Characterization of the Spikelet Number per Panicle QTL qSPP7 Using a Nearly Isogenic Line Derived from an Interspecific Cross in Rice

Previously, we mapped the qSPP7 QTL affecting the number of spikelets per panicle (SPP) on rice chromosome 7 using near-isogenic line (NIL WH29001) derived from an interspecific cross between the japonica ‘Hwaseong’ and Oryza minuta. In the present study, we confirmed this QTL using progeny derived from a cross between IL102, a WH29001 sister line and Hwaseong. Genetic analysis determined that qSPP7 was located between a KASP marker KJ07-049 and RM21605. The O. minuta segment on chromosome 7 introgressed into the Hwaseong background was associated with an increase in SPP. The panicle structure of IL102 revealed that not only the number of SPP increased significantly, but also the number of branches per panicle increased as compared to Hwaseong suggesting that the donor allele of qSPP7 promotes branching in the genetic background of Hwaseong. Linkage analysis indicated that qEhd1 on chromosome 10 is involved in the difference in heading date of IL102 and Hwaseong. Experiments under 3 different day length conditions revealed that IL102 always showed earlier heading and higher SPP as compared to Hwaseong indicating that the effect of qSPP7 in the Hwaseong background was not dependent on photoperiod, and SPP increased in proportion to the number of days to heading.