The plant growth regulator PGR-IV has been shown to improve the growth, development and yield of cotton under ideal conditions. However, cotton responses to PGR-IV under conditions of water stress (flooding and water deficit) have not been investigated. The objective of this study was to investigate the effects of PGR-IV application on the growth and physiological characteristics of flooded and water-stressed cotton.

The experiments were conducted under controlled environment conditions at the Altheimer Laboratory, University of Arkansas in Fayetteville in 1992 and 1993. The growth chamber was programmed for a 12-h photoperiod with day/night temperatures of 30/25°C, and relative humidities of 60/80%. Cotton (Gossypium hirsutum L.) cultivar Stoneville 506 was planted in 2-L pots containing washed sand and 3 small holes at the bottom for drainage. The flooding experiment consisted of the following treatments: (1) control with no PGR-IV and no flooding, (2) flooding after planting, (3) flooding at the second true-leaf stage, and (4) flooding at the pin-head square stage. The duration of the flood at each growth stage was 14 days. All flooding treatments were split with or without PGR-IV one day before flooding. In the water deficit experiment, the water stress treatment started at the pin-head square stage. On the 5th day after PGR-IV application, water was withheld from the water-stressed plants with or without PGR-IV application until the plants wilted, after which they were rewatered.

The results of the experiments indicated that flooding at different growth stages significantly decreased plant height, leaf area, number of lateral roots, total root length, photosynthetic rate and dry matter accumulation of cotton plants. Application of PGR-IV decreased the detrimental effects of flooding on cotton growth, and improved photosynthesis and dry matter production of flooded cotton plants. There were no significant effects of PGR-IV on leaf water potential components of drought-stressed cotton plants. However, the water-stressed plants treated with PGR-IV had higher stomatal resistance and lower transpiration rates during the early period of water deficiency compared to the untreated plants, and had lower stomatal resistance and higher photosynthetic rates during the late period of water stress. The average photosynthetic rate of the plants treated with PGR-IV increased by 13.5% compared to untreated plants during the water deficit stress. In conclusion, PGR-IV has the potential to partially alleviate the detrimental effect of water stress on photosynthesis and dry matter accumulation, and improve plant growth, especially root growth.