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

Abstract

Asian rust, caused by the fungus Phakopsora pachyrhizi, is the most severe disease currently threatening soybean crops in Brazil. The development of resistant cultivars is a top priority. Genetic characterization of resistance genes is important for estimating the improvement when these genes are introduced into soybean plants and for planning breeding strategies against this disease. Here, we infected an F 2 population of 140 plants derived from a cross between 'An-76', a line carrying two resistance genes (Rpp2 and Rpp4), and 'Kinoshita', a cultivar carrying Rpp5, with a Brazilian rust population. We scored six characters of rust resistance (lesion color [LC], frequency of lesions having uredinia [%LU], number of uredinia per lesion [NoU], frequency of open uredinia [%OU], sporulation level [SL], and incubation period [IP]) to identify the genetic contributions of the three genes to these characters. Furthermore, we selected genotypes carrying these three loci in homozygosis by marker-assisted selection and evaluated their genetic effect in comparison with their ancestors, An-76, PI230970, PI459025, Kinoshita and BRS184. All three genes contributed to the phenotypes of these characters in F 2 population and when pyramided, they significantly contributed to increase the resistance in comparison to their ancestors. Rpp2, previously reported as being defeated by the same rust population, showed a large contribution to resistance, and its resistance allele seemed to be recessive. Rpp5 had the largest contribution among the three genes, especially to SL and NoU. Only Rpp5 showed a significant contribution to LC. No QTLs for IP were detected in the regions of the three genes. We consider that these genes could contribute differently to resistance to soybean rust, and that genetic background plays an important role in Rpp2 activity. All three loci together worked additively to increase resistance when they were pyramided in a single genotype indicating that the pyramiding strategy is one good breeding strategy to increase soybean rust resistance.

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

“…Although this study primarily focused on the reactions for 16 differentials, of which 13 contained Rpp1-5 and their associated alleles, the preliminary results demonstrate that PI 567102B carrying Rpp6 (Li et al 2012) and the No6-12-1 line pyramided with Rpp2, Rpp4, and Rpp5 (Lemos et al 2011) produced a resistant reaction to some recent rust populations from the three South American countries (data not shown). and South America.…”

“…This work elucidates the pathogenicity of P. pachyrhizi populations from Argentina, Brazil, and Paraguay from the 2010/2011-2014/2015 seasons, and provides a dataset useful for comparing pathogenicity data obtained in the past and for the future monitoring of pathogen populations. In an on-going study, the pathogenicity of the P. pachyrhizi populations from the three countries has been evaluated using the differentials with Rpp1-5 and their additional alleles, PI 567102B carrying Rpp6 (Li et al 2012) and the No6-12-1 line pyramided with Rpp2, Rpp4, and Rpp5 (Lemos et al 2011). In the future, a more informative dataset containing infection types of the two new differentials would be useful in breeding programs to develop rust resistant cultivars for P. pachyrhizi populations outside of Argentina, Brazil, and Paraguay (e.g., Central America).…”

“…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.…”

Fine mapping of the Asian soybean rust resistance gene Rpp2 from soybean PI 230970

“…The recessive allele rpp2 [? It was later confirmed to map to the same region in a population consisting of 140 F 2 plants derived from a cross between 'An76,' which carries Rpp2 and Rpp4, and 'Kinoshita,' carrying Rpp5 (Lemos et al 2011). The gene was localized to a 12.9-cM interval between the SSR markers Sat_255 and Satt620 on chromosome 16 using a population of 130 F 2:3 derived lines developed from a cross between 'BRS 184' and PI 230970 (Silva et al 2008).…”

Asian Soybean Rust Resistance: An Overview

“…Varieties with two pyramided resistance genes tend to express greater durability of resistance than varieties with a single gene [73,74]. Lemos et al [75] and Yamanaka et al [76] reported that a variety with three resistance genes (Rpp2, Rpp4 and Rpp5) showed significantly higher resistance than its ancestor, showing that pyramiding strategy is effective to increase the rust resistance.…”