PJB-2013-88
INFLUENCE OF DIFFERENT PHOSPHORUS REGIMES ON DISEASE RESISTANCE IN TWO COTTON (GOSSYPIUM HIRSUTUM L.) CULTIVARS DIFFERING IN RESISTANCE TO COTTON LEAF CURL VIRUS (CLCUV)
ZAFAR UIIAH ZAFAR* AND HABIB-UR-REHMAN ATHAR
Abstract
In recent years, plant diseases are major limiting factor in agricultural production. However, severity of disease incidence can be reduced by nutrient management. Therefore, understanding physiological and biochemical changes in relation to disease incidence will help in devising economic approaches to control crop damages due to different diseases. Therefore, two cotton (Gossypium hirsutum L.) cultivars, S-12 (CLCuV-susceptible) and CIM-448 (CLCuV-resistant) were grown at varying concentration [62, 31(control) 15.5 and 3.88 mg P L-1] of phosphorus supplied with Hoagland’s nutrient solution. Throughout the experiment, cv. CIM-448 remained free from CLCuV disease, whereas plants of cv. S-12 showed a degree of disease symptoms. Increasing P supply caused a consistent increase in growth of both cotton cultivars with concomitant increase in disease symptoms in only cv. S-12. The CLCuV-resistant cultivar, CIM-448 was higher in growth than that of cv. S-12 at all external phosphorus regimes. Leaf epicuticular wax content was greater in diseased leaves of CLCuV-susceptible S-12 as compared to its healthy leaves and CLCuV-resistant cultivar CIM-448. Lowering in P supply caused a decline in leaf K+ in both healthy leaves of S-12 and CIM-448 but it remained unchanged in diseased leaves of S-12. 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 that to diseased or healthy leaves of S-12 at all P levels. Accumulation of N remained unchanged with decrease in P levels. Leaf P content was decreased with decrease in external P levels in all the cultivars. Total soluble proteins and amino acids increased with the decrease of P levels. Total soluble sugars were lower in healthy leaves of S-12 as compared to diseased leaves of S-12 and CIM-448 at all external P levels whereas starch content decreased in diseased leaves of S-12 with decrease in P levels but it remained unchanged in diseased leaves of S-12 and CIM-448. Net CO2 assimilation rate decreased in both cultivars with decrease in P levels. In conclusion, low P supplies decreased the severity of disease in S-12. Disease resistance in S-12 and CIM-448 was positively associated with P and Mg2+ accumulation, photosynthetic rate and low accumulation of soluble sugars, soluble proteins and total free amino acids.
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