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First Report of Fusarium Head Blight of Wheat Caused by Fusarium sacchari in China

Fusarium head blight (FHB), or scab, caused by Fusarium species, is an economically devastating disease of wheat and other cereal crops worldwide. FHB epidemics in wheat occur frequently in China, especially along the middle and lower reaches of the Yangtze River, including Jiangsu and Shanghai. In 2013, wheat spikes showing clear FHB symptoms were collected from fields in Jiangsu and Shanghai. Symptomatic seeds were surface-sterilized for 1 min with a 5% sodium hypochlorite solution and dipping in 70% ethanol for 30 s, then rinsed three times in sterile distilled water and dried. They were placed onto potato dextrose agar (PDA) and incubated for 3 to 5 days at 28°C in the dark. Fungal colonies displaying morphological characteristics of Fusarium spp. (1,2) were purified by the single-spore technique and characterized at the species level by morphological observations (1,2) and translation elongation factor 1-α (TEF) gene sequencing. The results indicated that members of the Fusarium graminearum clade were predominant on wheat, while the morphological characteristics of 16 isolates were found to be identical to those of F. sacchari (1,2). Colonies on PDA were densely cottony, initially pale but becoming violet with age. The average growth rate was 6 to 8 mm per day at 25°C in the dark. Reverse pigmentation was brownish red to violet-brown. Microconidia, abundant in the aerial mycelium and formed in false heads, were oval to ellipsoidal in shape, primarily zero-septate, measuring 5.7 to 18.8 (average 10.6) μm in length. Macroconidia were slender, three- to five-septate, with a curved apical cell and a poorly developed basal cell, 26.3 to 68.9 (average 44.0) μm in length. No chlamydospores were observed. Two F. sacchari strains (Y37 and S43), isolated from Jiangsu and Shanghai, respectively, were investigated by sequence comparison of their partial TEF gene sequences (Accession Nos. KM233195 and KM233196). BLASTn analysis of the TEF sequences obtained with sequences available in the GenBank database revealed 99.8 and 99.5% sequence identity to F. sacchari (GenBank Accession Nos. JF740708 and JF740709). Pathogenicity tests were conducted by injecting 10 μl of a spore suspension (5 × 10⁵ spores/ml) into wheat florets (20 per isolate of cv. Yangmai16), which were then grown under field conditions in Shanghai. Control plants were inoculated with sterile distilled water. Spikes were harvested and evaluated 14 days post-inoculation. Reddish white mold was observed on inoculated wheat spikes; in addition, spikelets adjacent to the inoculation point and the infected florets were brown. No symptoms were observed on water controls. Koch's postulates were fulfilled by reisolating the pathogen from infected florets and identifying them by TEF gene sequencing. F. sacchari is the cause of an important disease of sugar cane, pokkah boeng (1), and has been reported to produce the mycotoxin beauvericin, which causes toxicosis in human and other animals (3). To our knowledge, this is the first report of F. sacchari causing wheat head blight in China. The report contributes to an improved understanding of the composition of Fusarium species on wheat in the lower reaches of the Yangtze River in China, which will be useful for exploring appropriate disease management strategies in this region.

References: (1) J. F. Leslie and B. A. Summerell. The Fusarium Laboratory Manual. Blackwell Publishing, Ames, IA, 2006. (2) J. F. Leslie et al. Mycologia 97:718, 2005. (3) A. Moretti et al. Int. J. Food Microbiol. 118:158, 2007.