Biocontrol Agents: Toolbox for the Screening of Weapons against Mycotoxigenic Fusarium

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.

Biocontrol Agents Reduce Progression and Mycotoxin Production of Fusarium graminearum in Spikelets and Straws of Wheat

“…The activity of BCAs against perithecia of F. graminearum was then evaluated. These results are consistent with those obtained in vitro on Carrot agar in another study (80% inhibition on average, [33]. All BCAs showed a substantial reduction in the number of mature perithecia; however, the mechanisms involved in this reduction seem to vary according to the BCA considered.…”

“…During this first phase, all BCAs demonstrate potentialities for the reduction of colonization and mycotoxins production of F. graminearum. As suggested by the analyses on the modes of action of these BCAs in vitro, competition, mycophagy or mycotoxin bio-transformation phenomena could be responsible for the success of these BCAs [17,33]. The mechanisms implemented by these BCAs during in vitro tests could be investigated more precisely in order to prove their deployment in natural conditions.…”

Trichoderma Species: Our Best Fungal Allies in the Biocontrol of Plant Diseases—A Review

“…Commercial formulations T34 Biocontrol (Biocontrol Technologies S.L) from T. asperellum T34 and Trianum P (Koppert) from T. harzianum T22 induced systemic resistance in tomato plants, repressed reproduction of the plant nematode Meloidogyne incognita and, T34 Biocontrol also reduced the nematode infectivity [ 229 ]. The commercial product Xedavir made with T. asperellum (Xeda International ® ) was tested in vitro against F. graminearum and F. verticilloides [ 230 ]. As spore suspension, Xedavir inhibits germination of F. graminearum up to 53%, F. verticilloides up to 22%, and as the cell-free extract, Xedavir inhibits F. graminearum and F. verticilloides germination up to 82% and 76%, respectively.…”

Recent Research on Fusarium Mycotoxins in Maize—A Review

“…Many aspects must still be investigated to enable effective integration, and understanding the processes that govern the interaction of BCAs and pathogens throughout time is especially important. Four common modes of actions of BCAs that have been identified and described by various researchers: antibiosis, competition for niche or nutrients, mycoparasitism, and stimulation or enhancement of plant defence [ 157 , 158 , 159 ]. BCAs typically rely on more than one mode of action to combat the pathogen, and the existence of one dominant mode of action does not preclude the presence of the others [ 157 ] and modes may depend on the parameters and kind of BCAs under consideration.…”

“…Trichoderma are soil-dwelling, free-living filamentous fungi that include rhizosphere-competent strains connected with root ecosystems. As potential antagonistic microbes, the genus Trichoderma has been widely studied for their capabilities against plant pathogenic fungi, and their biological control mechanisms mainly include faster growth speed and antibiotic production to compete for nutrients and living space with pathogens, mycoparasitism mediated by producing cell wall degrading enzymes, and the ability to induce plant’s defence systems [ 157 , 159 , 160 ]. The general mechanisms of Trichoderma spp.…”