The physiology of salt tolerance of lentils genotypes (Lens culinaris Medik.) in seedling stage

Salinity stress is one of the most important abiotic stresses which results in significant damages to agricultural production, which has affected about 20% of the world's agricultural lands, and its constantly increases. Plant responses to salinity stress have been depending on the severity, species, and even genotype. Different accessions of a species may also use different mechanisms to cope with salinity stress and complete their life cycle. Therefore, the identification mechanism of salt-tolerant plants is necessary to select plants for high salinity conditions. With the development of the cultivation of tolerance plants in saline soils, it is possible to use the soil more efficiently; but salt tolerance is controlled by complex physiological and genetic processes, and understanding these mechanisms is essential to improving yield in saline soils. Different strategies can be used to prevent a decrease in yield in these areas. Plant adaptation to salinity stress in low or medium salinity stress has been suggested as a way to increase plant yield in saline soils. Considering the importance of salinity stress and also the beneficial environmental effects of legumes on crop rotation as well as the role of physiological and antioxidant characteristics in salinity tolerance and genetic diversity between lentil genotypes, this study was conducted to select lentil genotypes under salinity in a controlled environment.

This study was carried out in hydroponic conditions in the greenhouse of the Faculty of Agriculture, Ferdowsi University of Mashhad Iran in 2019. The experiment was performed as split plots in a randomized complete block design with three replications. The 24 lentil genotypes were selected in the pretest and two salinity stress levels 12 and 16 dS.m-1 and 0.5 (control) were investigated. Seeds of lentil genotypes were prepared from the seed bank of the Research Center for Plant Sciences, Ferdowsi University of Mashhad. Seeds were sown in the hydroponic environment in the greenhouse with light and dark periods according to natural day length, day and night temperatures of 25 and 18 °C respectively with ±5 °C variations and natural light conditions. One week after planting, salinity stress was applied. Four weeks after applying salinity stress, traits including photosynthetic pigments, DPPH radical activity, malondialdehyde, total phenol, soluble carbohydrates, catalase, peroxidase, ascorbate peroxidase, osmotic potential, and proline were measured. To calculate the percentage of survival before salinity stress, the number of plants was recorded and before harvest, the number of live plants was recorded and the percentage of survival was calculated.

The results showed that at the salinity of 12dSm-1 MLC6, MLC12, MLC26, MLC120 and MLC178 had a survival of over 60%. Under 16dSm-1 salinity except for MLC57, MLC73, MLC94, MLC104, and MLC108 genotypes, other genotypes survived and MLC178 and MLC26 genotypes had the highest survival with 30% and 25%, respectively. With increasing salinity stress levels, the content of chlorophyll a, total photosynthetic pigments, and total phenol in all genotypes had a decreasing trend. Chlorophyll a content increase with an increase salinity from controll (0.724 mg.g-1 Fw) to 16 dSm-1 (0.220724 mg.g-1 Fw). Osmotic potential with increasing salinity was a more negative state of values at 16dSm-1 of MLC178     (-3.91 MPa) and MLC26 (-5.62 MPa). Increasing salinity stress from 0.5 to 16 dS.m-1 increased inhibition of the free radical activity of DPPH, activity of catalase, peroxidase, and ascorbate peroxidase in MLC117 and MLC178 genotypes. Also, except for two genotypes, MLC5 and MLC14, the other remaining genotypes had a good ability to reduce the osmotic potential at the salinity of 16dSm-1. Principal component analysis (PCA) showed that the first component explained 50.14% of the changes and properties related to photosynthetic pigments and osmotic potential and the second component explained the antioxidant properties, metabolites, and survival percentage with 12.66%.

Generally, results showed the superiority in most of the studied traits of the MLC6, MLC12, MLC26, MLC117, MLC120, and MLC178 compared to the total average. Due to the relative superiority of this genotypes of genotypes, it is recommended that perform additional studies to evaluate their salinity tolerance in field conditions.