Water Deficit Effects On Growth and Reproductive Performance of Cotton.

Drought and temperature are the two most important abiotic factors affecting crop growth and yield. An experiment was conducted in sunlit, controlled environment facility to study the impacts of water deficits on cotton (Gossypium hirsutum L.) growth and physiology. Water deficit treatments of 100, 80, 60 and 40% of evapo-transpiration of control (100%) were imposed from flowering to maturity. Stem lengths and node numbers were recorded weekly. Leaf wax, cell membrane thermostability, chlorophyll stability, pigments and leaf water potential were also recorded. Flowers and bolls were tagged to estimate boll maturation period. Boll numbers and biomass were recorded at end of the experiment. Temporal trends in leaf water potential showed significant variability among the water deficit treatments. Maximum photosynthesis (31.1 µmol m^-2 s^-1) and stem elongation (4.89 cm d^-1) rates were observed at -1.5 MPa midday leaf water potential. The carbon fixed at all light levels was much lower in the water-stressed plants, and the plants light saturated at lower light intensities when water stressed. Photosynthesis and stomatal conductance measured at fixed light level (1500 µmol m^-2s^-1) declined linearly with increased water deficits, but the decline in vegetative growth was greater than the decline in gas exchange processes. Stomatal conductance, declined faster than photosynthesis with increased midday leaf water deficits. Wax content and relative injury to cell membranes increased with water deficits treatments while pigments, pollen germination and viability were unaltered. The decreased photosynthesis resulted in fewer numbers of retained bolls per plant under water deficit conditions. The results show the importance of maintaining optimum water conditions during flowering and boll growth period to obtain potential cotton yield in the field.  In addition, the functional algorithms developed in this would be useful to improve the predictive capability of the cotton models for natural resource management in the field.