Till now, no published study is available on the variation in pathogenicity of Fusarium head blight (FHB) pathogens in relation to their isolation origin in barley head. To end this, two barley cultivars of contrasting quantitative resistance were artificially infected by four FHB species under field conditions over two consecutive growing seasons. Then, pathogenicity tests were conducted under in vitro conditions on single-spore cultures originated from both kernels and glumes in the heads. Different pathogenicity was detected among Fusarium species originated from both kernels and glumes, indicating that the same isolate from glumes and kernels differs in pathogenicity on leaves/seedlings. Isolates of Fusarium culmorum and Fusarium verticillioides originated from infected kernels had shorter latent periods and higher area under disease progress curves compared to isolates originated from glumes, and the reverse was observed for the Fusarium equiseti isolate. In the case of Fusarium solani, isolates originated from kernels or from glumes were equally pathogenic. Primarily findings in this first in-depth study have implications for breeding programs relied principally on actual quantification of pathogenicity in Fusarium species present in a given environment. The sampling of fungi should take into account the presence of Fusarium species of interest on kernels or glumes.
Fusarium head blight (FHB) is consistently one of the most important barley diseases worldwide. This study aimed to evaluate the pathogenicity of 16 isolates of four Fusarium species under controlled conditions and their genetic variability using 22 random amplified polymorphic DNA (RAPD) markers. Pathogenic variation was characterized based on disease development rates and disease index on two Syrian barley landraces with varying resistance to FHB, Arabi Aswad (AS) and Arabi Abiad (AB). Significant differences in intra- and inter-Fusarium species pathogenicity and in susceptibility between the above-mentioned cultivars were highlighted. Overall, the two barley landraces showed moderately susceptible to moderately resistance levels to fungal infection and FHB spread within the head. Quantitative traits showed significant correlation with previous data generated in vitro and under field conditions, suggesting that growth chamber indices can predict fungal pathogenicity and quantitative disease resistance generated under various experimental conditions. Based on PCR amplification with seven different primers, the isolates showed genetic variation. Dendrogram generated by cluster analysis based on RAPD markers data showed two main groups, suggesting that a possible clonal origin could exist in the four Fusarium species. RAPD fingerprints are not useful to distinguish the 16 Fusarium isolates with different levels of pathogenicity.
A simple and reliable method for quantifying Fusarium head blight (FHB), a widespread disease of barley, would enhance our capacity in identifying resistance sources and highly aggressive isolates. A detached head assay (DHA) was used to reliably assess: (i) resistance of two barley cultivars, Arabi Aswad (AS) and Arabi Abiad (AB) with different susceptibility to FHB and (ii) aggressiveness in a set of 16 fungal isolates of four Fusarium species. The two inoculated cultivars showed different responses in FHB incidence (DI) and severity (DS) using spray and point inoculation on detached barley heads, respectively. On AB, susceptible under several experimental conditions, inoculation with different Fusarium species resulted in significantly higher DI and DS, compared with AS, which showed Fusarium resistance. Furthermore, the values of DI and DS were significantly correlated with the previous findings generated under several experimental conditions. The use of this simple and reliable method in barley breeding programs can speed up the process of identification of sources of resistance to multiple FHB isolates. To our best knowledge, this is the first in-depth report investigating the usefulness of DHA for distinguishing susceptibility of barley plants and aggressiveness of diverse Fusarium species from a breeder's point of view.