Selection of endophytes as antagonists of Colletotrichum acutatum and elucidation of their mode of action

Abstract: Olive anthracnose, caused by several fungi of the genus Colletotrichum, is one of the main diseases affecting the olive tree worldwide. There is currently no effective treatment against it. A strategy for control this disease could rely on the use of naturally occurring endophytic antagonists, such as bacteria and fungi, as biocontrol agents. Thus, in this work, six endophytic bacteria and fungi previously isolated from olives of cultivar Cobrançosa (considered to be tolerant to anthracnose), were screened for their antagonistic activity against the causal agent C. acutatum, by using both dual-culture and bioassays with detached olive leaves. The involvement of lytic enzymes on the antagonistic activity displayed by the screened endophytes was also investigated. Among the six endophytes tested in dual-culture, three were able to reduce significantly the growth of C. acutatum on more than 10 % when compared to single culture of C. acutatum, being the greatest inhibition displayed by Microbacterium sp. and Bacillus sp.. The qualitative detection of cellulase, protease, laccase and lipase produced by endophytes during the interaction with C. acutatum, suggested their involvement in the mechanism of antagonism. In detached leaves, the reduction of both incidence and severity of anthracnose ranged between 25% and 38% for the three most efficient endophytes Bacillus cf. pumilus, Microbacterium sp. and Pseudomonas cf. cedrina. These three endophytes are potential biological control agents of C. acutatum, whose effect in preventing pathogen infection in olive tree should be tested.