Effect of time of harvest on the incidence of Fusarium spp. in kernels of silage corn

The effect of time of harvest (at 75, 50 and 25% of milkline) on the incidence of kernel-borne Fusarium spp. was examined in four silage corn (Zea mays) hybrids (MAIZEX Leafy 4, NK BRAND Enerfeast 1, PIONEER 37M81 and MYCOGEN TMF94) in Ottawa, Ontario, in 2001 and 2002. Eleven Fusarium species were isolated over the 2 yr. Fusarium subglutinans was the dominant species recovered from 28.8% of the kernels. Other frequently isolated species included F. oxysporum (2.6%), F. graminearum (2.5%), F. proliferatum (0.3%) and F. sporotrichioides (0.2%). Trace amounts (< 0.1%) of the remaining six species, F. avenaceum, F. crookwellense, F. culmorum, F. equiseti and F. solani, were recovered from the kernels. When the kernels were harvested at 75, 50 and 25% of milkline, the incidence of F. subglutinans increased from 20.9 to 26.7 and to 38.7%, respectively; that of F. graminearum increased from 1.7 to 2.9 and to 3.1%; and for the total of the five main Fusarium species it increased from 28.7 to 32.2 and to 42.3%. Incidence of the other species was not affected by harvesting date. Of the four silage corn hybrids, NK BRAND Enerfeast1 had a significantly lower incidence of Fusarium species in kernels than the other hybrids, indicating a genotypic variation in resistance to kernel-borne infection by Fusarium species.L’effet de trois temps de récolte, correspondant à 75, 50 et 25 % de l’état laiteux, sur l’incidence des espèces de Fusarium a été étudié chez les grains de quatre hybrides de maïs (Zea mays) ensilage (MAIZEX Leafy 4, NK BRAND Enerfeast 1, PIONEER 37M81 et MYCOGEN TMF94) en 2001 et 2002 à Ottawa, en Ontario. Onze espèces de Fusarium ont été isolées pendant ces deux années. Le F. subglutinans a été l’espèce dominante, trouvée sur 28,8 % des grains. Les autres espèces détectées ont été les F. oxysporum (2,6 %), F. graminearum (2,5 %), F. proliferatum (0,3 %) et F. sporotrichioides (0,2 %). Des traces (< 0,1 %) des six autres espèces, les F. avenaceum, F. crookwellense, F. culmorum, F. equiseti et F. solani, ont aussi été détectées sur les grains. L’incidence du F. subglutinans a augmenté respectivement de 20,9 à 26,7 puis à 38,7 % en fonction du temps de récolte (75, 50 et 25 % de l’état laiteux), tandis qu’elle a augmenté de 1,7 à 2,8 puis à 3,1 % pour le F. graminearum et de 28,7 à 32,2 puis à 42,3 % pour les cinq espèces principales confondues. L’incidence des autres espèces n’a pas été affectée par les dates de récolte. Parmi les quatre hybrides à l’essai, l’hybride commercial NK BRAND Enerfeast1 a eu la plus basse incidence d’espèces de Fusarium dans le grain, ce qui indique qu’il existe une variation génotypique de la résistance des grains aux infections causées par les espèces de Fusarium

Genetic diversity and recombination within populations of Fusarium pseudograminearum from western Canada

Genetic diversity within populations of Fusarium pseudograminearum isolated from wheat grains from the Canadian provinces of Alberta and Saskatchewan was investigated. Three restriction enzymes (EcoRI, HaeIII, and PstI) were used to carry out restriction analysis of the nuclear ribosomal DNA (nrDNA) intergenic spacer region (IGS region) and eight primers were used to generate inter-simple sequence-repeat (ISSR) molecular markers. Our study indicated substantially high genetic diversity within these two populations, but low genetic differentiation and frequent gene flow among populations. The IGS data showed no genetic distinction between the two Alberta populations and only minor genetic differentiation between the Saskatchewan and Alberta populations. Analysis of molecular variance indicated that most genetic variability resulted from differences among isolates within populations. Multilocus linkage disequilibrium analysis suggested a panmictic population genetic structure and the occurrence of significant recombination in F. pseudograminearum. Regular gene flow and random mating between isolates from different populations could result in novel genotypes with both improved pathological and biological traits. [Int Microbiol 2006; 9(1):65-68

The geographic distribution and complex evolutionary history of the NX-2 trichothecene chemotype from Fusarium graminearum

Fusarium graminearum and 21 related species comprising the F. sambucinum species complex lineage 1 (FSAMSC-1) are the most important Fusarium Head Blight pathogens of cereal crops world-wide. FSAMSC-1 species typically produce type B trichothecenes. However, some F. graminearum strains were recently found to produce a novel type A trichothecene (NX-2) resulting from functional variation in the trichothecene biosynthetic enzyme Tri1. We used a PCR-RFLP assay targeting the TRI1 gene to identify the NX-2 allele among a global collection of 2515 F. graminearum. NX-2 isolates were only found in southern Canada and the northern U.S., where they were observed at low frequency (1.8%), but over a broader geographic range and set of cereal hosts than previously recognized. Phylogenetic analyses of TRI1 and adjacent genes produced gene trees that were incongruent with the history of species divergence within FSAMSC-1, indicating trans-species evolution of ancestral polymorphism. In addition, placement of NX-2 strains in the TRI1 gene tree was influenced by the accumulation of nonsynonymous substitutions associated with the evolution of the NX-2 chemotype, and a significant (P < 0.001) change in selection pressure was observed along the NX-2 branch (ω = 1.16) in comparison to other branches (ω = 0.17) in the TRI1 phylogeny. Parameter estimates were consistent with positive selection for specific amino-acid changes during the evolution of NX-2, but direct tests of positive selection were not significant. Phylogenetic analyses of fourfold degenerate sites and intron sequences in TRI1 indicated the NX-2 chemotype had a single evolutionary origin and evolved recently from a type B ancestor. Our results indicate the NX-2 chemotype may be indigenous, and possibly endemic, to southern Canada and the northern U.S. In addition, we demonstrate that the evolution of TRI1 within FSAMSC-1 has been complex, with evidence of trans-species evolution and chemotype-specific shifts in selective constraint.Fil: Kelly, Amy. United States Department of Agriculture; Estados UnidosFil: Proctor, Robert H.. United States Department of Agriculture; Estados UnidosFil: Belzile, Francois. Laval University; CanadáFil: Chulze, Sofia Noemi. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas, Fisicoquímicas y Naturales. Departamento de Microbiología e Inmunología. Cátedra de Micología; Argentina. United States Department of Agriculture; Estados UnidosFil: Clear, Randall M.. Winnipeg; CanadáFil: Cowger, Christina. University of North Carolina; Estados UnidosFil: Elmer, Wade. The Connecticut Agricultural Experiment Station; Estados UnidosFil: Lee, Theresa. National Institute of Agricultural Sciences; Corea del SurFil: Obanor, Friday. Commonwealth Scientific and Industrial Research Organization; AustraliaFil: Waalwijk, Cees. University of Agriculture Wageningen; Países BajosFil: Ward, Todd J.. United States Department of Agriculture; Estados Unido