Climate Data and Delta-7-Stigmastenol Value
In this study, multiple regression analysis (multiple linear regression) was performed on climate data (Table 4) and delta-7-stigmastenol values by years. Unfortunately, multiple regression analysis could not be performed on the climate data of 2017, since the total precipitation values in 2017 were different from other years. Maximum temperatures of 31.9 °C, 32.0 °C and 33.2 °C in 2018, 2019 and 2020 were determined in Gaziantep, Şanlıurfa and Şanlıurfa, respectively. In Mersin, Gaziantep and Şanlıurfa, temperatures above 30 °C were detected in every three years. The maximum temperatures in 2018, 2019 and 2020 were determined in Gaziantep with 43.5 °C, 45.6 °C and 42.6 °C. In 2018, 2019 and 2020, the minimum humidity was determined as 32.2%, 30.8% and 44.0% in Şanlıurfa, Şanlıurfa and Antalya, respectively. The minimum average total precipitation was 0 mm=kg÷m² in Balıkesir, Hatay, Kilis and Gaziantep in 2018, Aydın, Kilis, Gaziantep and Şanlıurfa in 2019 and Bursa, Muğla, Antalya, Mersin, Hatay, Kilis, Gaziantep and Şanlıurfa in 2020.
TABLE 4 Monthly climate data (temperature, precipitation and humidity)
First of all, correlation analysis was made between climate data and delta-7-stigmastenol values, then 5 candidate climate data with the highest absolute correlation coefficient were selected and multiple regression analysis was performed (Table 5).
TABLE 5 Climate data by years and delta-7-stigmastenol correlation table
In Figure 2 there is a 3D scatterplot graph of the annual average temperature, annual average relative humidity and delta-7-stigmastenol value according to the varieties 2018 (a), 2019 (b) and 2020 (c).
As it can be seen from Table 1 and Figure 2 (a), in 2018 it is determined that the delta-7-stigmastenol values of Gaziantep (NY) and Bursa and Şanlıurfa (G) olive oils are above the limit value of 0.5%, while Mersin (A) olive oil is at the limit. In 2019, we observed that the delta-7-stigmastenol values of Manisa (G) and Mersin (A) olive oils is above the limit value of 0.5% (Table 1 and Figure 2 (b)). According to the Figure 2 (c) the delta-7-stigmastenol values of Bursa, Antalya, Manisa, Hatay and Şanlıurfa (G), Mersin (A), Muğla and Aydın (M) and Gaziantep (NY) olive oils are above the limit value of 0.5% (Table 1). According to the Figure 2 it is observed that the delta-7-stigmastenol values are high when the annual average relative humiditiesare low and the annual average temperatures are high. Efe et al. (2009) investigated the effects of temperature on the phenological and pomological characteristics of different olive cultivars in Turkey and found that extremely high and low temperatures had negative effects on olive growth, quality and yield. High temperature stress, especially high temperatures exceeding 35 to 40 C, affects olive leaf cell membranes and adversely affects olive plants by reducing the leaf water content. Unfortunately, these high temperatures it stops vegetative growth by reducing the rate of photosynthesis (Ozturk et al., 2021).
FIGURE 2 3D scatterplot graph of annual average temperature, annual average relative humidity and delta-7-stigmastenol values according to varieties in 2018 (a), 2019 (b) and 2020 (c)