Detection and Characterization of Lasiodiplodia pseudotheobromae Associated with Stem Wilt on Ficus hirta (Vahl) and Its Fungicidal Sensitivity

Ficus hirta Vahl is an important medicinal and edible plant in southern China. Typical green wilting on leaves and brown necrotic spots on the stems were observed since mid-June 2022 in an F. hirta plantation in Danzhou, Hainan (China). The disease rapidly developed, causing stem withering and plant death. The disease incidence varied from 45 to 85% prevalence, and the average disease index was 47 in the period of outbreak during June to December. Relevant hypothetical fungi were isolated from naturally infected wilt tissues, and their pathogens were preliminarily confirmed to be Lasiodiplodia pseudotheobromae through hypothetical fungal culturing, morphological characteristic observations, and pathogenicity testing on F. hirta plants. The phylogenetic tree constructed based on partial ITS, translation elongation factor (TEF1-α), and the β-tubulin gene (TUB2) further confirmed the identity of the pathogen as L. pseudotheobromae. Further research on the biological characteristics of L. pseudotheobromae showed that the optimal temperature for the growth of L. pseudotheobromae was PDA medium, with a temperature of 30 °C and pH of 6. Peptone and fructose were the optimal nitrogen and carbon sources for it. In vitro efficacy testing showed that among eleven fungicides, fluazinam and prochloraz had the highest mycelial growth inhibition, with an EC50 of 0.0477 µg/mL and 0.0996 µg/mL, respectively. And the two fungicides showed significant control on the stem wilt of F. hirta in a pot. To our knowledge, this is the first comprehensive report on the pathogen identification and biological characteristics of L. pseudotheobromae infecting the stem wilt of F. hirta in China. Our results provide important information for developing effective management measures and controlling this disease.