| Stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is the most important foliar disease of winter wheat in eastern United States. Growing resistant cultivars and applying foliar fungicides are the most important means for managing stripe rust and other fungal foliar diseases. At the beginning of this study, Yr17 was the only effective all-stage resistance gene against stripe rust in the eastern United States, but it was difficult to determine at the seedling stage which cultivars had Yr17 and whether Pst isolates were virulent or avirulent on Yr17. Furthermore, there was little information on the most profitable means of managing foliar wheat diseases on contemporary cultivars. The objectives of this study were to determine i) how best to identify Yr17 resistance in wheat lines and avirulence/virulence to Yr17 in Pst isolates, ii) the level of adult-plant resistance (APR) in wheat lines with Yr17, and iii) the most profitable wheat disease management strategy in Arkansas. The findings of this study indicate that host-pathogen interactions involving Yr17 at the seedling stage are complicated by the effects of temperature, time after inoculation, and particular wheat lines and Pst isolates. Heterozygosity and partial dominance for avirulence may explain differences among isolates. However, interactions on adult plants were definitive, indicating that Yr17 should be classified as an APR gene. Most lines with Yr17 had additional genes that conferred various levels of APR, and at least some of these genes were shown to be race specific. Yield differences among contemporary cultivars were greater than yield differences among fungicide treatments, and stripe rust was the only disease significantly correlated with yield response from a fungicide application. Test weights of cultivars were high enough to avoid discounts without a fungicide, so there was no economic benefit for improving test weights with a fungicide application. Based on costs for fungicide applications and prices for grain, the most profitable wheat disease management strategy was to plant the highest yielding cultivars with resistance to prevalent diseases, especially stripe rust, and to apply a foliar fungicide only if diseases were above threshold levels. |
