Multi-Year Evaluation of Commercial Soybean Cultivars for Resistance to Phytophthora sojae

Abstract

Phytophthora sojae causes damping-off, root rot, and stem rot of soybean, particularly in poorly drained soils. Soybean cultivar resistance is one of the primary methods to control this disease, with Rps1c, Rps1k, and Rps1a being the most commonly used genes. The Varietal Information Program for Soybeans (VIPS) at the University of Illinois evaluates soybean cultivars for resistance to a number of diseases including Phytophthora root rot (PRR). The objectives of this research were to evaluate PRR resistance among commercial cultivars or advanced lines, and to compare these results with the information on PRR resistance provided by the company that entered the cultivar in VIPS. Each year from 2004 to 2008, between 600 and 900 cultivars were evaluated for resistance to either race 17 or 26 of P. sojae using the hypocotyl inoculation method. P. sojae single resistance genes were reported in 1,808 or 51% of the entries based on company information. Of these, the most commonly reported resistance genes were Rps1c (50%), Rps1k (40%), and Rps1a (10%). To a much smaller degree, companies reported using Rps3a (0.3%), Rps1b (0.2%), and Rps7 (0.2%). For the duration of the 5-year testing period, almost half of the cultivars (46%) were entered in VIPS with no reported resistance genes, and only nine out of a total of 3,533 entries (less than 0.3%) reported a stacked combination of resistance genes. Agreement between company-reported genes and any resistance found in the VIPS PRR evaluation was highest for those cultivars claiming to have Rps1c (90%) and Rps1k (83%), followed by Rps1a (70%). On average, 54% of the cultivars submitted to VIPS each year were new, reflecting the rapid development and turnover of soybean cultivars provided by the soybean seed companies.

Pathogenic diversity of Phytophthora sojae pathotypes from Brazil

“…In the USA, P. sojae populations reportedly have a low incidence of virulence for Rps1d collected in Arkansas (10 %), Illinois (38 %), Ohio (3 %), North Dakota (19 %), Iowa (2 %), and Indiana (14 %) (Yang et al 1996;Abney et al 1997;Dorrance et al 2003;Jackson et al 2004;Malvick and Grunden 2004;Nelson et al 2008). In contrast to USA populations which almost all have virulence to Rps1a, the great majority of Brazilian populations have no virulence response to Rps1a, Rps1c, or Rps1k, which are the most commonly deployed resistance genes in American soybean cultivars (Slaminko et al 2010).…”

Discriminant haplotypes of avirulence genes of Phytophthora sojae lead to a molecular assay to predict phenotypes

“…Alternatively, another explanation could lie in the efficiency of Rps3a. Rps3a is the least deployed of Rps genes accounting for about only 0.3% in commercially released varieties (Slaminko et al, 2010). Field observations have also reported the somewhat random nature of its efficiency (Dorrance et al, 2003).…”

Polymorphism in natural alleles of the avirulence gene Avr1c is associated with the host adaptation of Phytophthora sojae

“…Rps1c is the most commonly used Rps gene in commercial soybean cultivars in the United States (Slaminko et al 2010) and in domestic cultivars in China (unpublished data). However, the pathogens were under high selection pressure, causing complex pathotypes in yield population so that the resistant cultivars controlled by a single Rps gene were easy to be overcome (Dorrance et al 2016).…”