Submitted to: Midwest Soybean Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 7/6/2000
Publication Date: N/A
Citation: Interpretive Summary:
Technical Abstract: Soybean yield losses due to diseases occur regularly. New insights about pathogen variability and soybean disease problems are identified in this manuscript. Although information is available about disease resistance, seed companies may not be utilizing the information effectively. For instance, Phytophthora root rot is potentially devastating in soybean varieties that do not have the Rps gene that confers resistance to different races of the Phytophthora sojae pathogen. Soybean gene(s) known as "Rps" confer race-specific resistance to different strains (races) of this pathogen. Recent publications by Abney et al. verifying races in Indiana soybean fields strongly suggest that combinations of Rps resistance genes are needed to control this disease. New data in this paper confirm the dominant races of the pathogen in the 1990s and include an evaluation of Rps resistance in soybean varieties. Of the 450 soybean varieties merchandised by 14 different seed companies, 58% did not have resistance genes and were susceptible to all races of the pathogen. Resistance genes Rps 1c and 1k occurred in 17-19% of the varieties, respectively. Rps 1b and 3a occurred in less that 1% and Rps1a, which is relatively ineffective, occurred in 5% of the varieties. Only four soybean varieties contained more than one Rps resistance gene. Data for the P. sojae races isolated from each county in Indiana indicate that Rps gene combinations will control races identified in 95-98% of the counties. In contrast, control of the P. sojae races using individual Rps resistance genes would be much less than 70% effective. This information will permit pathologists and breeders to employ, recommend, and emphasize control strategies that can minimize yield losses caused by soybean pathogens.