Effect of exogenous application of triacontanol on wheat (Triticum aestivum L.) under salt stress

Abstract

In order to investigate the effect of exogenous application of triacontanol (TRIA) on two wheat (Triticum aestivum L.) cultivars [S-24 (a salt tolerant) and MH-97 (a moderately salt sensitive)] under salt stress, two independent experiments were conducted in a greenhouse. Both wheat cultivars were grown in full strength Hoagland’s nutrient solution under non-saline (0 mM NaCl) and saline (150 mM NaCl) conditions. Three optimized TRIA levels (0, 10 and 20 μM) were used both as foliar sprayed at three growth stages i.e. vegetative, boot and veg. + boot stages and as seed-priming. In foliar-spray set of experiments ninety two-day old, while in seed-priming experiment twenty four-day old plants were subjected to data analysis for various growth, physiological and biochemical attributes. Salinity stress adversely affected growth and yield (shoot and root fresh and dry weights, total leaf area per plant, shoot and root length, grain yield, number of grains and number of tillers per plant, 100-seed weight), photosynthetic rate (A), transpiration rate (E), stomatal conductance (gs), chlorophyll contents (chl. a, b and a/b ratio), leaf water relations (water potential, osmotic potential and turgor potential), relative water content (%), electron transport rate (ETR), shoot and root K+ and Ca2+ ions and K+/Na+ ratios, superoxide dismutase (SOD) activity, peroxidase (POD) activity (in cv. MH-97 only), Rooting medium salinity stress did not alter sub-stomatal internal CO2 concentration (Ci), Ci/Ca ratio, water use efficiency (WUE), efficiency of PS II (Fv/Fm), photochemical quenching (qP) and non-photochemical quenching exiton (NPQ) of both wheat cultivars, but increased co-efficient of non-photochemical quenching (qN), membrane permeability (%), hydrogen peroxide (H2O2), malonedialdehyde (MDA), shoot and root Na+ and Cl- contents, activity of catalase (CAT), leaf soluble proteins and total free amino acids, free proline, glycinebetaine and total phenolic contents. Exogenous application of TRIA as a foliar spray significantly increased all growth and yield attributes, photosynthetic rate (A), stomatal conductance (gs), chl. a and b contents and ETR value, leaf water potential, decreased leaf osmotic potential at vegetative stage, while increased at boot stage of both cultivars at all growth stages, shoot and root K+ (cv. S-24) and Ca2+ in both cultivars, root K+/Na+ ratios in cv. S-24 under non-saline conditions, increased Cl- contents under non-saline, while decreased under saline conditions. Foliar spray of TRIA increased photochemical quenching at boot and veg. + boot stages under non-saline conditions, while decreased non-photochemical quenching exciton (NPQ) value in both cultivars at all growth stages, qN values only in cv. MH-97 at vegetative + boot stages, total phenolics at boot and veg. + boot stages and shoot Na+ in both wheat cultivars under saline conditions. Pre-sowing seed treatment of TRIA did not improve growth or yield attributes, gas exchange characteristics, leaf osmotic and turgor potentials, and enzyme activities of SOD and CAT. However, TRIA application increased stomatal conductance under non-saline conditions and net CO2 assimilation rate under saline conditions of both cultivars, while POD activity (both cultivars) and water potential (only cv. S-24) under both saline and non-saline conditions. Performance of salt tolerant cultivar S-24 was good in growth (shoot fresh and dry weights, and shoot length), stomatal conductance (gs), chl. a/b ratios and ETR value, leaf water relations, shoot and root K+, Ca2+ and Cl- ions, K+/Na+ ratios, soluble proteins and free amino acids, free proline, in terms of foliar spray experiment. The design of both experiments was completely randomized with four replicates in each set.