Fusarium is an important genus of fungal pathogens that are responsible for devastating diseases, such as Fusarium ear rot on maize, which may result in yield losses and/or mycotoxin contamination. In September 2013, a survey to determine population composition of Fusarium species on maize was conducted at 22 fields in 18 counties in Gansu Province. Maize ears with clear symptoms (with a white to pink- or salmon-colored mold at the ear tip) were collected. Symptomatic seeds were surface-sterilized with 70% ethanol and 10% sodium hypochlorite and rinsed three times with sterile water to eliminate hypochlorite residues. After drying on sterile filter paper, the seeds were placed on potato dextrose agar (PDA) and incubated at 25°C in the dark for 3 days. Mycelium that was characteristic of Fusarium spp. (2) was purified by transferring single spores to fresh PDA. Fusarium species were identified by morphological characteristics (2), multilocus genotyping assay (MLGT) (3), and sequence analysis of the translation elongation factor-1α (TEF) gene. Several Fusarium species were identified and Fusarium verticillioides and F. proliferatum were the predominant species. Based on MLGT, two strains from Chenghong County were identified as F. meridionale with NIV chemotype, a species in F. graminearum species complex (FGSC). Morphological characteristics were also identical to FGSC. Colonies grew rapidly on PDA and produce relatively large amounts of dense mycelia and red pigments. Slender, thick-walled, and moderately curved or straight macroconidia were observed with 5- to 6-septate. Furthermore, conidia on SNA also showed typical characteristics of F. meridionale, as the dorsal and ventral lines were often parallel and gradually curved. Sequences comparison of the partial translation elongation factor (TEF-1α, 644 bp) gene (1) was used to validate these observations. BLASTn analysis with the FUSARIUM-ID database revealed 100% sequence identity to F. meridionale (GenBank Accession No. KJ137017). Thus, both morphological and molecular criteria supported identification of the strains as F. meridionale. A pathogenicity test was performed on Zhengdan958, the maize variety with the largest planted acreage in China. Four days after silk emergence, 2 ml conidial suspension (105 macroconidia/ml) of each isolate were injected into each of 10 maize ears through silk channel. Control plants were inoculated with sterile distilled water. Typical FER symptoms (reddish-white mold) was observed on inoculated ears and no symptoms were observed on water controls. Koch's postulates were fulfilled by re-isolating the same fungus from the infected seeds. F. meridionale was one of the pathogens causing Fusarium head blight on wheat and barley in China and produced nivalenol (4,5) and it also has been isolated from maize in Korea and Nepal. To our knowledge, this is the first report of F. meridionale causing Fusarium ear rot on maize in China. Further studies on biological characteristics such as temperature sensibility and fungicide resistance are needed to gain a better understanding of this new pathogen.
References: (1) D. M. Geiser et al. Eur. J. Plant Pathol. 110:473, 2004. (2) J. F. Leslie and B. A. Summerell. The Fusarium Laboratory Manual. Blackwell Publishing, Ames, IA, 2006. (3) T. J. Ward et al. Fungal Genet. Biol. 45:473, 2008. (4) L. Yang et al. Phytopathology 98:719, 2008. (5) H. Zhang et al. Plos one 7:e31722, 2012.