A Modified Method to Screen for Partial Resistance to Phytophthora sojae in Soybean

Abstract

Phytophthora root and stem rot, caused by Phytophthora sojae Kauf and Gerd, is one of the most damaging diseases of soybean [Glycine max (L.) Merr.] in the United States. Partial resistance (PR), which is defined as the relative ability of a soybean plant to survive root infection without showing severe symptoms, is an effective way to manage this disease. A modification of the layer test method used to screen for PR to P. sojae in soybean was evaluated. Instead of the P. sojae‐colonized agar layer, which is used in the current greenhouse cup assay, P. sojae‐infested rice (Oryza sativa L.) grains were used. In addition, a dry root weight (Drw) measurement was compared to a disease severity root rot score, which uses a 1 to 10 visual scale. The rice method was not statistically different from the layer test for the variables evaluated. Advantages of the rice method include reduced cost and the ability to screen soybean germplasm with more than one pathotype of the pathogen in a single assay. A mixture of several pathotypes of P. sojae ensures compatible interactions between isolates used and all known Rps genes, thus avoiding Rps genes that could go undetected and mask PR during screening. Although collecting and handling of roots for Drw data may require more time, it is a more objective variable, which assures precise scoring, it is not rater dependent, and less training of personnel is required.

Phytophthora Species Recovered From Irrigation Reservoirs in Mississippi and Alabama Nurseries and Pathogenicity of Three New Species

“…Phytophthora-colonized rice grain used as inoculum was prepared by autoclaving 25 g of long grain rice in 18 ml distilled water in a 250-ml Erlenmeyer flask twice within a 24 h period. Cooled rice grains in each flask were inoculated with 10 pieces (0.5 cm 2 ) of an actively growing culture of the test isolate on cV8A (Stewart and Robertson 2012). Inoculated rice grains were kept at room temperature (about 22°C) for 14 days and shaken by hand once per day to prevent clumping.…”

Variation in the Resistance of Japanese Soybean Cultivars to Phytophthora Root and Stem Rot during the Early Plant Growth Stages and the Effects of a Fungicide Seed Treatment

“…In this study, we evaluated the resistance of Japanese soybean cultivars to Phytophthora root and stem rot using a P. sojae –V8 culture flooding method modified from the procedure described by Mukobata and Sekihara (2005). Diverse inoculation methods have been developed, including the hypocotyl inoculation, greenhouse inoculum-layer test, and slant-board test as well as the application of a zoospore suspension and a mixture of agar culture homogenate and soil ( Dorrance et al, 2004b , 2008 ; Dorrance and Mc-Clure, 2001 ; Guérin et al, 2014 ; Jiang et al, 2017 ; Stewart and Robertson, 2012 ; Sugimoto et al, 2006 ; Tooley and Grau, 1982 ). Some of these methods are used to evaluate complete resistance (e.g., Rps -mediated resistance), while others have been designed to assess incomplete resistance.…”

A Novel Phytophthora sojae Resistance Rps12 Gene Mapped to a Genomic Region That Contains Several Rps Genes

“…The differential lines include lines that carry Rps1a , Rps1b , Rps1c , Rps1d , Rps1k , Rps2 , Rps3a , Rps3b , Rps3c , Rps4 , Rps5 , Rps6 , Rps7 , and Rps8 genes [19, 62]. Seedlings were grown in the greenhouse for a week.…”