Effect of salinity on the physiological and biochemical responses of neem

Salinity is a widespread problem across the world and it has been interpreting considerate impacts on crop growth and productivity. The saline land is unfit for crop cultivation and the EC (Electrical Conductivity) value of that saline soil is more than 4 dS/mwould adversely affect crop growth and productivity [1]. High content of soluble salt, usually sodium chloride causes high osmotic pressure which results reduction of absorption of water and nutrients that suppress the seedling growth and plant development [2]. These changes are also associated with decrease in chlorophyll and carbohydrate contents in leaves [3]. There is strong evidence that one of the adaptation mechanisms of plants to salinity and water deficit by accumulation of compatible solutes and proline in cytoplasm [4]. Additionally, salinity also induces osmotic and ionic imbalance and toxicity in plants that induces oxidative stress [5], which initiates antioxidant system of the plants to cope up with oxidative damage to stressed plants [6]. Many researchers explored the salt resistant plants and their tolerance mechanism. There have been prompt attempts to generate agricultural crop varieties tolerant to salinity stress. However, very few reports are available on the identification and utilization of perennial tree species, tolerant to salinity stress. Screening salt stress tolerance has been investigated in woody plant species such as olive [7], mango [8], acacia [9] and pine [10]. In Bangladesh, about 650 species have been identified as medicinal plants because of their therapeutic properties [11]. Many government and non-government organizations have had focused attention on improving the medicinal plants sector. But still the medicinal plant cultivation is in avery rudimentary stage. In order to meet the ever increasing demand for medicinal plants, for the indigenous systems of medicine as well as for the pharmaceutical industry, some medicinal plants need to be cultivated commercially. In addition, coastal area of Bangladeshis the potential area for crop cultivation. Coastal area in Bangladesh constitutes 20% of the country of which about 53% are affected by different degrees of salinity. So it seems valuable, to test the important medicinal plants for their salt tolerance capacity. Effect of salt stress has been studied in some medicinal plants such as aloe vera, golden shower, madagaskar periwinkle [12], drumstick [6]. This study is related to the effect of salt stress on our selected medicinal plants, neem.

Neem is an important multipurpose agroforestry species under the family Meliaceae, which is well-known for its medicinal value. The plant is a source of several potent botanical insecticides, soap, lamp oil, lubricants and lumber. It is a good shade tree and reduces soil erosion. Different parts like bark, leaf, seeds, root of neem have very strong medicinal value and the seeds of this species can also be used as biological control of fungicide and pesticide of agricultural crops. Besides its use in medicine, the neem tree has great importance for its anti-desertification properties and possibly as a good carbon dioxide sinks [13]. Plantations of neem can improve the environmental condition of Bangladesh, if it can be introduced allover the country. Soil of the southern part of the country is saline affected and it is noteworthy that till date there are no reports of salt stress tolerance ability of the important medicinal plants, neem. Therefore, the objectives of the study were to understand the effect of different salinity levels on growth as well as the physiological and biochemical responses of neem.