Fusarium species, particularly Fusarium graminearum and F. culmorum, are the main cause of trichothecene type B contamination in cereals. Data on the distribution of Fusarium trichothecene genotypes in cereals in Europe are scattered in time and space. Furthermore, a common core set of related variables (sampling method, host cultivar, previous crop, etc.) that would allow more effective analysis of factors influencing the spatial and temporal population distribution, is lacking. Consequently, based on the available data, it is difficult to identify factors influencing chemotype distribution and spread at the European level. Here we describe the results of a collaborative integrated work which aims (1) to characterize the trichothecene genotypes of strains from three Fusarium species, collected over the period 2000–2013 and (2) to enhance the standardization of epidemiological data collection. Information on host plant, country of origin, sampling location, year of sampling and previous crop of 1147 F. graminearum, 479 F. culmorum, and 3 F. cortaderiae strains obtained from 17 European countries was compiled and a map of trichothecene type B genotype distribution was plotted for each species. All information on the strains was collected in a freely accessible and updatable database (www.catalogueeu.luxmcc.lu), which will serve as a starting point for epidemiological analysis of potential spatial and temporal trichothecene genotype shifts in Europe. The analysis of the currently available European dataset showed that in F. graminearum, the predominant genotype was 15-acetyldeoxynivalenol (15-ADON) (82.9%), followed by 3-acetyldeoxynivalenol (3-ADON) (13.6%), and nivalenol (NIV) (3.5%). In F. culmorum, the prevalent genotype was 3-ADON (59.9%), while the NIV genotype accounted for the remaining 40.1%. Both, geographical and temporal patterns of trichothecene genotypes distribution were identified.

The objective of this work was to study the effect of ecophysiological factors on fumonisin gene expression and growth in Fusarium verticillioides. The effects of ionic and nonionic solute water potentials, matric potential, and temperature on in vitro mycelial growth rates and on expression of the FUM1 gene, involved in fumonisin biosynthesis, were examined. FUM1 transcript levels were quantified using a specific real-time reverse transcription-PCR (RT-PCR) protocol. Low temperature and water stress reduced fungal growth. Water stress increased FUM1 transcript levels, especially in the case of stress caused by nonionic solute. The temporal kinetic assays showed that water stress had opposite effects on fungal growth versus FUM1 expression. These results indicate that water stress may be an important factor for fumonisin accumulation, particularly in the later phases of maize colonization when water availability decreases. The quantitative RT-PCR methods described here provide a valuable tool for investigating the ecophysiological basis for fumonisin gene expression and ultimately may lead to more effective control strategies for this important mycotoxigenic pathogen.During the life cycle of Fusarium verticillioides in maize, the pathogen colonizes soil and survives effectively on crop residue and spores are dispersed predominantly via rain splash and sometimes by wind. The pathogen's life cycle is significantly influenced by environmental factors, especially water availability and temperature (14). In terrestrial ecosystems, water availability can be expressed by the total water potential (⌿ t ), a measure of the fraction of the total water content available for microbial growth in pascals (10). This is the sum of three factors: (i) osmotic or solute potential (⌿ s ) due to the presence of ions or other solutes, (ii) matric potential (⌿ m ) due directly to forces required to remove water bound to the matrix (e.g., soil), and (iii) turgor potential of microbial cells balancing their internal status with the external environment. The influences of both ⌿ s and ⌿ m were of interest in this study because growth on crop residue and in ripening silks is determined predominantly by tolerance to solute potential, while growth in soil is determined mainly by matric potential, except in saline soils. The effects of ionic and nonionic ⌿ s stress on germination, growth, and fumonisin production by strains of F. verticillioides and Fusarium proliferatum have been determined in vitro and in stored maize grain (13). However, no information is available on the effect of soil ⌿ m water stress and how F. verticillioides responds to such stress in terms of growth capability and production of fumonisins.Fungi vary in their ability to tolerate ⌿ m stress. For example, basidiomycetes such as Rhizoctonia solani and the cultivated mushrooms (Agaricus bisporus and Pleurotus ostreatus) are very sensitive to matric forces compared to ionic or nonionic ⌿ s stress (1, 11). Interestingly, xerotolerant mycotoxigenic species such as Aspergill...

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The effects of ecophysiological factors, temperature and solute potential, on both the growth and the regulation of the fumonisin biosynthetic FUM1 gene were studied and compared in one isolate each of the two closely related fumonisin-producing and maize pathogens Fusarium verticillioides and Fusarium proliferatum. The effect of solute potential and temperature was examined on in vitro mycelia growth and on the expression of the FUM1 gene, quantified by species-specific real-time reverse transcriptase-PCR assays. Although both isolates showed similar two-dimensional profiles of growth, for F. verticillioides, optimal growth conditions were maintained at higher temperatures and lower solute potential values. FUM1 gene expression was markedly induced at 20 degrees C in both isolates, under suboptimal conditions for growth; however, their expression patterns differed in relation to solute potential. Whereas FUM1 expression was induced in response to increasing water stress in the isolate of F. verticillioides, the F. proliferatum one showed a stable expression pattern regardless of water potential conditions. These results suggest a differential regulation of fumonisin biosynthesis in these isolates of the two species that might be related to their different host range, and play an ecological role. Additionally, environmental conditions leading to water stress (drought) might result in increased risk of fumonisin contamination of maize caused by F. verticillioides.