeding program.

Highlights

Asian soybean rust (ASR), caused by the obligatory biotrophic Basidiomycota fungus Phakopsora pachyrhizi (Sydow & Sydow), is one of the most severe diseases affecting soybean (Glycine max), causing losses of up to 80% in ideal conditions in the various geographic regions where it has been reported, costing annually an estimated US $1.77 billion, on average (Godoy et al 2016).Currently, the strategies for ASR management and control include the application of chemical fungicides (Embrapa 2019) and the use of specific cultivation practices, such as the elimination of secondary hosts and the introduction of soybean-free growth periods 53 Page 2 of 12(sanitary periods) (Langenbach et al 2016)
Depending on the Rpp gene present in the soybean and the Avr gene of the P. pachyrhizi isolate involved in the interaction, different symptoms are observed: an incompatible-type interaction of the soybean plant in response to the pathogen; an expressed immune reaction governed by the resistance gene Rpp1, or the formation of reddish-brown lesions (RB) governed by the other Rpp genes resulting from programmed cell death and promoting the limitation of sporulation and fungal growth; and the susceptible reaction, characterized by tan-colored lesions (TAN), resulting from the total sporulation of P. pachyrhizi pustules (Van de Mortel et al 2007)
The three selected resistant genotypes were crossed with an ASR-susceptible Brazilian cultivar BRS 184 (BRS 184 × WC2, BRS 184 × WC51, and BRS 184 × WC61), resulting in the F2 mapping populations with 187, 152, and 137 plants from six, eight, and three F1 plants, respectively, which were used in the present study

Summary

Introduction

Asian soybean rust (ASR), caused by the obligatory biotrophic Basidiomycota fungus Phakopsora pachyrhizi (Sydow & Sydow), is one of the most severe diseases affecting soybean (Glycine max), causing losses of up to 80% in ideal conditions in the various geographic regions where it has been reported, costing annually an estimated US $1.77 billion, on average (Godoy et al 2016).Currently, the strategies for ASR management and control include the application of chemical fungicides (Embrapa 2019) and the use of specific cultivation practices, such as the elimination of secondary hosts and the introduction of soybean-free growth periods 53 Page 2 of 12(sanitary periods) (Langenbach et al 2016). The strategies for ASR management and control include the application of chemical fungicides (Embrapa 2019) and the use of specific cultivation practices, such as the elimination of secondary hosts and the introduction of soybean-free growth periods 53 Page 2 of 12. The genetic resistance identification in different soybean genotypes as well as the elucidation of defense mechanisms that contribute to the resistance to attack by P. pachyrhizi, represents important strategies for ASR control. Depending on the Rpp gene present in the soybean and the Avr gene of the P. pachyrhizi isolate involved in the interaction, different symptoms are observed: an incompatible-type interaction of the soybean plant in response to the pathogen; an expressed immune reaction governed by the resistance gene Rpp (the plant shows no visible symptoms), or the formation of reddish-brown lesions (RB) governed by the other Rpp genes resulting from programmed cell death and promoting the limitation of sporulation and fungal growth; and the susceptible reaction, characterized by tan-colored lesions (TAN), resulting from the total sporulation of P. pachyrhizi pustules (Van de Mortel et al 2007) Eight different P. pachyrhizi resistance loci (resistance to P. pachyrhizi: Rpp) have been identified and mapped in the soybean genome (Rpp to Rpp7): Rpp from PI 200492 (Hyten et al 2007), Rpp1-b from PI 594538A (Chakraborty et al 2009), Rpp from PI 230970 (Silva et al 2008), Rpp in PI 462312 (Hyten et al 2009), Rpp in PI 459025 (Silva et al 2008), Rpp in PI 200456 (Garcia et al 2008), Rpp in PI 567102B (Li et al 2012), and Rpp in PI 605823 (Childs et al 2017).

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