Abstract Rice brown spot, caused by Bipolaris
oryzae, can be a serious disease causing a considerable
yield loss. Trichoderma harzianum is an effective
biocontrol agent for a number of plant fungal diseases.
Thus, this research was carried out to investigate the
mechanisms of action by which T. harzianum antagonizes
Bipolaris oryzae in vitro, and the efficacy of
spray application of a spore suspension of T. harzianum
for control of rice brown spot disease under field
conditions. In vitro, the antagonistic behavior of T.
harzianum resulted in the overgrowth of B. oryzae by
T. harzianum, while the antifungal metabolites of
T. harzianum completely prevented the linear growth
of B. oryzae. Light and scanning electron microscope
(SEM) observations showed no evidence that mycoparasitism
contributed to the aggressive nature of the