2018 ASHS Annual Conference

Citrus production in south Texas is largely affected by Phytophthora foot and root rot disease. The causal agent, Phytophthora nicotianae, is an oomycete that causes root rot and trunk gummosis, leading to poor yield, tree decline, and eventually tree death. Trichoderma spp. is a soil fungi capable of suppressing several plant pathogenic fungi including Phytophthora spp. Our previous studies revealed that native Trichoderma isolates possess anti-fungal activity against P. nicotianae in vitro. One isolate showed strong mycoparasitism and sequence analysis confirmed it as Trichoderma asperellum. Greenhouse evaluations showed that T. asperellum protected citrus seedlings from P. nicotianae infection and promoted seedling growth. The aim of this study was to continue the evaluations of Trichoderma by performing field evaluations on the effectiveness of T. asperellum in preventing Phytophthora infections and its impact on tree growth. Applications of T. asperellum were performed in three different locations in South Texas, with each site planted with Rio Red grapefruit trees at different developmental stages (new planting, 2 years old and mature trees), Phytophthora populations, and infection levels. Initial measurements were recorded to assess differences between treated and untreated trees. Evaluation of tree growth parameters such as tree height, leaf area and trunk diameter have been performed every three months in each location for a year. Phytophthora quantification revealed that soil propagules were reduced after six months post application. Significant differences were not observed in growth parameters of trees between treated with T. asperellum and untreated control within first year of the study. The ongoing field studies will further determine T. asperellum as potential biocontrol agent against Phytophthora foot and root rot.