Identification of native endophytic Trichoderma spp. for investigation of in vitro antagonism towards Armillaria mellea using synthetic‐ and plant‐based substrates

Aims
To isolate endophytic Trichoderma species and investigate the potential for biological control of the root rot pathogen Armillaria mellea.

Methods and Results
In all, 40 Trichoderma isolates were obtained from a range of host plants and identities were confirmed by ITS, rpb2 and tef1 sequence. When tested in dual culture assays for antagonism against A. mellea, Trichoderma isolates overgrew the A. mellea colonies within four days and by eight days 38 Trichoderma isolates significantly reduced A. mellea colony size. Armillaria mellea was unable to be recovered from five of eight co-cultivations tested, suggesting Trichoderma had killed the A. mellea in these cases. Pre-colonized hazel disks were used to determine what happens in a more heterogeneous situation with A. mellea and a refined set of eight Trichoderma isolates. Similar to plate-based assays, Trichoderma quickly covered A. mellea stopping any further growth and two Trichoderma isolates were able to eradicate A. mellea.

Conclusions
Of the Trichoderma spp. tested, endophytic isolates of Trichoderma virens and T. hamatum offered the greatest antagonism towards A. mellea. Using pre-colonized hazel disks was of great importance for this work to demonstrate the fungal interactions in plant material.

Significance and Impact of the Study
Controlling Armillaria root rot is difficult with chemical treatments, thus an environmentally benign and cost-effective alternative is required. This study highlights the prospect of biological control as an effective, environmentally friendly alternative to chemicals.