Isolation And Identification Of Causal Pathogen Of Sugarcane Leaf Scald And Evaluation Of Disease-resistance Of New Sugarcane Clones In China

The leaf scald caused by Xanthomonas albilineans is a systemic bacterial disease that occurs worldwide,posing a potential threat to the development of the sugar industry.So far,there have been few reports on the molecular identification of the causal agents of sugarcane leaf scald in China.Also,the disease resistance of main cultivars and important germplasm resources are still unclear.In this study,a total of 357 sugarcane leaf samples were collected from four provinces（Fujian,Guangdong,Guangxi,and Hainan）in China during 2013-2017.All of them,141 samples were taken from plants showing leaf scald symptoms and 216 samples were taken from asymptomatic plants.A pair of primers（XAF1/XAR1）targeting a putative ATP（adenosine triphosphate）-biding cassette（ABC）transporter gene（XALc₁791）were used to detect X.albilineans in these leaf samples.The pathogen was detected in 73%and 17%of symptomatic and asymptomatic leaf samples,respectively.Our findings suggested that X.albilineans contributes to leaf scald of sugarcane in Guangxi,Guangdong,Hainan,and Fujian provinces,suggesting that this disease could be a potential threat to the sugarcane industry in China.The PCR-amplified fragments（608 bp）from 140 Xa-positive samples were cloned and sequenced.A total of 241 XALc gene sequences were obtained and compared to 13 sequences of X.albilineans isolates retrieved from GenBank.The isolates from China had 99.1-100%sequence identity with one another and 99.5-100%with four strains from the French West Indies（GPE PC73,GPE PC 17,GPE PC86,and MTQ032）and one from Florida/USA（XaFL07-1）.Additionally,the causal pathology X.albilineans of leaf scald was confirmed by morphological observation,physical and chemical characteristics tests,PCR molecular identification and the confirmation of Koch’s postulates.Besides,we evaluated the disease-resistant of 18 newly released sugarcane varieties（clones）using an artificial inoculation method.A total of eleven varieties/clones were identified as a resistant of leaf scald and three of them（Y50,YZ11-3898,and FN09-7111）were identified as high resistance level.Our findings provide a technical support for the effective prevention of this disease.