Variability of Fusarium Crown Rot Tolerances Among Cultivars of Spring and Winter Wheat.

Crown rot caused by Fusarium pseudograminearum reduces the yield of wheat (Triticum aestivum) in Oregon. Observations of crown rot symptoms in traditional breeding and yield testing nurseries have not been useful for describing tolerance ratings of wheat cultivars. Yield data from inoculated experiments were therefore evaluated to determine if differences in cultivar response could be identified. A comparison of yields in inoculated and noninoculated plots was made for one group of spring wheat entries and four groups of winter wheat entries. Significant differences among spring wheat entries were identified and were validated against standards for tolerance and intolerance to F. pseudograminearum in Australia. Locally adapted and Australian standards exhibited a comparable range of yield reduction due to inoculation. Spring wheat tolerance reactions can be accurately described using as few as 24 yield comparisons. However, this screening method will not be practical for winter wheat due to stronger effects of year and location on the phenotypic tolerance response, requiring about 95 yield comparisons to accurately define the crown rot phenotype of a winter wheat cultivar.