ENHANCING RESISTANCE TO ROOT ROT PATHOGENS OF SOYBEAN
Crop Production and Pest Control Research
2009 Annual Report
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.
Research involving soybean germplasm and pathogens to minimize disease losses: Studies established in previous years were continued in FY09 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. The Lead Scientist continued to identify and provide selected P. sojae races for germplasm enhancement 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. Seven elite lines are included in advanced tests and 28 lines are in preliminary tests for 2009 Northern Uniform Soybean Tests. All of the IN-lines in theses tests are conventional soybeans with improved yield and disease resistant characteristics. Ongoing collaborative research with Univ. of Missouri was continued to verify and update the ability of P. sojae isolates to damage soybeans with the Rps8 resistance gene. Studies documenting the role of Fusarium solani f. sp. glycines (=F. virguliforme) root infection and sudden death syndrome yield losses in soybean with tillage (no-till vs. chisel tillage), crop rotation, and host resistance, were continued in FY09. The limited research reported to date has indicated SDS (Sudden Death Syndrom) 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.
Coordination of Northern Region Uniform Soybean Tests. The need for regional evaluation of soybean germplasm to enhance seed yield and composition along with the need to minimize disease losses is increasing. The Northern Region USDA Uniform Soybean Tests were coordinated by this project in 2009. Elite, publicly developed breeding lines (>450) were evaluated. There were 34 participants or cooperators representing 18 public soybean improvement programs involved in the Northern Region Uniform Soybean Tests. Data from the regional tests provide new insights about performance and genetic characteristics of elite soybean breeding lines that have high potential for use by the soybean industry. Test participants use the data annually to critically evaluate the best of the soybean lines developed by federal and state researchers for their potential release as germplasm or as improved varieties for commercial production. This new germplasm is important to the soybean industry; it represents 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 improved soybean lines to meet the needs of the soybean industry.
Documentation of Phytophthora sojae infecting soybeans with Rps8 gene. Recently as the Rps gene has been challenged by a larger diversity of P. sojae isolates it has become evident that the new Rps8 gene does not control all races of P. sojae as initially suggested. Root rot caused by specific strains or races of P. sojae is a serious yield-limiting disease and major emphasis for the control is by race specific Rps resistance genes. The Rps virulence data for the P. sojae isolates evaluated in 2009 conclusively suggest Rps ‘gene-stacking’ or combinations (1-k or 1-c + 3-a or the Rps8 gene) are needed to control races identified in many soybean fields. Awareness of the need to have specific Rps gene combinations for effective P. sojae resistance in soybean germplasm will be useful to public and private soybean breeders for the development of cultivars that will improve disease control and minimize yield losses. This Rps virulence information is particularly important to breeders and pathologists developing soybean varieties adapted to south-central and southern regions of the U.S.
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