Type I host resistance and Trichothecene Accumulation in Fusarium-infected Wheat Heads

Problem Statement: The objective of this study was to examine the influence of the type I host resistance and pathogen variation with respect to mycotoxin and aggressiveness, on infection, FHB disease development and mycotoxin accumulation in planta. Approach: Greenhouse experiments were conducted utilizing a spray inoculation method. Five single isolates of F. graminearum were tested. Three wheat cultivars were used; Alsen (moderately resistant), 2375 (moderately susceptible) and Wheaton (susceptible). At anthesis spikes were spray inoculated to run off with inoculum at the concentration of 10,000 conidia ml^-1. Inoculated whole spikes were sampled at different growth stages up to soft dough. Kernels of sampled spikes were dissected from the spike and analyzed for mycotoxins. Results: The highest FHB severity and mycotoxin accumulation was observed in the susceptible cultivar Wheaton. Though deoxynivalenol (DON) did not peak and decline in all experiments, when a peak in the DON content was present it was earlier in 2375 (early milk) than in either Alsen (early dough) or Wheaton (late milk). Though the isolates did not rank similarly in all experiments and in all cultivars, generally isolates Butte86Ada-11 and B63A were more aggressive and isolates 49-3 and B45A were less aggressive in terms of disease severity and mycotoxins accumulation. The levels of 15-acetyldeoxynivalenol, 3-acetyldeoxynivalenol and nivalenol were less than 4.5, 0.8 and 0.3% to that of DON in a given sample. Conclusion: DON levels appear to provide a more precise measure of mycotoxin contamination of grain. The use of mixtures of isolates, representative of the local population, in resistance screening appears advisable in order to avoid the misinterpretation of a cultivar’s resistance with the use of single isolate. Screening of cultivars likely requires both greenhouse and the field testing.