Selecting cultivars for organic horticulture in the south of Russia

Fruits are a primary source of the following substances:

• Sugars (fructose, glucose, sucrose);
• Organic acids;
• Water-soluble vitamins (ascorbic acid, and P-active catechins and leucoanthocyanins);
• Tannins and coloring agents;
• Pectic substances and mineral salts.

The study of the protective and medicinal components of fruits and berries has intensified significantly thanks to the work of L. I. Vigorov (1976). He identified species, cultivars, and forms – sources of vitamins and other biologically active substances, many of which (ascorbic acid, polyphenols, b-carotenes, etc.) are antioxidants capable of increasing the body's resistance to environmental pollution, radiation, and stress factors.

Similar research is being conducted with cultivars of fruit crops in the south of Russia (Doroshenko, Ostapenko, Ryazanova, 2006). The results obtained can be used when selecting the optimal assortment for organic orchards in this region.

However, an improved chemical composition of fruits is by no means the only requirement for modern cultivars intended for organic plantations. Alongside this, they must be resistant to a complex of abiotic and biotic stress factors in the corresponding territories (Doroshenko, Kondratenko, 1998; Ostapenko, 2003; 2004; Doroshenko et al., 2005). The latter ensures the possibility of eliminating the use of fungicides in orchards and, as a result, producing environmentally safe fruit products.

The south of Russia is a key region for industrial fruit growing, encompassing vast areas characterized by a specific ecological situation. These include, in particular, resort, recreational, and water-protection areas, which preclude the use of technological processes that involve polluting the natural environment and agricultural products with pesticides. Cultivation of fruit crops in this region and other natural analogues of southern Russia must be carried out using ecologized technologies.

Organic gardening best meets the modern ecological and economic requirements of the industry. Its implementation will facilitate solving a dual task: the harmony between humans and nature, and the stabilization of production volumes of environmentally safe products.

An important condition for the effective functioning of a technological system for producing high-quality products is constant monitoring and regulation of the vital factors of fruit plants based on the use of high-precision tools. The resolution of this task must be preceded by the development of a production process management program for fruit crops, which includes selecting an optimal assortment.

As is known, a specific feature of fruit growing is the cultivation of plants in one location for a more or less extended period of time. Therefore, the efficiency of orchard management largely depends on how fully the natural conditions of a specific area meet the biological requirements of fruit crops.

Given the importance of this issue for industrial fruit growing in Russia, work has been carried out on its ecologically sound placement. For example, the Azov-Kuban plain within the Krasnodar Territory is represented by two fruit-growing zones: steppe and Kuban-adjacent. Their location near the Sea of Azov and the Black Sea creates a favorable climate for this geographical area.

The Greater Caucasus mountains play an important role in climate formation, preventing the movement of cold northern air masses to the south. When moist air masses enter, precipitation increases.

The hydrothermal regime of the zone, which influences the rate of decomposition and leaching of organic residues, the decay of minerals, and the direction of substance movement in the soil profile, has led to the formation of deep and very deep chernozems (black soils) here, which are among the best soils in Russia.

Based on the results of the assessment of climate features and soil characteristics, one can expect effective cultivation of various agricultural crops, including apple trees, in these natural conditions. However, the current reality in fruit growing clearly does not justify such expectations. In particular, as statistical data show, the average yield of perennial plantations (including apple plantations) in the southern fruit-growing zone of Russia is unacceptably low.

It is regrettable that such fruit yields are obtained against the background of the apple tree's vast biological potential, which, according to some calculations, reaches 150–200 t per 1 ha in the south of the country and in a number of foreign countries. In other words, the yield of modern apple plantations in the region is far from the potential maximum.

When analyzing the numerous reasons for this discrepancy, the main ones were identified (Gudkovsky, Tsukanova, 1999; Terenko, 1999). These are:

• the presence in orchards of low-productivity cultivars that are also susceptible to major fungal diseases and characterized by low resistance to the effects of various adverse environmental factors;
• insufficient stability of orchard agroecosystems;
• errors in plantation placement.

The validity of this conclusion is confirmed by well-known facts regarding the rather frequent occurrence of epiphytotics in southern Russia in recent years, as well as abiotic stress factors and the resulting consequences.

Protection against freezing and scab: major winter risks

Scab remains one of the most aggressive threats to apple orchards in southern Russia. In years of severe epiphytotics, this disease can deprive a farm of 60–70% of the harvest of susceptible cultivars. Scab outbreaks occur regularly — up to eight times every ten years in all southern horticultural zones. Damage from other diseases of fruit crops can also be quite significant.

Winter frosts are another critical factor capable of completely destroying perennial plantations. For example, the severe winter of 1993/94 led to the death of 11.6 thousand hectares of orchards in the Krasnodar Territory, with apple trees also suffering. Less large-scale but regular freezing occurs approximately once every five years, weakening the vital functions of trees and reducing their productivity.

Prolonged January frosts, accompanied by strong winds at speeds of 15 m/s or more, pose a particular danger. During such weather anomalies, low temperatures persist for 10–12 consecutive days. Agronomists must take these risks into account when planning plantings and selecting cultivars for specific microzones.

The hardiness of trees largely depends on the dynamics of their hardening during autumn and winter. The main areas under winter cultivars in the south are occupied by Rennet Simirenko, which is extremely sensitive to early frosts. Trees of this cultivar delay growth and enter winter unprepared, reaching the necessary level of winter hardiness only by December. However, at the end of winter, Rennet Simirenko withstands frost better than most other cultivars.

Combating summer heat, drought and soil salinization

Among all unfavorable natural factors, drought ranks second in terms of threat to southern orchards. A moisture deficit in the region is consistently recorded every third year, and in recent decades — even more often. A lack of water disrupts metabolic processes in plants and prevents trees from fully preparing for winter. Due to water stress, agronomists may lose up to 60% of the planned fruit harvest.

Prolonged exposure to excessive heat degrades the commercial quality of products. Because of the heat, fruits ripen unevenly, are poorly colored, lose their shelf life and flavor properties, and also begin to fall off in large numbers before harvesting begins. In addition, overheating makes trees more susceptible to certain diseases and pests.

Proper selection of heat-resistant cultivars helps solve the problem of summer stress. Tests show that the introduced cultivar Prima copes with overheating significantly better than Florina. Additionally, when establishing an orchard, it is necessary to take into account soil factors: for example, in the south, areas with a weak degree of soil salinization have been recorded, covering a total area of about 400 hectares.

• Harvest losses from scab — up to 60–70 %
• Yield reduction due to drought — up to 60 %
• Leaf damage of the Prima cultivar at 50 °С — 25 %
• Leaf damage of the Florina cultivar at 50 °С — 40 %
• Area of slightly saline soils under orchards — about 400 ha

Harvest shortfalls, deterioration of its quality, and a decrease in soil fertility are also caused by the unfavorable environmental situation in the industry, associated with the contamination of orchards (soil, plants, and even fruits) with heavy metals, pesticides, radioactive substances, etc. Thus, according to the results of surveys conducted in the Krasnodar Territory by the Scientific and Production Geoecological Center "Geoekologiya Kubani", soils contaminated with heavy metals occupy an area of approximately 20 thousand km2. Moreover, in some places, there is a very high zinc content (up to 1500 mg/kg), and the copper concentration is 150–600 mg/kg, significantly exceeding the maximum allowable concentration (MAC).

In this regard, in the process of producing environmentally safe fruit products, special attention must be paid to the correct selection of a site for the corresponding perennial plantations, taking into account soil properties. In particular, the reaction of the soil solution (pH) affects the solubility of toxicants and their uptake into plants.

In soils with a reaction close to neutral, the risk of agricultural product contamination (e.g., with heavy metals) decreases. When acidity increases, the solubility of heavy metals rises, and their migration into plants increases. Thus, taking into account the soil environment reaction when placing fruit crops and preventing the negative impact of excessive acidity through the selection of an optimal assortment is very important for obtaining safe products.

Currently, anthropogenic loads are reaching such a level that nature can no longer perform its self-purification functions. It is no coincidence that a shift in perspectives is taking place in modern agriculture: the one-sided intensification is being replaced by other principles that consider not only the possibility of obtaining production today, but also the preservation of resources and the human habitat for the future. Note that the idea of greening agriculture, including fruit growing, had already been implemented in more than 30 countries as early as the 80s of the last century.

Guided by the obtained results, it can be concluded that one of the ways for stable production of fruit crops in various gardening zones of Russia is the widespread introduction into production of cultivars possessing the following properties:

• resistance to biotic stress factors;
• resistance to abiotic stress factors;
• ensuring annual harvest of high-quality fruits on various soils;
• stability of yield even in years that are unfavorable in terms of weather conditions;
• minimal labor and financial costs.

Humanity has long been engaged in the selection of plant genotypes with required traits and properties. Continuous improvement of the breeding process in the industry has allowed for the creation of new cultivars that realize their biological potential for a number of economically valuable characteristics at a high level.

An example of this is the first domestic scab-immune (with the Vf gene) apple cultivars of various ripening periods, created at the All-Russian Research Institute of Fruit Crop Breeding (Sedov, Zhdanov, Sedova, 1989; Sedov, Zhdanov, Sedova, 1999). Significant work in this direction is also being carried out in other scientific institutions, including the North Caucasian Regional Research Institute of Horticulture and Viticulture. Achievements in apple breeding for winter hardiness, drought resistance, and other indicators have been demonstrated (Savelyev, 1998; Sedov, Zhdanov, Serova, 1999). It is expected that in the near future, through the efforts of physiologists, geneticists, and breeders, new genotypes characterized by increased resistance to edaphic stress factors will be created.

The problem of realizing the biological potential of the apple tree can be solved by growing it only in those areas whose soil and climatic features largely correspond to the actual requirements of the cultivars of this crop. In other words, cultivars that are well "adapted" in their ecological and biological properties to the natural conditions of a specific zone should be introduced into production.

This conclusion is based on previously published data (Kashin, 1998, 1999; Dragavtseva, Savin, Ovechkin, 2005), in particular on the assertion that the potential yield of fruit crops can be realized within a wide range depending on environmental conditions:

Moreover, to increase the productivity of perennial plantations, it is recommended (Dragavtseva, Savin, Ovechkin, 2005) to carry out the optimal placement of cultivars across appropriate landscapes even within the range of a specific fruit crop.

Equally well-known is another statement, which has long since become an axiom, about the need to select cultivars (scion-rootstock combinations) when establishing an orchard whose rhythm of growth and development corresponds to the rhythm of weather changes during the year in a given area. Such correspondence largely determines the adaptability of plants to growing conditions and their winter hardiness. A classic example of this is the Antonovka Obyknovennaya apple cultivar, the trees of which are characterized by high winter hardiness in the central zone but lose this property in the southern regions of the country: they are damaged by low temperatures after winter thaws and by spring frosts.

In this regard, the concern of a number of experts regarding the emerging dangerous trend of unsystematic selection of the assortment for industrial apple plantations in the south of Russia, which leads to a decrease in orchard productivity, is quite legitimate. The main reason for this is the insufficient resistance of the assortment, renewed through introduction, to the region-specific unfavorable climatic factors and fungal diseases – scab and powdery mildew.

Taking into account the importance and complexity of the problem under discussion, a number of researchers have made serious attempts to develop scientific foundations for the rational placement of fruit crop cultivars. Promising results have already been achieved in solving this issue. For example, in some scientific institutions of the industry (Kashin, 2003; Dragavtseva, Savin, Ovechkin, 2005), the following are being implemented:

• zoning of industrial horticulture;
• comprehensive territory assessment;
• mathematical modeling of its compliance with the requirements of fruit crop cultivars, which is particularly promising for forecasting purposes.

The listed facts give grounds to assert that for the maximum (or close to such) realization of the biological potential of fruit crops, a reliable assessment of the possible degree of adaptability of the tested cultivar (especially an introduced one) to the soil-climatic and orographic conditions of a specific agricultural landscape must be carried out. Similar requirements are also imposed on fruit crop rootstocks.

When it comes to creating organic gardens, one should primarily focus on the preliminary assessment of cultivars of fruit crops that are immune or resistant to fungal diseases, the cultivation of which will ensure a sharp reduction in the costs of plant protection measures.