Limiting Losses to Phytophthora sojae in the North Central Region
Goals for 2006

Continue to develop materials on Phytophthora sojae for the Plant Health Initiative web site, including fact sheets, disease management guidelines, and powerpoint presentations.

Fact sheets and powerpoint presentations can then be used by soybean producers, county extension agents, company agronomists and technical service reps for pesticide applicator training, field days or as self-study units. 

Screen the soybean Plant Introductions that have been identified with novel Rps genes for resistance/susceptibility to P. sojae isolates representing diverse populations from all of the North Central States. 

New sources of resistance to P. sojae have been identified in a number of studies. The next phase is to determine if these new sources are effective against the populations of P. sojae that exist in the north central region. 

Identify the Rps genes that may exist in soybean Plant Introductions that are currently being incorporated into northern soybean germplasm. 

Many plant introductions have been identified in recent years with desirable traits for yield, protein, SCN resistance, SDS resistance etc. These favorable traits are currently being incorporated into new US soybean varieties. These PI’s may also carry unfavorable traits, such as super susceptibility to P. sojae. We plan to evaluate a number of these PI’s for resistance to P. sojae for both the Rps genes and the levels of partial resistance.

Characterize the Phytophthora sojae population across the region for pathotype (races) as well as metalaxyl sensitivity. 

All states are involved at this time in collecting isolates from either soil and plants, characterizing these isolates for races. This will allow states to make recommendations to soybean seed companies on which Rps genes to deploy within a specific region. Metalaxyl and Mefenoxam are the only two fungicides that are effective against Phytophthora sojae. When these products have been used extensively overtime, Phytophthora spp. have adapted or developed insensitivity to these compounds. To date: No P. sojae isolates have been identified that have developed insensitivity to these compounds – so they are still useful seed treatment compounds for the north central region. 

Evaluate the effect of cultural practices on minimizing losses to Phytophthora sojae on varieties with different levels of partial resistance. 

Several states are examining the effects of cultivars with partial resistance with and without Rps genes, seed treatment rate studies, as well as the effects of soil drainage. 

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5/9/06

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