Evaluation of Barley and Wheat Germplasm for Resistance to Head Blight and Mycotoxin Production by Fusarium asiaticum and F. graminearum.

Fusarium head blight (FHB) is one of the most serious diseases in barley and wheat, as it is usually accompanied by the production of harmful mycotoxins in the grains. To identify FHB-resistant breeding resources, we evaluated 60 elite germplasm accessions of barley (24) and wheat (36) for FHB and mycotoxin accumulation. Assessments were performed in a greenhouse and five heads per accession were inoculated with both Fusarium asiaticum (Fa73, nivalenol producer) and F. graminearum (Fg39, deoxynivalenol producer) strains. While the accessions varied in disease severity and mycotoxin production, four wheat and one barley showed <20% FHB severity repeatedly by both strains. Mycotoxin levels in these accessions ranged up to 3.9 mg/kg. FHB severity was generally higher in barley than in wheat, and Fa73 was more aggressive in both crops than Fg39. Fg39 itself, however, was more aggressive toward wheat and produced more mycotoxin in wheat than in barley. FHB severity by Fa73 and Fg39 were moderately correlated in both crops (r = 0.57/0.60 in barley and 0.42/0.58 in wheat). FHB severity and toxin production were also correlated in both crops, with a stronger correlation for Fa73 (r = 0.42/0.82 in barley, 0.70 in wheat) than for Fg39.

Species composition of and fumonisin production by the Fusarium fujikuroi species complex isolated from Korean cereals.

To assess the risk of fumonisin contamination in Korean cereals, we isolated colonies of the Fusarium fujikuroi species complex (FFSC) from barley, maize, rice and soybean samples from 2011 to 2015. A total of 878 FFSC strains were isolated mostly from maize and rice, and species identity of the isolates were determined using the DNA sequence of the translation elongation factor 1-α (TEF-1α) and RNA polymerase II (RPB2) genes. Fusaria recovered from Korean cereals included F. fujikuroi (317 isolates and a frequency of 36%), F. proliferatum (212 isolates and 24.1%), F. verticillioides (170 isolates and 19.4%), F. concentricum (86 strains and 9.8%), F. andiyazi (56 isolates and 6.4%), F. subglutinans (28 isolates and 3.2%), F. thapsinum (5 isolates and 0.6%), and F. circinatum (2 isolates and 0.2%). The rice samples were dominated by F. fujikuroi (47.4%), F. proliferatum (27.3%), and F. concentricum (15.1%), whereas maize samples were dominated by F. verticillioides (33.9%), F. fujikuroi (25.3%), and F. proliferatum (21.1%). A phylogenetic analysis of 70 representative isolates demonstrated that each species was resolved as genealogically exclusive in the ML tree. Fumonisin production potential was evaluated using a PCR assay for the fumonisin biosynthesis gene, FUM1 in all of the isolates. Most of the isolates tested (94%) were positive for FUM1. All of the isolates assigned to F. fujikuroi, F. proliferatum, F. verticillioides and F. thapsinum were positive for FUM1 irrespective of their host origin. Seventy-seven representative isolates positive for FUM1 were examined for fumonisin production in rice medium. The majority of F. proliferatum (26/27, 96.3%), F. verticillioides (16/17, 94.1%) and F. fujikuroi (19/25, 76.0%) produced both FB1 and FB2. Notably, 16 of 19 fumonisin-producing F. fujikuroi produced >1000µg/g of fumonisins (FB1+FB2) in rice medium, which is higher than that in previous reports. These results suggest that F. fujikuroi can produce high levels of fumonisins similar to F. verticillioides and F. proliferatum.

Occurrence of Toxigenic Fusarium vorosii among Small Grain Cereals in Korea.

Fusarium graminearum species complex (FGSC) causes Fusarium head blight in small grain cereals. To date, four species (F. graminearum, F. asiaticum, F. boothii, and F. meridionale ) belonging to FGSC frequently occur in Korean cereals. In addition, we first reported the occurrence of additional species (F. vorosii ) within FGSC, which was isolated from barley, corn, and rice in Korea. Phylogenetic analysis of the Fusarium isolates of this group using combined multi-gene sequences confirmed species identification. Moreover, the macroconidia produced by these isolates were morphologically similar to those of the F. vorosii holotype. Chemical analysis indicated that the F. vorosii isolates produced various trichothecenes such as nivalenol and deoxynivalenol with their acetyl derivatives along with zearalenone. Pathogenicity tests demonstrated that all of the F. vorosii isolates examined were pathogenic on barley, corn, and rice with variation in aggressiveness. This study is the first report of F. vorosii in Korean cereals, their pathogenicity towards barley and corn, and their ability to produce trichothecenes and zearalenone.