| Summary: | Botryosphaeria dieback (BD) is a grapevine trunk disease (GTD) causing significant yield losses and limiting the lifespan of vineyards worldwide. Fungi responsible for BD infect grapevines primarily through pruning wounds, and thus pruning wound protection, using either synthetic chemicals or biological control agents (BCAs), is the main available management strategy. However, no products to control GTDs are currently registered in Canada. With a focus on more sustainable grapevine production, there is an increasing demand for alternatives to chemical products to manage GTDs. Accordingly, the objective of this study was to identify <i>Trichoderma</i> species from grapevines in British Columbia (BC) and evaluate their potential biocontrol activity against BD fungi <i>Diplodia seriata</i> and <i>Neofusicoccum parvum</i>. Phylogenetic analyses identified seven species, including <i>T. asperelloides</i>, <i>T. atroviride</i>, <i>T. harzianum</i>, <i>T. koningii</i>, <i>T. tomentosum,</i> and two novel species, <i>T. canadense</i> and <i>T. viticola</i>. In vitro dual culture antagonistic assays showed several isolates to inhibit fungal pathogen mycelial growth by up to 75%. In planta detached cane assays under controlled greenhouse conditions identified <i>T. asperelloides</i>, <i>T. atroviride</i> and <i>T. canadense</i> isolates from BC as providing 70% to 100% pruning wound protection against BD fungi for up to 21 days after treatment. In addition, these isolates were shown to provide similar or better control when compared against commercial chemical and biocontrol products. This study demonstrates the potential that locally sourced <i>Trichoderma</i> species can have for pruning wound protection against BD fungi, and further supports the evaluation of these isolates under natural field conditions.
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