The rice of 15-day-old greenhouse-grown plants was used for the blast disease resistance assay. Initially, each leaf was cleaned with 70% ethyl alcohol to form a surface sterile flower for the microorganisms. In an order of 106spores/ml, the spores/ml (added with 0.001% tween 20) of Pyricularia grisea (Fig. 3) were prepared for the test. The rice leaf was wounded each in three regions with a total of ten pinpricks using the method described by Mahadtanapuk et al. [16]. Phenotypic variation in the plant disease resistance of the rice was studied and compared with that of the KDML105control. The high percentage of the disease resistant rice was screened as mutants and analyzed with DNA fingerprint Comparison of the plant heights, number of leaves and leaf lengths between the mutant and control was made and analyzed by analysis of variance (ANOVA). Values were presented as mean ± standard deviation (SD) (n = 20). Statistically significant differences among values were recognized at the significance level p 6 0.05.