| الوصف: |
Investigations on putative interactions among Fusarium species colonizing wheat ears were carried out to understand the high frequency of species with low virulence in the presence of more virulent ones. To determine inter-species interactions among the major Fusarium head blight pathogens, wheat ears were inoculated at mid flowering either with F. graminearum, F. culmorum, F. avenaceum and F. poae alone or in combinations of two, three or four isolates under field and greenhouse conditions. The isolates and the composition of inoculum significantly affected FHB severity, kernel weight, number of Fusarium -infected kernels, fungal biomass and mycotoxin production. In single or mixed inoculations, F. graminearum resulted in the highest disease ratings, frequency and intensity of kernel colonization and mycotoxin production, followed by F. culmorum, F. avenaceum and F. poae , respectively. In mixtures, the frequency of F. culmorum, F. avenaceum and F. poae infected kernels and fungal biomass in most cases was lower than in single inoculations, while the mycotoxin productivity significantly increased. The study demonstrated that significant interactions exist between or among Fusarium isolates during kernel colonization, such as competition and amensalism. These interactions were disadvantageous to less-virulent isolates, although to different degrees, no additive effects were detected. Competitiveness and virulence of isolates varied as quantified by the different parameters; they decreased in the order Fusarium graminearum, F. culmorum, F. avenaceum and F. poae , respectively. The frequency of infected spikelets increased with sampling time either in inoculation alone or in mixtures. For F. graminearum , the increase in the percentage of infected spikelets was unaffected by the presence of other isolates, while the other isolates were inhibited by its presence in mixed inoculations. The frequency of infection of wheat flower parts by Fusarium isolates decreased in the order lemma, palea, glume and developing ... |