, Volume 35, Issue 4, pp 441-452

Ascosporic and conidial inoculum of Gibberella zeae play different roles in Fusarium head blight and crown rot of wheat in Australia and the USA

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Air-borne spores of the Fusarium head blight (FHB) pathogenwere trapped at field sites in both Australia and the USA using susceptible wheat plants to establish whether ascospores or conidia were the dominant FHB inoculum. Although both ascospores and conidia were recovered from flowering spikes during a 28-day period between anthesis and grain filling, ascospores were the dominant spore type at Fargo, North Dakota in the USA. Conversely in Australia, conidia were the dominant spore type trapped during 16 and 21-day periods of sampling over 2 years at two sites in northern New South Wales. The effectiveness of Gibberella zeae ascospores and conidia as inoculum for FHB and crown rot (CR)was compared in plant infection assays using 10 isolates each from the USA and Australia. Overall, ascospores were less effective in causing FHB and CR than conidia, although the difference in FHB severity between the two spore types was small. Ascospores of isolates from the USA caused significantly less severe CR on three North American cultivars and some isolates with highly aggressive conidial inoculum were weakly aggressive with ascosporic inoculum. In contrast, both spore types of the Australian isolates caused severe CR and there was no significant difference between the spore types for CR severity on three North American cultivars. Studies such as these on pathogen biology and epidemiology are essential to examine whether the information gained in one geographical location can be effectively used to manage the pathogen in another location.