STRESS WEATHER FACTORS OF MANDARIN CULTIVATION (CITRUS RETICULATA BL. VAR. UNSHIU TAN.) IN THE SUBTROPICS OF RUSSIA

Abstract

The aim of the research was to study the weather risks when growing the main commercial citrus crop, mandarin, in the subtropics of Russia. The most informative sources for a complex of environmental factors are temperature and precipitations. The characteristics of the main weather factors are given, which can determine both the optimal growing conditions for the mandarine (Citrus reticulata Bl. var. unhiu Tan.) varieties ‘Unshiu’, ‘Iveria’, ‘Kovano-Vase’, ‘Miagava-Vase’, and limiting factors of plant cultivation in the studied region. Phenological observations have established that the first phase of “budding” depends on the sum of temperatures in March-April. It was 113 °C in 2015, 225 °С in 2016, 183 °С in 2017 and 244 °С in 2018. Flowering begins in May-June when the sum of effective temperatures reaches 502 °С, at min 490 °С and max 512 °С. The duration of the full period, from «budding» to «fruit ripening», varies depending on weather conditions: temperature, precipitation, and can last from 170 to 191 days. A more significant role in the timing of the onset and duration of the phenological phases of mandarin development is played by the water-thermal regime of the year. Weather factors manifested themselves on the growth processes of the studied varieties of mandarin. The total length of growth in ‘Iveria’ and ‘Kovano-Vase’ was higher than that in ‘Unshiu’ and ‘Miagawa-Vase’. The same feature was noted in the growing shoots of the vigorous variety ‘Unshiu’, it was 8.5 cm, and of the medium-sized ‘Iveria’ — 7.5 cm. For the dwarf forms ‘Kovano-Vase’ and ‘Miagawa-Vase’ it was 7.5 cm and 6.8 cm respectively. Weather conditions and the limiting factor (lack of atmospheric precipitation) have a negative impact not only on the timing of the main phenological phases of mandarin development (flowering, second growth of shoots), but also on their productivity.