Harnessing Chaetomium globosum for fungal biocontrol: pigmentation and metabolic responses in Bipolaris sorokiniana

In fungal biocontrol strategies, the interaction between phytopathogenic and antagonistic fungi elicits diverse phenotypic and metabolic responses, influenced by the fungal isolates and culture conditions. This study aimed to evaluate the in vitro growth and pigmentation of three Bipolaris sorokiniana isolates with contrasting pigmentation when interacting with three isolates of Chaetomium globosum species group in dual and volatile-mediated systems. Volatile and diffusible metabolites produced individually and in co-culture were assessed using cellulose strips, mimicking barley stubble. Among the strains tested, C. globosum LPSC 1569 showed the strongest inhibition of B. sorokiniana LPSC 1609, reducing its growth by 62.95 ± 1.5% in dual culture and by 47.27 ± 0.31% under volatile-mediated conditions and inducing marked pigmentation changes absent in axenic cultures. Volatile profiles shifted during interactions: methyl anthranilate and (Z)-α-bisabolene decreased, while (+)-sativene increased. Diffusible prehelminthosporol decreased, whereas chaetoglobosins and chaetoviridins showed isolate-specific responses. Interactions also altered B. sorokiniana cell wall composition, increasing melanin and polysaccharides in response to antagonistic volatiles. These modifications, associated with visible pigmentation shifts, highlight pigmentation as a potential phenotypic marker to select effective antagonists against melanized phytopathogens. Overall, the results demonstrate that metabolic and phenotypic outcomes depend on both the fungal identity and culture system, providing new insights into fungal biocontrol strategies.