Ultraviolet-B radiation effects on cotton growth, development and physiology

Depletion of global stratospheric ozone could intensify ultraviolet-B radiation, which can alter crop productivity. Little is known about the response of cotton, a major economic crop grown over 32 Mha worldwide and over 5 Mha in the United States to changes in UV-B. Two experiments were conducted during the summer of 2001 using sunlit plant growth chambers using wide range of UV-B radiation under optimal growing conditions. Critical limits, defined as 90% of the optimum, were 4 kJ for reproductive growth, 6 kJ for root and 7 kJ for leaf and stem biomass, respectively indicating reproductive and vegetative sensitivity to UV-B. The critical limit was lower (70) for stem elongation than for leaf expansion (11 kJ), reflecting stem elongation's relatively higher UV-B sensitivity. Decreased photosynthesis due to UV-B was closely correlated with lower boll numbers and weights. High UV-B adaptive mechanisms included changes in leaf anatomy, decreased leaf thickness, increased palisade layer thickness, and phenolic and wax concentrations. Traits highly sensitive to enhanced UV-B can be used to screen for UV-B-tolerant cotton genotypes.