Entoleuca sp. infected by mycoviruses as potential biocontrol agents of avocado white root rot

Rosellinia necatrix Prill. the causal agent of white root rot diseases causes major losses in avocado crops in Spain. To study the biocontrol of this disease, 31 antagonistic isolates were collected from the avocado rhizosphere and identified as Entoleuca sp. Studies were carried out in mycovirus detection, in vitro optimal growth temperature, mycelial compatibility groups of these isolates, and their inhibition of R. necatrix growth. The pathogenicity of these antagonistic isolates and their biocontrol of white root rot on avocado plants were also studied. The presence of mycoviruses was detected in all 31 Entoleuca sp. isolates studied and the optimal growth temperature for almost all the isolates (> 80%) was 25 °C. Dual culture showed different responses, with some isolates compatible and others incompatible with each other, showing inhibition halos and black lines. Twenty-five of the 31 isolates showed significant growth inhibition to a virulent R. necatrix isolate in in vitro conditions. In addition, none of the Entoleuca sp. isolates produced any symptoms on inoculated avocado plants and in 24 of them, symptoms of avocado white root rot were reduced, with significant differences among the Entoleuca sp. isolates when they were used as biocontrol agents. New virus-carrying Entoleuca sp. isolates were obtained, which are capable of controlling avocado white root rot.