Mutual influence of rootstock and scion in intensive fruit growing

Rootstock and scion form a single system where the above-ground and underground parts continuously influence each other. Roots synthesize organic compounds that directly determine the protein and nucleic acid metabolism of the scion. In turn, the canopy provides the rootstock with assimilation products and regulates the growth of the root system. For a gardener, this means that by selecting the right rootstock, one can manage the development, longevity, and yield of the orchard.

A compatible vigorous rootstock ensures powerful growth of the above-ground part, and the longevity of the root system directly determines the lifespan of the tree. Furthermore, the rootstock type affects the canopy habit—it can be shaped to be spreading or pyramidal. The correct choice of combination allows you to establish the desired orchard architecture at the planting stage.

Influence of rootstock on precocity and yield

The rootstock directly determines when an orchard will begin to produce a commercial harvest. On dwarf rootstocks, trees develop faster and enter the fruiting stage significantly earlier than on vigorous ones. At the same time, trees of the same growth vigor on different rootstocks demonstrate different productivity over the years.

• Start of fruiting on dwarf rootstocks — 2–3rd year
• Start of fruiting on vigorous rootstocks — 5–8 years
• Difference in productivity due to rootstock type — 1.5–2.0 times or more

Under the conditions of the Kuban horticultural zone in the Krasnodar Krai, the choice of rootstock significantly changes tree productivity. For example, the Renet Simirenko apple cultivar on M2 rootstock yields on average 23–34 kg more fruit than on M3 and SK1 rootstocks. The Korey cultivar shows high yield and canopy load on M3, M2, and SK1 rootstocks. However, selecting the superior SK1 rootstock allows for an additional yield of more than 6.0 tonnes of fruit per 1 ha without increasing current costs.

The rootstock determines not only the volume of the harvest but also the commercial properties of the fruit. On dwarf and semi-dwarf rootstocks, apples grow larger, color up faster, and ripen earlier. The rootstock also influences the biochemical composition of the fruit, altering their taste and shelf life during storage.

Cultivars and rootstocks are still being regionalized. Data from research institutions and the state cultivar testing network indicate that there is an urgent need to regionalize the best cultivar-rootstock combinations, identify low-productivity combinations, and cease the cultivation of their nursery plants. Accomplishing this complex task will be facilitated by the widespread use of methods for early diagnosis of the potential productivity of graft combinations developed at the North Caucasian Federal Scientific Center of Horticulture, Viticulture and Winemaking, which allow for the assessment of the prospects for cultivating grafted fruit plants in specific soil and climatic conditions as early as the first year of life. 3. Influence on resistance to adverse environmental factors. Many researchers have noted the influence of the rootstock on the frost resistance of the scion, its resistance to a lack or excess of soil moisture, etc. In these cases, the normal development of the rootstock and its ecological adaptability are important conditions for the general resistance of the scion and the tree as a whole. 4. Influence on the progression of phenological phases of growth and development of the scion. Usually, the rootstock does not affect spring phenophases. However, in the summer-autumn period of the growing season, a change in the timing of the end of shoot growth shoot growth, fruit ripening time, and autumn leaf fall is noted. These changes are especially clear in partially compatible graft combinations. 5. Influence of the rootstock on scion resistance to diseases and pests. A hardy and compatible rootstock non-specifically enhances the scion's natural ability to withstand diseases and pests, thereby increasing the overall resistance of the tree. Correspondingly, a rootstock affected by diseases and pests exerts a negative influence on the growth and fruiting of the scion. Since the scion retains its cultivar characteristics regardless of the rootstock it is grown on, changes in growth intensity, start, progression, nature of fruiting, etc., are within genetically determined limits. The cultivar often significantly changes the physiological and biochemical processes occurring in the rootstock and the growth dynamics of active roots. The scion can change root anatomy and, as our research results prove, their absorption capacity. Vigorous cultivars enhance the growth and branching of the root system. For instance, one-year-old Rozmarin Belyi trees have up to seven orders of root branching, whereas nursery plants of Kandil Sinap on the same rootstocks have only five. The extent of root systems also depends to a large extent on the scion. The architectonics of root systems are determined primarily by the type of rootstock, the characteristics of the soil, and agricultural practices. However, the grafted cultivar also influences the nature of root growth and placement. The root system of cultivars with a spreading canopy is characterized by wide root branching, and in nursery plants, by a large divergence angle of the skeletal roots. When noting the influence of the grafted cultivar on physiological and biochemical processes, as well as the anatomical and morphological structure of the root system, it should be kept in mind that the inherited characteristics of the rootstock prevail over the variability of its traits.

What influence does the rootstock have on the properties of the grafted cultivar? 2. Within what limits can the productivity of a cultivar be regulated by means of the rootstock? 3. How can the regularity of fruiting of a cultivar be influenced? 4. What influence does the cultivar have on the properties of the rootstock?

By selecting rootstocks, one can successfully regulate the growth vigor of a fruit tree, its precocity, productivity, regularity of fruiting, and fruit quality. One of the factors in the intensification of fruit growing is the rational use of dwarfing and semi-dwarfing rootstocks, which, in combination with cultivars suitable for intensive culture, allow for the creation of highly productive, less labor-intensive orchards adapted for widespread mechanization.

The winter hardiness and salt tolerance of trees, the strength of their anchorage in the soil, the resistance of the root system to pests and diseases, and other properties of trees that determine the possibilities and economic efficiency of the intensification of fruit production depend significantly on the rootstock.

The selection of rootstocks for fruit plants is carried out by research institutions. The most valuable forms of rootstocks, submitted for state cultivar testing and regionalization, must meet the following requirements:

• be adapted to the natural conditions of the region where they are used;
• be resistant to adverse factors that limit the culture of fruit trees in the given area (drought resistance, salt tolerance, resistance to the most common pests and diseases in the area);
• have a high degree of physiological compatibility and strong union with the grafted regionalized cultivars;
• have a positive influence on the production and biological properties of the trees, yield, and fruit quality of the grafted cultivar;
• possess a high propagation coefficient;
• be easy to propagate;
• ensure high indicators — labor productivity, output of standard nursery plants from the nursery, and profitability of their production.

Rootstocks that do not meet at least one of the listed requirements are not included in regionalization.

The regionalization of rootstocks is carried out on the basis of data from comprehensive study and evaluation of rootstocks at state cultivar testing sites. The regionalization project is reviewed and approved by republican, regional, and district agricultural authorities. Regionalization determines the composition and approximate percentage ratio of rootstocks by republic and fruit growing zones, which are periodically updated taking into account the identification of more valuable types.