DEVELOPMENTAL RESPONSES BY TALL AND DWARF ISOGENIC LINES OF SPRING WHEAT TO APPLIED GIBBERELLINS

Tall (rht) and dwarf (Rht) isogenic lines of two Mexican spring wheat cultivars were grown at 25/20 degrees C day/night in short (8 h) days of either natural or artificial light to determine their relative stem, leaf and flowering responses to one or two long days, 11 different gibberellins (GAs) and the growth retardant Cycocel (CCC). Although stem and leaf elongation in the dwarf lines did not respond to a GA application, inflorescence initiation and development was enhanced by several GAs, reduced by CCC, and restored by subsequent GA application. The floral response of tall lines to GAs was greater than that of the dwarf lines, whereas the reverse was the case with their exposure to long days. These results suggest that endogenous GAs are involved in the floral induction of wheat, and that although the stems and leaves of dwarf lines may not be able to respond to exogenous GAs, their shoot apices can do so and are sensitive to endogenous GA levels.