Antagonistic responses of native Trichoderma spp. vary among Bipolaris sorokiniana isolates.

Spot blotch caused by Bipolaris sorokiniana is a major threat to barley production worldwide. Although the genus Trichoderma is widely recognized for its biocontrol potential, the extent to which genetic diversity among distinct pathogen isolates influences antagonistic responses remains poorly understood. This study screened eight native Trichoderma isolates from threatened Araucaria Forest remnants against six B. sorokiniana field isolates using exclusively in vitro assays. Pathogen genetic diversity was assessed using inter-simple sequence repeat (ISSR) markers, while biocontrol potential was evaluated through dual culture and volatile/non-volatile metabolite production. Nei's genetic diversity (h = 0.444) and Shannon's information index (I = 0.634) revealed high genetic diversity among B. sorokiniana isolates, with no obvious relationship to sampling location. Our results showed that the antagonistic efficacy of Trichoderma varied according to the B. sorokiniana isolate. Although all Trichoderma isolates inhibited pathogen growth, their performance was highly isolate-dependent: the commercial standard T. harzianum exhibited the highest inhibition (up to 94%), followed by the native isolates T. harzianum LMA A14 and T. azevedoi LMA A22 (up to 82%) in dual culture, whereas T. asperelloides (LMA A20 and LMA A24) and T. longibrachiatum LMA A21 excelled differentially in volatile and non-volatile metabolite production, showing distinct suppression profiles across different B. sorokiniana genotypes. This study suggests that microbial biocontrol is a dynamic interaction in which variability among pathogen isolates may influence antagonist performance, highlighting the importance of evaluating a range of them when screening broad-spectrum native biocontrol candidates for sustainable disease management.