Influence of Night Temperature on Growth and Development of Cotton (Gossypium hirsutum L.). I. Fruiting and Boll Development1

Different night temperature regimes were maintained throughout the boll development period on cotton growing in the field during the 1963, 1964, and 1965 seasons. Both fruiting and boll development were found to be closely associated with night temperature. Decreased night temperature resulted in the formation of more flowers and, in some cases, increased fruit set. Relative fruitfulness increased as night temperature decreased between the interval of 21 and 8.8 C and 21 and 14.4 C with ‘Paymaster’ and ‘Acala’ varieties respectively. Temperatures above 19.4 and below 13.3 C reduced fruiting index. Rate of boll development was inversely related to temperature, with a decrease of either day or night temperature resulting in slower boll dvelopment, thus, increasing boll periods. However, in this work night temperature was the dominant environmental factor associated with boll periods. In general, the Paymaster variety appeared to be better adapted to low night temperatures than the Acala variety.