Comparison of salinity tolerance of basil, Denaee thyme, hyssop and Moldavian balm medicinal plants seeds based on germination characteristics

salinity stress is one of the most important abiotic stresses limiting plant cultivation. Evaluation of germination characteristics under salinity stress conditions is one of the fastest methods for selecting resistant plants to this stress.

Ocimum basilicum L. (Basil), Thymus daenensis Celak. (Denaee thyme), Hyssopus officinalis L (Hyssop). And Dracocephalum moldavica L. (Moldavian balm) seeds were subjected under six salinity treatments (0, 3, 7, 10, 15 and 20 ds/m) in growth chamber with daily mean temperature 25 °C, night mean temperature 18 °C, day length 14 hours and night length 10 hours. After germination (emergance of 2mm root),were evaluated germination characteristics such as seedling fresh weight, fresh weight of radicle and shoot, ratio of shoot/ radicle weight, seedling length, length of radicle and shoot, ratio of shoot/ radicle weight, germination percentage, seed vigor index, germination rate, mean of germination time and tolerance index. Experiment was conducted as factorial based on completely randomized design with three replicates at research center of medicinal plants breeding and development, university of Kurdistan in 2018.

seeds of these plants were unable to germinate at salinity level of 10 ds/m or more. Mean of germination time, seedling weight and shoot weight in all of plants were significantly affected by salinity, but in other characteristics, effect of salinity was different depend on plant species. Germination rate decreased in all plants with increasing level of salinity. Basil and Moldavian balm seeds required the lowest and the highest time for germination, respectively. Seed vigor index similar to germination rate decreased with increasing level of salinity. The highest of seedling weight, shoot weight and radicle weight in all studied plants was observed in salinity level of 3 ds/m. It seems that increasing in weight at low level of salinity can be due to existence and efficacy of Na and Cl ions on membrane penetrability and also enzyme activity relevant to germination that finally will be led to increase in growth rate and seedling weight, but in continue with increasing salinity level and further decreasing of osmotic potential, division, turgescence and cell volume decrease and eventually weight loss in the seedling will be seen. Seedling weight of Basil, Hyssop and Moldavian balm decreased with increasing level of salinity, but seedling weight in Denaee thyme increased at first and then decreased with increasing in salinity level from salinity level of 3 to 7 ds/m. Seeds germination percentage of Denaee thyme, Moldavian balm and Hyssop decreased significantly with increasing level of salinity and in all of three mentioned plants, germination stopped in salinity level of 10 ds/m. But in Basil against to other plants, germination percentage increased with increasing level of salinity up to salinity level of 7 ds/m and then germination reach to zero with increasing in salinity level from 7 to 10 ds/m. The highest tolerance to salinity level of 3 ds/m was observed in Basil, Moldavian balm, Hyssop and Denaee thyme seedling respectively and the highest tolerance in salinity level of 7 ds/m was observed in Basil, Moldavian balm, Denaee thyme and Hyssop seedling, respectively. Whereas with increasing in salinity level, osmotic potential of water will be decreased, therefore water absorption by seed will be decreased and subsequently rate of metabolic activates in seed such as carbohydrates hydrolysis and breaking will be decreased and therefore germination characteristics such as percentage and rate of germination and also length of root and length of shoot will be reduced.

Generally, based on results of this research, it has been suggested that salinity had not unfavorable effects on germination until special level and even same to basil can be improved germination characteristics. But, if salinity be upper than tolerance threshold of plant, can lead to undesirable effects on germination characteristics. Tolerance threshold to salinity stress is varying in different plants and as the results showed, the highest and the lowest of tolerance threshold was related to basil and Hyssop, respectively.