The Effect of Weather Conditions in the Dry Subtropics on the Phenolic Compounds Accumulation in Olea europaea L. during the Cold Period

We studied the effect of the cold season climatic parameters on the phenolic compounds (PC) amount in the leaves of three Olea europaea L. cultivars (Nikitskaya, Coreggiolo, Ascolyano) and subspecies O. europaea subsp. cuspidata (Wall. and G. Don) Cif. growing in dry subtropical conditions on the Southern coast of Crimea. Based on the data for the 8-year research period, it is shown that cold winters with stable temperatures below 5°C lead to a stable low amount of PC, while unstable weather with sharp changes in heat/cold stimulates their accumulation. Significant changes in the PC content in leaves of O. europaea genotypes during cold periods with sharp temperature fluctuations may be due to the activation of growth processes. It was revealed that the weakly frost-resistant subspecies O. europaea subsp. cuspidata is characterized by the highest PC amount, whereas the frost-resistant cultivar Nikitskaya has the lowest one. These data characterize high efficiency of the antioxidant system in Nikitskaya cultivar. The results of three-factor analysis of variance showed that the variability in the intensity of PC biosynthesis in the cold season depends more on the weather conditions of a particular year (67.5%) than on the genotype (2.6%). A reliable positive correlation between PC accumulation and the sum of precipitation, and a negative relationship with the duration of sunshine was established. Multiple regression equations were made in order to show the correlations between the amount of PC in leaves of O. europaea genotypes and environmental conditions in the cold season of the year: sunshine, precipitation and air temperature. The results obtained confirm the value of PC for the realization of protective mechanisms in O. europaea, against the unfavorable external conditions pressure during the cold period.