Aggressiveness of Fusarium species causing head blight on wheat plants determined in detached leaf and seedling in vitro assays

Fusarium head blight (FHB) is a serious disease of wheat. In vitro assays for reliable prediction of the head blight reaction in whole plant was investigated. The capacity of 16 fungal isolates of four FHB species to cause disease on individual plant organs was evaluated in vitro. Six quantitative components related to detached leaf and seedling assays were analyzed in six durum and bread wheat cultivars with known resistance. Differences in inoculated treatment were observed on young plant parts relative to water controls, indicating that these FHB species were found to be suitable for the differential expression of all tested quantitative components. There was a wide variation in aggressiveness among the 16 FHB isolates for latent period (LP) in detached leaf assay. Nevertheless, the other five components: incubation period and lesion length of detached leaf assay, percentage of infected seedlings (of foliar-spraying and pin-point inoculations) and lesion length (of clip-dipping inoculation) did not distinguish isolates. Significant correlation was found for the aggressiveness measured by LP of 16 FHB isolates and the previous pathogenic component ratings generated in vitro and in growth chamber and field study. These results suggest that LP predicts aggressiveness occurring at the earliest and latest wheat development stages during FHB infection. To our best knowledge, this is the primary in-depth report combining six different quantitative components delivered from two distinct in vitro assays to quantify aggressiveness in FHB species complex. Our data also highlighted, for the first time, the utility of LP for rapid and early determination of aggressiveness in FHB-wheat pathosystem.