Borage (Borago officinalis L.) response to salinity at early growth stages as influenced by seed pre-treatment

Knowledge of plant response to salinity, especially at early growth stages, is critical to optimizing crop production in salt-affected soils. In this paper we explore quantitatively the effectiveness of seed pre-treatment to lessen the effects of salinity on Borage (Borago officinalis L.) seed germination and subsequent seedling growth. Two independent experiments were conducted with nine salinity levels and five seed pre-treatments using Lake Urmia saline water (LUsw), ascorbic acid (Asc), proline (Pro), potassium silicate (K2SiO3) and spermidine (Spd). The first set of experiments was used to obtain the most effective pre-treatments for seed germination. The second set of experiments investigated the combined effects of salinity and seed pre-treatment concentration on the emergence process. Salinity was found to have considerable inhibitory effects on seedling growth, but pretreating the seeds alleviated some of these effects. Seedling response to salinity could be described well using the threshold-slope salinity response function of Maas and Hoffman (1977) and the S-shaped function of van Genuchten and Hoffman (1984). A means comparison (using Tukey's test) showed that the mean salinity threshold of all seedling traits, EC*, increased markedly (P <= 0.001). For example, EC* increased 60% using K2SiO3 as compared to the control, with Spd and Pro having less of an effect on on EC* than K2SiO3. The mean EC value at which various seedling traits were reduced by 50% (i.e., EC50) increased from 10.8 dS m-1 for the control to 12.5, 12.5 and 12.1 dS m-1 for the Pro, K2SiO3 and Spd pre-treatments, respectively. Statistically, the effects of Pro, K2SiO3, Spd on EC50 were essentially the same. The effects of Asc, and LUsw on EC50 were not significant compared to the control. The increased vigor of seedlings obtained by seed pre-treatment, particularly when using K2SiO3, should lead to more salt-tolerant plants and higher yield potentials in saline environments.