In-vitro evaluation of selected native Trichoderma species for management of Pyricularia oryzae

Rice blast, caused by Pyricularia oryzae, is one of the most destructive fungal diseases limiting rice productivity worldwide. Species of Trichoderma are widely recognized as effective biological control agents against fungal pathogens. This study aimed to evaluate the in vitro antagonistic efficacy of native Trichoderma spp. isolates collected from Tanzanian lowland rice agroecosystems against P. oryzae. A total of 47 native Trichoderma spp. isolates were evaluated for antagonistic activity against P. oryzae. Direct antagonism was evaluated using dual-culture and slide-culture bioassays and indirect antagonism was evaluated using inversion and culture filtrate methods. These assays measured inhibition of pathogen mycelial growth and sporulation to determine the effectiveness of the isolates. Trichoderma isolates significantly inhibited P. oryzae across all assays. Dual culture reduced mycelial growth by 63-83% (p < 0.001), while non-volatile metabolites caused 57-83% inhibition (p < 0.001). VOCs suppressed pathogen growth by 43-75% (p < 0.001) and reduced sporulation by up to 90% (p < 0.001). Microscopy confirmed mycoparasitism (hyphal coiling, adhesion, penetration), with antibiosis and overgrowth covering 75-100% of colonies. Indigenous isolates outperformed commercial T. harzianum, with T. virens (KT8-4, NH7-3), T. harzianum (NH3-3), T. pleuroti (KT8-1), and T. paraviridescens (KT7-1) most effective. The strong antagonistic activity of the native Trichoderma isolates against P. oryzae supports previous reports on their biocontrol potential. These findings highlight their promise as eco-friendly alternatives to chemical fungicides and provide a benchmark for research on identifying active metabolites and validating the most effective isolates under greenhouse and field conditions.