In Magnaporthe species and other plant pathogenic fungal species, the appressoriu, (infection structure) is responsible for breaching the host plant cell wall and gaining entry into the host tissues. Magnaporthe ABC3 protein is an MDR transporter that plays an important role during host penetration and also is involved in regulating fungal response to intracellular oxidative stress. The insertional mutant abc3Δ, in which the ABC3 efflux pump function is blocked, lacks functional appressoria and is therefore incapable of causing disease in host plants. This invention provides the abc3 nucleic acid (gene) and ABC3 protein from Magnaporthe or from Aspergillus, Ustilago or Fusarium and describes methods for reducing plant pathogenicity for important rice pathogens.