عنوان مقاله [English]
Belonging to the Lamiaceae family, Daenensis thymus is a wild plant and native to Iran which grows in habitats with suitable environmental conditions. In the recent decades, by discovering the side effects of chemical drugs, the demand for herbal medicines and substances has been increased; therefore, manufacturers of medicines and industrial products have sought to increase the production of this plant. To do this, the environmental conditions of the farm, especially its weather conditions, should be quite similar to the habitat of the plant to maximize the yield of the crop. The aim of this study was to investigate and determine the calculation of plant thermal needs and also to investigate the dry and wet yields in three elevation zones (950, 1650, 2220) in Kashan, Nabar and Berezk located in northwest of Isfahan in Kashan city so that its favorable cultivation areas in these areas are identified for further production and introduced to scientific centers and pharmaceutical industries of the country.
Materials and Methods
To conduct the study, thymus Daenensis seeds were planted in the greenhouse on March 2017. Then, three experimental farms were constructed under three elevation zones of plain, foothills, and mountains in the northwest of Isfahan province located in Kashan city, which is one of the centers for planting and producing medicinal plants in the country. They were located in one area that plain, foothills, mountains have relatively small distances from each other and despite being located in a relatively hot and dry area, due to the difference in height, they have a climate diversity in the local area. When the seedlings were ready to grow in the field in May 2017, they were transported to the constructed sites; farm (1): Dares Salaam area located in Kashan with geographical coordinates were E,(29°51N,̍57°33) at an altitude of 950 meters above the sea level, farm(2): Berzak located in the northwest of Isfahan province and southwest of Kashan E,) ̍14°51N,̍45°33) at an altitude of 2220 meters above the sea level, and Farm (3): Nabar village 17 km in the north of The Berzak district at the position of E (12°51N ,̍51°33) at an altitude of 1650 meters above the sea level. They were planted through a completely randomized blocks design with 3 replications. In this study, the data used in the constructed farms were collected. These data included phenological information and climatic parameters. To record climate data in each region, automatic meteorological devices were installed by meteorologists and the necessary climatic parameters were collected by them. Due to the proximity of the Kashan farm to Kashan synoptic station, the data related to this region were taken from this station. Finally, the collected data were analysed and the findings were extracted.
At harvest time, morphological traits were measured on 10 booths each year and dry and wet yields were determined. All data were analyzed by IBMSPSS20 software and Duncan's multi-range test was used to compare the mean of traits.
Two common methods of effective degree-day and active degree-day were used to calculate the required temperature in phenological growth stages of the plant. In the effective degree-day method, the biological base temperature of the plant is used and in the active degree-day method, usually the zero degree temperature is used as base temperature.
The effective degree-day is determined through the equation 1, where Tb is the base temperature and Tᵢ is the average daily temperature and n is the time space between the two growth stages based on day.
the base temperature is considered 4c in order to calculate the effective temperature(Ashorabady et al 2016).
Results and Discussions
The results showed that thymus Daenensis plant needs 4160.3, 1946.1, 1947.8 degrees per day in terms of effective degree-day and 4820.3, 2298.1, 2391.8 degrees active degree-day, respectively, to complete its biological activities from transplanting to the end of flowering period in the first year. In addition, in the second year, the plant, totally, requires 1091.8, 874.5, 911.7 according to the effective degree-day and 1363.8, 1146.5, 1271.7temperature unit based on active degree-day to complete its biological activities from vegetation to the end of flowering period in Kashan, Nabar, Barzak farms. In the first year, it took 162, 89 and 109 days, respectively from the time of planting thyme until the end of flowering in Kashan, Nabar and Barzak regions (July20 & 21th). Therefore, from the beginning of the flowering phase to the end of flowering in Kashan, Nabar and Barzak areas, it took 109, 32 and 35 days, respectively. The results indicated that although Kashan enters the flowering stage earlier than other regions, the duration of flowering period in this region is much longer than other ones, which can be pertinent to the increasing of air temperature during the flowering period. Hence, temperature increase has stopped the growth period of the plant in the above-mentioned area and caused the flowering period to be longer.
The specific findings of the present study demonstrated that if the date of cultivation is not proportional to the climatic conditions of the planting site and according to the trend of increasing Julius days on which the ambient heat increases, based on the amount of energy from the environment and in the desired range of each phase and from low to high in the growth process, the plant will be disrupted in its different growth phases and will suffer from heat and cold stress. To get rid of it, we have to consume more energy and as a result, if it survives resilience against unfavorable conditions, the duration of growth will be increased and may not be able to produce seeds due to delays in the resucogenic stage and sterilization process. However, when it harvests in determined date, although the duration of each phase and the amount of energy gained in each region are different, the total amount of energy acquired in all regions will be approximately equal. Comparing the findings of the second year of cultivation showed that although the amount of energy gained in each phenological phase and the length of that phase in all three regions in the second year was different, the total degree-days of growth in all three regions were approximately equal. This finding showed that the use of this law as a model of prediction and decision making is absolutely correct and very careful if all stages of growth are done in an environment and under normal (not stressful) conditions. The best weather conditions for obtaining the best yield of wet and dry crops are 24138.2 and 6568.2 kg/ha, respectively. The weather conditions are similar to the foothills (Nabar) area located at an altitude of 1654 meters above sea level. After that, the best weather conditions for this plant are conditions that in mountainous regions during growth period, the average minimum and maximum temperatures are 9 and 23 and in foothills, equal to 12 and 24 degrees Celsius, respectively.
Keywords: daenensis thymus, thymus phenology, medicinal plants, Kashan city