Biological control of Phytophthora collar rot of pear using regional Trichoderma strains with multiple mechanisms

The Alto Valle of Rio Negro is the main exporter and producer region of pear in Argentina, ʻBartlett’ being the most important cultivar. Phytophthora cactorum and Phytophthora spp. cause significant economic losses in commercial pear production from tree death and weakening and fruit rot. The harmful effect of fungicides and market regulations have created the need to search for promising natural biocontrol agents in integrated crop management programmes. As regional isolates of Trichoderma spp. can be effective biological controllers, Trichoderma was selectively isolated from healthy trees next to trees with collar rot, using Rose Bengal selective medium. All Trichoderma isolates (n = 88) were evaluated against four Phytophthora spp., pathogens of pear by inhibition of mycelia growth (MG) and mycoparasitism. Eighteen isolates reduced the MG of at least two species of Phytophthora by more than 45% and showed mycoparasitism (2–4 scale degrees). These isolates were molecularly identified and evaluated in vitro (growth and metabolite production) and in vivo (growth promotion) against P. cactorum. From six isolates selected by PCA, three regional T. harzianum strains with the best antagonistic attributes and PHI K tolerant were evaluated against P. cactorum in a semi commercial bioassay in young pear trees. During the first year of our two-year study, all regional isolates of preventively evaluated Trichoderma spp. decreased the severity of collar rot on pear to a large extent, but without significant differences with the commercial T. atroviride strain and PHI K. Trichoderma harzianum 1330 and 1377 strains preventively reduced pear collar rot by 97% with respect to the diseased control. In the second year, the regional isolates again reached higher biocontrol percentages against P. cactorum. In the curative experiment, regional Trichoderma strains showed no significant differences from PHI K and the commercial isolate. Among all curative and preventive treatments, the regional T. harzianum 1367 strain controlled the rot area caused by P. cactorum by 97%, with the lowest average lesion area (0.11 cm2).