Germination, growth, and yield of rocket populations show strong ecotypic variation under NaCl stress

Abstract

Rocket (Eruca sativa L.) is an old native plant well adapted to diverse climates in Iran. It’s known for the ability to grow and produce seeds rich in protein and oil as well as edible foliage under marginal conditions and has a potential as a promising oil seed. Nonetheless, little is known about its response to salt stress. This study aimed to evaluate possible genetic diversity of local landraces of rocket in terms of salinity tolerance both in germination and whole plant level. In the first experiment, germination characteristics of seven ecotypes of rocket named based on the region of collection as Sirjan, Bardsir, Rigan, Shahdad, Abadeh, Lamerd and Darejove were assayed under increasing salinity from 0 to 18 dS/m. Increasing salinity decreased all germination indices but ecotypes significantly differ in the magnitude of response. Averaged over salinity levels and based on scoring values for final germination percentage, germination rate and seed vigor, one superior (Sirjan), one inferior (Bardsir) and one moderate (Darejove) ecotype were selected for further investigation in the second experiment in which plants were subjected to three salinity levels (1.8, 6 and 12 dS/m) in a hydroculture system and some of their biochemical, physiological and dry matter accumulation attributes were evaluated. Results showed that increasing salinity decreased grain and biological yield, relative water content, leaf chlorophyll content and leaf area but increased leaf carotenoids content, electrolyte leakage, proline and soluble sugars concentrations and shoot and root Na content. Also, in all three ecotypes activities of catalase, superoxide dismutase, guaiacole peroxidase and ascorbate peroxides increased in response to application of 6 or 12 dS/m salinity, but these alterations were not correlated with dry matter or grain production. Na shoot content, however, was closely and negatively associated with grain and biological yield and differ significantly among ecotypes. Interestingly, Bardsir, the least salt tolerant ecotype at germination, was the best in hydroculture experiment and often showed the highest values for the most growth parameters measured. These differential responses suggest a possible change in salt tolerance mechanism along with developmental stages transition.