فهرست مطالب وحید اردکانیان

Salinity as one of the environmental stresses, limits the growth and performance of plants. Plants hurt with exposing to the salty environment by negative osmotic potential of soil solution and aggregation of toxic ions such as sodium and chlorine. So, the need to select resistant plants to salinity has increased because of shortage in sweet waters and increasing in salinity of soils. In this study, the effect of humic acid application in reducing salinity stress in different varieties of radish was investigated. For this purpose, a pot experiment as factorial based on completely randomized design in three replications was carried out in experimental greenhouse of Ferdowsi University of Mashhad. Treatments consisted of three varieties of radish (Cherry belle, Sparkler and Scarlett cincinnati) as the first factor and humic acid in 2 levels of 0 and 1.5 grams per liter as the second factor and salinity stress at four levels of 0, 33, 66 and 99 mM NaCl solved in water as third factor. The results showed that in some physiological characteristics such as leaf solution sugar and potassium to sodium ratio in root were decreased in salinity stress. Humic acid reduced many harmful effects of salinity, particularly caused to significant reduction in sodium levels in different varieties of radish. Humic acid caused to increase electrolyte leakage, total chlorophyll and the ratio of potassium to sodium in aerial parts and root of radish. The highest and lowest amounts of electrolyte leakage obtained at 99 mM and 33 mM salt level without using humic acid, respectively. The highest (12 mg/g) and the lowest (8 mg/g) amounts of total chlorophyll were obtained in 33 mM and 99 mM salinity levels without using humic acid, respectively. The highest (110 micrograms) and lowest (50 micrograms) amounts of solution sugar were observed in 33 mM salinity without using f humic acid and 99 mM salinity with humic acid application, respectively. Also the highest amount of rootsʼ anthocyanin at salinity level of 66 mM without using humic acid and the lowest amount in this salinity level with humic acid application was measured 3.5 and 1.8 mmol/fresh weight, respectively. Maximum rate of potassium of aerial parts and root were obtained in control level of salinity with 240 and 260 mmol kg-1, respectively. Moreover, the highest (4000 mmol kg-1) and the lowest (800 mmol kg-1) amounts of sodium in aerial parts were obtained in 66 mM salinity without the humic acid application and 99 mM salinity with humic acid application, respectively. The sodium content of root was much lower than aerial parts and its highest amount ​​was observed in 99 mM salinity without using humic acid with 670 mM per gram. Among the radishes varieties, the most effect of salinity and humic acid was observed on Cincinnati scarlet cultivar as that was allocated the maximum amount of many measured traits to it.

Salinity is a limiting factor in agricultural production that inflicts great damages on agricultural products. In order to decrease or stop salinity stress, numerous methods are proposed by different researchers. One of the methods to reduce the damages of salinity stress is cultivating tolerant plants to salinity. In this research, resistance of three radish cultivars to salinity stress was investigated, from physiological points of view, and the best resistant cultivar was introduced. This factorial experiment was carried out in Research Greenhouse of Ferdowsi University of Mashhad, Iran, based on complete randomized design, with three replications. Treatments included three commercial cultivars of radish (Cherry belle, Sparkler and Scarlett Cincinnati) as the first factor and four levels of salinity (control, 33, 66 and 99 mM NaCl) as the second factor. Salinity levels, as soluble form in irrigation water, were applied at the four-leaf stage of the plants. Results showed that salinity decreased the amount of soluble sugars and potassium content of aerial parts and tubers, and also increased stomatal conductance, anthocyanin content of tubers and sodium content of aerial parts and tubers. The highest tolerance of different radish cultivars to salinity stress was observed at 66 mM salinity level and the 33 mM salinity level had no significant difference, compared to control, in most physiological characteristics. Under salinity stress conditions, sodium accumulation in aerial parts was more than tubers. The highest amount of tuber anthocyanin was measured at 66 mM salinity level in Scarlett Cincinnati cultivar. Among the radish cultivars, the highest salinity tolerance and salt accumulation was obtained from Scarlett Cincinnati cultivar. Considering that the apparent shape of this cultivar (stretched appearance with red color) is very different from Cherry belle and Sparkler cultivars, and more water is stored in its tissues, thus, this trait has caused high resistance to salinity stress.