Effect of Drought and Salinity Stress on Growth, Flowering and Biochemical Characteristics of Narsicuss tazetta L.

Salinity and drought have adverse impacts on crop production throughout the world, especially in arid and semiarid areas. Salinity decreases crop growth and yield through modifications of ion balance, water status, stomatal behavior, photosynthetic efficiency, salinity-induced nutrient deficiency and changes to the soil structure. Drought is another one of the main factors limiting the growth and development through the anatomical, morphological, and physiological and biochemical changes that the severity of drought damage varies depending on the duration of the stress and plant growth stage. Water stress reduces relative water content, photosynthesis pigments, stomatal conductance, biomass, growth and ultimately plant performance. Narcissus (Narcissus tazetta L. cv. ‘Shahla’) belongs to the Amaryllidaceae family is grown as a cut flower, landscape and medicinal plant that grows throughout the world except tropical regions. It is necessary to know the tolerance of N. tazzeta to drought and salinity stress in order to produce optimal product. According to previous studies, no complete research has been done on the effects of drought and salinity stress on N. tazzeta. Therefore, the present study was carried out with the aim of investigating the combined effects of drought and salinity stress on growth, flowering and biochemical characteristics of N. tazzeta.

This research was carried out in Faculty of Agriculture, University of Birjand, in 2017. A pot experiment was conducted in completely randomized deign with factorial arrangement and three replications. The treatments included sodium chloride (NaCl) in four levels 0 (control), 20, 40 and 60 mM and drought stress in four levels 30, 50, 70 and 90% of field capacity. The plants were harvested four months after the start of salt and drought treatments. The investigation traits were included vegetative, reproductive and biochemical characterizes. Measured traits were included root length, volume of root, root fresh weight, bulb length, bulb fresh weight, shoot fresh weight, total dry weight, flower diameter, flower crown diameter, stem diameter, days from planting to flowering, days from flowering to senescence, antioxidant activity, total phenolic content and total soluble sugar of leaf and root. The data were analyzed by SAS version 9.4 and the means separated by Duncan's multiple range test at p < 0.05. Excel was used to draw graphs.

The results of simple effects showed that drought and salinity stresses decreased the values of flowering stem diameter, flower diameter, root length, root volume, root fresh weight, bulb fresh weight, bulb length, shoot fresh weight, total dry weight and days from flowering to senescence. In contrast, the values of the number of days from sowing to flowering, total soluble sugars of leaf and root, antioxidant activity and total phenolic content increased under the influence of these two stresses. The results of interaction effects showed that the destructive effects of salinity and drought stress were intensified in co-application conditions, so that the lowest values of growth and reproductive traits were observed in the most severe stress (30% field capacity × 60 mM salinity). Usually, root and shoot length in sodium chloride solution is reduced due to the toxicity of ions and their negative effects on cell membranes. Drought stress and salinity reduce cell division and also reduce the size of cells and consequently the length of the plant decreases. Delay in flowering is due to multiple stresses (osmotic imbalance, nutrient insufficiency and cellular toxicity) that is caused by salinity and drought stresses. These stresses produce ROS compounds that damage the proteins, lipids, carbohydrates, and nucleic acids. Plants for scavenging and detoxifying these compounds from the cell surface use enzymatic (catalase, superoxide dismutase, etc.) and non-enzymatic (phenolic compounds and carotenoids) defense systems that increase the antioxidant activity of the plant.

The results of this study showed that drought and salinity stresses had negative effects on growth and flowering traits, which was exacerbated by the combined application of these two stresses. On the other hand, the highest levels of antioxidant activity, total phenolic content and total soluble sugars were obtained under severe stress conditions (drought or salinity). Salinity and drought stress reduced the flowering rate, quality of flowers and the flower life on the plant, but all the levels of stress reached to flowering stage. Also, the growth of narcissus plant was not affected by the highest levels of drought (30% crop capacity) and salinity (60 mM) stress. In general, the results showed that both drought and salinity stress reduced the growth and yield of narcissus flower, but the destructive effects of salinity stress on the growth, ornamental and physiological traits of narcissus flower were more than drought stress.