We also quantified by LC ⁄MS the production of T22
and T39 secondary metabolites in liquid cultures
amended with viable or nonviable pathogen biomasses.
Interestingly, in T. harzianum strain T22 the interaction
with fungal pathogens seemed not to be correlated with
the accumulation of antibiotic compounds. In fact, the
secretion of T22azaphilone, a compound that demonstrated
strong antifungal activity in vitro, was not particularly
induced in co-culture with R. solani or B. cinerea,
and appeared to be even repressed when nonviable pathogen
biomass or P. ultimum living mycelia were applied
(Table 2). Conversely, increased amounts of anthraquinones
were found in P. ultimum-treated samples, even
though these compounds did not demonstrate significant
antifungal properties. Similarly, Donnelly and Sherida
(1986) isolated anthraquinones in elicited co-culture of
T. polysporum and Heterobasidion annosum, but no
marked inhibition of pathogen growth was observed. In
fact, anthraquinones are pigments and have been considered
among the most abundant fungal natural products
giving colour to spores, appressoria, sclerotia, sexual
bodies and other developmental structures (Yu and Keller
2005). In addition because of their chemical structure, anthraquinones
could act as ROS scavengers in Trichoderma and their accumulation could be stimulated by using
appropriate elicitors (i.e. fungal pathogen biomasses) to
increase resistance of beneficial strains against biotic or
abiotic stresses (Yu and Keller 2005).