| Cotton is an important economic crop. Hybrid cotton can significantly improve the yield and quality, whereas manpower hybridization breeding was laborious and time-consuming. So the glandless trait of cotton can help to improve the efficient of hybridization breeding.In this study, F1 and F2 of 20 combinations were made by using 10 glandless cottons as male parent and two glanded cottons as female parent according to incomplete diallel cross design. The heterosis performances of agronomic, yield traits and fiber quality between parents and their hybrid crosses were compared, and the relationship was analyzed between F1, F2 heterosis performances and genetic distances of their parents. In addition, SPAD, photosynthetic characteristic, chlorophyll fluorescence between parent and F1 was compared and the relationship among those index with yield and fiber quality of F1 was also compared. The results were as follows:1. The heterosis of F1 and F2 of 20 hybrids in this study were compared. F1 showed obvious heterosis in the agronomic trait, yield and fiber quality. The mid-parent heterosis was much higher than the over-parent heterosis. F2 did not showed heterosis in yield, but there was an obvious inbreeding depression in yield traits and light inbreeding depression in fiber quality. The trait which showed higher heterosis in F1 had a higher inbreeding depression in F2. Shengwu235 was a better hybrid parent in ten glandless cultivars used in this study, and Shengwu235×Nongdamian8 hybrid had a higher heterosis of yield.2. The relationship between phenotype performances of parents and hybrids was compared and path coefficient of parents and hybrids between lint yield and its components was analyzed. The results revealed that the high output glandless cotton should be chosen as female and high fiber quality parents should be chosen for the cross breeding of glandless cotton with phenol cotton. Also more attention should be paid on increasing lint percentage and plant height of hybrid cultivars and fiber quality should be cooperatively improved.3. By calculating the boll numbers of“before hot days, hot days and autumn”of hybrids and their parents, we found that the hybrids and the parents had the remarkable difference in the constitution of the before hot-boll, hot-boll and autumn-boll. The law of heterosis in number of boll was consistent in F1, F2. Before hot-boll had the higher heterosis, the seed yield of F1, F2 were mainly influenced by the number of hot-boll. The number of before hot-boll and hot-boll can reflect yield of hybrid cotton and can be used as a reference index of hybridization.4. The SPAD of parents and F1 had significant difference between varieties and combinations. The SPAD of F1 simply showed light heterosis or no heterosis, and had a significant correlation with fiber length and lint percentage. The photosynthesis rate of F1 showed heterosis at boll stage, while transpiration, stomatal conductance and intercellular concentration of CO2 had the highest heterosis at stage of full bloom. During different periods the heterosis of Fv/Fm of F1 had no significant change. At bolling stage, Fv/Fm of F1 had a significant negative correlation with lint percentage and lint yield and a significant positive correlation with fiber length during flowering and boll setting stage.5. The relationship between F1, F2 performances, mid-parent heterosis and genetic distance was determined by SSR molecular markers and phenotype performances. The results revealed that genetic distance had a significant or extremely significant negative correlation with F2 yield, but a significant or extremely significant positive correlation with F1, F2 fiber strength and the mid-parent heterosis of F2 micronaire. Molecular genetic distance had a significant or extremely significant negative correlation with F1 micronaire and the mid-parent heterosis of F1, F2 fiber elongation, but a significant or extremely significant positive correlation with the mid-parent heterosis of F1 seed-yield and most of F2 cross’s yield. |
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