Complementary Approaches to Developing Scab Resistant Wheat Varieties

NON-TECHNICAL SUMMARY: Fusarium head blight is a serious disease of wheat in Kentucky. Our crop is at risk due to the cropping system and rotation we follow. Consequences include reduced yield, test wt. and grain quality as well as reduced food safety through toxin accumulation. All of these factors lead to reduced dollars to farmers and to the entire wheat industry. The best approach to solving this problem is through breeding integrated with management tools such as fungicides. The impact of this work is on the order of mult million dollar savings in a year with moderate disease pressure in KY.

<P>APPROACH: All material will be screened in a misted, inoculated nursery at Lexington, KY (approximately 0.5 acres; 3000 plots). All material other than the F2 and F3 bulks and the Max test will be grown in a randomized complete block design with two replications. The Sumai 3 -derived resistant check cultivar Pioneer 25R18 and the susceptible check cultivar Pioneer 2555 will be planted frequently throughout both nurseries. The grain spawn method will be used to inoculate the irrigated nursery at Lexington; scabby corn will be applied at a rate of 40 g m-2 at approximately the early boot stage (Feeke's GS 8). Mist irrigation will be applied daily until the material reaches flowering, and from this point through mid grain fill the irrigation regime is as follows: the nursery will be mist irrigated daily for five minutes every ten minutes between 6 and 8 AM and between 10 PM and 12 AM. At Princeton, we will also distribute scabby corn as inoculum, but since there is no irrigation, a conidial suspension will also be applied twice, beginning when the earliest lines flower and repeated one week later. Approximately 1.2 x 108 conidia are delivered with each application. Chaff symptoms will be scored as follows: incidence is measured as the percentage of symptomatic heads to total heads counted in a 1 m2 area of the plot. Average head severity is determined by counting the number of infected spikelets divided by the total number of spikelets per head on 10 infected heads per plot. In all of the breeding material (lines) chaff symptoms will be rapidly assessed on a visual scale, 0 (resistant) - 6 (completely susceptible). Fusarium damaged kernels (FDK) will be assessed on all material using a modified Precision machine head thresher and vacuum to separate kernels by air. Using this method, kernels are separated into two classes: scabby and healthy. DON will be assessed on sub-samples sent to the University of Minnesota lab of Dr. Yanhong Dong. In general, the focus of screening will be on kernel symptoms and DON levels rather than chaff symptoms. In the F2 and F3 populations heads with low scab severity will be tagged before senescence and will be harvested and threshed separately. Breeding: The most efficient approach to breeding scab resistant wheats relies on a combination of conventional and marker-assisted efforts. The conventional breeding program functions as a long term recurrent selection program in that promising lines are cycled back into the program as parents. Our target is to have a population of parents with an acceptable baseline level of scab and DON resistance so that there is a high probability of recovering resistant progeny from any given cross. Each year we make approximately 400-600 crosses which involve various sources of "native" resistance (e.g.Truman) or Sumai 3 - derived SRW wheats like Pioneer 25R18 or VA01W-476. One problem with the native resistance is that it is quantitative in nature and haplotypes are unknown, so the transfer of the resistance must be achieved through phenotyping and selection of resistant progeny.