INHIBITION OF FORMATION OF PERITHECIA OF FUSARIUM GRAMINEARUM BY ANTAGONISTIC ISOLATES OF TRICHODERMA SPP.

Fusarium head blight (FHB) is a world-wide occurring disease of wheat and other grain crops that causes yearly considerable losses in terms of yield and quality of grains. The severity of the disease is aggravated by intensive crop management and some cultural practices, such as monocropping and conservation tillage. Moreover a further increase of FHB is expected in temperate areas as a result of the global climate change. The infection of wheat heads is primarily caused by spores of Fusarium graminearum (teleomorph: Gibberella zeae) that infect the spikes at flowering and impair formation of the embryos and accumulation of starch in the endosperm of the developing kernels. Besides being small, shrunk and whitened, the infected kernels may also contain mycotoxins produced by F. graminearum (mainly deoxynivalenol and zearalenone), which enter the food and feed chains and pose safety concerns for human and animal health. The main source of inoculum for flowers infection are the ascospores, which are formed inside perithecia, the flask-shaped fruiting bodies of the fungus that are developed by the overwintering mycelium on the infected plant debris of previous susceptible crops. Since chemical control is difficult and raises environmental and safety concerns, prevention of perithecia formation and ascospore release appears a feasible means for FHB control. We investigated the capability of seven Trichoderma spp. strains to inhibit perithecia formation in dual culture tests. One isolate of F. graminearum was challenged with the antagonistic Trichoderma spp. strains on carrot-agar medium; after 7 days of co-culture the mycelium was peeled off the plates and production of perithecia was induced by fertilization of cultures. After 7 more days of incubation at 25 °C, the number of perithecia formed was assessed in the plate sectors that were pre-colonized by either Trichoderma or Fusarium. In the Trichoderma pre-colonized sectors, perithecia formation was inhibited by 80 to 100%. In the Fusarium pre-colonized sectors, perithecia formation was totally inhibited by 3 out of 7 tested Trichoderma isolates, while the other 4 isolates showed not significant perithecia inhibition. Further investigations on the mechanism of perithecia inhibition showed that the Trichoderma strains released unidentified metabolites that were able to reduce the number of perithecia formed. The reduction of number of perithecia formed by F. graminearum colonies exposed to Trichoderma cell-free metabolites ranged from 27% to 91%, depending on the Trichoderma strain. To explore the effect of Trichoderma metabolites on the regulatory mechanisms of perithecia formation, we carried out a preliminary study of genes involved in the perithecia developmental process. This study allowed to identify a first group of genes associated with different stages of the perithecia formation, whose expression rate in response to Trichoderma metabolites is under investigation.