Response of Photosynthetic Processes of Cotton to a Short-Term Drought Stress during the Reproductive Stage.

Plants respond to drought stress initially with stomatal closure to prevent water loss. Further drought period leads to nonstomatal limitation with the reduced CO₂ assimilation by the plants, which results in reduction in photosynthesis and possibly damage of photosynthetic apparatus. However, cotton cultivars vary in tolerance regarding physiological response to drought during the reproductive stage of the plants. The objective of this research was to characterize the photosynthetic response of commercial cotton cultivars under short-term drought stress during the squaring stage. A complete randomized block experiment with five replications was conducted in 2013 under field conditions in Marianna, AR. Treatments consisted of three commercial cotton (Gossypium hirsutum L.) cultivars, DP0912, PHY499, and ST5288, and two water regimes; well-watered control and water-stressed. Plants were well-watered until the pinhead square stage, at which time stress was imposed in the water-stressed treatment by withholding water for fourteen days. Stomatal conductance, actual quantum yield of photosystem II (Ф_PSII) and electron transport rate (ETR) were recorded between 12:00 and 14:00 h every seven days from forth main-stem leaves. Samples were collected from the forth main-stem leaf for pigments, chlorophylls a and b, and carotenoids, concentration. Cottonseed yield was recorded at the end of the season. Stomatal conductance was reduced throughout the stress period. Stressed plants presented significantly (P≤0.05) lower Ф_PSII and ETR than the control. Pigments concentration was decreased by the stress. Among the cotton cultivars, ST5288 appeared to exhibit higher acclimation to drought, even though all cultivars had the physiological processes reduced by the stress. Further studies are needed to clarify the variation and tolerance to drought among modern cotton cultivars.