| Recently, Bt type cotton which is resistance in insects is planted in much acreage of higher soil fertility. At the same time, with the adjustment of crop plant structure, intercrop acreage between cotton and other crops (like melons, vegetables and legume) spreads promptly. Since much fertilizer is applied in the cotton field of intercrop acreage, Bt cotton grows higher in plant height, deeper in color of leaf, longer in date of maturity, higher in yield of biology, but lower in yield of economics. Whereas, Okra-leaf cottons were associated with production advantages, such as early maturity, reduced boll rot, lower leaf area index, higher canopy CO2-uptake and light-saturated, higher single-leaf photosynthesis per unit leaf area (Pettigrew et al., 1993), shorter sympodial plastochron (Kerby and Buxton 1978), increased numbers of flowers per season (Wells and Meredith 1986), better pesticide penetration (James and Jones 1985;Thomson et al.,1987), and moderate levels of pink bollworm resistance (Wilson 1986;1990). Although Okra-leaf type cotton yielded less than their normal-leaf counterparts (Wilson, 1987), Semi-okra leaf hybrid developed by crossing with Okra-leaf and normal-leaf cotton was of benefits to expression of heterosis.To understand the heterosis mechanism of CMS-based hybrid cotton with okra leaf indicator, 24 CMS-based hybrids with five leaf types in upland cotton were made among super okra leaf, okra leaf and normal leaf parents by NCII mating design to compare photosynthetic properties of different leaf type hybrids and to study their relationships with yield and fiber properties. Correlations were detected with the relationships between genetic distance by molecular markers or on the genotype performance and the performance of yield traits and photosynthetic properties of hybrids. Differential gene expression patterns in functional leaves between parents and CMS-based hybrids at bolls-setting stage were analyzed by using cDNA-AFLP. The correlation analysis of various differential gene expression patterns with the performance and heterosis of main cotton agronomic and photosynthetic traits was also carried out. The main results are as follows:1. Hybrid cotton production by utilizing CMS lines with okra leaf characters had some advantages. Firstly, it was easy to distinguish "True" hybrids from "False" hybrids according to okra leaf indicator, guaranteeing purity of hybrid seeds. Furthermore, it was saving procedure of "Manual Demasculation" and reducing production costs. Finally, mix planting of okra leaf CMS and normal leaf restorer could shorten the space distance which honeybee bee was visiting flowers between sterile and restorer plants, thereby notably increasing yield of hybrid seed. The yield of hybrid cottonseed of mix planting per ha was the highest for the A '. R ratio of 3 : 1, about 1323.89 kg. while interval planting was the highest for the A : R ratio of 1 :1, about 1146.39kg. The yield of hybrid cottonseed of mix planting per ha was increased by 15.48% than that of interval planting.2. Compared with Zhongza29 (CK hybrid with normal leaf), yield of super okra leaf and okra leaf hybrids were obviously lower, but semi-okra leaf hybrids were higher 1.16% in yield of seed cottonand 2.06% in yield of lint cotton, were earlier 10 days in maturation. For photosynthetic indexes at different development stages of plant, semi-okra leaf hybrids showed higher Pn (net photosynthetic rate), Gs (stomatal conductance ) and Tr (transpiration rate) than normal leaf hybrids at all stages except the harvesting stage, especially Pn was the highest in the flowering stage, but Ci was lower than normal leaf hybrids. There were positive correlation coefficients between Pn and yield-relative traits at different development stages, of them, yield of seed cotton was the most significant relationship with Pn, boll number and bolls weight were in middle, fruiting branches was the smallest. Investigation of photosynthetic indexes in top, middle and low layer leaves of hybrid plants at the boll-setting stage showed that light intensity, light transmittance, Pn and Gs of super okra leaf and okra leaf hybrids were higher in the low layer leaves than those of other leaf hybrids, especially those of super okra leaf hybrids was the highest values in light transmittance and Pn, increased by 94.12% and 45.54% over CK respectively, but Pn was lower in the top and middle leaves. Pn and Gs of semi-okra leaf hybrids were higher in the top, middle and low layer leaves than those of normal leaf hybrids, such as Pn, increased by 8.06% for the top layer, 1.7% for the middle layer and 30.77% for the low layer leaves than CK respectively. The study indicated that semi-okra leaf hybrids had better photosynthetic properties which were of benefits to expression of heterosis of yield and fiber properties.3. Genetic distance among 10 cotton parents of steriles and restorers was from 0.1507 to 0.2683 with the mean of 0.2235 based on molecular markers of AFLPs and SSRs, and from 2.9794 to 6.7246 with the mean of 4.9609 based on the genotype performance for two-years field experiments. Relationship between genetic distances of molecular marker and genotype performance had a significant positive correlation (r=0.5939).Parent genetic distances which were determined from molecular markers or the genotype performance showed positive correlations with the performance of yield traits of hybrids. Of them, genetic distance of the genotype performance had significant positive correlations with the performance of yield traits of hybrids, especially for the number of bolls per plant. For the relationships between the hybrid heterosis of yield traits and parent genetic distance of molecular markers or of the genotype performance, positive correlations also were detected, but not significant. Noticing hybrid photosynthetic indexes, parent genetic distances showed positive correlations with Pn, Tr, and Gs, significant with LAI, but negative correlations with Ci. Hybrid heterosis of Pn and LAI was positively correlated with parent distance, but were not significant.4. There were 4 kinds of differential gene expression patterns between hybrids and their parents: bands expressed only in one parent (UNP), bands expressed in both parents (ABF,), bands expressed only in one parent and F| (DMP), and bands expressed only in Fi (UNF|).At bolls-setting stage, there were 16.98% UNF,, 29.32% DMP, 13.70% ABF,, 40.01% UNP in hybrid on an average. There was significant positive correlation between UNP and the heterosis of yield of seed cotton and lint, no significant correlation between DMP, or UNFi, or DFi(bands in two parents or only in F|) and the heterosis of all agronomic traits. However, significant negative correlation was detected between ABF| and the heterosis of yield of seed cotton. For the relationshipwith photosynthetic traits, UNP had a significant positive correlation with the heterosis of Pn and Tr, while DMP, or UNF|, or DF| no significant correlation with all photosynthetic traits, but ABF, significant negative correlation with Pn and Gs.The gene expression patterns of hybrids with different heterosis showed that the bands of gene expression in high heterosis hybrid were more than that in low one at bolls-setting stage. UNP bands in high heterosis hybrid were more than that in low one, which could be inferred that there was possible a certain relationship between the number of expression gene and the heterosis. Therefore, more bands of gene expression were in high heterosis hybrid at bolls-setting stage, the more genes participant into photosynthesis, the higher of yield of seed cotton. The tendency was in accord with the results of correlations of various differential expression patterns with heterosis of photosynthetic characters of cotton hybrid. |
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