Identification and Characterization of a New Fungal Pathogen Causing Twisted Leaf Disease of Sugarcane in China

Sugarcane twisted leaf disease, caused by Phoma sp., was first reported in Guangxi, China, in 2012, when more than 5% of sugarcane was infected in the field. Three single-spore isolates were recovered from symptomatic leaves. Sequences from five fungal loci, 28S nrDNA (LSU), 18S nrDNA (SSU), the internal transcribed spacer regions 1 and 2 and 5.8S nrDNA (ITS), β-tubulin (TUB), and the translation elongation factor alpha (TEF-α) were amplified from the disease-associated isolates. The twisted leaf disease pathogen was identified and formally described as Phoma sorghina var. saccharum through phylogenetic analyses, morphological observations, and the pathogenicity of the isolates on sugarcane. P. sorghina var. saccharum can be differentiated from related species based on the morphology of pycnidia and chlamydospores that formed regular, glabrous, papillate ostioles. Chlamydospore-anamorph was unicellular, botryoid-alternarioid shape, as well as the binucleate, frequently branched hyphae. We also showed that mycelial growth of P. sorghina var. saccharum was optimal at pH 4.0 and 20 to 25°C. Additionally, among 13 chemical compounds tested, carbendazim was found to be the most effective in suppressing the radial growth of the fungus. Mycelial growth in vitro was completely inhibited at concentrations of 100 and 50 ppm, and 87.6% of mycelial growth was inhibited at 10 ppm. Carbendazim is therefore a potentially effective fungicide to control this disease in China.