First Report of Fusarium incarnatum Causing Stalk Rot on Maize in China.

Stalk rot caused by Fusarium spp. is one of the most destructive diseases of maize, occurring in most corn-producing regions worldwide. This disease causes damage to the vascular bundles and may undermine absorption and translocation of water and nutrients, thereby reducing photosynthesis and grain development (Li et al. 2010). Normally, yield losses are estimated at about 10%, but this could increase to 30 to 50% under adverse conditions. In June 2013, lodged maize plants with dark pith disintegration of the stalks were collected in Dalian Lushun, China. Pith tissues (approximately 5 mm2) were dissected, soaked in 1% NaOCl for 30 s and 70% ethanol for 30 s to surface-sterilize, and rinsed three times in sterile distilled water. After being dried with blotting paper, three pieces were placed on potato dextrose agar (PDA) medium amended with streptomycin sulfate (130 μg/ml). Cultures were grown on PDA and carnation leaf agar (CLA) at 26°C in complete darkness for about 2 weeks. Morphological characteristics of the fungal isolate on PDA were as follows: colony were cotton-like and white to yellowish brown; macroconidia produced on CLA were slightly curved, mostly 3 to 5 septate, with a tapering apical cell and a foot-shaped basal cell, measuring 36.5 ± 5.5 μm × 4.5 ± 0.8 μm; microconidia were fusoid, 1 to 5 septate, measuring 22.8 ± 5.0 μm ×3.6 ± 0.6 μm; chlamydospores were absent. DNA was extracted from a single spore isolate. For DNA amplification, a partial elongation factor-1 alpha (EF-1α) gene was amplified using the PCR with two different sets of primers, EF-1H and EF-2T (Geiser et al. 2004). The resulting sequences were aligned to GenBank sequences that shared 99% similarity with that of Fusarium incarnatum. Sequences were deposited in GenBank (Accession No. KT313002). Pathogenicity tests were conducted by inoculating maize plants at the seedling stage. Colonized corn kernels (20 g) were mixed with sterilized soil in 10-cm-diameter pots. Three kernels per pot were placed on the soil surface and covered with a 2-cm layer of sterilized sand. Five pots were inoculated and three uninoculated controls were included. Pots were maintained at 26 to 28°C. All materials, including pots and soil, were disinfected. After 2 months, the inoculated plants were stunted with light-colored leaves and fewer lateral roots than control plants. No symptoms were observed on the controls. The fungus reisolated from the infected mesocotyls showed the same characteristics as the original isolates. No colonies of F. incarnatum were isolated from noninoculated. F. incarnatum was previously reported to be affecting sorghum in China (Funnell-Harris et al. 2010). To our knowledge, this is the first report of stalk rot caused by F. incarnatum on maize in China. © 2016, American Phytopathological Society. All rights reserved.