The fungus Fusarium cerealis (Cooke) Sacc. (1886) (synonym F. crookwellense L.W. Burgess, P.E. Nelson et Toussoun (1982)) is one of the causal agents of Fusarium head blight (FHB), a significant fungal disease of small grains and maize in many countries (3). Miller et al. identified trichothecene chemotypes from three F. cerealis (F. crookwellense) strains collected from Chinese wheat in 1991 (2). However, there have been no other reports of this Fusarium species in China since then. The disease has been an important threat to the production of wheat and barley in China, and has caused yield losses of approximately 212,000 t (data from China National Agro-Technical Extension and Service Center) in 2008, one of the most severe FHB epidemic years in Chinese wheat in the past 10 years. Scabby heads of barley and wheat were collected from Yuxi and Zhaotong in Yunnan Province, respectively, in 2008. Each of 15 strains was isolated from a different spike of barley and eight isolates were derived from different wheat spikes. All strains were single spored. On the basis of a multilocus genotyping assay (4), all 15 isolates from barley and six of the eight strains from wheat were identified as F. cerealis with the nivalenol (NIV) genotype. To validate this result, partial translation elongation factor (TEF-1α, ~700 bp) gene sequences of isolates were generated (GenBank Accession Nos. HQ824369 and HQ824370) and then compared with the FUSARIUM-ID database (1). The TEF-1α sequences of all 21 isolates were highly conserved and showed 100% identity with the sequences of F. cerealis in the database. A pathogenicity test was performed on a winter wheat cultivar, Yangmai158, using a three-replicate randomized complete block design in Langfang Experimental Farm. Langfang is not an FHB-endemic area and is very dry, with almost no infection source in normal years. At anthesis, the central floret of each of five spikes was injected with 20 μl of a conidial suspension (106 macroconidia/ml) of each isolate in each block, such that 105 spikes were injected per block. An equal amount of water was injected into five heads in each block as a control. The inoculated spikes were enclosed in sandwich bags misted with water for 3 days to ensure infection by the inoculated pathogen and prevent infections from other sources. The plots were misted twice daily after inoculation. The average night and day temperatures were 19.0 and 25.2°C, respectively. Typical FHB symptoms (light tan or bleached spikelets, bases of infected spikelets, and portions of the rachis were dark brown), which were observed in the heads inoculated with F. cerealis 7 days after inoculation, were similar to the original symptoms in the sampling sites. The control plants remained asymptomatic. F. cerealis was reisolated from the infected heads, indicating it was the pathogen causing this disease. To our knowledge, this is the first report of F. cerealis causing FHB on barley in China, and also the first time that a high proportion of F. cerealis strains were isolated from one sampling site (15 of 15 in Yuxi and 6 of 8 in Zhaotong). More isolates must be collected in Yunnan Province and further studies conducted to gain a better understanding of the spatial and temporal dynamics of this pathogen.
References: (1) D. M. Geiser et al. Eur. J. Plant Pathol. 110:473, 2010. (2) J. D. Miller et al. Mycologia 83:121, 1991. (3) D. W. Parry et al. Plant Pathol. 44:207, 1995. (4) T. J. Ward et al. Fungal Genet. Biol. 45:473, 2008.
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