Ecological conditions and limiting factors of mandarin (Citrus reticulata Blan. var. unshiu Tan.) cultivation in the subtropics of the Black sea coast of Russia

Abstract. The main environmental factors determining the optimal conditions for the growth of the main species of the genus Citrus on the example of mandarin (Citrus reticulata Blan. var. unshiu Tan.) and limiting factors of environmental impact on plants are considered. The most informative sources in this case are: temperature (minimum, average, maximum) and the amount of precipitation). The study of weather conditions of five growing seasons (2019-2023) revealed the main environmental factors that expose early-maturing (Kawano-Wase) and late-maturing (Unshiu) citrus varieties in the subtropical zone of Russia to waterthermal stresses. The likelihood of devastating frosts (-5 °C for lemon and -12 °C for mandarin and orange) pose a threat to citrus farming in this region. The relationship between precipitation and HTC is shown. The correlation coefficient is statistically significant r = 0.98. The connection is strong and direct. The largest number of temperature stressors (seven) has been established in 2020, 2022, and 2023. At the same time, the maximum temperature reached from 26.9 °C – 2.10.2022, to 35.9 °C – 6.08.2023. Frosts were not critical, the minimum temperature reached -7.2 °C (09.02.2020) and -4.3 °C (23.12.2021). The last frost – -2.4 °C was observed late on March 18, 2022, but was no longer dangerous for plants. The lack of precipitation creates a stressful situation along with the temperature. 2020 was the most critical year due to the values of this indicator. Precipitation was distributed: 25 mm in June, 11 mm in August and 30 mm in September, that is only 66 mm (19 %) with a norm of 341 mm. Water deficiency affects the growth, generative processes and metabolism of mandarin plants. Mandarin plants exposed to stress exhibit adaptive responses to stressors regardless of the biological characteristics of low-growing (Kawano-Wase) or strong-growing (Unshiu) plants varieties. Keywords: vegetation, environment, stress, adverse effects, temperature