Sugarcane is a major sugar and the leading energy crop worldwide and Guangxi is the largest sugarcane production area in China (2011 Sugar Annual China, www.gain.fas.usda.gov). During survey of sugarcane crops in September 2012 and June 2013, ~5 to 10% of sugarcane (cvs. FN-40 and ROC22) planted in Chongzuo and Laibing, Guangxi Zhuang Autonomous Region, P. R. China, had twisted and curling symptoms of crown leaves similar to sugarcane Pokkah boeng disease (caused by Fusarium moniliforme Sheldon). The symptoms started appearing as yellowing on midribs and leaf margins that spread further to the entire leaf, along with twisting and curling of crown leaves. The symptomatic leaf tissues (5 × 5 mm) were surface-sterilized by 0.1% HgCl2 solution for 30 s, followed by rinsing three times in sterile water, placed on potato dextrose agar (PDA), and then incubated in darkness at 28°C. After 3 days of incubation, the isolated fungal colony appeared as white villous, spherical, radial, and dense colorless mycelium from the top, while it was reddish-brown at the bottom and later became grayish. Chlamydospores were also observed with a diameter of 5 to 10 μm and were dark brown, unicellular, intercalary, and smooth. The binucleate hyphae were colorless and transparent. Pycnidia appeared on the colonies after 20 days, and were dark brown, subglobose, and 150 to 230 μm in diameter, and the conidia were ~3 to 7 × 2.5 to 6 μm, unicellular, colorless, and ovoid to oval. The fungal isolates from the symptomatic leaves were obtained and pathogenicity was evaluated. Conidial suspensions (107 CFU/ml) of the single isolate from FN-40 were micro-injected into 20 sugarcane seedlings of cultivar FN-40. Another 20 seedlings were injected with water without conidia as control. The inoculated plants were grown in a growth chamber at 28°C with a 16-h photoperiod. Twisted and curly symptoms similar to the field appeared on the inoculated leaves at 10 days after inoculation, while the control leaves remained asymptomatic. The fungus was re-isolated and identified. Genomic DNA from the cultured fungal isolate was extracted with a modified Fungal DNA Midi Kit (Omega Bio-Tek, Inc., Norcross, GA), and amplified using fungus-conserved primer sequences (ITS1: 5′-TCCGTAGGTGAACCTGCGG-3′ and ITS4: 5′-TCCTCCGCTTATTGATATGC-3′). The consensus rDNA-internal transcribed spacer sequence (GenBank Accession No. KC524502) was 100% identical with 97% coverage to the ITS sequence from Phoma sp. 3. TMS-2011 (HQ631000.1) in GenBank (3). The fungus Phoma sp. was identified on the basis of morphological characteristics (2,4) and the ITS sequence of rDNA (1,3). Disease caused by Phoma sp. has been reported earlier on sugarcane from Pakistan, Hawaii, and Taiwan, causing leaf blight and curling (2,4). However, to the best of our knowledge, this is the first report of Phoma sp. causing twisting and curling of crown leaves of sugarcane in mainland of China.
References: (1) M. M. Aveskamp et al. Stud. Mycol. 65:1, 2010. (2) A. Sanguino and H. Tokeski. ISSCT Proc. 17:1555, 1980. (3) P. Shrestha et al. Appl. Environ. Microbiol. 77:5490, 2011. (4) Z. N. Wang. Rep. Taiwan Sugar Res. Inst. 129:1, 1980.