Fusarium proliferatum Associated with Basal Rot Disease of Bambusa pervariabilis × Dendrocalamopsis grandis in China

Bambusa pervariabilis × Dendrocalamopsis grandis is the main cultivated bamboo species used for ecological construction in the Yangtze River basin. This species has the advantages of easy reproduction, wide adaptability and strong resistance and has high economic, ecological and social benefits (Peng et al. 2020). One area of B. pervariabilis × D. grandis with basal rot disease was discovered in Renshou County, Sichuan Province, China (29°41'N, 104°11'E) in June 2020. The disease occurrence area was 68 hm2 in Renshou County, with an incidence rate of 34.8%, and 5% of the B. pervariabilis × D. grandis with basal rot disease died. The pathogen initially invaded from the first section of the base of the bamboo stalk, appearing as black to yellowish brown strips or lumps of disease spots, and rapidly developed horizontally and vertically, which caused the whole plant to wither in severe cases. Diseased tissues were collected from the base of a 4-year-old bamboo stalk with a sterile blade. 100 pieces (5 × 5 × 2 mm) of diseased tissues were sterilized with 3% NaClO for 30 s and in 75% ethanol for 90 s, rinsed three times with sterile distilled water, dried with sterile surface water on sterile filter paper, plated onto potato dextrose agar amended with streptomycin sulfate (Solarbio, 50 µg/ml), and incubated at 25 °C for 7 days with light. A total of five isolates were obtained, of which four isolates were similar in morphology. Using the method of monospore isolation (Leslie and Summerell 2006) and culturing it on PDA, the fungus produced round colonies with a diameter of approximately 8.4 mm and a surface color ranging from white to purple within 7 days at 25 °C. For identification by typical spores, the fungus was cultured on carnation leaf agar (CLA) medium at 25 °C for 7 days. The microconidia by the isolates BD2002, BD2004, BD2008 and BD2010 cultured on CLA medium were elliptical, ovoid, without septum, and measured 4.56 to 15.53 μm long × 1.36 to 6.98 μm wide (n=100). The macroconidia were rod-shaped or slightly curved, tapering apically with three to five septa, and measured 18.86 to 52.99 × 1.56 to 6.42 μm in size (n=100). According to the morphological characteristics of macroconidia and microconidia, the isolates were identified as Fusarium sp. (Leslie and Summerell 2006). For molecular identification, fungal DNA of isolates BD2002, BD2004, BD2008 and BD2010 was extracted by a fungal genomic DNA extraction kit. Polymerase chain reactions (PCRs) were p