Biocontrol Agents: Toolbox for the Screening of Weapons against Mycotoxigenic Fusarium
Lucile PellanCheikh Ahmeth Tidiane DieyeNoël DurandAngélique FontanaCaroline StrubSabine Schorr‐Galindo
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Abstract:
The aim of this study was to develop a set of experiments to screen and decipher the mechanisms of biocontrol agents (BCAs), isolated from commercial formulation, against two major mycotoxigenic fungi in cereals, Fusarium graminearum and Fusarium verticillioides. These two phytopathogens produce mycotoxins harmful to human and animal health and are responsible for the massive use of pesticides, for the protection of cereals. It is therefore essential to better understand the mechanisms of action of alternative control strategies such as the use of BCAs in order to optimize their applications. The early and late stages of interaction between BCAs and pathogens were investigated from germination of spores to the effects on perithecia (survival form of pathogen). The analysis of antagonist activities of BCAs revealed different strategies of biocontrol where chronological, process combination and specialization aspects of interactions are discussed. Streptomyces griseoviridis main strategy is based on antibiosis with the secretion of several compounds with anti-fungal and anti-germination activity, but also a mixture of hydrolytic enzymes to attack pathogens, which compensates for an important deficit in terms of spatial colonization capacity. It has good abilities in terms of nutritional competition. Trichoderma asperellum is capable of activating a very wide range of defenses and attacks combining the synthesis of various antifungal compounds (metabolite, enzymes, VOCs), with different targets (spores, mycelium, mycotoxins), and direct action by mycoparasitism and mycophagy. Concerning Pythium oligandrum, its efficiency is mainly due to its strong capacity to colonize the environment, with a direct action via microbial predation, stimulation of its reproduction at the contact of pathogens and the reduction of perithecia formation.Keywords:
Antibiosis
Spore germination
Trichoderma
Pathogens belonging to the Fusarium genus are causal agents of the most significant crop diseases worldwide. Virtually all Fusarium species synthesize toxic secondary metabolites, known as mycotoxins; however, the roles of mycotoxins are not yet fully understood. To understand how a fungal partner alters its lifestyle to assimilate with the plant host remains a challenge. The review presented the mechanisms of mycotoxin biosynthesis in the Fusarium genus under various environmental conditions, such as pH, temperature, moisture content, and nitrogen source. It also concentrated on plant metabolic pathways and cytogenetic changes that are influenced as a consequence of mycotoxin confrontations. Moreover, we looked through special secondary metabolite production and mycotoxins specific for some significant fungal pathogens-plant host models. Plant strategies of avoiding the Fusarium mycotoxins were also discussed. Finally, we outlined the studies on the potential of plant secondary metabolites in defense reaction to Fusarium infection.
Secondary metabolite
Secondary metabolism
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Abstract Fusarium mycotoxin contamination of both foods and feeds is an inevitable phenomenon worldwide. Deoxynivalenol, nivalenol, zearalenone, T-2 toxin and fumonisin B1 are the most studied Fusarium mycotoxins. Co-contamination of mycotoxins has also been studied frequently. Fusarium mycotoxins occur frequently in foods at very low concentrations, so there is a need to provide sensitive and reliable methods for their early detection. The present review provides insight on the types, toxicology and occurrence of Fusarium mycotoxins. It further elucidates various detection methods of mycotoxin production from Fusarium strains, with a special focus on chromatographic and immunochemical techniques.
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In vitro production of trichothecene mycotoxins, deoxynivalenol, nivalenol, T-2 toxins, and their derivatives was studied in rice culture using 30 strains from seven Fusarium species. Six strains of three Fusarium species were selected for the evaluation of mycotoxin production and pathogenicity after artificial inoculation to seven wheat lines with different levels of resistance or susceptibility and their eight F 1 's. Three criteria were used for the evaluation: the reduction of seed set, the reduction of grain weight, and the concentration of mycotoxins in infected grain. Significant variability was observed among Fusarium strains, wheat genotypes, and in the interaction between them. The contribution of Fusarium strains, however, was far greater than that of the other two factors. The kinds and relative amounts of mycotoxins produced in rice culture were consistent with those present in infected grain with some exceptions. Significant correlations were found between the grain weight reduction and the mycotoxin concentration and between the level of resistance of the wheat genotypes under the artificial and natural conditions of infection. The biological role of Fusarium mycotoxins in pathogenicity and wheat resistance to Fusarium head blight is discussed. Key words: Fusarium head blight (scab), Fusarium mycotoxins, Fusarium pathogenicity, wheat resistance to Fusarium head blight.
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Fusarium species cause not only root, stem and ear rot with severe reductions in crop yield, they produce also toxic secondary metabolites (mycotoxins) such as deoxynivalenol (DON) and zearalenone (ZEA). During several growing seasons the presence of Fusarium spp was followed up. DON and ZEA were determined and related to infection levels. The distribution of DON and ZEA in the different plant parts was studied as well as the influence of the ensiling process on the mycotoxin content. More or less important varietal differences in susceptibility for Fusarium spp. could be detected. DON and ZEA were clearly present in most of the analysed samples. No clear relationship could be detected between visual disease symptoms and mycotoxin content. The accumulation of DON and ZEA was different for the analysed aerial plant parts. The ensiling process gave no reduction of the mycotoxin content.
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Combined analyses of the natural occurrence of fusarium head blight (FHB), mycotoxins and mycotoxin‐producing isolates of Fusarium spp. in fields of wheat revealed FHB epidemics in 12 of 14 regions in Hubei in 2009. Mycotoxin contamination ranged from 0·59 to 15·28 μg g −1 in grains. Of the causal agents associated with symptoms of FHB, 84% were Fusarium asiaticum and 9·5% were Fusarium graminearum , while the remaining 6·5% were other Fusarium species. Genetic chemotyping demonstrated that F. asiaticum comprised deoxynivalenol (DON), 3‐acetyldeoxynivalenol (3‐AcDON), 15‐acetyldeoxynivalenol (15‐AcDON) and nivalenol (NIV) producers, whereas F. graminearum only included DON and 15‐AcDON producers. Compared with the chemotype patterns in 1999, there appeared to be a modest shift towards 3‐AcDON chemotypes in field populations during the following decade. However, isolates genetically chemotyped as 3‐AcDON were present in all regions, whereas the chemical 3‐AcDON was only detected in three of the 14 regions where 3‐AcDON accounted for 15–20% of the DON and acetylated forms. NIV mycotoxins were detected in seven regions, six of which also yielded NIV chemotypes. The number of genetic 3‐AcDON producers was positively correlated with amounts of total mycotoxins (DON, NIV and acetylated forms) or DON in wheat grains. Chemical analyses of wheat grains and rice cultures inoculated with different isolates from the fields confirmed their genetic chemotypes and revealed a preferential biosynthesis of 3‐AcDON and 4‐AcNIV in rice. These findings suggest the importance of chemotyping coupled with species identification for improved prediction of mycotoxin contamination in wheat.
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Most Fusarium species are capable of producing mycotoxins that may cause adverse effects on human or animal health. The most commonly studied Fusarium mycotoxins include trichothecenes, zearalenone and fumonisins. However, it seems that nearly all of the most prevalent Fusarium species infecting grains are also capable of producing other toxic metabolites. The existing studies, although exiguous, have clearly demonstrated that other toxic metabolites of Fusarium spp. are also present in our foods and feeds, occasionally at very high levels. It is apparent that since mycotoxins, including these 'other' metabolites, are natural toxins, they cannot be completely eliminated from food and feed chains. However, scientific studies are needed to determine their true significance. Thus, the mechanism and level of toxicity as well as presence and concentration levels will have to be fully clarified. In this paper, we briefly review the prevalence of the dominant Fusarium species contaminating maize and small-grain cereals worldwide, and the current knowledge on the biological activity as well as the natural occurrence of their selected less-known toxic metabolites. Additionally, the significance of these 'other' Fusarium mycotoxins is discussed.
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