THE EFFECT OF PLANT-GROWTH REGULATORS AND NITROGEN ON FUSARIUM HEAD BLIGHT OF THE SPRING WHEAT CULTIVAR MAX

Application of the growth regulators chlormequat and ethephon and fert ilization with nitrogen had no significant effect on the progress of h ead blight caused by Fusarium graminearum on the red spring wheat (Tri ticum aestivum) cultivar Max in greenhouse experiments in which heads were inoculated at anthesis with suspensions of macroconidia. A factor ial field experiment was conducted in Quebec in 1991 with three variab les: nitrogen (0 or 140 kg/ha), growth regulator (none, ethephon, or c hlormequat), and inoculation (none, inoculation with macroconidia at a nthesis, or inoculation 1 wk after anthesis). Because of dry condition s that year, no head blight symptoms developed on plants in the field. Seed infection by F graminearum was evaluated with a Fusarium selecti ve medium. Nitrogen and growth regulators had no effect on wed infecti on. In 1992, a 3 X 3 factorial experiment was conducted in Ontario usi ng the same growth regulator treatments and three inoculation treatmen ts (no inoculation, heads inoculated with macroconidia, or rows infest ed with Fusarium-colonized corn kernels that produced ascospores). Bot h ethephon and chlormequat increased the incidence of spikelet infecti on, but only in treatments inoculated with infested corn. Chlormequat also increased the incidence of seed infection in noninoculated treatm ents and treatments with infested corn. These data suggest that growth regulators and nitrogen do not change the inherent susceptibility of wheat heads to F. graminearum, but shortened plants may be subject to higher inoculum doses because they art closer to ejected ascospores. T he dwarfed plant architecture also may influence the microclimate and production of perithecia and ascospores by the perfect stage on the so il surface.