The Development of Scab (fusarium Graminearum) Resistant Varieties of Wheat

Fusarium head blight (FHB) is a serious disease of wheat and barley that is best controlled by host resistance. In KSU Extension publications, the reaction to FHB for winter wheat cultivars is reported to producers using a 1-9 scale where 1-3 = resistant, 4-6 = intermediate, and 7-9 = susceptible. This research sought to determine how many location-years are needed to accurately determine the reaction of a cultivar to FHB. Twenty-nine different winter wheat cultivars were screened 2-12 times in 12 field nurseries over a 3-yr period (n=133). Experimental design for each location-year was a randomized complete block with four replications. Corn grains, colonized by Fusarium graminearum and spread on the soil surface, followed by sprinkler irrigation were used to produce the epidemic. FHB index (% diseased spikelets) was determined for each cultivar between four and six times for each experiment and averaged. To compare data across location-years, linear regression was used to fit a 1-to-9-scale model to the data for each location-year. To produce the model, an index value of zero was assigned a scale value of 1 and the highest index value in a location-year was assigned a scale value of 9. The model was then used to calculate scale values for all other cultivars in that location-year. A mean scale value was calculated for each cultivar (n=2-12 location-years) and an overall standard deviation for all cultivar-location-years (n=133) was calculated using the departure from the mean for each scale value for each cultivar-location-year. To estimate the number of location-years needed to determine the reaction of a cultivar to FHB, the formula x-bar +/t(alpha/2) * s / sqroot(n) was used to calculate 95% confidence intervals. In this formula, x-bar is the observed mean scale value (1-9 scale) of a cultivar, t(alpha/2) is the t-value corresponding to the desired alpha level (0.05) divided by 2, s is the standard deviation among location years, and n is the sample size (number of location years). If an observed mean scale value is within +/0.5 units of the correct value, it will be rounded to the correct scale value. Required standard deviations to produce a mean within +/0.5 units were calculated for samples of n=2-20 (not shown). If an observed mean scale value is within +/1.5 units, it will be rounded to a scale value that is +/1 unit from the correct scale value. To achieve a mean scale value within +/1.5 units, required standard deviations for samples of n=2, 3, 4, and 5 are 0.167, 0.604, 0.943 and 1.208, respectively. In our data, the overall standard deviation for departure from the mean for all cultivar-location-years (n=133) was 1.05. Based upon the overall standard deviation, 20 location-years would be needed to have a mean scale value that would have a 95% chance of being within +/0.5 units of the correct mean and, therefore, rounded to the correct scale value. Based upon the overall standard deviation (1.05), 5 location-years would be needed to have a mean scale value that would have at least a 95% chance of being within +/1.5 units and, therefore, rounded to +/1 unit of the correct scale value. For most purposes, +/1 unit is sufficient accuracy for producers; therefore, we recommend that reactions of winter wheat cultivars that are reported to producers be based upon data from at least five location years. 2002 National Fusarium Head Blight Forum Proceedings 229 Variety Development and Uniform Nurseries IDENTIFICATION OF DNA MARKERS FOR FUSARIUM HEAD BLIGHT RESISTANCE OF WHEAT LINE HUAPEI 57-2 William Bourdoncle and Herbert W. Ohm* Department of Agronomy, Purdue University, West Lafayette IN 47906 *Corresponding Author: PH: (765) 494-8072; E-mail: [email protected]