Characterization of Arabidopsis thaliana-Fusarium graminearum interactions and identification of variation in resistance among ecotypes

Fusarium graminearum causes fusarium head blight (FHB) of wheat and other cereals. Resistance of wheat to FHB is incomplete and the defence mechanisms involved are poorly understood owing to the complex genome and long life cycle of the host. A robust and reproducible bioassay system was established for the study of interactions between F. graminearum and Arabidopsis by wound inoculation of detached leaves embedded in agar medium. Amendment of the inoculum with deoxynivalenol enhanced symptom development and conidial production. Colonization of leaf tissue was by both inter- and intracellular growth and extensive cell death was observed ahead of advancing hyphae indicating the presence of phytotoxic compounds or host-initiated programmed cell death. Expression of defence response genes associated with jasmonic acid/ethylene and salicylic acid pathways indicated that both pathways were activated in response to F. graminearum with expression of the jasmonic acid/ethylene pathways being more enhanced than that of the salicylic acid pathway, as expected for a necrotrophic pathogen. A large variation in resistance among Arabidopsis ecotypes was revealed. The ecotype Col-0 was significantly more resistant than Ler using both the detached leaf and a detached flower assay. Foliar resistance was shown to be controlled largely by a single genetic factor on chromosome 4 near the RFLP marker O6455. The detached leaf assay described herein provides a means to enable fundamental studies on the defence mechanisms of Arabidopsis in response to F. graminearum.