Responses of two cotton (Gossypium Hirsutum L.) cultivars differing in resistance to leaf curl virus disease to nitrogen nutrition

Use of pesticides to eradicate pest attack on cotton crops has increased substantially during the past decade posing a serious threat to environment and human health. Application of nitrogenous fertilizers which modulates plant metabolism might reduce pest and pest-induced viral diseases. Understanding physiological basis of nitrogen nutrition on disease incidence in cotton may help in developing strategies to prevent, avoid, escape and control viral diseases. Thus, responses of two cultivars of cotton (Gossypium hirsutum L.), S-12 (CLCuV-susceptible) and CIM-448 (CLCuV-resistant), to varying concentrations of nitrogen were examined. Plants of both cotton cultivars were grown at varying concentration [224, 114 (control) and 56 mg N L-1] of nitrogen supplied with Hoagland's nutrient solution. The virus resistant cultivar, CIM-448 remained free of all disease symptoms throughout the experiment, whereas in virus susceptible cultivar S-12 leaf curling and vein thickening occurred at all external nitrogen regimes. However, severity of disease symptoms decreased with decreasing external N supply. Growth of both cotton cultivars increased due to increasing external N supply. The CLCuV-resistant cultivar, CIM-448 had significantly greater fresh and dry biomass as compared to the virus susceptible cultivar S-12 at all external nitrogen regimes. Leaf epicuticular wax content was greater in CLCuV-resistant cultivar as compared to that of non-diseased leaves of CLCuV-susceptible cotton cultivar S-12. However, the diseased leaves of CLCuV-susceptible cultivar S-12 had higher epicuticular wax content as compared to those of healthy S-12 and CIM-448. Leaf K+ decreased with decrease in N regimes in both cultivars. However, diseased leaves of S-12 had significantly higher leaf K+ and Ca2+ as compared to those of healthy S-12 and CIM-448. Leaf Mg2+ concentration was higher in CIM-448 as compared to that in diseased or healthy leaves of S-12 at all N levels. Accumulation of N declined with decrease in N levels. However, CIM-448 had higher N content as compared to healthy or diseased leaves of S-12. Leaf P content was inconsistent in two cotton cultivars at different N levels. In conclusion, growth of both cotton cultivars increased with increase in N nutrition in growth medium, which in turn was associated with higher accumulation of N and K accumulation. However, vigorous growth of S-12 cultivar with high N supply enhanced the disease susceptibility due to change in pattern of N and K accumulation at different N levels, whereas the disease resistance of CIM-448 remained unchanged at changing N levels.