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.
