Identification And Characterization Of New Sugarcane Fungal Diseases

Sugarcane is one of the major sugar and energy crops worldwide. By the falling of sugar prices, the sugarcane planting and management were not in place. Along with large-scale and long-term cultivation of unitary sugarcane varieties, sugarcane disease are aggravating year by year. Thus, the rapid and accurate detection and identification of the pathogen is urgently required to manage and prevent the spreading of sugarcane new disease. In this study, two kinds of new sugarcane disease collected from Guangxi, Yunnan and Fuzhou have been identified their pathogens. Furthermore, this study have been described the character of those two pathogens. According to the experiment, we drew the following conclusions:1. Sugarcane brown leaf streak disease, characterized by brown leaf streak on midrib, vein and leaf margins. Two single-spore isolates YZ05-51 and YN7 were recovered from symptomatic leaves. According to Koch’s postulates the pathogens that inoculated onto the sugarcane seedlings, they were re-isolated from representative lesions completing. The morphology of these isolates conidium was distinctive, appear as regular obclavate, obpyriform to ovate catenulate with 0 to 3 longitudinal and 1 to 5 transverse septa tapering to a prominent beak attached in chains on a simple conidiophore. Sequences from three regions of the genome (OPA10-2, OPA1-3 and OPA2-1) were amplified from the disease-associated isolates. The brown leaf streak disease pathogen was identified and formally described as Alternaria tenuissima through phylogenetic analyses, morphological observations and the pathogenicity of the isolates on sugarcane. Furthermore we showed that mycelial growth of Alternaria tenuissima was optimal at pH 5.0 and 25℃-30℃. Additionally, among 14 chemical compounds tested, copper 8-hudroxyquinoline and mancozeb were found to be the most effective in suppressing the radial growth of the fungus. Mycelial growth in added copper 8-hudroxyquinoline vitro was 73.02% inhibited at concentrations of 100 ppm and 49.05% inhibited at concentrations 50 ppm. Therefore, copper 8-hudroxyquinoline and mancozeb are potentially effective fungicide to control this disease in China.The pathogen of sugarcane twisted leaf disease was Phoma sorghina var. Saccharum, caused twisting and curling symptoms of crown sugarcane leaves. This disease was particularly acute in Chongzuo, Guangxi. Three single-spore isolates Fn40, FJ-1 and FJ-2 were recovered from symptomatic leaves. According to Koch’s postulates those two single-spore isolates had been confirmed as the pathogen. This pathogen can be differentiated from related species based on the morphology of pycnidia and chlamydospores which formed regular glabrous, papillate and non-papillate ostioles pycnidia. Chlamydospore-anamorph was unicellular, botryoid-alternarioid shape, as well as the binucleate, frequently branched hyphae. Sequences from three fungal loci,28S nrDNA (LSU), the internal transcribed spacer regions 1& 2 and 5.8S nrDNA (ITS) and β-tubulin (TUB) 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. We also showed that mycelial growth of Phoma sorghina var. saccharum was optimal at pH 4.0 and 20℃ to 25 ℃. 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 ppm 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.This study was the first time to identify two species of sugarcane pathogens— Alternaria tenuissima and Phoma sorghina var. saccharum that were causal brown leaf streak of sugarcane and twisted leaf disease of sugarcane in world, also the first time to finish the characterization of two pathogens, respectively. This research will be very useful for the regulatory response and management of sugarcane diseases.