DOI: 10.1094/PDIS-05-16-0723-PDN

¡¾ABSTRACT¡¿Fusarium culmorum (W.G. Smith) Sacc. is one of the most important causal agents of crown rot of cereals. In addition to the significant disease, F. culmorum can cause a reduction in grain yield. Although it has been reported as one of the main fungal pathogens of wheat worldwide (Burgess et al. 2001; Hogg et al. 2010), there are no reports of this pathogen causing crown rot of wheat in China. Diseased plants of common wheat (Triticum aestivum L.) ‘Hengguan35,’ with whiteheads, brown discoloration on the first two or three internodes of the main stem, and pink mold, at about a 5% incidence in the field, were collected in Xingtai County (37.107750°N, 114.567690°E), Hebei Province, China, in May 2015. Isolates were obtained from diseased stem bases. Samples were surface-disinfested in 75% ethanol for 20 s and 0.3% NaClO for 2 min, then rinsed with sterile distilled water, and cultured on potato dextrose agar (PDA) acidified with 0.2% lactic acid. Pure cultures were subsequently established on carboxymethylcellulose agar (CMC) from single spores. Macroconidia were produced in CMC broth \culture after 6 to 10 days shaking at 25°C. The macroconidia were relatively short, thick-walled, and curved, with 3 to 4 septa, and measured 26.7 to 45.4 × 5.1 to 8.1 μm. The basal cell of the macroconidia was foot-shaped or just notched. Microconidia were absent. Chlamydospores were oval to globose. Aerial mycelium on PDA was abundant, floccose, and light yellow. The colony pigment on the underside of PDA plates ranged from grayish-rose, carmine red, to light yellowish brown. Isolate XT-5A was selected for molecular identification. The rDNA-ITS gene and translation elongation factor 1 alpha (TEF-1α) gene region were amplified by PCR with ITS1/ITS4 (White et al. 1990) and EF-1/EF-2 (O’Donnell et al. 1998) primers. The PCR products were sequenced (GenBank accession nos. KU885984 and KU885985). A BLAST search of PCR sequences of ITS and EF-1 alpha showed 97 to 100% identity with F. culmorum, and the morphological characteristics fit with F. culmorum, thus the isolate was identified as F. culmorum. The molecular identification was also confirmed by the F. culmorum species-specific PCR primers (FcOIF and FcOIR; Nicholson et al. 1998). The expected PCR product, a 570-bp fragment, was obtained with these primers for isolate XT-5A only. No bands were produced for F. equiseti, F. graminearum, and F. pseudograminearum examined in the same test. Pathogenicity tests were performed by soil inoculation of winter wheat ‘AK58’ with XT-5A. Inoculum was prepared using autoclaved millet seeds infested with agar blocks with mycelium of F. culmorum isolate XT-5A cultured on PDA. Millet culture was mixed with sterilized soil at 0.5% (w/w). No inoculum was added to the control treatment. The pathogenicity test was performed in three replicate 15-cm pots in a greenhouse at 20 to 25°C with 10 plants per pot. Crown browning occurred in the inoculated wheat plants after 4 weeks with 100% incidence, while no symptoms developed in the control plants. The pathogen was reisolated from the crowns of diseased plants by the method described above and identified by morphological and PCR amplification using primers FcOIF/FcOIR. No F. culmorum was isolated from control plants. Thus Koch’s postulates were fulfilled. This is the first report of F. culmorum causing crown rot of wheat in China and its potential distribution and impact on the wheat crop needs further investigation.