A Genetical Scheme for Isolating Cotton Cultivars1

When the diploid cotton (Gossypium davidsonii Kell.) species, is crossed with cultivars of the tetraploid species, G. hirsutum L. and G. barbadense L., the hybrid embryos abort, or the seedlings become necrotized and moribund shortly after germination. A complementary lethality intereaction is indicated, the cultivated cottons contributing the factors Le1 and Le2, whereas G. davidsonii contributes at least one factor, Ledav. A rare genotype in G. barbadense is le1le1le2le2. Crosses between plants of this genotype and G. davidsonii yield viable triploids. Using the technique of hexaploid bridging, I transferred Ledav from G. davidsonii to the cross‐compatible stock, 15‐4. The resulting stock—genotype le1le1le2le2LedavLedav—is not cross‐compatible with a series of cultivars of G. hirsutum and G. barbadense. Utilizing the le and Ledav alleles, I produced stocks of G. hirsutum that proved to be genetically isolated from a series of G. hirsutum cultivars under both greenhouse and field conditions. The use of the le ‐ Ledav genetical system for isolating cotton cultivars grown for special purposes, such as gossypol‐free seeds, is discussed.