Effects of Water-Deficit Stress On Cotton Reproductive Development.

In recent years, the U.S. cotton yield has shown extreme and unpredictable year-to-year variability, which has been attributed to genetics, management practices, and unfavorable environmental conditions with water deficit generally considered to be the most limiting environmental factor affecting plant development. Cotton yield is greatly correlated with the number of bolls produced however, to our knowledge the pathways of carbohydrate metabolism and subsequent energy production, as well as antioxidant metabolism of cotton flowers and bolls under water stress along with their interactions with their subtending leaves have received little attention. We hypothesized that water-deficit stress severely impairs cotton gas exchange functions which consequently results in a perturbation of carbohydrates and energy production metabolism of reproductive units, which would decrease seed set efficiency and yield. To study this hypothesis, three growth chamber studies were conducted in 2008-2009 at the University of Arkansas. Cotton (Gossypium hirsutum L.) cultivar ST4554 B2RF was planted in 1L pots in growth chambers set for 12h photoperiods, 60% relative humidity, and normal day/night temperatures of 32/22°C. Plants were separated in three groups of 12 replications. Control group plants received optimum the quantity of water daily, while for early and late stress group plants water was withheld until plants reached the desired stress levels and then, they were watered daily with the half quantity of water needed, in order to remain under stress. Overall duration of stress for both groups was ten days, and water stress was induced fourteen days after planting and at flowering, for early stress and late stress group plants, respectively. Measurements of leaf photosynthesis, water potential, and stomatal conductance were taken the 1^st, 5^th and 10^th day after the initiation of stress. Flowers were collected during the stress period from all three groups for carbohydrate, antioxidants, ATP and nutrient analysis, while subtending leaves were collected 5 and 10 days after the late stress initiation. This is an ongoing research and the data are still analyzed.