Cotton fiber development is characterized by two overlapping phases, elongation and secondary wall thickening. It has been determined from field studies that cool temperatures can alter both of these phases. Although results of field studies are not always consistent, it can be generally concluded that cool field temperatures cause reduced rates and prolonged periods of elongation and thickening. They also cause final fiber length to be unchanged or slightly reduced and final fiber weight to be reduced.

We have used cotton (Gossypium hirsutum cv. Acala SJ-1) ovules cultured in vitro in cycling temperature incubators to investigate further the cool temperature response. Cycling regimes included 34/28 C, 34/22 C, and 34/15 C, with 34 C constant growth providing the control. Analyses of patterns of fiber length and weight accumulation showed that 34/22 C and 34/15 C cycling were detrimental to fiber elongation and thickening. These data on length could be correlated with observations in the scanning electron microscope to show that cool temperatures severely hindered fiber initiation and early elongation, whereas later stages of elongation occurred at the same rate as in controls. The elongation period was also prolonged under low temperature cycling. Analysis of fiber weight showed the 34/22 C and 34/15 C cycling delayed the onset, slowed the rate and prolonged the period of wall thickening. Control fiber length and weight were eventually reached if the growing period was long enough. Together, these data demonstrate that fibers of cultured ovules are remarkably similar to field fibers in their coot temperature response. These in vitro studies have provided much clearer data than previously available on the effect of cool temperatures on the onset of elongation and thickening.