Antifungal Activity of Rubiaceae Leaf Extracts Against Pathogenic Fungi Isolated From Durian ( Durio zibethinus )

ABSTRACT Fungal diseases significantly reduce the postharvest quality and marketability of durian ( Durio zibethinus ), especially in regions with humid tropical climates such as the Mekong Delta, Viet Nam. This study aimed to isolate and identify pathogenic fungi associated with diseased durian fruits and leaves, and to evaluate the antifungal potential of leaf extracts from five Rubiaceae species ( Ixora duffii , Neonauclea orientalis , Neolamarckia cadamba , Paederia lanuginosa , and Paederia scandens ). Nine fungal isolates were first obtained, among which three representative isolates were identified through morphological and molecular analyses as Lasiodiplodia theobromae , Diaporthe lithocarpus , and Lasiodiplodia pseudotheobromae . Pathogenicity tests confirmed their ability to induce fruit rot or leaf lesions. Antifungal assays revealed that all Rubiaceae extracts inhibited mycelial growth in a concentration‐dependent manner. Notably, Ixora duffii and Neonauclea orientalis demonstrated the highest activity, achieving complete suppression of Lasiodiplodia theobromae at 6.4 mg/mL, comparable to commercial fungicide control. These results indicate that Rubiaceae species, especially Ixora duffii , may serve as useful sources of antifungal compounds for improving the sustainable management of postharvest diseases in durian.