The present inventors succeeded in isolating the rice field resistance gene pi21 by linkage analysis, and found that field resistance to blast in plants could be modified by introducing or controlling the expression of the gene. Thus, it became possible to efficiently confer plants with field resistance. It also became possible to select, at an early stage, rice plants having field resistance to blast. Moreover, by changing the tissue specificity of expression and the expression level of the gene involved in field resistance, varieties having resistance as well as high practical use can be grown.