Characterization and In Vitro Fungicide Sensitivity of Two Fusarium spp. Associated with Stem Rot of Dragon Fruit in Guizhou, China.

Dragon fruit (Hylocereus polyrhizus) constitutes an important economic industry in Guizhou Province, China, and the occurrence of stem rot has become increasingly severe. In this study, we aimed to determine the causative pathogens of stem rot in this region and analyze their sensitivity to fungicides. Twenty-four fungal isolates were obtained from diseased tissues, from which H-4 and H-5 were confirmed as pathogens based on Koch's postulates. Based on the morphological characteristics of macroconidia, microconidia, and colony morphology, the polygenic phylogenetic tree constructed using internal transcribed spacer, elongation factor 1-alpha, and retinol-binding protein-2 gene fragments, and carbon source metabolism analysis using FF microplates, the two pathogens were identified as F. oxysporum and a newly discovered pathogen, F. concentricum. In addition, the in vitro toxicity of eight fungicides against both pathogens was measured based on the mycelial growth rate. The results showed that trifloxystrobin 25%·tebuconazole 50% (75 WG) exhibited the strongest inhibitory effect against both isolates, with EC50 values of 0.13 µg/mL and 0.14 µg/mL, respectively. These findings hold significant potential for guiding the effective treatment of stem rot in dragon fruit in Guizhou, China.