Salinity stress mitigation by humic acid application in strawberry (Fragaria x ananassa Duch.)

To consider the interaction effects of salinity (0 and 50 mM) and hurnic acid (0,150 and 300 ppm) on vegetative, yield and physiological characteristics of Kurdistan and Paros strawberry cultivars, an experiments were conducted during 2014-2015 growing seasons. Implementation of salt stress decreased almost all vegetative traits in line with the change in some studied biochemical and physiological responses. Under salt stress conditions, more Na+ accumulated in shoot and root of both cultivars while K+ content decreased. In contrary, humic acid reduced Na+ and increased K+ accumulation under salinity treatment. Salinity stress increased leaf necrotic area, the activity of antioxidant enzymes, hydrogen peroxide, lipid peroxidation, proline and total soluble carbohydrates while the supplementation of nutrient solution with humic acid recovered these traits and increased salt tolerance index. Leaf relative water content, membrane stability index, chlorophyll content, total biomass and yield were also negatively affected by salt stress, however, humic acid mitigated the adverse effects of salinity on these traits. Principle component analysis (PCA) based on vegetative, physiological and yield traits across two strawberry cultivars showed that 96 and 87.1% of the total variance were explained by the first two principal components in 2014 and 2015, respectively. Moreover, The heatmap from hierarchical clustering analysis (HCA) showed that all the measured parameters under different humic acid and salinity treatments in 2014 and 2015 were grouped into four clusters. Similar trends were also observed in the PCA for almost all of the studied traits. One interesting result from the HCA and PCA score plot was that the related attributes (i.e. hydrogen peroxide, lipid peroxidation) were grouped together. According to our study strawberry plants fed with humic acid were able to compensate for the negative effects of salinity.