MICROSCOPIC STUDY OF MATURE SEED COATS AND ABORTED STRUCTURES OF INTERSPECIFIC COTTON HYBRIDS

Seed coats and fibers of aborted structures (termed ''motes'') and mat ure seeds from an interspecific hybrid (ISH) of cotton (Gossypium hirs utum x G. barbadense) were studied by microscopy to determine (a) the developmental stages at which motes of various sizes stop growing and (b) the origin of lint-contaminating fragments. Small motes (1-2 mm wi de, up to 3 mm long) were identified as ovules whose growth had been a rrested before anthesis or soon afterwards, medium-size motes (1-3 mm wide, 3-5 mm long) as those whose growth had been arrested up to 10 da ys post-anthesis, and large motes (3-5 mm wide, 5-8 mm long) as those which had stopped growing about 20 days post-anthesis. Microscopic exa mination of lint-contaminating fragments showed that they derive mainl y from medium-size motes and partly from mature seed coats. Reducing t he number of medium-size motes by breeding can, therefore, improve the lint quality of ISHs of cotton.