**Abstract**

An important requirement for varieties is adaptation to growing conditions. The main indicators of water regime, photosynthesis, and productivity of representatives of different species of *Ribesia* (Berl.) Jancz. subgenus to drought and high temperatures have been studied. Quantitative and qualitative changes of the photosynthetic apparatus are the response to drought and high temperatures. The ratio of chlorophylls to carotenoids is considered to be one of the indicators of adaptability. The total water potential in red currant leaves depends on shoot growth, leaf age, berry formation, variety, and weather conditions, and it is not the main indication of drought resistance. The ratio of bound and free water and water-holding capacity of the leaves is considered to be a determining sign of resistance to hyperthermia. Red currant genotypes do not possess high indicators of heat resistance. The prospects of using physiological rapid diagnostic methods in breeding for adaptability to destructive factors of the growing season are shown. The representatives of *Ribes petraeum* Wulf. ("Hollandische Rote") and *R. multiflorum* Kit. (1426-21-80) have high levels of drought resistance, making them highly potential for wider growing in (semi)arid agroecological condition.

**Keywords:** *Ribesia* (Berl.) Jancz. subgenus, genotypes, drought resistance, heat hardiness, water regime

#### **1. Introduction**

The ecological factors of the environment play an important role in the resistance of fruit plants, their productivity, and crop quality [1, 2]. Global climate change is now threatening. Air and soil summer droughts reduce the quality and quantity of horticultural products. Weather anomalies lead to an imbalance of the protective mechanisms of fruit and berry crops and adversely affect the physiological processes occurring in plants [3, 4]. Recently, the task to obtain new high-yielding, precocious genotypes with an amplitude of adaptation to different conditions, with a high content of nutrients and biologically active substances in the fruit, is faced by scientists from different countries [5]. The search of express methods of plant diagnostics to destructive factors of the environment is a priority direction. It is known that the temperature increase causes morphological and anatomical, physiological, and biochemical changes, which affect the growth and development of plants and can lead to large economic losses

[6, 7]. The study of morphological features, structure of photosynthetic apparatus, and water exchange of plants in connection with the area of growth is the main condition for solving fundamental and applied problems in the biology of the culture. The use of physiological and biochemical rapid methods of diagnostics of plant resistance to adverse weather and climatic factors can significantly optimize the long breeding process, minimize crop losses, and obtain genotypes resistant to the destructive effects of climatic anomalies [8–10]. Plant organisms have different mechanisms of adaptation to stressors [9, 11]. Xeromorphic structure of a plant leaf, changes in a pigment complex, and water balance are important diagnostic signs of drought resistance and heat resistance [12–14]. Issues of adaptation of berry crops to drought and high temperatures are poorly studied. Red currant is one of the valuable berry crops due to the high content of vitamins, microelements, sugars, and organic acids. It is valued as a source of healthy nutrition [15–18]. Vitamin and the healing properties of the berries of this culture are also preserved in processed products [19]. Introduction is considered to be an important link in the distribution and production of new red currant genotypes. The success of the introduction is determined by the nature of the interaction of hereditary biological characteristics of plants with specific environmental conditions [18]. Red currants belong to the *Ribes* L. genus and *Ribesia* (Berl.) Jancz. subgenus. As a culture, it was developed on the basis of four species, i.e., *Ribes vulgare* Lam., *Ribes petraeum* Wulf., *Ribes multiflorum* Kit., and *Ribes rubrum* L., and their hybrids [20]. The world assortment of the *Ribes* L. genus includes more than 200 varieties; however, the genetic resources of the *Ribesia* (Berti.) Jancz. subgenus are poorly studied, since there are a number of wild species that exceed the existing varieties by a number of economic and biological characteristics [21].
