COTTON RESPONSES TO DIFFERENT LIGHT-TEMPERATURE REGIMES

A series of experiments investigating the interactive effects of light and temperature on vegetative growth, earliness, fruiting, yield and fibre properties in three cultivars of cotton, was undertaken in growt h rooms. Two constant day/night temperature regimes with a difference of 4 degrees C (30/20 and 26/16.5 degrees C) were used throughout the growing season in combination with two light intensities (75 and 52.5 W m(-2)). The results showed that significant interactions occurred fo r most of the characters studied. Although the development of leaf are a was mainly temperature-dependent, plants at harvest had a larger lea f area when high temperature was combined with low rather than with hi gh light intensity. Leaf area was least in the low temperature-low lig ht regime. However, the plants grown under the high temperature-low li ght combination weighed the least. Variations in the number of nodes a nd internode length were largely dependent on temperature rather than light. Light did, however, affect the numbers of branches, sympodia an d monopodia. The first two of these were highest in the high light-hig h temperature regime and the third in the low light-low temperature re gime. All other characters, except time to certain developmental stage s and fibre length, were reduced at the lower light intensity. Variati on in temperature modified the light effect and vice versa, in a chara cter-dependent manner. More specifically, square and boil dry weights, as well as seed cotton yield per plant, were highest in high light co mbined with low temperature, where the most and heaviest bells were pr oduced. But flower production was favoured by high light and high temp erature, suggesting increased boil retention at low temperature, espec ially when combined with low light. Low temperature and high light als o maximized lint percentage. Fibres were shortest in the high temperat ure-high light regime, where fibre strength, micronaire index and matu rity ratio were at a maximum. However, the finest and the most uniform fibres were produced when high light was combined with low temperatur e. Cultivar differences were significant mainly in leaf area and dry m atter production at flowering.