Preliminary Study On The Genetic Effect Of Pyramiding Major QTLs For Cotton Fiber Quality Through Marker-assisted Selection

With the development of molecular biology and molecular marker technology more and more QTLs for cotton fiber quality had been identificatied, which provide an opportunity for molecular marker-assisted breeding in cotton fiber quality. Owing to small effect for single QTL to fiber quality, it is necessary to pyramid a few QTLs of fiber quality to improve cotton fiber quality. Two commercial cotton cultivars (lines), TG41 and sGK156, and three elite fiber quality germplasm lines, HS427-10,7235 and 0-153 were used as parents to develop three double-cross F₁ populations ( sGK156×HS427-10 )×(0-153×7235), ( TG41×HS427-10 )×(0-153×7235) and (sGK156×0-153)×(sGK156×HS427-10), in which the effect and stability of the major QTLs for fiber strength, fiber length and micronaire were studied by SSR markers and the effect of different QTLs'pyramiding for fiber quality was identified.1. The effect and stability of nine QTLs, in which four are relevant with fiber strength, three are relevant with fiber length and two are relevant with micronaire, were identified in the three populations'F₁ and F₂ through single marker-assisted selection with eight markers. As a result, all the markers showed significant effect in the double-cross F₁ population. Moreover, significant selection effect were identified with BNL1521, MUSS034, TMK19, CM67 for fiber strength and NAU1043, MUSS497 for fiber length at least in two populations'two generations. The QTLs linked with BNL1521 and NAU1043 were derived from 7235, but it could be detected in HS427-10, which shows the QTL could be used extensively for marker assisted selection.2. The effect of two different QTLs'pyramiding for fiber strength were studied in the three populations'F₁ generation, including 78 pairs of compared datas with two QTLs and one QTL, in which 69 pairs (88.5%)showed the plants with two QTLs had stronger fiber than those with one QTL, and 25 pairs (32.1%) showed the plants with two QTLs had significantly stronger fiber. This indicated the QTL effects could be added for fiber strength. The plants with two QTLs showed more significantly additive effect than one QTL in 6 combinations (NAU1262 and TMK19, NAU1262 and CM67, MUSS034 and MUCS616, MUSS034and CM67, MUSS034 and TMK19, TMK19 and MUCS616)for fiber strength in Pop2 and two combinations (CM67 and MUSS497, NAU1043 and MUSS497) for fiber length. The prominent effects were identified in the combinations of MUSS034 and MUCS616, MUSS497 and Nau1043, which show epistatic effect exists in the two combinations. With those markers'combinations, the fiber qualities could be improved significantly.3. The pyramiding effect for 3 and 4 QTLs were studied with QTLs with significant effects for fiber strength in combination of two QTLs. It indicated the fiber strength was improved significantly with more QTLs for fiber strength, and the fiber strength reached the highest when four QTLs were pyramided in the plants. In conclusion, with pyramiding more QTLs in the plant, the fiber qualities could be improved more significantly.4. The three double-cross populations we developed have very complicated genetic playground, and most of QTLs exist in heterozygous genotype. But the significant effects were identified for single QTL and combination of QTLs in the populations, this indicated the genetic effect could be identified in the early populations for breeding selection with heterozygous genotype for most of plants.5. Some excellent materials with high fiber strength and high yield were identified in double-cross F₂ populations, especially for 9075426,9075389 and 9075587 with fiber strength more than 33.0cN∕tex, and fiber yield above 80% of sGK156 or TG41.