Relationships among verticillium wilt development, leaf water potential, phenology, and lint yield in cotton

Acala S,J,2 cotton plants were tagged and observed individually every week in the field through the entire growing season to identify the physiological time when foliar symptoms of verticillium wilt first appeared. The midday leaf water potentials (ψ₁) of newly diseased plants were consistently lower than those of comparable healthy plants. Midday ψ₁ of newly diseased plants ranged from −15·7 to −24·6 bars with an average of −19·4 bars, whereas those of healthy plants ranged from −11·2 to −19·3 bars with an average of −14·7 bars. Differences in midday ψ₁ between healthy and newly diseased plants were greater prior to than after boll set. Leaf water potentials of cotton plants with disease symptoms that first appeared before boll set returned to normal about 3 weeks after the onset of foliar symptom development. However, when foliar symptoms first appeared after boll set, the midday ψ₁ of diseased plants remained consistently lower than that of comparable healthy plants for the remainder of the growing season. Healthy plants continued to grow during the early stages of boll set (before the peak boll stage), whereas growth of diseased plants with foliar symptoms was greatly reduced or stopped. The results indicate that water stress was one of the main reasons for growth retardation and lint yield reduction of cotton plants which developed foliar symptoms of verticillium wilt during early stages of plant development.