Morphological Properties of Catharanthus roseus L. Seedlings Affected by Priming Techniques Under Natural Salinity Stress

Catharanthus roseus is a great medicinal plant used for treating diseases such as cancer, as it contains different biochemicals including terpenoids. Salinity is a major stress, significantly decreasing the growth and yield of medicinal plants, worldwide. However, to our knowledge, there is not any data on the growth improvement in C. roseus seedling under salinity stress using the priming techniques tested in the presented research. The objective was to investigate the effects of seed priming including hydro- (distilled water), osmo- (KNO3 1%), and hormonal priming (salicylic acid, SA 0.5 mM) on the seedling growth of C. roseus under natural salinity (salt obtained from Qom Lake, Iran) of 0, 2.95, 5.66, 8.13, and 10.66 dSm−1. The treated seeds were grown in Petri dishes and placed in a germinator (25 ± 1 °C) for germination and the growth of seedlings. The plant seedlings were planted in the greenhouse conditions and treated during the V6–V8 growth stage with the salinity treatments (a factorial design on the basis of a completely randomized block design with three replicates) under hydroponics conditions. Different morphological properties of C. roseus including the length and the dry weight of rootlet, plumule, and seedling as well as leaf relative water content (RWC) were measured. The results indicated the alleviating effects of different priming techniques on the growth of C. roseus under natural salt stress. Although the effect of priming was not significant on RWC, salt stress and its interaction with priming significantly affected RWC indicating that the alleviating effect of priming on RWC is a function of salinity level. With increasing the level of salinity, rootlet dry weight increased, which indicates the allocation of more carbon to the roots under stress. It is possible to plant C. roseus in saline fields using the priming techniques tested in this research work.