The influence of applied plant growth regulators (PGR) on growth, development and yield in cotton (Gossypium hirsutum L. and Gossypium barbadense L.) has been studied for over half a century. Studies of PGR containing cytokinin alone or in combination with gibberellins applied at the pinhead square developmental stage have reported both positive and negative effects; however, a majority of the studies report no significant effects on cotton. The objective of this study was to evaluate the effects of a foliar application of a commercial formulation of cytokinin (6-benzyladenine) during the early stages of seedling development, long before the pinhead square stage. Greenhouse studies in 2004 to 2006 compared untreated controls with 6-benzyladenine treated seedlings at the two to four-leaf stage. Initial studies determined that 25 µmol/mol 6-benzyladenine was optimal at this developmental stage. Concentrations of 30, 40 and 50 µmol/mol resulted in phytotoxic lesions on the leaf surfaces. Seedlings treated with 25 µmol/mol 6-benzyladenine approximately two-weeks after planting exhibited increased hypocotyl diameters, increased lateral root proliferation, and a breaking of apical meristem dormancy within one-week of treatment. Samples taken later in development exhibited increased boll weights and total root lengths in treated plants compared with untreated controls. Studies of plant water usage and water stress responses showed less water use and stress avoidance in the 6-benzyladenine treated plants. This study showed that application of 6-benzyladenine to cotton early in development has the potential to increase yields and reduce water stress in cotton.
