Fungal Pathogens of Peach Palm Leaf Spot in Thailand and Their Fungicide Sensitivity

Peach palm (<i>Bactris gasipaes</i> Kunth) is a long-lived tropical palm valued for its edible, nutritious fruits. The cultivation area of peach palm, which was introduced to Thailand for fruit production, has been steadily expanding. Small brown spots that expanded into irregular lesions with dark margins were first observed on <i>B. gasipaes</i> seedlings in commercial nurseries in Phetchaburi Province, southern Thailand. To identify the causal pathogens, ten fungal isolates were obtained from symptomatic leaves and subjected to pathogenicity tests, confirming their ability to cause the disease. Morphological and molecular analyses identified five isolates as <i>Colletotrichum fructicola</i> (BGC02.2, BGC03) and <i>C. theobromicola</i> (BGC01, BGC02.1, BGC04) and five isolates as <i>Fusarium pernambucanum</i> (BGF01, BGF02, BGF03, BGF04.1, BGF04.2). Phylogenetic analysis was based on <i>act</i>, <i>cal</i>, <i>gapdh</i>, ITS, and <i>tub2</i> regions for <i>Colletotrichum</i> spp. and <i>cal</i>, <i>rpb2</i>, and <i>tef1-α</i> for <i>Fusarium</i> spp. In vitro fungicide assays revealed that <i>C. fructicola</i> and <i>C. theobromicola</i> were the most sensitive to carbendazim, mancozeb, and prochloraz, while <i>F. pernambucanum</i> was effectively inhibited by mancozeb and prochloraz. This study represents the first report of <i>C. fructicola</i>, <i>C. theobromicola</i>, and <i>F. pernambucanum</i> causing leaf spot disease on <i>B. gasipaes</i> in Thailand, providing essential insights for disease management strategies in the region.