RESEARCH ARTICLES/INFORMATION

Research Category: Soybean Disease and Insect Control Year: 2004 Researcher: Albert Tenuta and Terry Anderson Institution: OMAF AAFC Topic: Limiting losses to phytophthora sojae in Ontario and the North Central U.S. soybean region Funding: $5,000 Research Details: Research and extension specialists from Ontario and twelve U.S. states agreed to collaborate on a joint communication and research project aimed at limiting producer losses from Phytophthora root rot. Phytophthora root rot is caused by the soil-borne fungus, Phytophthora sojae and the disease continues to be a major threat not only in Ontario but also in the entire north central U.S. Participation in this joint proposal allows Ontario researchers and producers full access to the research results, materials and products that are derived from this study. Materials have been developed on Phytophthora sojae. Information obtained from this project is being developed and will be made available to the Plant Health Initiative and the OSG for inclusion or links on their websites. The information that will be included is i) links to screening results of Rps genes in commercial varieties for Ontario and the specific states; ii) information on the biology, identification, and management of P. sojae; and iii) fact sheets which explain management tools across the region for different pathotypes as well as soil types. The number of Plant Introductions that are being incorporated into northern soybean germplasms and varieties has expanded dramatically. Many PI’s have been identified with resistance to Soybean Cyst Nematode, White Mould (Sclerotinia) and Sudden Death Syndrome. In many cases, these PI’s carry uncharacterized Rps genes or lack any protection to Phytophthora. In addition, some PI’s have been identified that were thought to have new novel Rps genes when in fact it was a combination of Rps genes that already existed. This complexity of Rps gene deployment makes screening and resistance characterization much more difficult. The goal is to identify Plant Introductions that have not only Phytophthora resistance but multiple disease resistance, which would speed-up variety development. In addition, some of the Phytophthora isolates obtained from this study have been able to bypass the newest source of resistance (Rps 8) developed in Ohio. This ability comes naturally in these isolates since the Rps 8 gene has not been used in Ontario soybean varieties but Ontario Phytophthora isolates are able to bypass the Rps 8 gene. This is one of the difficult challenges when dealing with this disease. It has many inherent disease causing genes that are present in the fungus genome even when it has never come into contact with a new resistance gene. The potential to stack multiple resistance genes (Rps) into Ontario soybean varieties may overcome this problem. Considerable progress has been made in collecting and screening of Ontario Phytophthora isolates. In addition, a uniform set of soybean differentials have been developed that will be used to characterize the isolates within Ontario and the U.S soybean region. This will make it easier to compare between Ontario and the North Central U.S. States. This has led to a database, which will outline the races, or pathotypes that exist within Ontario and each state. Public and private breeders to assist in soybean variety development will use this information. Phytophthora sojae populations are in the process of shifting towards more complex pathotypes (isolates that can kill plants with 4 or more Rps genes). Partial resistance or tolerance will become more important in the long-term management of this pathogen. The development of new races that can by-pass Rps 1k resistance has been occurring in Ontario and recent work at Harrow has found that for example in Essex county, 44% of the Phytophthora races present in producer fields could cause disease in soybean varieties with Rps 1k. During this study we have found that a similar situation exists in Eastern Ontario where 47% of the isolates are able to damage Rps 1k. Concern has arisen recently that the increased damage from Phytophthora in Ontario and the North Central region could be the result of the development of tolerance to chemical seed treatments (Metalaxyl or Metalaxyl-M, also known as mefexonam). Isolates obtained in Ontario were found to have no tolerance and are still susceptible to these seed treatments. Therefore, these seed treatments remain effective management tools for Ontario producers. Similar results were found in Ohio and Illinois. File: