| Lack of significant growth in the world average yield in upland cotton since 1991 reinforces the impression that the cotton industry has entered into a long梩erm period of slow growth in production. Breeding contribution to the yield growth has sharply decreased, and the result of cotton cultivar 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 diversity of cotton cultivers and genetic mechanism for yield traits. As it is relatively easy for cotton hybrids to combine the high梱ielding, high梣uality, 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梡ollinated crop) and rice ~self梡ollinated crop) by niolecular marker were different in same crop and various crosses within the same crop , which implies that it is complexity involved in genetic bases of hetcrosis. Cotton is a very important economical crop, and an often cross梡ollinated crop as well. The genetic mechanism for yield and its heterosis were studied by molecular markers with multiple environment experiments and a new genetic model analysis method for heterosis in this paper. Genetic diversity of Upland cotton (Gossypium hirsulum I..) cultivars was evaluated by SSR, ISSR, and RAPD. The genomic DNAs o1~36 domestic and exotic cultivars were amplified with 81 SSR primer pairs~ 7 ISSR primers and 53 RAPD primers, which yielded 282 polymorphic bands. The range ol pair similarity coefficient (Nei M. and W. II 1979) between cultivars is from 0.5745 to 0.9291. 慬he result indicated that although the presented cultivars have genetic variation to a certain extent, the genetic basis of them is relatively narrow , and it is essential to find some new germplasm fir the development of?new culti vars. As expected. the c lassi licatioii of the cotton cul Ii vars L1S1 ng the I Inweighted Pair梘roup Method with Arithmetic Average based on the pair Si m i Ian K coe the ieiits IS mostly consistent ~ ithi k iiown pedigree i ri formation and breeding experience. [he 36 cotton cuhtivars have been mainly classed iiltO exotic cultivar group. Chinese Xi,igiung ecological region cultivar group, early梞ature domestic cutivar group and mediate-mature domestic cultivar group. (慉RMFN and COl.ORAI)() cultivars from Spain have the lowest similarity with other cultivars, while tM- I (genetic standard line). MD5lne and PD9364 cultivars from American have higher similarity with domestic cultivars. The reason may be that the parents of the domestic cultivars were mainly introduced from American. I lowever. clusters of domestic cultivars are not all in accordance with their ecological regions, which may result from the pedigree complexity of the cultivars. Meanwhile the gemletic diversity of 36 cultivars was investigated at phenotypic level with agronomic and fiber quality traits in the field experiments in 1999 and 2000. and was measured by l{uclidcan distance on the genotypes. Although grouping result of?cluster analysis based Ofl the l{uclidean distance is similar to that of?molecular data with a significant negative correlatio...
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