Journal of Plant Process and Function

 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.