Study On The Interspecies Hybrid And Genetics And Systematic Development Between The Four Cultivated Cotton Species

Cotton (Gossypium sps) being the world's major fiber crop, it has been growing in more than 80 countries. It has four cultivated species namely G. arborewn, G. herbarium which are diploids and G. hirsutum, G. barbadense which are allotetraploids. These species have been the important source of the germplasm for cotton inheritance and breeding programmes, and these species are valuable in the cotton genetic improvement research. Studies on the interspecific crossing among the four species and their relationships not only provides enough intermediate quality materials, but also explains their genetics, evolution and phylogenetic relationships, which will be significant for the theory and practice. The characteristics of the karyotype, chromosomes, the relationships and evolution among the four species and their hybrids (F1) were studied by using the morphology, cytogenetics, physiological-biochemical characteristics, fluorescent in-situ hybridization (FISH) and molecular markers and so on. Results of all these studies are as follows and they would provide the scientific evidence for the resources of the cotton germplasm. 1. Study on the morphology and cytogenetics among the four cultivated cotton speciesand their hybrids (F1).The characteristics of the plants, leaves, stems and floral tissues between the four cultivated cottons were found to be significantly different. The leaves of the G. arborewn and G. herbarium were isobilateral leaves, and those of G.hirsutum and G. barbadense were dorsiventral leaves. The reciprocal F] of cross G. arborewn x G. herbarium were also isobilateral leaves, while reciprocal F1 cross of G.hirsutum x G. barbadense were also dorsiventral leaves. The quadrispecific hybrids F1 were isobilateral leaves, regardless of their cytoplasms. The structures of the leaf stalks and the stems were analogous to each other among the four cultivated cotton species except their diameters varied with species.The cytogenetics of interspecific hybrids (F1) among the four cultivated cotton species were studied in this paper and results are as follows: The diploid interspecific hybrid (G arborewn XG. herbarium) F1had a four-chromosome-ring at the meiotic metakinesis. The synapses of tetraploid hybrid (G. hirsutum x G. barbadense) F1 was found to be regular, which mainly formed bivalents, sometimes some univalents, multivalents and chromosome bridge. The diploid interspecific hybrid and the tetraploid hybrid grown and fruited regularly, but the pollen were semisterile. All these showed that the relationship was close between G. arborewn, G herbarium, and between the G. hirsutum and G. barbadense. The meiosis of the quadrispecific hybrid (F1) was abnormal, The chromosome configurationof the quadrispecific hybrid (F,) 2n=52=5.141+14.69 II+2.46 III+1.50 IV+0.70V+0.15VI. There were lots of multiad at the anaphase, which resulted pollen sterility which were the reason for sterility of the quadrispecific hybrid F1. These showed that the A-sub-genome of the tetraploid cultivated cotton species were homologous incompletely with the diploid A genome of the cultivated cotton species. The donor of A-sub-genome for tetraploid cultivated cottons were still studied on.2. Study on the FISH of the four cultivated cotton species and their hybrids.We concluded the results from the analysis of the rDNA-FISH for the four cultivated cotton species: 2 pairs of satellites of G herbarium were 'c', those of G. arboreum were 'b' and 'c', G.hirsutum were 'c', 'a', 'a' , G barbadense were 'c' and 'a'. So we could infer that G herbarium was the original cotton species and the donor species of A-sub-genome of two allotetraploids. In addition, the results of the karyotype showed that chromosomes of G. arboreum and G herbarium were symmetrical, except that the chromosome length was different. Different numbers and types of satellites of G.hirsutum and G barbadense showed that G.hirsutum and G barbadense had different center of variation. The developmental origin of the tetraploid cultivated cotton species could be...