INITIATION AND EARLY DEVELOPMENT OF FIBER IN WILD AND CULTIVATED COTTON

Cultivated cotton fiber has undergone transformation from short, coarse fibers found in progenitor wild species to economically important, long, fine fibers grown globally. Morphological transformation requires understanding of development of wild fiber and developmental differences between wild and cultivated fiber. We examined early development of fibers, including abundance and placement on seed surface, nucleus position, presence of vacuoles, and fiber size and shape. Four species were studied using microscopic, morphometric, and statistical methods: Gossypium raimondii (wild D genome), Gossypium herbaceum (cultivated A genome), Gossypium hirsutum (wild tetraploid), and Gossypium hirsutum (cultivated tetraploid). Early fiber development is highly asynchronous in G. raimondii but more synchronous in other taxa. Significant changes associated with domestication include pronounced synchronization of fiber development in G. hirsutum relative to other taxa studied, implicating unconscious selection that shaped early molecular and cellular events, and a delay in some developmental features in fibers of G. herbaceum, including delayed vacuole formation and nuclear migration. Increased fiber cover and synchronized development selection in cultivated cotton may have facilitated both yield and uniformity of the crop. However, for the taxa and developmental timeframe studied, phylogeny is found to play a more important role than domestication in determining early fiber size and shape.