Study of the effect of cold stress on some physiological and morphological characteristics of pumpkin (Cucurbita moschata L.) seedling under cold resistance foliar spraying

Introduction and purpose Damage caused by the cold during the crucial stage of plant growth and development is one of the important factors that reduce the performance of the agricultural plants in the world. Frostbite causes damage in the tissues, cells and organs of these plants. The reduction of the product due to a decrease in the average temperature of 1°C estimated at about 40 percent. Cucurbita moschata L. with the scientific name of pumpkin belonging to the Cucurbitaceae family and from plants that are sensitive to low temperatures. Finding a suitable and economical way to protect plants from the frostbite, is one of the most important causes of damage and reduced production of these valuable products, which has particular importance in the field of production and agricultural economics. In this regard, the new Arman brand of organic compound has been introduced as a cold-resistance compound. Also, Salicylic acid is a hormone that plays an important role in resistance to biological and non-biological stresses, and Affects plant growth, germination of seeds, membrane structure, chlorophyll content, effloresce and fruit arrivals. The use of cold-resistance compounds in growth stages that have the highest probability of injury to frostbite stress, can reduce the percentage of damage. Material and methods To study the effect of some cold resistance (in four levels (control (spraying distilled water), salicylic acid 0.25, salicylic acid 0.5, Arman1 (1:20)) on the pumpkin characteristic at - 1, 1, 3, 5 and 7 °C, the experiment was performed in factorial randomized completely block design with three replications in the research greenhouse of Urmia University in 2016-2017 cropping years. The seeds were cultivated in pots at depths of 2-3 cm and grew for 2 weeks in a greenhouse (25 ± 2 °C). Foliar application was performed in 2-3 leaf stage. One day after foliar application, plants were transferred to freezer, and plants were exposed to thermal treatments (1-, 1, 3, 5 and 7 ° C) for 4 hours. After performing stress, the pots were placed at 4 °C for 24 hours and then plants were evaluated. Evaluated traits in current study were including chlorophyll , chlorophyll measured with SPAD,ionic leakage, seedling dry weight (dry weight of root and shoot), Seedling length (root and branch). To analyze of data we used of SAS software and mean comparisons based Duncan test in a significant level five percent. Results and discussion The results showed that the effect of temperature on all studied traits of pumpkin (chlorophyll a, b,ionic leakage, chlorophyll (SPAD), seedling weights, root dry weight, root length and seedling length) was significant. The highest chlorophyll b, SPAD, seedling weights, root length and seedling length were obtained at 7 °C, which was not a stress temperature, but with decrease of temperature, change process in this characters were descending, so that the lowest amount of traits were related to -1°C. chlorophyll synthesis is one of the sensitive processes and cold temperatures caused disorder in chlorophyll production and caused damage in chloroplast reactions. The negative effect of cold stress on the photosynthesis and chloroplast, decreases the power of photosynthetic system in energy production and CO2 assimilation which reduces the production of carbohydrates. The reduction of shoot dry weight and roots of plants under stress condition proves this subject. Frosting stress through changes in permeability increases the leakage of cellular solutions. The researchers stated that cold stress have caused increases in electrolyte leakage due to lipid peroxidation of the cell membrane and organelles. Peroxidation of lipids, which leads to the destruction of biological membranes, indicates oxidative stress in plants which is caused by various stresses such as cold stress. Root growth reduced by reducing the temperature, reduces the absorption capacity of water and minerals by the root, that followed by the emergence of secondary effects caused Nutritional restriction and disrupting the plant growth. With attention to the negative effects of the cold on Pumpkin growth and with regard to the results, it seems that applied cold resistance compound has caused maintain the stability of the membrane in front of the leak of the cell. Conclution In this experiment, salicylic acid 0.25 Mm and arman 1 treatments maintained the amount of pigments that probably due to the effect of salicylic acid on the production of free radicals as a result that prevented the destruction of chlorophyll, with using defensive mechanism could held the amount of chlorophyll that is better than the sensitive variety in the production and the negative effects of ROS species prevented, and with more energy and photosynthesis, it can increase tolerance to cold stress. So, application of salicylic acid 0.25 Mm and arman 1 improve the relative qualities of the above traits. Therefore, use of compounds in cold stress conditions is recommended.