Fine mapping of a QTL for the number of spikelets per panicle by using near-isogenic lines derived from an interspecific cross between Oryza sativa and Oryza minuta

We constructed a high-resolution physical map for the qSPP7 QTL for spikelets per panicle (SPP) on rice chromosome 7 across a 28.6-kb region containing four predicted genes. Using a series of BC7F4 near-isogenic lines (NILs) derived from a cross between the Korean japonica cultivar Hwaseongbyeo and Oryza minuta (IRGC Acc. No. 101144), three QTLs for the number of SPP, grains per panicle and primary branches were identified in the cluster (P <= 0.01). All three QTLs were additive, and alleles from the O. minuta parent were beneficial in the Hwaseongbyeo background. qSPP7 was mapped to a 28.6-kb region between the two simple sequence repeat (SSR) markers RM4952 and RM21605. The additive effect of the O. minuta allele at qSPP7 was 23 SPP, and 43.6% of the phenotypic variance was explained by the segregation of the SSR marker RM4952. Colocalization of the three QTLs suggested that this locus was associated with panicle structure and had pleiotropic effects. The NIL populations and molecular markers are useful for cloning qspp7.