Salicylic acid (SA) is a common plant-produced signal molecule that is responsible for inducing tolerance to a number of biotic and abiotic stresses. An experiment was, therefore, conducted to test whether acetyl salicylic acid (ASA) application at various concentrations through seed immersion or foliar spray would protect muskmelon [Cucumis melo L. (Reticulatus Group)] seedlings subjected to chilling stress. Twenty-one-day-old plants pre-treated with ASA (0, 0.1, 0.25, 0.50 or 1.0 mM) were subjected to chilling stress for 72 h at 3 ± 0.5°C. ASA, applied either through seed immersion or foliar spray, was effective within the range of 0.1 to 1 mM in inducing tolerance to chilling stress in muskmelon seedlings; however, there was no significant difference between application methods. ASA significantly and curvilinearly affected all seedling growth and stress indicator variables tested except shoot dry weight. The best protection was obtained from seedlings pre-treated with 0.5 mM ASA. The highest ASA concentration used was slightly less effective in providing chilling stress protection. Even though both methods provided similar means of protection, due to its simplicity and practicality, immersion of muskmelon seeds prior to sowing in 0.5 mM ASA would be a more desirable method to induce tolerance to chilling stress. Key words: Cucumis melo, aspirin, chilling stress tolerance, gas exchange, electrolyte leakage

The presence of melatonin, a known animal hormone, has been confirmed in many evolutionary distant organisms, including higher plants. It is known that melatonin increases tolerance to stress factors as a wide spectrum antioxidant. Tolerant genotypes have generally higher melatonin content than sensitive ones, and exposure to stressful conditions is known to increase endogenous melatonin levels. However, endogenous melatonin levels in seeds have never been used to select genotypes tolerant to abiotic stresses. Thus, in this study, the existence of possible relationship between seed melatonin levels of 28 pepper (Capsicum annuum L.) genotypes and their germination and emergence performance under chilling conditions (15°C) was investigated. The results indicated that these parameters were much better for pepper genotypes with higher seed melatonin contents while those having less than 2 ng g−1 additionally exhibited elevated levels of MDA and H2O2 but lower antioxidant enzyme activities. Thus, a positive relationship between seed melatonin content and chilling stress tolerance has been shown, suggesting a possible use of endogenous melatonin levels as a criterion in selecting chilling stress tolerant varieties. To save considerable time, money and labour, it is recommended that genotypes with lower melatonin contents are excluded from breeding programmes that aim to develop new stress tolerant genotypes.

In this study, the possibility of enhancing water stress tolerance of pepper during early growth stages by foliar application of glycinebetaine (GB) was investigated. Pepper seedlings with four true leaves were sprayed with three different concentrations (0, 5 or 25 mM) of GB after which they were subjected to water stress for 10 days. Water stress caused substantial reductions in shoot dry weight, leaf area, chlorophyll content, leaf water potential, gas exchange characteristics and efficiency of photosystem‐II while increasing membrane permeability and lipid peroxidation. However, foliar application of GB significantly counteracted the water stress‐induced adverse effects by increasing chlorophyll content, stomatal conductance, efficiency of photosystem‐II and proline content, while reducing visual damage symptoms, membrane permeability and lipid peroxidation. GB application also improved leaf water potential, relative water content and antioxidant enzymatic activity. Among the GB concentrations applied, enhanced water stress tolerance was obtained with 5 mM GB pre‐treatment. Results, therefore, indicate that GB, applied as foliar spray, could be used as an ameliorative agent for pepper seedlings against the deleterious effects of water stress.