Résumé
The genus Gossypium has a broad and diversified genetic base with 50 different species already described. These various species are found in distinct and distant regions of the World, located in the and zones of the tropics and the subtropics. The diploid species have been classified in 7 genomes, called A to G according to chromosome size, chromosomic affinities and geographical spray (Valicek, 1979). These genomes may be grouped geographically: a. The Australian group with 17 species (genomes C and G); b. The American group with 13 sbecies (genome D); c. The Asian-African group with 14 specics (genomes A, B, E, and F). Among the diploid species, only two G. arboreum and G. herbaceum have fiber-bearing seeds and the fiber produced is coarse and short. These two species have been cultivated for centuries in the Old World and they are still traditionally and even commercially grown in Asia. At present, they represent only 4% of the cotton World production. During evolution, crosses between species of genome A and D occured naturally. After spontaneous chromosomes doubling remained 6 known AD allotetraploid species. The main ones are G. hirsutum and its standard quality lint and G. barbadense with extra long staple and exceptionnal fineness. These two species are called New World cotton and they are currently responsible for most of the cotton World production (repectively 91% and 5%). They cultivars are grown worldwide from 46°N, China, to the 32°S, Australia. CIRAD-CA has developped and studied (Bourdon, 1984) an important germplasm bank