COOL TEMPERATURE EFFECTS ON COTTON FIBER INITIATION AND ELONGATION CLARIFIED USING IN-VITRO CULTURES

An understanding of the mechanistic basis of adverse environmental eff ects on cotton fiber development is a prerequisite to future improveme nt through genetic engineering and aids in field management to minimiz e such adverse effects. In order to clarify previous results from fiel d studies on the effects of cool temperatures on initiation, early elo ngation, and later elongation of cotton fibers, cotton ovules (Gossypi um hirsutum L.) cultured in vitro were used as a manipulable and repro ducible experimental system based on previous evidence that they provi de a valid model. Culture temperature varied from a control of 34 degr ees C constant to 34/15 degrees C cycling (12/12 h) to mimic a typical diurnal temperature cycle. Fiber initiation and early elongation were analyzed by scanning electron microscopy, and the progress of later e longation was determined by ruler measurements. The results demonstrat ed that fiber initiation and early elongation (up to about 0.5-mm leng th) were independently delayed by cycling cool temperatures, but that later elongation preceded in a temperature independent manner. The ear ly delay in fiber development caused by cycling cool temperatures was associated with a longer elongation period during which fibers could a ttain the control length. Therefore, the results suggest that there ar e three stages of fiber elongation as distinguished by different tempe rature responses: initiation, early elongation, and later elongation t o attain the genetically determined potential. Consequently, the field temperature during fiber initiation and early elongation may have a p rofound effect on the final fiber length attained in a limited growing season.