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
Research involved population dynamics of P. sojae, variability among isolates of Fusarium virguliforme, and host resistance to Phytophthora root rot (PRR) and soybean sudden death syndrome (SDS). Projects established in FYs 2007-2010 were assessed and either redesigned or discontinued in favor of new projects. All studies conducted in FY 2011 were essential to understanding the role of host and pathogen variability in disease development and for improving management of PRR and SDS. Isolates of P. sojae previously in the collection were assessed for viability and virulence. Those maintaining both aspects were cryogenically stored to better preserve these characteristics and were made available to researchers for soybean germplasm enhancement. Addition of isolates of P. sojae with unique pathotypes to the collection was also made. These isolates were obtained from soil samples collected from commercial farms throughout Indiana to monitor the population dynamics of this pathogen in the state. Collaborations with Agronomy faculty at Purdue University have continued in order to identify the gene(s) confirming PRR resistance in 2 plant introductions. Eight hundred and seventeen F3 were evaluated with 4 isolates of P. sojae. Data suggests that at least 2 unique genes are present. One of these may be a different allele of Rps 1. Long-term tillage plots were maintained at the Purdue University Agronomy farm to study the influence of tillage and rotation on populations of P. sojae and F. virguliforme. Soil samples were collected and efforts to isolate each pathogen and to characterize them for pathotypes/aggressiveness are in progress. Evaluation of public breeding lines for agronomic performance and disease resistance was continued in FY 2011 at the Purdue University Agronomy farm, as well as the South-East Purdue Agricultural Center and the Pinney-Purdue Agricultural Center. Information collected will be used to determine if varieties will be released to the public in 2012.
1. Re-establishment of the Phytophthora sojae isolate collection and implementation of cryogenic storage for isolate preservation. Isolates of Phytophthora sojae, the causal agent of Phytophthora root rot, are highly diverse with more than 55 recognized races. A collection of both established and uncharacterized races of Phytophthora sojae provides an essential resource for understanding the mechanisms that contribute to isolate diversity and for developing highly resistant soybean cultivars. The collection of isolates originally established by ARS scientists in West Lafayette, IN fulfilled this need for many years. However, the majority of these isolates have lost virulence or are no longer viable due to their long-term maintenance on culture media. In 2011, ARS scientists, in collaboration with research and extension specialists at Purdue University, re-established the Phytophthora sojae isolate collection and implemented the method of cryogenically storing these isolates in order to maintain their virulence and viability for many years. This collection is available to plant pathologists and soybean breeders as they work to improve our understanding of this disease and to mitigate its impact on soybean production.