First Report of Lasiodiplodia pseudotheobromae Causing Dry Rot Disease of Amorphophallus muelleri in China

Amorphophallus muelleri is a herbaceous perennial plant in the family Araceae (Yang et al. 2026). It is an economically important crop contributing significantly to the production and income of southwestern China's mountainous regions. In July 2025, A. muelleri plants with dry rot symptoms were observed in the germplasm nursery of Kunming University (24°58' N, 102°47' E), Yunnan Province, China. Approximately 18% of plants in a production-oriented germplasm nursery (81/452 plants) showed dry rot symptoms, with a mean disease severity of 36% based on the stem lesion area index. Infected A. muelleri plants at the seed-bearing stage manifested symptoms from the petiole base to the seed-producing zones. The affected tissues showed dark brown discoloration, abundant white mycelia, progressive tissue necrosis and rot. Symptomatic stem segments were aseptically excised from plants. The segments were then surface-sterilized by immersion in 75% ethanol for 3 min, followed by immersion in 1% sodium hypochlorite for 30 sec. Small tissue segments were aseptically excised from the margins of typical dry rot lesions and transferred onto potato dextrose agar (PDA) plates. Three morphologically similar isolates (ZYHB-2675, ZYHB-2676, and ZYHB-2677) were selected from six symptomatic samples and tested for virulence using a preliminary pathogenicity assay. The most virulent isolate, ZYHB-2676, was selected for further analysis. After incubation at 28℃ for 3 days, the mycelium had fully covered the PDA plate. The colony on PDA was initially white, turning gray to black, with dense, fluffy aerial hyphae. Conidia were ellipsoid, unicellular, hyaline turning dark brown at maturity with a median septum, measuring 17.6 to 26.8 × 11.5 to 15.4 µm (ave. 22.3 to 12.8 µm, n=50). These morphological characteristics matched Lasiodiplodia pseudotheobromae (Guo et al. 2023). For molecular identification of isolate ZYHB-2676, the internal transcribed spacer region (ITS), translation elongation factor 1-alpha (ef1-α) and beta-tubulin genes (TUB) were amplified and sequenced with primer pairs ITS1/ITS4, EF1T/EF2T and Bt2a/Bt2b, respectively. The obtained sequences were deposited in the GenBank database (ITS: PX788567, ef1-α: PZ200914, TUB: PX802684). BLASTn analysis of the ITS, ef1-α and TUB sequences from isolate ZYHB-2676 revealed high similarity to the ex-type strain L. pseudotheobromae CBS 116459T (ITS:NR111264, 100% similarity; ef1-α:EF622057, 100% similarity; TUB:EU673111, 100% similarity). Based on morphological and molecular data, the isolate was identified as L. pseudotheobromae. Pathogenicity tests were performed according to the methods described by Utpal et al (2026). Prior to inoculation, the stem of each intact A. muelleri plant at the seed-bearing stage was surface-sterilized by wiping with 75% ethanol for 30 sec, followed by 1% sodium hypochlorite for 30 sec, and then rinsed three times with sterile distilled water. For each replicate, five plants were inoculated by placing a 10 µL droplet of spore suspension (106 spores/mL) onto a shallow wound made at the stem base, while one plant treated with sterile water (applied onto an equivalent shallow wound) served as the control. Following inoculation, the plants were maintained in a growth chamber at 28℃(day) and 22℃(night) with a 12-h light/dark photoperiod and 75±3% relative humidity, similar to nursery growing conditions. Severe dry rot symptoms developed on 10 inoculated plants within 7 days, while control plants remained asymptomatic. Koch’s postulates were completed by the consistent reisolation of L. pseudotheobromae from lesions that developed on inoculated plants within 7 days, based on three independent replicate trials. L. pseudotheobromae has been reported to cause various diseases, including canker and shoot dieback of apple, dieback of Ormosia pinnata, and postharvest fruit rot of Indian jujube (Xue et al. 2019; Li et al. 2020; Guo et al. 2023). To our knowledge, this study represents the first report of L. pseudotheobromae causing dry rot on A. muelleri in China. This study expands the known host range of L. pseudotheobromae to include A. muelleri. Given the importance of Yunnan as a major production region for this crop, these findings highlight the necessity for enhanced monitoring and implementation of integrated management strategies against this emerging disease.