Developmental events and growth processes are quite temperature are primary differences amoung cultivars among cultivars and species. Temperature responses to those processes are often modulated by other environmental factors such as water and nutrient status. To predict plant field performances one needs information on responses of different processes to temperature as well as sensitivity of these rate functions to crop water deficits and other environmental factors.

We conducted a series of experiments determining rates of cotton developmental events and growth processes at various temperatures. We also determined some of the effects of water deficits on those processes. These were controlled temperature studies in natural radiation environment. Water and nutrients were not limiting except when those were controlled variables.

Days from emergence to first square was very temperature sensitive and was variable among cultivars and species. The shapes of temperature-response curves were essentially parallel indicating that cultivars responded similarly to different temperatures, but the time required to reach first square for an early maturing cultivar was less than that for a mid-season maturing cultivar at all temperatures. At 18 C, Delta cotton, cv. DPL 50, required 60 days to develop squares, but at 28 C only about 30 days were required. Pima cotton, cv. S-6, had a similar temperature-response curve with that of Delta cotton, cv. DES 119, at all temperatures except at higher temperatures. Pima cotton was more sensitive to above-optimum temperatures (27 C) than Delta cotton cultivars, resulting in squaring delay at higher temperatures.

The period from square formation to flower was slightly less temperature sensitive than the period from emergence to first square. The upland cultivars were not different in their response to temperature for this trait, but pima cotton required about 10 days longer at optimum temperatures.

The time required from flowering to open boll was very temperature dependent. The shortest time interval was at highest temperatures tested. The pima and upland type cotton temperature-response curves were very similar, but pima cotton required three to four days more to develop mature bolls than upland cotton types except at an average temperatures of 30 C above.

Leaves initiated more slowly on prefruiting mainstem nodes at all temperatures than on fruiting nodes. Leaf developmental rates on prefruiting nodes were particularly sensitive to low temperatures. At 20 C, about eight days were required to develop a prefruiting node leaf while only about 3.5 days were required at 30 C. Leaf development of fruiting nodes required only from about 4.5 to about 3 days per leaf at those temperatures.

Expansion duration of leaves and internodes were also temperature dependent. leases required about four days longer to expand at optimum temperatures than mainstem internodes. Leaves required about 16 days from unfolding to 80 percent of full expansion at 30 C.

Mainstem elongation was more sensitive to midday leafwater deficits than canopy net photosynthesis. Photosynthetic rate at 698 W m^-2 decreased progressively with midday leaf water potential between 1.9 MPa to 4.4 MPa while stem extension rate was almost zero at 2.4 MPa.