SSR marker-assisted improvement of fiber qualities in Gossypium hirsutum using G. barbadense introgression lines.

This study demonstrates the first practical use of CSILs for the transfer of fiber quality QTLs into Upland cotton cultivars using SSR markers without detrimentally affecting desirable agronomic characteristics. Gossypium hirsutum is characterized by its high lint production and medium fiber quality compared to extra-long staple cotton G. barbadense. Transferring valuable traits or genes from G. barbadense into G. hirsutum is a promising but challenging approach through a traditional interspecific introgression strategy. We developed one set of chromosome segment introgression lines (CSILs), where TM-1, the genetic standard in G. hirsutum, was used as the recipient parent and the long staple cotton G. barbadense cv. Hai7124 was used as the donor parent by molecular marker-assisted selection (MAS). Among them, four CSILs, IL040-A4-1, IL080-D6-1, IL088-A7-3 and IL019-A2-6, found to be associated with superior fiber qualities including fiber length, strength and fineness QTL in Xinjiang were selected and backcrossed, and transferred these QTLs into three commercial Upland cotton cultivars such as Xinluzao (XLZ) 26, 41 and 42 grown in Xinjiang. By backcrossing and self-pollinating twice, five improved lines (3262-4, 3389-2, 3326-3, 3380-4 and 3426-5) were developed by MAS of background and introgressed segments. In diverse field trials, these QTLs consistently and significantly offered additive effects on the target phenotype. Furthermore, we also pyramided two segments from different CSILs (IL080-D6-1 and IL019-A2-6) into cultivar 0768 to accelerate breeding process purposefully with MAS. The improved lines pyramided by these two introgressed segments showed significant additive epistatic effects in four separate field trials. No significant alteration in yield components was observed in these modified lines. In summary, we first report that these CSILs have great potential to improve fiber qualities in Upland cotton MAS breeding programs.