Quantitative Disease Resistance Loci towards Phytophthora sojae and Three Species of Pythium in Six Soybean Nested Association Mapping Populations

Abstract

Comparison of quantitative disease resistance loci (QDRL) towards the diverse array of soilborne pathogens that affect soybean [Glycine max (L.) Merr.] is key to the incorporation of resistance in breeding programs. The water molds Phytophthora sojae (Kauffman & Gerdmann), Pythium irregulare (Buisman), Pythium ultimum var. ultimum (Trow), and Pythium ultimum var. sporangiiferum (Drechsler) contribute to soybean yield losses annually. Six Soybean Nested Association Mapping (SoyNAM) populations were evaluated for resistance to one or more of these pathogens. Four were screened with a tray test to measure lesion length after inoculation with Ph. sojae; cup assays were used to screen three, three, and two populations for resistance towards Py. irregulare, Py. ultimum var. ultimum, and Py. ultimum var. sporangiiferum, respectively. There were two to eight major or minor QDRL identified within each SoyNAM population towards one or more of these water molds for a total of 33 QDRL. The SoyNAM populations evaluated for resistance to two or more water molds had different QDRL towards each pathogen, indicating that within a source of resistance, mechanisms are potentially specific to the pathogen. Only 3 of the 33 QDRL were associated with resistance to more than one pathogen. There was a major QDRL on chromosome 3 associated with resistance to Py. ultimum var. ultimum and Py. ultimum var. sporangiiferum, and QDRL on chromosomes 13 and 17 shared a flanking marker for both Py. irregulare and Py. ultimum var. ultimum. The SoyNAM population can serve as a diverse resource to map QDRL and compare mechanisms across pathogens and isolates.

Identification of Quantitative Disease Resistance Loci Toward Four Pythium Species in Soybean

“…The QDRL for P. irregulare in POP3 on chromosome 1 was in the same chromosomal region as a QDRL found for the same species by Scott et al (2019) in the NAM population of IA3023 × LG00-3372. The QDRL in the NAM population was found for the adjusted root weight trait and explained 6.9% of the variation.…”

“…Several studies have measured resistance toward different Pythium species ( Rod et al, 2018 ; Lerch-Olson et al, 2020 ) and have identified QDRL, mostly minor, in RIL populations of soybean ( Ellis et al, 2013 ; Stasko et al, 2016 ; Urrea et al, 2017 ; Klepadlo et al, 2019 ; Lin et al, 2018 , 2020 ; Scott et al, 2019 ). Almost all of the studies have shown partial resistance aside from one study by Rosso et al (2008) showing monogenic resistance.…”

“…Monogenic resistance to Pythium aphanidermatum was identified in an F 2:4 population of “Archer” × “Hutcheson” ( Rosso et al, 2008 ). Recently, several quantitative disease resistance loci (QDRL) for resistance to P. irregulare ( Ellis et al, 2013 ; Stasko et al, 2016 ; Lin et al, 2018 ; Scott et al, 2019 ), P. aphanidermatum ( Urrea et al, 2017 ), P. ultimum var sporangiiferum ( Scott et al, 2019 ), P. sylvaticum ( Lin et al, 2020 ), and P. ultimum var. ultimum ( Rod et al, 2018 ; Klepadlo et al, 2019 ; Scott et al, 2019 ) have been identified using biparental soybean populations.…”

“…Recently, several quantitative disease resistance loci (QDRL) for resistance to P. irregulare ( Ellis et al, 2013 ; Stasko et al, 2016 ; Lin et al, 2018 ; Scott et al, 2019 ), P. aphanidermatum ( Urrea et al, 2017 ), P. ultimum var sporangiiferum ( Scott et al, 2019 ), P. sylvaticum ( Lin et al, 2020 ), and P. ultimum var. ultimum ( Rod et al, 2018 ; Klepadlo et al, 2019 ; Scott et al, 2019 ) have been identified using biparental soybean populations. Overall, only minor QDRL have been identified and have explained 4.5–17.8% of the phenotypic variation and are located on most chromosomes within the soybean genome.…”

Genome-wide association analyses of quantitative disease resistance in diverse sets of soybean [Glycine max (L.) Merr.] plant introductions

“…Thus, studies to map the genetic positions of QDR can be applied to increase the efficiency of selection for these traits via MAS [41].Numerous biparental mapping studies identified QDR loci (QDRL) towards P. sojae in US cultivars Conrad, Sloan,. Recently, the soybean nested associated mapping populations were used to study P. sojae resistance, identifying four QDRL [49]. In addition to US cultivars, QDRL have been mapped in landraces originating from China and the Republic of Korea (South Korea, SK) using biparental mapping populations derived from crosses with eight accessions [50][51][52][53][54].…”