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Temperature Effects on Pima Cotton Leaf Growth

Dep. of Agronomy, Mississippi State Univ., Mississippi State, MS 39762

J. M. McKinion

USDA-ARS Crop Simulation Res. Unit, Crop Sci. Res. Lab., PO Box 5367, Mississippi State, MS 39762

^* Corresponding Author

Temperature is a primary environmental factor affecting cotton growth. Information on temperature effects on Pima cotton (Gossypium barbadense L.) growth is limited. The objective of this paper is to provide quantitative estimates of temperature effects on leaf emergence rates, the duration of leaf expansion, and rate of expansion. Pima cotton plants were grown from seed in naturally lit controlled environments with unlimited water and nutrients under five day/night temperature regimes ranging from 20/12 to 40/32 °C. Weighted average daily temperature was calculated from 900-s average temperatures. Carbon dioxide was maintained at 350 µL L–¹ during the daylight hours. Leaf area expansion and biomass accumulation were monitored from emergence to 64 d after emergence. Leaf initiation took about 2 d longer for prefruiting nodes at near optimum temperatures than for leaves formed after square initiation. Fruiting leaf initiation required about 4.5 d leaf–¹ at 20 °C and about 2.5 d leaf–¹ at 30 °C. Leaves expanded in excess of three times more rapidly at 31.3 °C than at 18.9 °C. The optimum temperature for leaf expansion was 31.3 °C. Leaf growth at 35.5 °C was only approximately 60% of that at 31.3 °C. Leaves required about 40~ longer to expand at 18.9 °C than at 31.3 °C. All leaves required the same length of time to expand when grown at the same temperature, regardless of position on the mainstem. Since leaves varied greatly in mature leaf size, depending on leaf position, rates of expansion also varied similarly. Maximum leaf growth rates occurred during the 28-to-64-days-after-emergence period compared with earlier growth periods, apparently reflecting greater light interception during that period. Biomass accumulation and growth rates were very temperature sensitive and closely related to leaf growth.

Received for publication February 23, 1991.