Evaluation of seedling emergence of basil (Ocimum basilicum L.) accessions under salinity and drought stresses

Basil (Ocimum basilicum L.) is a medicinal plant, annual herb of the Lamiaceae family. It is extremely important because of the large amounts of essential oils in the vegetative organs and the diversity of the secondary compounds in the essential oils. Salinity is one of the important factors limiting the growth of plants and causes osmotic stress and ionic toxicity. Drought stress reduces the rate and percentage of emergence and finally lead to delay seedling establishment. Therefore, tolerance to stress in the early stages of plant development is very important and seedlots that have the ability to germinate under stress conditions, have a successful establishment, have a good density and have a high crop yield. In this regard, the aim of this study was to identify tolerate basil accessions to salinity and drought stresses at the emergence stage. This experiment was conducted as a factorial based on a completely randomized design in 2017. Twenty basil accessions were planted under control, salinity and drought conditions in the greenhouse and seedling emergence were recorded daily. In this study rate and percentage of seedling emergence, mean emergence time (MET), and emergence energy (GE), genetic and phenotypic variations, coefficient of genetic and phenotypic variations, and broad sense heritability for the evaluated traits were calculated. The results showed that all of the accessions in the control conditions had a high emergence percentage of salinity and drought conditions. Under stress conditions, some of the accessions had high emergence percentage; the results of analysis of variance showed that the difference among the accessions for emergence percentage and rate, mean emergence time and emergence energy in the control conditions. However, most of these differences were not significant under drought and salinity stress conditions. This indicates the high susceptibility of the Basil, which, in the conditions of salinity and drought, has not been much disagreement among the accessions. In control conditions, the highest percentage of emergence was observed in Isfahan 2 accessions. Regarding the traits of emergence, the least time to emergence, the greatest energy of emergence of Shiraz accession was better than other accessions. In the conditions of control, the percentage of the accessions and the rate of emergence were higher in drought stress than in other accessions. In other words, the difference among accessions in terms of drought stress was lower. In the conditions of salinity stress, a similar trend was observed with drought stress, and the difference between the accessions in these conditions was less than the control conditions. In drought stress, the average time to emergence of Birjand (purple) in 7 days, and in Soiis and Gorgan in 11 days, it can be concluded that in drought stress of Birjand (purple) accession, less time needed for emergence and has better performance in dry soils, although its difference It was not meaningful with some other accession. With the stress, emergence energy decreased. The differences in emergence energy among accessions were significant in the control and drought conditions, but it was not significant in salinity conditions. In control conditions, the highest emergence energy was related to the Shiraz accession and the lowest amount of emergence energy was the Soiis accession. Also, under drought stress, the lowest emergence energy was associated with the Napoleonic accession and most related to the Malayer green accession. The results showed that Isfahan2 and Shiraz under control condition, Isfahan 2, 3 and Birjand under drought stress and Pishva (Green) and Zahedan under salinity conditions, had better seedling emergence and establishment than the other accessions. In this research, genotypic and phenotypic variances, genotypic and phenotypic variation coefficients and broad sense heritability were estimated for the traits. Finally, there was a good variation in tolerance of different accessions to salinity and drought stresses, which can be used to breed new basil cultivars tolerated to salinity and drought. It should be noted that further studies on essential oil content and yield of these accessions should be studied in future studies in order to make a better selection.