PRODUCTIVITY POTENTIAL OF DRUP FRUIT VARIETIES - BIOMORPHOLOGICAL FEATURES OF FORMATION AND REALIZATION UNDER THE CLIMATIC CONDITIONS OF SOUTH RUSSIA
Productivity, the main characteristic of a variety of fruit crops, which is due to a set of elements, determines the resistance of a crop to environmental stress factors and its suitability for industrial growing conditions. The impact of climatic stresses annually results in only 30-40% realization of productivity potential of fruit plants. In fruit plants, including sweet and ordinary cherries, fruit-bud differentiation takes a long time. In the conditions of the southern Russia (Prikubanskaya gardening zone of the Krasnodar Territory), it begins in July of the current year and ends in April-May of the next year. The climate in the Krasnodar Territory is quite mild, generally favorable for the cultivation of sweet and ordinary cherries. Nevertheless, even in the south of Russia, there is a high risk of annual abiotic stresses, negatively affecting fruit plants and impeding realization of their productivity potential. In the present work, a comprehensive biomorphological study was first undertaken to assess the regional productivity potential of sweet and ordinary cherries of various ecological and geographical origins. Our research aimed to establish the regional patterns of productivity element formation during morpho- and organogenesis in Prunus L. species and hybrids, to identify the most vulnerable stages in plant annual development cycles, and to distinguish the varieties with high and sustainable yielding under risky weather conditions. Three introduced Cerasus avium (L.) Moench varieties of different ecogeographic origins (Valerii Chkalov, Melitopolskaya Chernaya, and Polyanka), six domestic C. avium varieties (Kavkazskaya, Sashen’ka, Volshebnitsa, Dar izobiliya, Alaya, and Mak), four introduced C. vulgaris Mill. varieties (Kelleris, Nefris, Fanal, and Erdi Botermo), and seven interspecific hybrids C. vulgaris ½ C. avium (Kirina, Dombaziya, Duk Ivanovna, Duk Khodosa, Igrushka, and Shalun’ya) were studied during 2006-2019, Experimental Production Center of the North-Caucasian Federal Scientific Center of Horticulture, Viticulture, Winemaking, Krasnodar; 6½4, 7½3, and 5½3 m plant spacing). Cerasus mahaleb (L.) Mill. And Cerasus avium L. plants were rootstock plants, all experiments were arranged in three replications. Phenology of all stages and sub-stages of the annual (vegetative and generative) plant growth was described as per BBCH system (Biologische Bundesanstalt, Bundessortenamt and Chemische Industrie, Germany). Morphogenesis of yield components was investigated in 15 generative buds 2 times in December and February, weekly in March-April, and weekly in July-November by light microscopy (Olympus ВХ41, Olympus Corporation, Japan). In spring, flowers, ovaries, and fruits were gradually counted on third-order skeletal branches, and the degree of their reduction were calculated to estimate biological productivity. The number of fruit buds and growth buds was estimated 2 times a week in August and September. To assess the winter hardiness, 90 vegetative buds and 180 fruit buds from different sides of the lower and upper branches of 3 trees of the same variety were collected in 3 replicates. It was found that the reduction of productivity elements in the stressful conditions of southern gardening occurs annually at the same (critical) stages of development of fruit plants. These stages are i) reproductive organ initiation; ii) archesporium formation in anthers; iii) pollen mother cells, iv) mono- and binuclear pollen grains, and v) macrosporogenesis. The critical periods of yield formation in the conditions of the Krasnodar Territory are II-III decades of March, and I-II decades of April, May and July, when special agrotechnology should be applied to reduce the impact of stress and to increase yields. A direct correlation was revealed between temperature and air humidity during each critical period, the fruiting coefficient and the final yield ( r = +0,97, р < 0,001). In our tests, the following samples are characterized by high fruiting rates and sustainable yields: domestic cherry varieties Kavkazskaya (62 % and 31.3 t/ha, respectively), Alaya (46 % and 30.0 t/ha), Sashen’ka (45 % and 26.6 t/ha), and Volshebnitsa (42 % and 23.3 t/ha), interspecific hybrids Duk Khodosa (46 % and 23.3 t/ha), Kirina (44 % and 23.3 t/ha), and Duk Ivanovna (44 % and 20.0 t/ha), and an ordinary cherry variety Kelleris (45 % and 20.0 t/ha). These varieties and hybrids can be cultivated in commercial orchards and used as genetic donors in breeding for sustainable productivity.