Effect of calcium application on carbohydrate and calcium accumulation and storage improvement of potato cultivars under heat stress

Introduction The sever heat stress at the end of growing season in potato winter cultivation, always has been one of the major challenges in warm areas of Iran. Heat stress reduces the yield, quality and shelf life of the potato tubers by increasing the amount of respiration and changes at the balance of sugars and starch in the tubers. One of the suitable strategies to reduce the impacts of heat stress on potatoes is the use of calcium, especially calcium nitrate, which has been investigated in this experiment. Materials and methods This Study conducted as split-split plot experiment based on randomized complete block design with three replications in South Kerman Agricultural Research and Education Center during 2013-2014. The main factor was sowing date: suitable sowing time (31th Dec.) and delay sowing (4th Feb.) and three potato cultivars (Sante, Satina and Milva) were kept in sub-plot. Four calcium treatments (no calcium application, spraying 2500 ppm calcium nitrate in two stages (tuberization and 20 days after tuberization) and spraying 2500 ppm calcium nitrate in three stages (tuberization, 20 and 40 days after tuberization), and soil application of 75 kg/ha calcium nitrate in two stages (tuberizatin and bulking stages) were in sub-sub plots. The measured characteristics included the amount of calcium in the leaf and tuber, the amount of reducing sugars, total sugars and starch in tuber and the rate of rottenness of tubers after 60 days storage. Results and discussion The results showed that Sante and Satina cultivars had the highest amount of calcium in the tuber, and Milva cultivar had the lowest calcium content. The heat stress at the end of the growing season in delay sowing increased the amount of total and reducing sugars of tubers. The application of calcium especially its soil application, in both delay sowing and suitable sowing time reduced the amount of total and reducing sugars and increased starch and calcium content of the tubers and calcium content of leaves. The application of calcium nitrate in delay sowing reduced the amount of total and reducing sugars as compared to control (non-application of calcium in delay sowing) by 19.4 and 21.9 % respectively, which indicating the impact of calcium application under heat stress conditions on decreasing the tuber sugars and improving quality of tubers. Soil application of calcium in delay sowing reduced the amount of reducing sugars compared to foliar application. Interaction of soil application of calcium nitrate in suitable sowing time (non-stress) and delay sowing (heat stress) had the highest starch and calcium content, respectively. The interaction of sowing date and calcium application on the rate of rottenness of tubers after 60 days storage indicates that the highest levels of rottenness related to the no calcium application in delay sowing, which can be due to impact of higher temperature (heat stress) at the end of the growing season. The application of calcium reduced the rate of rottenness of tubers, so that the reduction in the rate of rottenness of tuber in the soil application of calcium nitrate in delay sowing compared to control (non-application of calcium in delay sowing) was 30.5 percent. There was significant positive correlation between rottenness of tuber and tuber sugars, and significant negative correlation between rottenness with starch and calcium of tuber. The mention results indicate the role of calcium application in improving the shelf life and storage of potato tubers. Conclusions The application of calcium in delay sowing (under heat stress) reduced the total and reducing sugars and increased starch and calcium content of the tubers compared to control. Probably due to the effect of calcium on reducing the amount of tuber sugars, as well as its role in strengthening the cell wall of the tuber tissue, the rate of rottenness of tuber decreased. Therefore, the application of calcium nitrate especially its soil application by 75 kg/ha, in order to increasing the shelf life and storage of potato tubers, is recommended in delayed planting in warm southern areas of the Iran.