Molecular marker assisted selection and pyramiding of two QTLs for fiber strength in upland cotton.

Based on two major QTLs that control high fiber strength which originated from an elite fiber germ-plasm line 7235 (Gossypium hiusutum L.), the efficiency of molecular marker-assisted selection (MAS) was investigated using two populations from pedigree selection and modified backcrossing pyramiding developed for the breeding purpose. Simian 3 (SM3), a widely planted variety in the Yangtze River Valley, and 7235 were used as parents to develop the two populations. In the two major QTLs for fiber strength from 7235, QTLfs-1 could explain more than 30% of the phenotypic variation (PV) in the (7235 x TM-1) F2 population. QTLfs-2 was at first identified in another super quality fiber line HS427-10 from (HS427-10 x TM-1) F2 population with 12.5% of PV explanation,which was further also identified in 7235 line but was non-allelic with QTLfs-1. The result of molecular marker-assisted selection for fiber strength showed that the genetic effect of the QTLfs-1 was stable under different environmental conditions, and its molecular marker-assisted selection showed significant selective efficiency among breeding populations with different genetic backgrounds. QTLfs-2 also showed high selective efficiency in advanced generation populations though its effect was a little lower than the former. When QTLfs-1 was selected simultaneously with 2 molecular markers with known genetic distance, the selection efficiency for the fiber strength was greatly increased. The pyramiding for two QTLs that control high fiber strength by MAS greatly improved the selection efficiency for cotton fiber strength. This report provides a successful example of MAS pyramiding for QTL for favorable traits in breeding programs.