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Pak. J. Bot., 45(3): 1029-1038, 2013.

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REDUCING DISEASE INCIDENCE OF cotton leaf curl virus (CLCuV) In cotton (Gossypium hirsutum L.) BY POTASSIUM SUPPLEMENTATION

Zafar Ullah Zafar* and Habib-ur-Rehman Athar

Abstract: Severity of various diseases in plants can be reduced by nutrient management. The knowledge of K nutrition on relationship between plants and pests may help in devising strategies to set up high yielding production system by reducing disease incidence. Therefore, two cotton (Gossypium hirsutum L.) cultivars, S-12 (CLCuV-susceptible) and CIM-448 (CLCuV-resistant) were supplied with varying concentration of potassium [40, 120, and 236 mg K L^-1]. During the experiment, only virus susceptible cultivar S-12 exhibited typical disease symptoms on leaves, while that of CIM-448 did not show any degree of disease incidence. Moreover, at lower K supply, severity of disease incidence significantly enhanced. Although growth of both cotton cultivars decreased at low K concentration, cv. CIM-448 was superior in growth than that of virus susceptible cv. S-12 at all K concentrations. Virus resistant cultivar, cv. CIM-448 had higher leaf epicuticular wax than that of cv. S-12. However, it is interesting to note that diseased leaves of cv. S-12 had greater epicuticular wax content than that of healthy leaves of cv. S-12. Leaf K⁺ decreased with decrease in K regimes in both cultivars. Diseased leaves of virus susceptible cv. S-12 had higher leaf Ca²⁺ and N than those in healthy leaves of cvs. S-12 and CIM-448, whereas CIM-448 had higher leaf Mg²⁺ as compared to diseased or healthy leaves of S-12. Total soluble proteins, total free amino acids, total soluble sugars did not show any relationship with disease incidence. Photosynthetic rate and stomatal conductance were higher in CIM-448 than that in cv. S-12. Moreover, photosynthetic rate was higher in healthy leaves of cv. S-12 than that of diseased leaves.  Chlorophyll ‘a’ was higher in cv. CIM-448 than that in the leaves of cv.S12. In conclusion, low supply of K decreased the growth of both cultivars, but it also increased the severity of disease incidence in cv. S-12. Increase in disease incidence in cv. S-12 is possibly associated with lower photosynthetic pigments, lower rates of photosynthesis, and lower K and N use efficiency and low accumulation of Mg²⁺in the leaves.

Institute of Pure and Applied Biology, Bahauddin Zakariya University, Multan 60800, Pakistan

*Corresponding author’s e-mail: zafarbzu@yahoo.com