EFFECTS OF FOLIAR ORANGE PEEL EXTRACT AND FARMYARD MANURE ON GROWTH, PHYSIOLOGICAL AND BIOCHEMICAL ATTRIBUTES OF ICEBERG LETTUCE (LACTUCA SATIVA L.) UNDER SALINITY STRESS

Abstract

Lettuce (Lactuca sativa L.) is a high-value vegetable crop whose production is constrained by soil salinity, a major abiotic stress. This study evaluated the effects of salinity stress, foliar-applied orange peel extract (OPE) and soil-applied farmyard manure (FYM) on the growth, physiological and biochemical attributes of iceberg lettuce under controlled greenhouse conditions. The experiment was laid out in a completely randomized design (CRD) with a factorial arrangement of three salinity levels (0, 3 and 7 dS m⁻¹), three OPE concentrations (0, 5 and 10%, v/v) and two FYM rates (0 and 10 t ha⁻¹), giving 18 treatment combinations with three replications. Data were analyzed by three-way analysis of variance, and means were compared using Fisher’s least significant difference (LSD) test at P ≤ 0.05. Increasing salinity from 0 to 7 dS m⁻¹ significantly reduced plant height (28.81 to 18.74 cm), leaf area (366.86 to 240.19 cm²), biomass (74.15 to 48.70 g), chlorophyll content (48.87 to 31.16), stomatal conductance, photosynthetic efficiency and relative water content, and increased electrolyte leakage (30.38 to 46.95%), proline content, malondialdehyde (MDA) content and the Na⁺/K⁺ ratio (0.77 to 1.19), indicating osmotic, oxidative and ionic stress. Foliar OPE at 10% significantly increased plant height (21.86 to 26.24 cm), chlorophyll content (36.58 to 44.24) and biomass (56.58 to 67.65 g) compared with the untreated control, and both 5% and 10% OPE significantly reduced electrolyte leakage (from 41.32% to 37.48% and 34.34%, respectively). FYM at 10 t ha⁻¹ produced only small, statistically non-significant (P > 0.05) changes in the measured traits. These results indicate that foliar OPE is a promising, low-cost bio stimulant for improving the salinity tolerance of lettuce, whereas the benefit of FYM at this rate needs to be confirmed in longer-term or field studies.