Melatonin effects in enhancing chilling stress tolerance of pepper

Chilling stress is a type of low temperature stress that occurs when plants are exposed to temperatures below optimum but above 0 degrees C. It determines the geographical distribution of crop species that are of tropic and sub-tropic origin and causes huge losses every year. Thus, besides developing stress tolerant crop varieties, the use of various substances has become an important way of alleviating the adverse effects of abiotic stress conditions and melatonin has gained huge attention lately due to its proven anti-oxidative nature. The objective of the present study was to explore if exogenous application of melatonin through soil drench would mitigate the damage caused by chilling stress in pepper at seedling and flowering stages. Pepper seedlings and flowering plants were treated with melatonin after which they were subjected to chilling stress at 5 degrees C/10 degrees C (night/day) for 3 days. The results indicated that melatonin application resulted in reduced visual damage but increased leaf area and shoot mass in pepper seedlings. Melatonin treatment also improwed water relations, photosynthetic parameters and the activities of antioxidant enzymes while lowering malondialdehyde (MDA) and H2O2 contents and membrane permeability. When applied at flowering stage, melatonin doubled the early yield but caused slight increase in the final yield. Thus, the results of this research indicate that treatment of pepper plants with 5 mu M melatonin through soil drench could be used to improve plant growth and early yield potential under chilling stress conditions.