1. We completed a multi-lab study evaluating performance of six qPCR assays developed for F. virguliforme and the manuscript has been published in Phytopathology. In this study, we compared the strengths and weakness of all six assays under different research facilities in terms of their specificity, sensitivity, and consistency and also identified an effective protocol for better diagnosis and quantify SDS pathogen. To summarize, assays differed in their performances and also the performance of the same assay varied among the laboratories. Overall, A single copy gene (FvTox1)-based assay showed the highest specificity (with lowest false positives), while multi-copy gene based assays were more sensitive (with their ability to detect very small amount). A recent assay developed in chilvers lab showed the highest sensitivity and the second highest specificity, and thus is suggested as the most useful qPCR assay for F. virguliforme. This assay is currently being used for quantifying F. virguliforme population in root and soil in other projects.
2. Effect of planting date on SDS e.g., how mid- or late April planting compares with early to mid-May plantings, is better understood. We completed this study comparing effect of planting date and seed treatment on resistant and susceptible cultivars. To summarize, ILeVO seed treatment reduced disease severity and increased yield nearly in all plantings and cultivars, with a maximum yield response up to 21% (Roland Iowa). Effect of planting date on foliar SDS symptoms was inconclusive. Although Mid-June plantings did not have higher disease than early plantings it yielded lower grain up to 19 bu/A than early May plantings.
3. We also evaluated different fungicide products and application methods to see if any would complement cultivar resistance. From this study, the main conclusion was that ILeVO® seed treatment or in-furrow was effective at reducing SDS severity levels in many different environments compared to control plots. Foliar applications of any chemicals including ILeVO showed no effect on SDS reduction.
4. Information on the importance of early season root and soil health on SDS development is generated that will elucidate i) If increased nematode reproduction on SCN resistant cultivars based on PI88788 resistance need to be considered in SDS management decisions. We are still collecting data on SCN, SDS and yield and it will be summarized as soon as the data are collected. So far we found varieties with Peking source of resistance for SCN had lowest SDS in many environments and varieties with no resistance to SDS and SCN had the highest disease.
5. Understanding for farmers and agronomists on shifts in herbicide regimes and the associated effect on SDS risk is improved. Our study suggested that glyphosate had no association with SDS incidence or severity. Farmers will be able to make informed decisions regarding herbicide choice for the weed management strategy.
6. Effect of seed treatment and herbicide interaction on root health and SDS will be better understood. Seed treatment effectiveness in light of different management strategies for example different soil-applied herbicides, different cultivars, and other crop cultivation strategies are being investigated.
7. We improved existing NCSRP resources to better communicate with farmers, agribusinesses and other soybean stakeholders. We will also evaluate the impact of our management and educational efforts.