In Vitro Antagonistic Activity of Indigenous Trichoderma Isolates Against Lasiodiplodia Isolates Associated with Stem-End Rot of Star Apple (Chrysophyllum cainito L.)

Stem-end rot (SER) is an important postharvest disease that reduces the quality and marketability of star apple (Chrysophyllum cainito L.), while biological control offers a more sustainable alternative to chemical management. This study aimed to (i) select fungal strains causing SER disease in star apple and (ii) select and appraise strains of Trichoderma spp. fungi as antagonists to the selected fungi causing SER disease under in vitro conditions. Ten fungal isolates were obtained from symptomatic fruits, and 35 Trichoderma isolates were recovered from star apple rhizosphere soils. Five rapidly growing fungal isolates were evaluated using a detached-fruit pathogenicity assay, with three fruits per treatment. The five strains with the strongest expression of SER were selected and identified as Lasiodiplodia theobromae L-SA01, L-SA03, and L-SA07, L. venezuelensis L-SA02, and L. egytiacae L-SA06. Among 25 Trichoderma isolates screened for extracellular enzyme activities, T-SA05, T-SA30, and T-SA32 were selected for broad antagonistic activity and were provisionally associated with T. asperellum, T. yunnanense, and T. viride, respectively. At 72 h, these isolates showed antagonistic efficiencies of 55.4–58.9% against L-SA01, 64.9–69.6% against L-SA02, 80.8–82.4% against L-SA03, 58.6–59.3% against L-SA06, and 49.9–54.1% against L-SA07. L. venezuelensis and L. egytiacae were the two fungal species first found to cause SER. T. yunnanense was recently proven to control the Lasiodiplodia spp. fungi that cause SER. The selected isolates also exhibited chitinase and glucanase activities, although their enzyme profiles did not fully correspond to their antagonistic efficiencies. These findings identify indigenous Trichoderma isolates for further taxonomic confirmation and evaluation in postharvest fruit assays.