A mutant of panicle differentiation in rice called non-panicle (nop) was discovered in the progeny of a cross between 93-11 and Nipponbare. The mutant exhibits normal plant morphology but has apparently few tillers. The most striking change in nop is that its panicle differentiation is blocked, with masses of fluffy bract nodes generate from the positions where rachis branches normally develop in wild-type plants. Genetic analysis suggests that nop is controlled by a single recessive gene, which is temporarily named Nop(t). Based on its mutant phenotype, Nop(t) represents a key gene controlling the initiation of inflorescence differentiation. By using simple sequence repeat markers and sequence tagged site markers, Nop(t) gene was fine mapped in a 102-kb interval on the long arm of chromosome 6. These results will facilitate the positional cloning and functional studies of the gene. A mutant of panicle differentiation in rice called non-panicle (nop) was discovered in the progeny of a cross between 93-11 and Nipponbare. The mutant exhibits normal plant morphology but has apparently few tillers. The most striking change in nop is that that its panicle differentiation is blocked, with masses of fluffy bract nodes generate from the positions where rachis branches normally develop in wild-type plants. Genetic analysis suggests that nop is controlled by a single recessive gene, which is temporarily named Nop (t). Based on Its mutant phenotype, Nop (t) represents a key gene controlling the initiation of inflorescence differentiation. By using simple sequence repeat markers and sequence tagged site markers, Nop (t) gene was fine mapped in a 102-kb interval on the long arm of chromosome 6. These results will facilitate the positional cloning and functional studies of the gene.