QTL analysis for panicle characteristics in temperate japonica rice

To understand the genetic background of panicle characteristics in temperate japonica rice (Oryza sativa L.), we genetically analyzed DH lines derived from a cross between two temperate japonica rice cultivars, 'Akihikari' and 'Koshihikari', in 1996 and 1997. Four traits of panicle characteristics, number of primary branches per panicle (NPB), number of secondary branches per panicle (NSB), average number of spikelets on one primary branch (NSP) and average number of spikelets on one secondary branch (NSS), in 212 DH lines were measured, and the interval mapping of QTLs for these traits was carried out using 169 DNA markers with an LOD threshold of 2.5. Five, three and one putative QTLs for NPB, NSB and NSS were identified, respectively, and no QTLs relating to NSP appeared. The percentages in total phenotypic variation explained by all putative QTLs for NPB were 35.5% and 43.8% in 1996 and 1997, respectively. All putative QTLs for NSB accounted for 35.5% and 27.5% of total phenotypic variation in 1996 and 1997, respectively. The QTLs identified in this study will be useful in temperate japonica rice breeding for improved spikelet yield.