Carbon and Water Economies of Well‐Watered and Water‐Deficient Cotton Plants Treated with Mepiquat Chloride

Abstract

The growth regulator mepiquat chloride (MC) (1,1‐dimethylpiperidinium chloride) inhibits leaf expansion, reduces leaf diffusive resistance, and reduces leaf photosynthetic rates when applied to cotton (Gossypium hirsutum L.). Whole‐plant studies in a controlled environment were conducted to evaluate the effect of MC on the C and water economies of ‘Stoneville 825’ cotton plants growing under well‐watered and water‐deficient conditions. Single, well‐irrigated plants were transferred from a nursery room into test chambers when they reached a leaf area of 0.05 m2 and were exposed to the following combinations of treatments: treated or not treated with MC and maintained well irrigated or not irrigated. MC treatment consisted of spraying 12 ± 1 mL plant−1 of a solution with a concentration of 27.3 mg a.i. L−1. Environmental conditions were typical of sunny humid days in central Texas. Carbon exchange rates and water loss rates were monitored hourly; leaf area, leaf water potential, and leaf osmotic potential were measured daily. Mepiquat chloride inhibited plant leaf area expansion, daily transpiration, daily gross C uptake, daily C loss, and daily net C gains in both water regimes; however, transpiration, gross C uptake, and net C gains of water‐stressed plants were less inhibited in MC‐treated plants than in nontreated plants toward the end of the water stress cycle. Mepiqnat chloride did not affect C‐use efficiency of cotton plants under either water regime nor the water use efficiency (WUE) of well‐watered plants, but reduced WUE of water‐stressed plants, which indicates a possible inhibition of the leaf internal photosynthetic capacity. Mepiquat chloride did not affect leaf water and osmotic potentials of well‐watered plants, but helped to maintain leaf turgor potential in water‐stressed plants. It was concluded that MC induces a water‐conservative behavior in cotton through its effect on plant leaf area and delays the onset of water stress in plants growing under water‐deficient conditions.