Antagonistic activity of endophytic fungi towards Diplodia corticola assessed by in vitro and in planta tests

One isolate each of Trichoderma viride, Epicoccum nigrum, Fusarium tricinctum, Alternaria alternata, Sclerotinia sclerotiorum and Cytospora (teleomorph: Valsa sp.) present in epigeous declining oak tissues was evaluated for its ability to control Diplodia corticola (isolate 79). This fungus is the causal agent of cankers, vascular necrosis and dieback on various oak species. Among the isolates tested, T. viride and F. tricinctum showed maximum in vitro inhibition of mycelial growth of D. corticola (isolate 79). Species were also evaluated for their ability to reduce mortality caused by D. corticola (isolate 79) of Quercus cerris and Q. pubescens seedlings under controlled conditions. Two series of inoculations were carried out through wounds in the stem; in the first, the distance between the point of inoculation of the antagonist and the pathogen was 6 cm, whereas in the second series the distance was shortened to 3 cm. In seedlings of Q. cerris and Q. pubescens at a distance of 3 cm, inoculation with F. tricinctum and A. alternata significantly reduced mortality caused by D. corticola (isolate 79). Inoculation of T. viride through artificial cuticular wounds in the stem of seedlings prevented the proliferation of D. corticola (isolate 79) only on seedlings of Q. cerris. All Q. pubescens seedlings treated with T. viride manifested pathological symptoms subsequent to proliferation of D. corticola (isolate 79). These observations indicate that the interactions between endophytes in planta and D. corticola (isolate 79) are complex and merit further study.