Selection of Trichoderma spp. isolates antagonistic to Rosellinia necatrix

Fifty-six bulk isolates of Trichoderma spp. from avocado (Persea americana Mill.), carnation (Dianthus caryophyllus L.), litchi (Litchi chinensis Sonn), rice (Oryza sativa L.) and sugar beet (Beta vulgaris L.) crops located in southern Spain were evaluated for antagonism against one isolate of Rosellinia necatrix Prill. Isolates of both types of fungi were tested in dual and cellophane culture. The origin, cultural characteristics, overgrowth sporulation and staining of growth medium were recorded. As a result, 21 Trichoderma bulk isolates were selected and their corresponding monoconidial isolates were evaluated as above. Next eight monoconidial Trichoderma isolates with the largest in vitro antagonism were selected, and they were additionally tested against nine representative isolates of R. necatrix from nine virulence groups. These were established after pathogenicity tests on 57 isolates of R. necatrix from diseased avocado orchards in southern Spain. These monoconidial Trichoderma isolates were considered as potential biological control agents with a high potential for effective control of white root rot of avocado.