Identification of endophytes and of their volatile compounds with biocontrol potential towards olive anthracnose

Abstract: Anthracnose, mainly caused by Colletotrichum acutatum, is the main disease of olive fruit worldwide. Strategies for controlling this disease are mostly based on the use of copper-based pesticides. Besides its limited efficacy, this approach is not compatible with sustainable production systems. Therefore, there is a need to develop more environment-friendly alternatives to these pesticides. Accordingly, this work aims to study the effect of two endophytes previously isolated from olive tree, namely Aureobasidium pullulans and Sarocladium summerbellii, on anthracnose infection by using in vitro and in vivo assays. Endophyte-mediated changes in plant volatiles (VOCs) and their consequences for anthracnose disease development were also evaluated. Among the two endophytes tested, only A. pullulans showed capacity to inhibit significantly the growth (up to 1.3-fold), sporulation (up to 5.9-fold) and spore germination (up to 3.5-fold) of C. acutatum in relation to the control (self-paired C. acutatum) in in vitro dual-culture assays. Similarly, in inoculated olive assays, only A. pullulans was able to reduce significantly progress curve for incidence (up to 10-fold) and severity (up to 35-fold) of anthracnose, as well as both sporulation (up to 90 %) and germination (up to 70 %) of C. acutatum, in comparison with olives inoculated solely with C. acutatum. Gas chromatography – mass spectrometry analysis of olives inoculated with A. pullulans + C. acutatum and controls (olives inoculated with C. acutatum, A. pullulans or tween) led to identification of 29 VOCs, belonging to 10 different chemical classes, being alcohols the most diversified and abundant ones. The volatile profile of A. pullulans + C. acutatum treatment revealed quali- and quantitatively differences from the controls, due to the production of recognized antimicrobial compounds, namely 1-hexanol, 1-heptanol and 2-methyl-1-propanol. These findings provide new viable possibilities of controlling olive anthtacnose using the endophyte A. pullulans and/or their VOCs. These volatile inhibitory metabolites should be further tested against anthracnose.