SELECTION OF THE APRICOT (ARMENIACA VULGARIS LAM.) CULTIVAR-ROOTSTOCK COMBINATIONS TO CREATE INTENSE ORCHARDS IN THE UKRAINE`S LISOSTEPPE

Abstract

To establish intense apricot orchards it is of importance to select correctly a cultivar and rootstock since the trees growing energy and their longevity and early maturity depend just on cv and rootstocks. Today the mentioned crop is cultivated in Ukraine mainly on the wild apricot seedlings and myrobalan plum. It causes too high growing energy of the trees and technological inconveniences as regards the management of such orchards. In this connection the use of adapted cultivar-rootstock combinations with low growing energy is actual for the Ukraine`s Lisosteppe. They would provide low growing energy of trees, early beginning of their fruit-bearing and high stable yield.

Our researches were carried out at the Institute of Horticulture (NASS) in 2011-2016 in the apricot orchard planted in the year 2008 where the comparative appreiation of promise winter-hardy cvs was conducted bred at IH NASS (Osoblyvy Denysyuka – middle-ripening and Krasen` Kyyeva – late ripening) on different rootstocks in orchards with optimally dense planting, namely: on seedling rootstocks (wild apricot seedlings – control) and myrobalan plum – under the planting plan 5 x 4 m and on the clonal ones (VVA-1, Druzhba and Evryka 99) – 
4 x 2 m according to the accepted methods. In the process of the investigations the trees on VVA-1 and `Druzhba` have appeared to have the lowest growing energy. Since the volume of the crown on them is 35.8 – 46.1% and on Evryka 99 is 48.8- 50.7% as compared to the wild apricot seedlings the first two clonal rootstocks under the methods of their growing energy estimation have been included to the group of semi-dwarf rootstocks and the third one to those with the low growing energy. The mathematical modelling contributed to determine optimum planting plans for the trees on the mentioned rootstocks and to establish that the explored cultivar-rootstock combinations were perspective for intense orchards in the region where the studies were carried out.

The trees had high shoot formation power and anchoring of the root system in all the variants of the experiment. The symptoms of the incompatibility were not observed. In the fourth year after planting under favourable hibernation conditions and during flowering the first marketable crop was attained which was the highest by the trees of the cultivar Krasen` Kyyeva on seedling rootstocks (16.1-
17.1 kg/tree), somewhat lower on VVA-1 (14.4 kg/tree, on Evryka 99 and Druzhba 13.2-13.5 kg/tree. The productivity at the rate of the crown volume at the beginning of the fruit-bearing proved the highest on the clonal rootstocks, in particular, on VVA-1 by 1.6-3.7 times (4.5 kg/m³) and Druzhba (1.9 kg/m³).

Concerning the research years the most productive year was 2013 when the six-year orchards of `Krasen` Kyyeva` with the orbicular crown on VVA-1 ensured 52.3 t/ha. Under the indicator of the specific productivity at the rate of 1 m<sup>3</sup> of the crown on an average in 2011-2016 the trees on VVA-1 exceeded those with the high growing energy on the seedling rootstocks by 2.9 times, on Druzhba by 1.8 times and on Evryka 99 by 1.5 times. The average yield in the investigations years of the same cultivar on VVA-1, Evryka 99 and Druzhba was higher than on the wild apricot seedlings by 112.9; 114.0 and 81.2 % respectively. Cv Osoblyvy Denysyuka had this indicator higher by 63.3-95.9 % respectively. `Krasen` Kyyeva` proved the most large-fruited. Its average fruit mass was 60.6-70.0 g while that of `Osoblyvy Denysyuka` 41.7-48.9 g.

So the clonal rootstocks VVA-1 and Druzhba which, as it has been mentioned are semi-dwarf and Evryka 99 has average growing energy being combined with the adapted inland cultivars Krasen` Kyyeva and Osoblyvy Denysyuka provide higher specific productivity (by 1.5-2.9 times) and high yield of the apricot trees as compared to those grafted on the seedling rootstocks and are perspective for the establishment of the researched crop intense orchards in the Ukraine`s Lisosteppe under their distribution density on Evryka 99  667-
889 trees/ha and on VVA-1 and Druzhba 1000-1250 trees/ha.

Summary. To establish intense apricot orchards it is of importance to select correctly a cultivar and rootstock since the trees growing energy and their longevity and early ripening depend just on cvs and rootstocks. Today the mentioned crop is cultivated in Ukraine mainly on the wild apricot seedlings and myrobalan plum. It causes too high growing energy of the trees and technological inconveniences as regards the management of such orchards. In this connection the use of adapted cultivar-rootstock combinations with low growing energy is actual for the Ukraine`s Lisosteppe. They would provide low growing energy of trees, early beginning of their fruit-bearing and high stable yield.

Our researchers were carried out at the Institute of Horticulture (NAAS) in 2011-2016 in the apricot orchard planted in the year 2008 where the comparative appreciation of the cultivar-rootstock combinations was conducted in the orchards with optimally dense planting, namely: on the seedling rootstocks (wild apricot seedlings – control) and myrobalan plum – under the planting plan 5 x 4 m and on the clonal ones with low growing energy (VVA-1,  Druzhba and Evryka 99) – 4 x 2 m according to the accepted methods. VVA-1 and Druzhba appeared to be semi-dwarf and Evryka 99 to have average growing energy. Being combined with the adapted inland cultivars Krasen` Kyyeva and Osoblyvy Denysyuka they provide higher specific productivity and yield of the apricot trees (by 1.5-2.9 times) as compared to those grafted on the seedling rootstocks and are perspective for the establishment of the researched crop intense orchards in the Ukraine`s Lisosteppe under their distribution density on Evryka 99 667-889 trees/ha and on VVA-1 and Druzhba 1000-1250 trees/ha.