Alleviating the adverse effects of salinity in eggplant (Solanum melongene L.) by using plant growth enhancer

Abstract

Eggplant (Solanum melongena L.) locally known as ‗brinjal‘, ‗baengan‘ or ‗bataon‘, is a high value horticultural crop, playing important role in increasing income of farming community. Biotic and abiotic factors contribute in yield loss of eggplant but the saline underground water is the main reason and the cultivation of salt sensitive eggplant genotypes also yield. The objective of this research was to characterize the eggplant genotypes against salinity stress and to induce the salt tolerance in eggplant by foliar application of chitosan and to study the physiological, biochemical and ionic changes in eggplant in response to NaCl salinity and chitosan. Pot culture experiments were carried out in lath (screen) house of Institute of Horticultural Sciences, University of Agriculture, Faisalabad, to accomplish the investigation. Study comprised of two phases, each phase with two experiments. In first experiment 13 locally grown eggplant genotypes were exposed to different salinity levels [(control, 3, 6, 9, 12 and 15 dS m-1 (decisiemens per meter)]. Different growth (plant height, root length, shoot fresh weight, root fresh weight and plant dry matter) and ionic attributes (sodium and potassium) were recorded. All the eggplant genotypes showed a considerably variable respons under salinity stress. ‗Saadia‘ was found salt tolerant, while ‗Black Beauty‘ was salt sensitive genotype. In the second experiment growth, physiological, biochemical, and ionic attributes of Saadia-tolerant and Black Beauty-sensitive eggplant genotypes (screened out in first experiment) were investigated under different salinity levels (control, 3, 6, 9, 12 and 15 dS m-1) of NaCl. Results of second experiment showed that salt stress caused the reduction in growth (plant height, root length, shoot and root fresh weight, shoot and root dry weight), water relations (leaf water potential, leaf osmotic potential, leaf turgor pressure and RWC), physiological (photosynthesis rate, transpiration rate and stomatal conductance, except WUE) and biochemical (chlorophyll contents) traits of both tolerant and non-tolerant genotypes. But tolerant genotype (Saadia) showed less reduction in above traits in comparison to sensitive ones (Black Beauty). The enzymatic (SOD, POD and CAT) activities, proline and glycinebetaine were substantially increased in both eggplant genotypes under salt stress conditions. But tolerant (Saadia) showed the maximum increase. Among the ionic traits, Na+ and Cl- were increased while Ca2+ and K+ significantly decreased in response to salt stress. Whereas, tolerant maintained the high concentration of Ca2+ and K+ ions and the least amounts of toxic ions (Na+ and Cl-). xii In the third experiment diverse levels of chitosan i.e. 75, 100, 125, 150, 175 and 200 mg L-1 were supplemented as a foliar spray on tolerant (Saadia) and sensitive (Black Beauty) genotypes grown under 9 dS m-1. Chitosan 150 mg L-1 was found to be the optimum dose to increase eggplant growth attributes (plant height, root length, shoot fresh weight, root fresh weight and plant dry matter). Whereas, in fourth experiment Saadia (tolerant) and Black Beauty (non-tolerant) eggplant genotypes were grown under saline and non-saline conditions, with and without chitosan. Results showed that chitosan improved the physiological, turgor pressure, enzymatic activities (SOD, POD and CAT), biochemical attributes (proline and glycinebetaine) and beneficial ions (Ca2+ and K+) and decreased the toxic ions (Na+ and Cl-), lipid peroxidation and osmotic potential as well as water potential in both tested eggplant genotypes. Among the yield parameters chitosan increased the number of fruits, fruit diameter, average fruit weight and yield per plant in both eggplant genotypes under stressed and non-stressed environments. Overall, it can be concluded that salt stress reduced the eggplant growth and productivity. Foliar application of chitosan induced salt tolerance in eggplant and improved yield attributes.