The effect of different priming treatments on germination, morphophysiological, and biochemical indices and salt tolerance of basil (Ocimum basilicum L. cv. Keshkeni Levelou)

Introduction Basil (Ocimum basilicum) is one of the most important herbs of the Lamiaceae family, which is used as a medicinal herb, spices and fresh herbs . Salinity is an environmental factor limiting the growth and plant production ability . Delay in germination, decrease in the rate and percentage of germination and delay in emergence of radicle and plumule are the effects of salinity stress in the germination stage, which subsequently causes decrease of seedling growth. S Seed priming is one of the best biological methods for seed resistance during early germination and growth stages. Seed priming with different osmotic compounds increased the plant's compatibility with salinity and reduced the effects of ionic toxicity in salinity conditions. These studies were carried out to investigate the effect of seed priming on seed germination, morphophysiological and biochemical indices and increase salinity tolerance in basil seedlings for selecting the best treatments. Materials and methods In order to investigate the effects of types of seed priming on the some germination, morphophysiological and biochemical characteristics of basil under salinity stress, two individual experiment was conducted as factorial based on completely randomized design with 3 replications in the laboratory and greenhouse of Agriculture Faculty, Ferdowsi University of Mashhad. First factor included seed priming (sodium nitrate (3%) for 6 h, salicylic acid (0.5 mM) for 12 h, hydro priming with distilled water for 24 h and without priming). The second factor included NaCl stress at three levels (0, 50, and 100 mM). In first experiment, petri dishes were washed and heated at 120 °C for 2 hours to disinfect. After seed priming, they dried in a darkness condition. Then, in each petri dish, two layers of Watam's filter paper with 25 healthy seeds were placed. To apply salinity, 5 milliliters of various concentrations of NaCl (0, 50 and 100 mM) was added to each petri dish and the edge of them was covered with parafilm. Then, petri dishes were placed in germinator (25 °C, darkness and 85% relative humidity). Germination percentage and rate, average germination time, seedling vigor index, length of radicle and length of shoot, fresh and dry weight of seedling were measured. In second study, after applying different priming treatments, the seeds planted in cemetery at 1 cm depth of soil and at 4 points in the middle of the mowing period. After emergence of the seeds, the two-leaf thinning was performed so that at each point a healthy seedling (four plants per pot) was selected from among them. Application of salinity stress with irrigation water was carried out for 4 weeks (until flowering) when the plant reached stage 8. Results and discussion The results of first study showed that seedling growth factors were affected by priming treatments. Priming had a positive effect on germination percentage at high concentration of salinity. The results showed that seeds priming with hydro-priming, at the highest concentration of salinity (100 mM) had the highest germination percentage. The highest seed germination rate was recorded in priming with hydro-priming. Fresh and dry weight seedlings were also affected by priming. Priming in salinity stress condition improved these traits in basil seedlings. Salinity reduced the length of radicle and plumule, but priming with potassium nitrate and salicylic acid had a significant effect on the length of radicle and plumule compared to the control, respectively. Therefore, it seems that in primed seeds, due to the progression of seed activities for germination, the duration of exposure to limiting factors in salt stress conditions is reduced, and the seed will be less affected by stress due to greater readiness for rooting out. In other words, the ability to absorb more water in primed seeds than seeds without priming has a positive effect on germination indices. Our findings of second experiment indicated that morphological traits were significantly decreased with increasing salinity stress. Also, the highest chlorophyll a (7.12 and 6.33 mg/g fresh leaf) was obtained in control (without salt stress) and 50 mM salinity stress for plants which raised from seed priming with distilled water, respectively. The highest levels of antioxidant activity of leaf extract (80.66%) and total phenolic content (0.87) were observed in plants of obtained from primed seeds with distilled water under salinity stress of 50 and 100 mM respectively. The highest relative water content (71.55%) was observed in non-stressed treatments from plants which raised primed seeds with potassium nitrate. Conclusions Regarding the importance of germination stage in plant cultivation and also the environmental stress such as salinity, improving this growth stage in stressful conditions will have an effective role. So, priming of basil seeds will provide suitable metabolic in seeds and improve germination percentage and other growth factors. Seed priming also moderately reduce the harmful effects of salinity and improved some of the basil morphological, physiological and biochemical traits under salt stress conditions through its positive effect on germination and plant growth. In general, the results of this study showed that basil seeds priming with hydroperiming improved germination and growth traits of seedlings under salt stress conditions and applied them to improve germination basil is recommended under these conditions. Moreover, salt stress reduced basil plant growth, and hydroperiming somewhat reduced the damage and improved plant growth. Therefore, it can be stated that under moderate salinity stress condition (50 mM) and without salt stress (control), the growth of basil especially which raised from hydroperiming seeds (distilled water), improve.