| Lacking of significant increasing of average yield in upland cotton in the world since 1991 reinforces the impression that the cotton industry has entered into a long-term period of slow growth in production. Breeding contributing to the yield growth has sharply decreased, and the result of cotton cultivars performance of regional test displayed that the potentials for the growth of yield in new developed cultivars was delimited, which implies that we must pay more attention to the studies on the genetic mechanism for yield and qualities traits. As it is relatively easy for cotton hybrids to combine the high-yield, high quality, and resistance to diseases, and the developing period for hybrid cotton is shorter than that of cultivars in general, the utilization of cotton heterosis will simultaneously satisfy the needs of increasing yield and improving fiber quality. The studies on the genetic base of heterosis will greatly influence to select the breeding strategy in developing hybrid cotton. The studying results of genetic mechanism for maize (cross-pollinated crop) and rice (self- pollinated crop) by molecular marker were different in same crop and various crosses within the same crop, which implies that it is complexity involved in genetic bases of heterosis. Cotton is a very important economical crop, and an often cross-pollinated crop as well. Molecular markers with single environment and two years experiments studied the genetic mechanism for yield and fiber quality and its heterosis.Four hundreds and ninety five pairs of SSR primers were used in the Xiangzamian 2 population analysis, which screened 18 polymorphic loci involving 22 locus. The percentage of polymorphism is only 4. 65%. An analysis of these loci with the MAPMAKER/EXP (3.0b) (Lander et ah, 1987) program resulted in the establishment of two linkage groups with 8, 3 loci, respectively, ie s280, s3994, s264, s244, s3140, sl672, s3442, s1053 are onchromosome 22 and s253b, s253a, s296b are on chromosome 9, as well as 11 unlinked loci. Mapping results showed that on the conditions of linked in data set at minimum LOD 3. 00, and maximum distance 50cM. These two linkage groups covered a total genetic distance of 280.5 cM (centiMorgen). By MAPMAKER/QTL (version 1.1b) (Lander and Bostein, 1989), using interval mapping, one QTL of lint yield explained 6.6% phenotype variance. Two QTLs of yield explained 8. 4% and 25% phenotype variance. Four QTLs of boll size explained 15%, 35. 2%,6. 5% and 8% phenotype variance, respectively. Three QTLs of the number of boll branch explained 63. 6%, 21. 6% and 67. 8% phenotype variance, respectively. One QTL of the number of boll explained 17.4% phenotype variance. One QTL of the fiber length explained 19. 8% phenotype variance. One QTL of the fiber strength explained 46. 5% phenotype variance. Two, QTLs of micronaire of fiber explained7. 4% and 7. 2% phenotype variance. It was found that one marker associated with several QTLs of correlative traits, and QTL have positive effect for one trait, but negative for other traits, possibly caused by genetic correlation among traits.The path analysis showed that lint yield was more directly by the number of boll than by boll size, and the indirective effects on lint yield between boll size and lint percent were positive, but the higher indirective effects o the lint yield between the number of boll and boll size, and between lint percent and boll size were negative. The heterosis over the number of boll, boll size, seed cotton yield, lint percent and lint yield, measured as the departure from the averaged mid-parent value, were about 1. 04%, 3. 54%, 3. 31%, 1. 54%, 6. 05%o And measured as the departure from the averaged over-parent value, were about 3. 9%, 11. 39%, 6. 62%, 5. 79%, 13. 62% for F, hybrids respectively. It was found that the sum on yield component heterosis had much higher correlation with the heterosis of lint yield, which implies that they have equal accumulative effects on the heterosis of lint yield. The results of path analysis for yield com...
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