Discussion
Production of secondary metabolites in fungi is a complex
process associated with morphological development
(Calvo et al. 2002). Secondary metabolites are of tremendous
importance in biotechnological applications, but in
some cases seem not to have clear function for the producing
microbe. In a previous work, we analysed the
major secondary metabolites produced by two commercial
strains (T22 and T39) of T. harzianum (Vinale et al.
2006). Six compounds (1–6) obtained from fungal culture
filtrates were isolated and characterized. These metabolites
showed different levels of antibiotic activity against the
fungal pathogens G. graminis var. tritici, R. solani and
P. ultimum (Vinale et al. 2006). In this paper, their antifungal
activity against other important phytopathogens
such as L. maculans (causal agent of the blackleg disease
on crucifers), P. cinnamomi (causal agent of the forest
dieback disease), B. cinerea (causal agent of various grey
mould diseases) is reported. Both T22azaphilone and harzianopyridone
produced by T. harzianum strain T22
showed a broad spectrum of activity even if applied at
low concentrations (approx. 1–10 lg per plug in a standard
plate assay), while T39butenolide and harzianolide
secreted by strain T39 significantly inhibited pathogens
growth only when used at higher concentrations
(approx. > 100 lg per plug; Fig. 2). These data confirmed
and contributed to our knowledge of the spectrum of
antifungal activity of these secondary metabolites (Vinale
et al. 2006).