Introgression of a quantitative trait locus for spikelets per panicle from Oryza minuta to the O-sativa cultivar Hwaseongbyeo

A new QTL for spikelets per panicle (SPP) was detected on the long arm of chromosome 7 in an F(2) population derived from a cross between the japonica cultivar Hwaseongbyeo and WH29001. WH29001, an advanced backcross line was developed by introgressing chromosomal segments from an accession of O. minuta (2n = 48, BBCC, Acc. no. 101141) into the O. sativa subsp. japonica cv. Hwaseongbyeo. The O. minuta allele increased SPP in the Hwaseongbyeo background despite the fact that O. minuta was the small panicle parent. Using F(3) and F(4) progenies, spp7 was validated and mapped to a 2.3 Mb region in the interval between the SSR markers RM445 and RM21615 based on the japonica genome sequence. A yield trial using F(4) lines indicated that the lines carrying an O. minuta chromosome segment across the entire spp7 target region out-yielded its sister lines containing Hwaseongbyeo chromosome in the target region and Hwaseongbyeo by 14.3% and 15.9%, respectively. Increase in SPP in WH29001 was mainly because of the increase in primary branches per panicle. The locus, spp7 is of particular interest because of its independence from undesirable height and flowering time. SSR markers tightly linked to the spp7 will facilitate cloning of the gene underlying this QTL as well as marker-assisted selection for variation in SPP in an applied breeding program.