Control of fusarium head blight in wheat: I. Evaluation of host plant resistance and fungicides II. Molecular markers associated with QTL for resistance

Fusarium head blight (FHB) of wheat has become an increasingly important disease over the past 25 years. Significant grain and quality reductions due to FHB can be observed when there is a favorable environment for disease development. Fusarium graminearum, the primary fungal pathogen that causes FHB in the U.S. produces deoxynivalenol, a mycotoxin that can cause serious health problems for both humans and livestock when consumed in FHB infected grain. While cultural practices and fungicide treatments can suppress FHB, the use of resistant cultivars is also an essential tool for control of FHB. Breeding for resistance to FHB has become a very large part of wheat and barley breeding programs in temperate climates. Various sources of resistance have been used to develop new cultivars that have high levels of resistance. The primary objective of this study was to combine multiple sources of resistance using a recombinant inbred line (RIL) population derived from three FHB-resistant University of Illinois breeding lines (IL96-6472, IL97-6755 and IL97-1828) to obtain transgressive segregants that are significantly better than the three parents. The RIL population, consisting of 266 lines, was evaluated for FHB resistance in the greenhouse and in a mist irrigated, inoculated disease nursery. Forty-three simple sequence repeat (SSR) and 250 Diversity Arrays Technology (DArT) polymorphic markers were used to create a linkage map using Joinmap 3.0. PlabQTL was used for composite interval mapping and detection of significant QTL. QTL were found for all measured traits except for mean severity in the 2009 greenhouse evaluation. QTL on the short arm of chromosome 3B were identified for all measured traits and accounted for 4.2% to 18.8% of the phenotypic variation, depending on the trait. We believe that these markers are associated with Fhb1 or QTL tightly linked to Fhb1. Minor QTL were also found on chromosomes 7B, 1A, 5D, 6B and 6A and explained a smaller amount of phenotypic variation (between 2.5% and 8.7%). A total of 13 transgressive segregants were found that were significantly better than the mean of the three FHB-resistant parents for more than one trait. These thirteen lines were found to carry many of the resistance alleles associated with the QTL found in the study. Although the population was derived from three FHB-resistant parents, and there were likely QTL that were not detected due to a lack of polymorphism, we believe that multiple genes for resistance were combined in the transgressive segregants observed in the RIL. The second study examined the performance of FHB-resistant and susceptible cultivars with three fungicide treatments. Until recently, there were few fungicides labeled for suppression of FHB. Numerous studies have shown that fungicides containing the active ingredient tebuconazole are very effective in reducing losses caused by FHB. While fungicides can be a useful tool for FHB suppression, they do not provide complete control, and their efficacy is greatly affected by timing. Planting cultivars that are resistant to FHB infection provides farmers with continual protection against the disease. The experiment was grown as a split plot with fungicide treatment (No Fungicide, Prosaro?? (tebuconazole+prothioconazole) and Folicur?? (tebuconazole) as the main plot and cultivar (6 susceptible and 6 resistant) as the sub-plots. Based on the results of this experiment, it is apparent that resistant cultivars are a necessity to provide the best control of FHB. Under the extremely heavy disease pressure of our FHB nursery, fungicides did not provide sufficient control of FHB on susceptible cultivars. Not surprisingly, we found the best method for controlling FHB is to plant a resistant cultivar in addition to applying a fungicide; however, we were interested to see how resistant cultivars alone would perform when compared to susceptible cultivars treated with a fungicide. Resistant cultivars performed impressively, and it was apparent that resistant cultivars are an essential first step of an effective program for controlling FHB. Resistant cultivars without fungicides were able to yield well and provide excellent net economic returns that were not significantly different than resistant cultivars that were treated with a fungicide. This would suggest that under low to moderate disease pressure there no need for fungicide application for FHB control. This experiment illustrated that resistant cultivars provide sufficient protection from FHB; however, to achieve high quality grain with low levels of FDK and DON, fungicide application may be needed in years when there is a high risk of severe disease pressure