To probe the relationships between calcium nutrition and resistance to cotton leaf curl virus (CLCuV) in cotton two genetically different cultivars (S-12, CLCuV susceptible and CIM-448, CLCuV resistant) were grown in sand culture under low and high Ca regimes in respect of that in Hoagland's nutrient solution (160 mg L-1 Ca). The varying Ca regimes of the growth medium were 20, 80, 160 (control), 320, and 630 mg L-1 in Hoagland's nutrient solution. No significant effect of low or high Ca regimes was observed on the growth of both the cultivars. Analysis of different macronutrients (K, Ca, Mg, N, P) in the healthy and diseased leaves of S-12 and CIM-448 showed some contrasting results. K+ concentration in the diseased leaves of S-12 increased, whereas in the healthy leaves it decreased at lower and higher external Ca regimes. Ca2+ accumulation in the leaves of both cultivars was positively correlated with the external Ca levels. Cultivar difference was only evident at the highest Ca regime at which CIM-448 was the highest in Ca2+ accumulation. Mg2+ accumulation was maximum in the diseased leaves of S-12 and healthy leaves of CIM-448 at the lowest Ca regime. Nitrogen concentration was significantly higher in the diseased leaves of S-12 than the healthy leaves of S-12 or CIM-448, though the pattern of N accumulation in both cultivars was inconsistent with increase or decrease in external Ca level. Phosphorus showed an antagonistic effect at varying Ca levels of the growth medium. In conclusion, the study shows that lower or higher Ca regimes than that in the Hoagland's nutrient solution did not have any significant effect on the growth of two cultivars differing in resistance to CLCuV.
