Cold tolerance, productivity and phytochemical diversity in sweet basil (Ocimum basilicum L.) accessions

Sweet basil (Ocimum basilicum L.) is a widespread cultivated aromatic herb in the world. Information about both morphological and phytochemical characterization is very important prior to beginning of any breeding project. Therefore, the present study was conducted to investigate diversity of sweet basil accessions in cold tolerance, essential oil yield and essential oil compositions. The average of cardinal temperatures for seed germination were 7.9 (Tb) 21.7 (To) and 35.5 °C (Tc) and for germination rate were 7.9 (Tb) 25.7 (To) and 39.7 °C (Tc). Cumulative temperature response index (C-CTRI) was used to identify cold-tolerant accessions and based on C-CTRI, Pishva I and Zahedan II were the most cold-tolerant accessions. There was wide variation for herbage yield and contributing traits of sweet basil in two sites. The highest herbage yield was observed in Isfahan III and Birjand I at the normal and salinity conditions. Salinity decreased herbage yield, but increased essential oil content in all accessions. The highest essential oil content was recorded in Malayer and Birjand I at the normal and salinity conditions. Methyl chavicol (25.7-93.0%) was the main constituents of the essential oils among sweet basil accessions. We found four chemotypes based on the presence or absence of oil components: (1) high methyl chavicol (>80%) like Reunion basils, (2) medium methyl chavicol plus linalool like European basils, (3) high methyl chavicol (70-80%) along with neral, geranial, or linalool (all of them around 10%), and (4) medium methyl chavicol plus neral and geranial. Considering the yield and quality traits, Birjand I was significantly superior accession over studied accessions and thus, it has good potential for the cultivation and production of methyl chavicol rich essential oil.