1a. Objectives (from AD-416)
Objective 1: Identify predominant races of Phytophthora sojae and assess the effectiveness of soybean resistance genes for incorporation into improved germplasm. Objective 2: Determine variability in virulence patterns of new and established Phytophthora sojae races. Objective 3: Establish and maintain isolates of Phytophthora sojae races as a resource for soybean germplasm enhancement and race identification of new field isolates. Objective 4: Determine the influence of crop management practices on soybean root diseases.
1b. Approach (from AD-416)
Use standard pathological techniques to determine virulence and frequency of Phytophthora sojae races; cooperate with other soybean researchers to determine predominent P. sojae races in the North Central region, and utilize established tillage and rotation plots with a history of Phytophthora root rot and/or sudden death syndrome to enhance development of disease control strategies as they relate to crop management practices.
3. Progress Report
The Lead Scientist retired in FY09 but collaborated with the Research Leader and project personnel in FY10. Research involving soybean germplasm and pathogens to minimize disease losses: Studies established in previous years were continued in FY10 to verify and update the frequency of dominant races of Phytophthora sojae in soybean production fields. This information is needed to document changes in the pathogen and to develop control strategies. Management and culture of the P. sojae germplasm collection were continued. Critical P. sojae races were identified and provided for germplasm enhancement and studies of novel Rps genes in addition to coordinating the Uniform Soybean Tests for Northern States and Canada. Ongoing collaborative research with breeders at Purdue University emphasized P. sojae resistance and several outstanding breeding lines have two Rps genes for improved resistance. Thirty-five lines are being evaluated in advanced Indiana tests prior to submitting the elite lines for regional evaluation in the 2011 Northern Uniform Soybean Tests. All of the Indiana lines in theses tests are conventional soybeans with improved yield and disease resistance characteristics. Ongoing collaborative research with Univ. of Missouri was continued to further verify and update the ability of P. sojae isolates to damage soybeans with the Rps8 resistance gene. The virulence data for the P. sojae isolates evaluated suggest Rps gene stacking (1-k or 1-c + 3-a or the Rps8 gene) is needed to control races identified in many soybean fields. Studies documenting the role of Fusarium solani f. sp. glycines (= F. virguliforme) root infection and sudden death syndrome (SDS) yield losses in soybean with tillage (no-till vs. chisel tillage), crop rotation, and host resistance, were continued in FY10. The limited research reported to date has indicated that SDS is more likely to occur in soybeans with minimum tillage than with conventional tillage and that crop rotation has little impact on SDS. Currently, Indiana data do not agree with this statement. Root colonization of soybean plants by F. virguliforme and SDS yield reductions were higher in tilled (conventional plow and chisel) plots than in the no-till plots. Early appearance of foliar symptoms and root infection results also indicated that soybeans with continuous cropping or a corn-soybean rotation are more likely to develop SDS than plants in corn-soybean-wheat rotations. Germplasm enhancement relative to disease resistance is actively addressed by ongoing cooperative research with breeders and by the coordination of the USDA Uniform Soybean Tests for the Northern Region. Breeding lines in these tests represent the best of soybean germplasm relative to agronomic traits and unique characteristics such as seed quality and resistance to pests. Both public and private soybean researchers depend on this program as they utilize the elite soybean lines to meet the needs of the soybean industry.
1. Genetic dissection of novel Rps genes and/or gene combinations in soybean germplasm lines with potential for resistance to soybean rust (ASBR). The need for multiple disease resistance is important to the soybean industry with Phytophthora root rot caused by evolving Phytophthora sojae races and the recently introduced invasive Asian soybean rust in the U.S. Recently, this project identified P. sojae resistance in soybean lines evaluated for Asian soybean rust at the University of Georgia in 2005 and 2006 by R. Boerma et. al. (http://edge.cropsoil.uga.edu/soylab/rustresistance.html). Collaborative studies were initiated with a soybean geneticist at Purdue University to identify and describe the uncharacterized Rps gene or genes in two of the ASBR soybean lines identified by this ARS project as resistant to all known races of the P. sojae pathogen. This genetic dissection of uncharacterized Rps genes along with multiple disease resistance is very promising and important to ARS and the soybean industry. Crosses of lines with these Rps genes have been established and F2-seed increased with the two ASBR lines and selected soybean cultivars (Williams, Harosoy, Clark), and a strain from the wild soybean (Glycine sojae). Preliminary P. sojae inoculations of seedlings from F2-seed are being continued with progeny from the Williams x PI 567139B receiving major attention initially, since Williams Rps-isolines for most known genes are already available. If a novel Rps gene is verified, the need for the novel gene in the Williams germplasm is highly desirable and needed by soybean researchers and the soybean industry because deployed genes for resistance to Phytophthora root rot have a finite lifetime, new ones must be discovered and incorporated into germplasm to assure genetic control of the disease.