Influence of inoculation method and growth stage on fusarium head blight in barley

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Abstract
The effect of inoculation method and growth stage on the development of fusarium head blight (FHB) in barley were evaluated under controlled conditions. Barley cvs. Argyle, AC Oxbow, Chevron, and AC Lacombe were inoculated with macroconidial suspensions of Fusarium graminearum Schwabe either by single floret injection at preanthesis, anthesis, or postanthesis or by spray application to the entire spike at heading, 7 days after heading, or 14 days after heading. Four weeks after inoculation, heads were evaluated visually for symptoms of FHB, then the spikes were hand threshed and the seed assayed for F. graminearum colonization. Visual determination of FHB generally overestimated the F. graminearum seed colonization in the injected spikes and underestimated it in sprayed spikes. Infection resulting from floret injection was limited to the inoculated spikelet and immediately adjacent spikelets, so variation in FHB resistance among cultivars could not be satisfactorily distinguished using this inoculation method. The growth stage at the time of floret injection had no effect on seed colonization by F. graminearum. Spray inoculations produced more seed colonized by F. graminearum than single floret injection and was better for distinguishing the levels of resistance in the cultivars. The most resistant cultivar, AC Oxbow, could be distinguished from the other cultivars, using this inoculation method. Although the plants were susceptible to FHB infection from heading to 14 days after heading, the cultivars were best differentiated by inoculating at 14 days after heading. Seed colonization by F. graminearum among the first, second, or third tillers was similar using either inoculation method.