Influence of Planting Date and Foliar Application of Antifreeze Compounds on Some Morpho-physiological Traits of Potato Cultivars in Ardabil Region

Potato (Solanum tuberosum) is one of the most important food products in the world, which is rich in carbohydrates, proteins, vitamins and other nutrients. Choosing the suitable planting date and cultivars is one of the most important and effective ways to reduce the negative effects of environmental stresses on potato characteristics. Cold stress is one of the limiting factors for production of agricultural crops. One of the adverse effects of this stress is increasing the biosynthesis rate of reactive oxygen species that causes oxidative stress. Plants have enzymatic and non-enzymatic mechanisms to overcome oxidative stress. The enzymatic antioxidant defense system includes different enzymes such as superoxide dismutase, catalase, polyphenol oxidase, guaiacol peroxidases and ascorbate peroxidase, and the non-enzymatic antioxidants include the soluble sugars, proline, carotenoids and other compounds such as flavonoids, and polyphenols. Nowadays, application of antifreeze compounds in agriculture is widely used technique to overcome chilling injuries. These substances are quickly absorbed by plants and increase the metabolic activity rate of plants. As a result, the amount of antifreeze proteins, amino acids, carbohydrates, lipids, vitamins and minerals increases in the plant organs leading to more resistance rate of plant cells against freezing. Potassium is one of the elements that reduces the effects of environmental stresses such as drought, salinity, high temperatures, cold, etc. through the accumulation of soluble carbohydrates and osmotic regulation. Also, potassium plays a role in regulating the activity of enzymes related to the detoxification of reactive oxygen species. The aim of the current study was to investigate the influence of cultivar, planting date and foliar application of antifreeze compounds on some of most important morpho-physiological characteristics of potato crop.           

The current study was conducted as a split-factorial experiment based on randomized complete blocks design with three replications at Ardabil Agricultural and Natural Resources Research Station during two cultivation seasons (2018-2019 and 2019-2020). The investigated factors included planting date in two levels (August 1st and 11th), foliar application of antifreeze compound at two levels (foliar application with a mixture of Frezzebon amino acid + potassium, and water as a control) and potato cultivars at 10 levels (901375, 901475, 902375, 8708-7, 8709-106, 7009-3, 905675, 8707-26, Agria and Savalan). Foliar applications were performed at the end of the growth season as same time as the increased likelihood of cold weather (considering the weather forecasts and the measured temperatures in the field and their correlation, one week before the possibility of temperatures below 7 ºC). Furthermore, before the spraying treatments, samples were taken from the experimental treatments and frozen using liquid nitrogen and stored in a freezer. After 24 h of freezing, the samples were again collected from the experimental treatments and rapidly frozen using liquid nitrogen before being transferred to the laboratory for measurement of the desired characteristics. After collecting the samples, laboratory experiments were conducted at the Faculty of Agriculture of Ardabil University of Medical Sciences and the Agricultural and Natural Resources Research Station in Ardabil.

Based on the obtained results, it was found that the foliar application of the amino acid Freezbon combined with potassium increased the yield, number of tuber per plant, leaf relative water content, proline and the activity of antioxidant enzymes. Also, the planting date of August 1st has the highest yield, number of tuber per plant, leaf relative water content, potassium and proline content, and the activity of catalase, superoxide dismutase and polyphenol oxidase enzymes. In terms of yield, 901475 cultivar had the highest yield (43.02 ton ha-1) and Agria cultivar had the lowest yield (26.35 ton ha-1). Among the cultivars studied, 8708-26 cultivar had the highest leaf relative water content, potassium and sodium content. The maximum content of proline and antioxidant enzymes activity were related to 7009-3 and 8707-26 cultivars. Based on these results, it seems that the planting date of August 1st and the foliar application of Freezbon with potassium can enhance the cold tolerance threshold, growth, and performance of potato cultivars in regions with cold weather by regulating physiological and biochemical responses. The results of the current study in line with the observations of the other conducted researches on different horticultural crops demonstrated that choosing appropriate planting date and application of antifreeze compounds positively influence the accumulation rate of osmoprotectants, cells antioxidant capacity and plant water and nutrient status resulting in a significant increase in cold resistance rate of plant cells.

Foliar application of antifreeze compounds Frezzebon amino acid + potassium, and planting date on August 1st can positively influence potato cultivars yield and physiological characteristics under cold conditions, therefore this foliar treatment and planting date are recommendable to overcome negative effects of cold stress on potato characteristics in cultivation reigns with cold weather.