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Members of the Fusarium genus are important components of many plant–soil systems worldwide and are responsible for many crop diseases. Knowledge of the relative influence of biotic and abiotic factors on this genus is therefore of broad economic and ecological importance. In order to address this issue, we examined Fusarium communities in soils nearby apparently healthy and symptomatic asparagus plants in 50 fields scattered in four agricultural regions of Québec, Canada. Fusarium community structure and abundance were assessed using genus-specific PCR-denaturing gradient gel electrophoresis and CFU counts, respectively. Multivariate statistical analyses were used to detect community patterns related to spatial, abiotic and biotic factors. Results suggested that Fusarium community structure (i.e. the presence and absence of the different Fusarium sequence variants in the samples) in soil is mainly related to biotic factors (arbuscular mycorrhizal fungi and bacterial community structure), whereas Fusarium abundance is more closely related to abiotic factors (mainly clay, organic matter, NH4, Na and Cu). Some degree of influence of spatial patterns was also observed on both Fusarium community structure and abundance with, for instance, a large regional variation in Fusarium community structure. However, Fusarium community structure was not directly related to the disease status of nearby asparagus plants. [ABSTRACT FROM AUTHOR]

Abstract: A new species, Sphaerodes mycoparasitica (Ascomycetes, Melanosporales), was isolated from isolates of Fusarium avenaceum and Fusarium graminearum originating from wheat fields in Saskatchewan, and from Fusarium oxysporum originating from asparagus fields in Quebec, Canada. The species is characterized by a unique combination of ascospore size, shape (fusiform and triangular) and wall ornamentation (reticulate and smooth). Also, conidia are produced from simple phialides on the surface of ascoma peridial wall, on ascoma surrounding hyphae, and on irregularly branched conidiophores arising from hyphae. The closest relation of S. mycoparasitica is Sphaerodes quadrangularis, which has no detected anamorphic stage. The description of S. mycoparasitica, its phylogenetic position—based on DNA sequences of large subunit ribosomal RNA gene (LSU)—as well as a key for all known Sphaerodes species are provided. [Copyright &y& Elsevier]

Fusarium species cause important diseases in many crops. Lack of knowledge on how Fusarium species and strains interact with their environment hampers growth management strategies to control root diseases. A field experiment involving asparagus as host plant and three phosphorus fertilization levels was designed to examine the seasonal changes and ecological relationships between Fusarium populations and their soil and plant environments. Fusarium taxa were identified and assessed using PCR-denaturing gradient electrophoresis of the EF1-α gene. Resulting profiles were analyzed with respect to 17 ecological parameters measured during the three main asparagus phenological phases across a growing season. Multivariate statistical analysis showed that Fusarium population structure was strongly influenced by soil P level while seasonal variation was less important. A significant relationship between Fusarium population composition and Fusarium crown and root rot incidence was also found in September. Canonical analysis further revealed significant relationships between Fusarium population structure, and plant manganese and iron contents, soil dehydrogenase activity and soil calcium concentration. If higher Fusarium crown and root rot incidence is related to the Fusarium community structure, strategies to reduce the incidence in asparagus plantations may be found through manipulation of the soil fertility. [ABSTRACT FROM AUTHOR]

A new selective myclobutanil agar medium for the detection of Fusarium species is proposed. Ten media formulations based on various selective agents (pentachloronitrobenzene (PCNB), Rose Bengal, malachite green, sodium hypochlorite, captan, benomyl, chlorotalonil, myclobutanil, thiram, and cupric sulfate) were compared. First, mycelium growth and colony appearance of Alternaria alternata, Aspergillus flavus,Cladosporium cladosporioides, Epicoccum nigrum,Fusarium sp., Fusarium solani, Fusarium moniliforme, Fusarium oxysporum f.sp. dianthi, Penicillium sp., and Trichoderma viride isolates were compared. Second, the ability of the different media to isolate and enumerate fusaria from asparagus fields was evaluated. The myclobutanil-based medium showed the highest selectivity to Fusarium spp. growth but required a slightly longer incubation time (>5 d) than peptone–pentachloronitrobenzene-based agar (PPA) (< 5 d). PPA allowed a faster fusaria growth but also permited the growth of other moulds. The other media were less selective and did not allow to isolate fusaria or to differenciate them from other growing fungi.Key words: selective medium, myclobutanil, Fusarium, soil, Asparagus.Nous proposons un nouveau milieu sélectif au myclobutanil (MBA) pour la détection des espèces de Fusarium. Dix formulations basées sur différents ingrédients sélectifs (pentachloronitrobenzene (PCNB), Rose Bengal, vert de malachite, hypochlorite de sodium, captan, benomyl, chlorotalonil, myclobutanil, thiram et sulfate de cuivre) ont été évaluées. Premièrement, la croissance du mycélium et l'apparence des colonies d'isolats d'Alternaria alternata, Aspergillus flavus, Cladosporium cladosporioides, Epicoccum nigrum, Fusarium sp., Fusarium solani, Fusarium moniliforme, Fusarium oxysporum f.sp. dianthi, Penicillium sp. et de Trichoderma viride ont été comparées. Deuxièmement, la capacité des différents milieux à isoler et permettre le dénombrement des Fusarium spp. à partir de champs d'asperges a été évaluée. Le milieu à base de myclobutanil a montré la plus grande sélectivité pour la croissance des Fusarium mais il nécessitait une période d'incubation légèrement plus longue (>5 j) que le milieu gélosé à base de pentachloronitrobenzène et de peptone (PPA) (<5 j). Par contre, le PPA a permis une croissance des Fusarium plus rapide mais il a permis aussi la croissance d'autres champignons. Les autres milieux se sont avérés moins efficaces pour isoler sélectivement les Fusarium et permettre leur distinction des autres espèces de champignons croissant simultanément.Mots clés : milieu sélectif, myclobutanil, Fusarium, sol, Asparagus. [ABSTRACT FROM AUTHOR]