Evaluation of a detached leaf assay to measure fusarium head blight resistance components in barley

Barley genotypes with known field reactions to fusarium head blight (FHB) were evaluated for partial disease resistance (PDR) components using an in vitro detached leaf assay. The detached leaves were inoculated with Fusarium graminearum or F. culmorum and incubated at room (21 +/- 2 degrees C) or low temperature (10 +/- 1 degrees C). Both species were pathogenic and had a shorter incubation period and produced larger lesions at room temperature. Inoculation with F. culmorum produced less well-delineated necrotic lesions compared with those from inoculation using F. graminearum under both temperature regimes. On susceptible genotypes, inoculation with F. graminearum at room temperature resulted in significantly shorter latent and incubation periods, larger lesions and more macroconidial production compared with resistant genotypes. Inoculation with F. culmorum resulted in no significant differences in any PDR components measured. Several PDR components for F. graminearum, including latent period, lesion size and macroconidial production, were found to be significantly correlated. There was a negative correlation between incubation period and field ratings in one of three tests, latent period and field ratings in two of three tests, and a positive correlation between lesion size and field disease severity ratings for FHB only in one of three tests. Few PDR components for F. culmorum were found to be significantly correlated with each other. Overall, the best differentiation between resistant and susceptible barley genotypes resulted from inoculation with F. graminearum at room temperature, including a significant correlation between incubation and latent periods with field ratings. In general, given the variability observed, especially in relation to field ratings for FHB, measurement of PDR components cannot be routinely used to complement field-based ratings. However, the measurement of latent period did show promise as it was correlated to field ratings in two of three tests and as such measurement of latent period may be useful in identifying genotypes highly susceptible or resistant to FHB. Further research is required to evaluate the potential of using a detached leaf assay to complement field screening for FHB resistance.