Carbon balance of PGR-IV-treated cotton plants

A new plant growth regulator PGR-IV is made of a fermentation broth of soil bacteria, yeast, and fungi that contains gibberellic acid and indolebutyric acid in a nutrient solution blend. This growth regulator has been tested in cotton over the last 10 years and has been reported to enhance the capacity of the plant to sustain growth under suboptimal conditions for growth. Although research has been conducted to evaluate its effects on root growth, nutrient uptake, boll retention, earliness, leaf photosynthesis, and yield, no studies have been reported on the whole-plant carbon balance and transpiration responses of cotton at suboptimal conditions for growth. The objectives of these experiments were to determine the effects of PGR-IV on the carbon and water economies of cotton plants grown in whole-plant test chambers at low temperatures and under water stress.; PGR-IV applications to cotton plants grown at low temperatures (20{dollar}spcirc{dollar}C) increased rates of carbon uptake, carbon losses, and net carbon gains. The increases in carbon uptake at 20{dollar}spcirc{dollar}C were proportionally lower than the increases in carbon losses through respiration and consequently treated plants showed lower values of carbon use efficiency (CUE). At 30{dollar}spcirc{dollar}C, PGR-IV-treated plants showed reduced respiration and increased CUE and transpiration rates at 22 days after a first application at the fourth leaf stage.; Under water stress conditions the overall carbon fluxes and growth characteristics of cotton plants were severely affected, but applications of PGR-IV used no effects on the overall carbon and water fluxes of the cotton plant.; Under field conditions the photosynthetic responses of PGR-IV-treated cotton plants were evaluated under low nitrogen and water stress conditions. Water stress and low nitrogen were the major factors inducing reductions in the leaf CO, exchange rates (CER) and transpiration rates of cotton plants. PGR-IV applications caused no effects on the leaf CER and transpiration rates through most of the experimental period.; According to these results we conclude that PGR-IV did not alleviate the detrimental effects of water stress on the cotton plant, but it may favor growth of plants under low temperatures.