Time course of early and long-term colonization events of olive (Olea europaea L.) roots by Trichoderma harzianum

Abstract

Trichoderma harzianum CECT24l3 has been demonstrated to be an effective biocontrol agent (BCA) ofVerticillíum wilt ( Verticiilium dahliae K leb.) of olive (VWO) under control conditions. Previous works also sho\·ved in vitro mycoparasitism of V dahliae by strain CECT2413 and its ability to promote olivc growth and extemal!intemal colonization in tomato plants. The prcsent study aimed to evaluate the colonization capability of olive roots (var. Picual) by CECT2413 during a prolonged period oftime (> 100 days). A gfp-labelled derivative of CECT2413 and confocai laser scanning microscopy (CLSM) were used. CLSM image1y showed that CECT2413-gfp profusely colonized olive roots during the fírst three days after inoculation (DAI). Mycelium and abundant asexual reproductive structures (conidiophore-like) were clearly visible over the root surface. From this time point, tluorescent fm1gal structures resembling chlamydospores were observed, while a progressive loss of mycel ium became apparent. T'he majority of CECT2413-gfp biomass during this period (from 7-14 DAf) corresponded to conidia and chlamydospores found over the epidermis and root hairs. Colonization preference of specitic root si tes was not evident and conidia, chlamydospores and mycelium were found all over the examined roots. Long-term observations revealed the presence of chlamydospores and conidia on the rhizoplane but lack ofmycelium. !n conclusion, strain CECT2413 is an excellent colonizer of olive roots which helps to understand is dfectiveness asan efficient BCA against VWO.