Application of Trichoderma spp. to Antagonize Calonectria spp. That Cause Fruit Rot in Starapple (Chrysophyllum cainito L.)

Fruit rot disease is a major obstacle for starapple production in Vietnam. Therefore, the aims of the current study were (i) to identify the causing agents for fruit rot in starapple, (ii) to select isolates of Trichoderma spp. as antagonists, and (iii) to determine efficient approaches to control the disease. The pathogens were isolated from symptomatic starapple fruits collected in Can Tho City, Vietnam. The antagonists were isolated from the soils of healthy starapple farms. The three pathogenic isolates with the fastest growth (20.5–45.0 mm) and the largest infection spot (14.5–16.5 mm) were Calonectria candelabra C-SA01, C. candelabra C-SA06, and C. sulawesiensis C-SA07. Four Trichoderma isolates, T-SA01, T-SA06, T-SA10, and T-SA14, were selected because they consistently showed high antagonistic efficiency against C-SA01, C-SA06, and C-SA07 in dual-culture assays at 56.7–69.5%, 50.4–70.8%, and 62.6–69.2%, respectively. ITS-based results tentatively assigned T-SA01 to T. harzianum and T-SA06, T-SA10, and T-SA14 to T. asperellum. Under in vivo conditions, each Trichoderma sp. isolate was combined with different spraying methods. The result revealed that the four antagonists showed identical outcomes in reducing fruit rot disease. Spraying Trichoderma spp. both one day before and after inoculation resulted in the best biocontrol, with the highest disease-reducing rate at 44.2% at day 5. These newly found antagonists should be further tested in actual starapple farms to reveal their true potency.