Evidence of a Susceptible Allele Inverting the Dominance of Rust Resistance in Soybean

Abstract

Soybean rust (SBR) is the most threatening fungal disease in the major soybean [Glycine max (L.) Merr.] production areas around the world. In spite of the availability of chemical control with fungicides, the increase of production costs as well as operational difficulties associated with fungicide use for disease management has prompted the search for resistant genes in the soybean germplasm. Five genes (Rpp1, Rpp2, Rpp3, Rpp4, and Rpp5) have been reported as capable of conferring SBR resistance in soybean. Here we report the genetic segregation of the SBR resistance in two populations derived from crossing the SBR resistance source PI 594760B with the breeding lines TMG06_0012 (Population 1 [POP‐1]) and TMG06_0011 (Population 2 [POP‐2]). In both populations the resistance segregated as a single gene, but the resistance gene was dominant in POP‐1 and recessive in POP‐2. Molecular mapping of the phenotype placed it in the vicinity of the Rpp1 locus in both POP‐1 and POP‐2. When the breeding lines TMG06_0011 and TMG06_0012 where crossed with several other sources of resistance at the Rpp1, Rpp2, Rpp4, and Rpp5 loci or other putative loci, the inversion of gene action type observed with PI 594760B occurred only for the putative Rpp1 genotypes. We propose that a dominant susceptible allele, present in TMG06_0011, is causing the inversion of dominance observed in each of these crosses.

Molecular Characterization of Resistance to Soybean Rust (Phakopsora pachyrhizi Syd. & Syd.) in Soybean Cultivar DT 2000 (PI 635999)

“…The presence of mixed reactions was also reported in genetic populations derived from PI 200456 and PI 224270 [48]. In addition, inversion of dominance by a susceptibility allele has been reported in populations derived from the cross of some PIs crossed with different susceptible parents [49]. In our field evaluations in Ha Noi, the mapping population was inoculated with locally collected unpurified inoculum.…”

Characterization of genes Rpp2, Rpp4, and Rpp5 for resistance to soybean rust

“…Garcia et al (2011) reported the alteration of gene action type in Rpp1 locus pointing out the relative status of Rpp resistant genes. Differences in genetic behavior of rust resistance genes have been (Table 3) but further detailed analysis goes beyond the scope of this work.…”

Pathogenic Variation of South American <i>Phakopsora pachyrhizi</i> Populations Isolated from Soybeans from 2010 to 2015

“…Past researches on host resistance to soybean rust have identified six major resistance loci (Rpp: resistance to P. pachyrhizi), named Rpp1 to Rpp6 and an allele (Chakraborty et al 2009, Garcia et al 2008, Hartwig 1986, Hartwig & Bromfield 1983, Li et al 2012, McLean & Byth 1980, Ray et al 2009). These Rpp genes confer specific resistance to a limited set of P. pachyrhizi isolates, some of which have been used to develop Rpp gene-carrying cultivars (Garcia et al 2011, Hartman et al 2011 and Rpp-pyramided lines (Lemos et al 2011, Maphosa et al 2012, Yamanaka et al 2015b) using conventional strategies.…”