Estimation of introduced apricot cultivars drought resistance by the intensity of leaf chlorophyll fluorescence

In the conditions of the south of Russia in July-August, there is often a lack of moisture, which negatively affects important physiological processes that provide formation of the apricot fruit crop. The aim of the research was to study the fluorescence intensity of apricot leaf chlorophyll in the process of dehydration and to select the cultivars characterized with high drought resistance. In the experiment, leaves of four apricot cultivars were included: ‘Kryimskij Amur’ (control), ‘Budapest’, ‘Mindalnij’ and ‘Hong Iu’. Chlorophyll fluorescence was measured by a portable fluorometer “Floratest”. The studies were carried out in the second decade of August 2015-2016. Initial fluorescence levels after irradiation (F₀), maximum (F_m) and stationary (F_st) values after the light adaptation were recorded. Short dehydration (4 h) resulted in an increase of the fluorescence parameters. Long-term dehydration (24 h) caused a significant decrease of all the studied indexes. The lowest values were observed in ‘Kryimskij Amur’ (control) that demonstrated its lowest drought resistance in comparison with other studied cultivars. After a long wilting, leaf turgor in this cultivar restored poorly (7.5-64.5%). It was revealed a correlation (0.4-0.8) between the calculated fluorescence parameters and the total water content in the leaves. ‘Budapest’ was characterized by a slow loss of moisture and due to this high (32-81.4%) restoration of leaf turgor after 24 h wilting. However, indexes of leaf chlorophyll fluorescence hardly regenerated after a long wilting. In ‘Mindalnij’ leaf turgor was restored more slowly after a long wilting (7-62.4%), but it was characterized with high photosynthetic activity at low water content. ‘Hong Iu’ demonstrated high values of fluorescence process regeneration, as well as leaf turgor restoration. It was characterized with a high potential and is promising for the regions with insufficient water supply, as well as for use in breeding for drought resistance.