Using three selected overlapping RILs to fine-map the yield component QTL on Chro.D8 in Upland cotton

Cotton yield improvement is vital to fulfill rising global demands. The identification of major quantitative trait loci (QTL) for yield components was helpful in molecular marker-assisted selection (MAS) to improve cotton yield. We previously identified a densely populated QTL region for fiber qualities and yield components on chromosome D8 (Chro.D8) of Upland cotton from a (7235 x TM-1)RIL. In the present study, to fine-map yield component QTLs, we chose three overlapped recombinant inbred lines (RILs) with different intervals included the yield component QTLs, and backcrossed each line with TM-1 to develop three large sized mapping populations. Phenotypic data for yield components were collected in Nanjing (JES/NAU) and Xinjiang (BES/XJ) in 2006 and 2007. Three simple sequence repeat (SSR) genetic linkage maps on chro.D8 were constructed using 907 individuals in (7TR-133 x TM-1)F-2 (Pop A), 670 in (7TR-132 x TM-1)F-2 (Pop B), and 940 in (7TR-214 x TM-1)F-2 (Pop C). Three stable QTLs for boll size, two for lint percentage and one for boll number per plant,were detected on chro.D8 following analysis of three RIL backcrossed F-2/F-2:3 progeny at JES/NAU and BES/XJ although their cultivation practices differ greatly between these two cotton-growing regions. One QTL for boll number per plant exhibited a phenotypic variance (PV) of 5.6-10.1%, three QTLs for boll size exhibited 15.0-35.5% PV and two lint percentage QTLs exhibited 10.9-19.3% PV. Negative correlation between lint yield and fiber strength was confirmed.