LAUSR

Abstract German chamomile (Matricaria chamomilla L.), is one of the common medicinal plants cultivated most significantly for its pharmacological applications. Environmental stresses, especially cold stress, affect the total amount of active ingredient in plants. The effects of various temperatures, including 25, 10, 5, and 0 °C at flowering stage, were investigated on important traits of 5 German chamomile genotypes ('Bodegold', 'Isfahan', 'Ahwaz', 'Zabol', and 'Shiraz'). A number of important morpho-physiological traits were measured and essential oil was extracted (using hydro-distillation method) from flowers. According to the results of variance analysis, genotypes had significant differences for the measured traits except for the number of shoots per plant, the number of flowers, and flower diameter. Temperature affected all the traits significantly, except for root length, root dry weight, and relative water content. Interaction of genotype and temperature was significant for the number of flowers, percentage of electrolyte leakage, and percentage of essential oil. The results indicated that, essential oil percentage increased from 25 °C to 10 °C and then decreased with increasing cold stress in all the studied genotypes. 'Shiraz' genotype indicated the highest values regarding root length (31.66 cm) and root dry weight (0.32 mg). The highest value of plant height (53.44 cm) was observed in 'Zabol' genotype. 'Bodegold' (1.51%) and 'Isfahan' (1.44%) genotypes had the highest essential oil percentage in the cold-stress condition (5 °C). But this trend was not observed for the number of flowers per plant. Classification of genotypes showed that in conditions with high possibility of chilling stress occurrence at flowering stage, 'Bodegold' genotype is the most efficient followed by 'Isfahan' genotype. On the other hand, 'Bodegold' genotype can be crossed with 'Ahwaz' and 'Zabol' genotypes in order to improve the cold tolerance of new genotypes. These findings can help the researchers to investigate gene expression and identifying genes involved in cold tolerance of chamomile plants.