As modern cotton varieties including Bt (Bacillus thuringiensis) transgenic cotton are adopted and yield per unit area continues to increase, potassium deficiency is occurring with rising frequency in many cotton-growing countries. Symptoms of K deficiencies used to occur at the bottom of the plant on the older or mature leaves, but more recently described symptoms show up on young leaves near the top of the plant. Potassium deficiency induces numerous disorders in cotton, including decreased leaf area index, photosynthesis and plant biomass, but enhances specific leaf weight and earliness of maturity. Low supply and uptake of K, adoption of modern cotton varieties particularly Bt transgenic cotton, and environmental stress are obvious contributors to potassium deficiency. Single leaf photosynthesis (Pn) reduction results mainly from decreased stomatal conductance, low chlorophyl content, poor chloroplast ultrastructure, restricted saccharide translocation, and decreased synthesis of RuBP carboxylase under K deficient conditions. Canopy photosynthesis reduction in K-deficient plants is mainly attributed to both inhibited single leaf Pn rate and decreased leaf area index. Potassium concentrations in both blade and petiole of top fully expanded leaves on main stem are good indicators of K deficiency.

Cotton; potassium deficiency; physiological disorder; tissue diagnosis

Published by University of Zagreb, Faculty of Agriculture, Zagreb, CROATIA
Sponsored by Ministry Science and Education of the Republic of Croatia