First Report of Fusarium meridionale Causing Fusarium Head Blight of Wheat in Mexico

Fusarium head blight (FHB), also known as scab, is a destructive disease of small grain cereals caused by several species belonging to the Fusarium graminearum species complex (FGSC). Members of the FGSC produce trichothecene toxins that represent a threat to human and animal health (Aoki et al. 2012). Despite the global significance of FHB and trichothecene contaminated grain, little is known about the identity of FHB pathogens present in Mexico. During the growing seasons of 2013 and 2014, three wheat heads with symptoms of FHB were collected from each of 40 localities in Tlaxcala, Puebla, and Mexico states. Symptomatic seeds were surface-sterilized for 3 min in 3% sodium hypochlorite and rinsed three times with autoclaved distilled water. Fungi were isolated using the freezing blotter test (Warham et al. 1997). Isolated colonies that resembled Fusarium species were transferred to water agar and subcultured on potato dextrose agar (PDA) plates using a single spore technique. Pathogenicity tests were performed in a greenhouse by using single-floret point inoculation of 45-day-old wheat with a 10 [mu]l suspension of 10 super(5) macroconidia/ml. Inoculated heads were covered with a plastic bag for 3 days to ensure infection, and fungi were reisolated from wheat heads showing typical FHB symptoms after 6 days. Multilocus genotyping (MLGT), which uses a set of 52 species or trichothecene genotype-specific probes in a multiplexed allele specific primer extension (ASPE) assay (Ward et al. 2008), was used to determine the species identity and trichothecene type for each of the fungi recovered from the pathogenicity test. Three isolates were identified as F. meridionale with the nivalenol (NIV) trichothecene genotype. These isolates have been deposited in the ARS Culture Collection, Peoria, IL, under NRRL accession numbers F644, F585, and F572. These isolates produced abundant brown aerial mycelium and formed red-brown pigments on PDA after 7 days (12/12 h light cycle and 22[degrees]C). The isolates grown on Spezieller Nahrstoffarmer agar for 7 days at 25[degrees]C under black light produced abundant falcate macroconidia with the dorsal side more curved than the ventral, with 4 to 5 septae, 27 to 46 x 3 to 4 [mu]m. Microconidia were not observed. F. meridionale induced disease severity (AUDPC=200.65, 96.47% infected florets) similar to that of F. graminearum. FHB pathogens with the NIV toxin type are relatively rare in North America, with deoxynivalenol (DON) bei