Abstract:
This article reports a lack of pathogenic specialization among Australian
Fusarium graminearum and F. pseudograminearum causing crown
rot (CR) of wheat using analysis of variance (ANOVA), principal
component and biplot analysis, Kendall’s coefficient of concordance (W),
and κ statistics. Overall, F. pseudograminearum was more aggressive
than F. graminearum, supporting earlier delineation of the crowninfecting
group as a new species. Although significant wheat line–
pathogen isolate interaction in ANOVA suggested putative specialization
when seedlings of 60 wheat lines were inoculated with 4 pathogen
isolates or 26 wheat lines were inoculated with 10 isolates, significant W
and κ showed agreement in rank order of wheat lines, indicating a lack of
specialization. The first principal component representing nondifferential
aggressiveness explained a large part (up to 65%) of the variation in CR
severity. The differential components were small and more pronounced in
seedlings than in adult plants. By maximizing variance on the first two
principal components, biplots were useful for highlighting the association
between isolates and wheat lines. A key finding of this work is that a
range of analytical tools are needed to explore pathogenic specialization,
and a statistically significant interaction in an ANOVA cannot be taken as
conclusive evidence of specialization. With no highly resistant wheat
cultivars, Fusarium isolates mostly differ in aggressiveness; however,
specialization may appear as more resistant cultivars become widespread.
