Root-colonizing Fungi from Oilseed Rape and their Inhibition of Verticillium dahliae

Root!colonizing fungi obtained from thoroughly washed root segments of symptomless young oilseed rape plants growing in _eld soil were examined for their inhibitory e}ect on the wilt fungus\ Verticillium dahliae Kleb[ The isolated fungi that were possible to identify belonged to the di}erent genera Trichoderma\ Gliocladium\ Mort! ierella\ Fusarium and Alternaria[ Oilseed rape seedlings from seeds exposed to both sporulating and non! sporulating fungal isolates were shown to be colonized by their hyphae in gnotobiotic conditions and the emerg! ence:root growth was signi_cantly a}ected in their pres! ence[ Inoculation with a few isolates not only covered the root surface but also seemed to extensively colonize the inner root cortical tissues partly by producing charac! teristic structures in the roots[ All of these suppressed the pathogen in in vitro assays but the mode of suppression in most cases did not seem to be due to production of antifungal substances[ In nonsterile _eld soil\ several of the isolates conferred protection against V[ dahliae by delaying symptom development[ None of the isolates was shown to increase wilt symptoms[ In addition to protec! tion\ two isolates\ yet to be identi_ed\ also showed increased shoot dry weight compared with that of healthy controls[ A majority of the isolates showed proteolytic activity whereas only three produced chitinolytic enzymes[ Results for the isolates obtained by the method selected for this study could be considered as a starting point for evaluating antagonists capable of both com! peting for root colonization and preventing root infec! tion\ with the _nal aim being to achieve successful biological control of the wilt fungus[