Nonhost resistance is the most basic and common form of plant immunity.Increasing efforts have focused on nonhost resistance owing to its broad spectrum and stability.In previous studies, we got a rice mutant crrl (compromised resistance to rust 1) that was more vulnerable to Puccina striiformis f.sp.tritici (Pst), the causal agent of wheat stripe rust.More and larger infection sites were produced on crrl compared with wild type Nipponbare when inoculated with Pst.Genetic analysis revealed that the mutant phenotype was controlled by one locus localized between molecular marker RM25761 and RM25792 on chromosome 10.Although hydrogen peroxide (H2O2) was detected at the infection sites on crr1 as well as wild plants, the invasion and growth of Pst were not affected by the production of H2 O2 in the mutant.This implied that H2 O2 may act as signal molecules and mutant gene function at downstream of the pathway.