• biocontrol
• competition
• Fusarium graminearum
• Fusarium head blight
• Fusarium oxysporum
• Trichoderma gamsii
• wheat

Fusarium head bight (FHB) is one of the most important disease worldwide affecting wheat and other cereal crops. The disease is caused by a complex of fungal species, mostly belonging to Fusarium genus, with Fusarium graminearum and Fusarium culmorum as the most prevalent. FHB seriously affects crop yield due to a reduced kernel size and weight, reduced germination rate and protein content, lower baking quality of the flour and modification of other technological parameters. The importance of this disease is also connected with the risk of mycotoxin contamination, mostly due to trichothecenes, such as deoxynivalenol (DON) and its acetylated derivates - 3-and 5-acetyl-deoxynivalenol - and nivalenol (NIV). DON causes loss of appetite, vomiting, diarrhea and bleeding of the intestines at high doses. It can lead to further effects such as impairment of immune function in both humans and animals and may cause immunological and teratogenic problems in humans. That’s why legal limits for toxin concentrations in food and feed are regulated by European Community directives.
During the disease cycle, crop debris and spikes at anthesis are critical points. Pathogens use cultural debris to overwinter between two consecutive cultural cycles, while flowering is the most susceptible wheat growth stage for spike infection. Actually different approaches are used to control the disease and to reduce risk of mycotoxins contamination: cultural practices such as crop rotation or tillage, aimed to manipulate the cultivation environment; application of fungicides; genetic determinants of disease resistance. However none of these approaches alone are totally effective against the disease. In this context biocontrol, by the use of beneficial fungi, has often been considered a valid alternative to chemical control and, when not allowed, to the use of transgenic plants. When applied to spikes at anthesis, biocontrol agents can colonize that niche, preventing the pathogens entering at flowering and/or, when inoculated on cultural debris in soil, they can access to territory or resources previously held by the pathogens.
In the present work, with the aim to set up a multitrophic biocontrol strategy, two beneficial fungi - Trichoderma gamsii T6085 (well know for its ability to reduce growth and DON production by F. graminearum) and Fusarium oxysporum 7121 (a good competitor for cultural debris) - were used as possible competitors of F. graminearum on natural substrates. All the three fungi were inoculated on wheat and rice seeds and, after 21 days, the growth of both the pathogen and of the two antagonists was quantified by Real-Time PCR (relative and absolute). Results showed that the pathogen was significantly reduced by the two beneficial isolates, both alone and co-inoculated, while T. gamsii T6085 and F. oxysporum 7121 were not affected by the pathogen and by each other. F. graminearum can produce both asexual and sexual spores. These latter (ascospores) are usually differentiated within perithecia on cultural debris and play an important role as initial inoculum of the pathogen. In the second part of this work, all the three fungi, in all combinations, were inoculated on wheat straw by two different protocols: all the three fungi inoculated at the same time and with Fusarium graminearum inoculated 48 h before the two antagonists (alone and together), to simulate a more natural condition. After 9 weeks the effect of the two antagonists on F. graminearum was investigated and expressed as the numbers of perithecia developed on wheat straw. The two beneficial isolates were able to significantly reduce the number of perithecia both alone and in combination, in both the two experiments.
Results here obtained demonstrated that the two antagonistic fungi, T. gamsii T6085 and F. oxysporum 7121 are able to control the growth and the development of the pathogen on different natural substrates thus opening the possibility of their combined use in a multitrophic biocontrol strategy of FHB.