Using genetic resources to improve the cotton plant

The cotton plant is endemic and is cropped in very large tropical and subtropical zones on all 5 continents. The Gossypium L. genus is made up of about 50 diploid and tetraploid species. Seven genome groups have been identified. Only four species have been cultivated and these have been subdivided into numerous botanical races. Two of these have a diploid genome A and originate from the Old World. The other two have a tetraploid genome AD and originate from the New World. One of the latter, G. hirsutum L., accounts for about 90 percent of crops destined for the production of cotton fiber. Cotton plant improvement aims primarily to enhance the plant's productivity, improve fiber quality and increase resistance to insects. However, the narrow genetic basis within the G. hirsutum species restricts possible genetic progress. Recourse to the vast germplasm of the genus is therefore of primordial importance. Here, the cultivated or wild species, i.e. those not producing spinable fiber, posses genes that can be used to modify the principal characteristics of the cropped species and are therefore of considerable use in any selection program. The interspecific hybridizations have already met with considerable success in the past (varieties derived from HAR or ATH hybrids, transfer of oligogenic characters). However, cytogenetics is confronted with the problem of eliminating the unwanted characters that result from the presence of unfavorable links within the donor species. In the future, marker-assisted selection-i.e. the selection of introgressed individuals based solely on the fragments of chromosomes involved In the expression of the character sought-may resolve this problem as the rest of the recipient species genome will remain equilibrated. (Résumé d'auteur