The role and tasks of breeding in modern viticulture and cultivar renewal

The main lever for increasing vineyard profitability is the proper selection and renewal of cultivars. In global crop production, the introduction of new high-yielding, intensive-type cultivars over the last 25–30 years has provided a substantial increase in production. Today, this process is actively underway in viticulture as well, where cultivar characteristics determine the direction of processing and the quality of the final product much more strongly than in grain production.

• Growth in gross production due to new cultivars — 25–30%
• Annual harvest losses from pests and diseases — up to 30%
• Grape losses in years of severe epiphytotics — 50% or more

Why change the assortment: economics and vineyard protection

If a vine is not genetically predisposed to high yields, this deficiency cannot be compensated for by fertilizers, pruning, or stimulants. Productivity can be fundamentally increased and berry quality improved only through breeding. The second key factor remains resistance to an unfavorable environment, pathogens, and pests.

The transition to complex-resistant cultivars changes the entire economics of a farm. They allow for the abandonment of labor-intensive winter vine covering and the cultivation of grafted plants. Furthermore, such cultivars do not require a complex and expensive system of chemical treatments, which reduces the cost of the berries and lowers the pesticide load on the soil.

Requirements for new cultivars depend on their intended use. Table grapes must have large, attractive clusters and withstand transportation and long-term storage. Seedless (sultana and raisin) cultivars are valued for their extra-early ripening, firm, fleshy pulp, and moderately loose clusters for drying. For wine cultivars, the primary focus is high juice yield with an optimal balance of sugar content and acidity.

Methods for working with grape assortments

To create and introduce new cultivars, viticulturists use a proven set of breeding methods. Each of them solves specific tasks at certain stages of work with the vine. The entire cycle from searching for initial material to introducing a cultivar to the vineyard is built sequentially.

1. Study of indigenous (local) assortments and identification of the most economically valuable forms.
2. Creation of new cultivars using hybridization, clonal selection, or artificial mutagenesis.
3. Cultivar evaluation of the resulting forms in collection plantings of research institutions.
4. Cultivar testing in specialized plots to confirm productivity.

Study of the indigenous assortment and identification of economically valuable forms and cultivars from it. N. I. Vavilov, the founder of the theory on centers of origin for cultivated plants and many theoretical and methodological principles of breeding, repeatedly emphasized the necessity for all breeders to follow an mandatory rule: any breeding work, regardless of the crop being addressed, must begin with the study of the indigenous assortment, with a revision of what nature has created and left for us through centuries of natural and artificial selection (folk breeding).

This guidance from N. I. Vavilov is of great importance for grape breeders, as our country has many ancient centers of origin for cultivated grape forms and their further evolution. These include the Transcaucasian center, which encompasses the territory of the modern Georgian SSR, Azerbaijan SSR, Armenian SSR, and part of the Dagestan ASSR. Within this region, especially in its foothill and mountainous areas where ancient agriculture first emerged, many valuable grape cultivars were formed, which currently form the basis of the grape assortment in the Transcaucasian republics. Another equally large center of origin for cultivated grapes in our country is the Central Asian region, which includes the territory of the Uzbek SSR, Tajik SSR, Turkmen SSR, and Kirghiz SSR. Geographically, the territory of Southern Kazakhstan also joins this area. This is primarily a center of origin for cultivated table-raisin and sultana cultivars of the Eastern ecological-geographical group. The most valuable of these, tested by centuries of cultivation practice, constitute the basis of the modern table-raisin and sultana assortment. Many indigenous cultivars have also been identified and established in the territory of modern Moldova, Crimea, and other regions.

Identifying and studying aboriginal grape forms makes it possible to use the best of them directly for economic purposes. Many of them also serve as valuable source material for further breeding work using hybridization and clonal selection. Currently, due to the rather complete study of the aboriginal cultivar assortment, the effectiveness of this breeding method has somewhat decreased compared to the initial stage; however, even today, thanks to the efforts of breeders, collection funds of local forms and cultivars continue to be replenished.

The practical significance of this breeding method in improving the grape cultivar assortment can be judged by the following data. Of the grape cultivars zoned in the USSR, over 35% are aboriginal. Out of more than 600 cultivars undergoing state variety testing, more than 15% are aboriginal.

The method of studying the aboriginal grape cultivar assortment continues to be highly effective and promising for those countries and ecological-geographical regions where ancient centers of grape origin and the formation of cultivars under cultivation are located, and where this work is just beginning (Afghanistan, Iran, Iraq, Turkey, Syria, etc.). Economically valuable grape forms identified in the process of studying the aboriginal cultivar assortment in these areas are of great interest to other countries as well.

Breeding new cultivars by hybridization. Currently, this is the main method of grape breeding. Its advantage lies in the fact that, through directed, scientifically based selection of initial parental pairs for crossing, it is possible to combine individual desired traits of the parental pairs or their complex in one hybrid organism. By the hybridization method, it is possible to obtain grape cultivars with a new, modified genotype that did not previously exist in nature and cultivation. Their breeding through crossings can be carried out at different taxonomic levels: intergeneric, interspecific, intraspecific (intervarietal), and in individual cases, even intravarietal (inbreeding).

The choice of initial forms for crossings is determined primarily by the task facing the breeder.

Cultivars resistant to adverse environmental conditions, diseases, and pests are created mainly through interspecific and sometimes intergeneric crossings. When conducting breeding work by the method of interspecific crossings, in most cases, it is most advisable to use not pure species as initial forms, but the best hybrid forms of the second, third, and subsequent generations obtained from crossing Vitis vinifera cultivars with American and East Asian species.

Grape species used for crossing:

• American species: V. vulpina, V. rupestris, V. labrusca, V. berlandieri, etc.
• East Asian species: V. amurensis.

The expediency of using hybrids with complex heredity in breeding is explained by the fact that pure species, due to the dominance of their inherent traits, more strongly transmit to the hybrid offspring of the first generation, along with desirable traits (immunity, tolerance, and resistance), undesirable ones, including low harvest quality, which, while maintaining the resistance of cultivars to adverse environmental conditions, diseases, and pests, as a rule, improves during repeated crossings.

For a correct, scientifically based choice of paths and methods of breeding work, taking into account the assigned task, deep knowledge of the initial material, gene pool, and the peculiarities of the origin of species and cultivars selected for inclusion in crossings is necessary.

The theoretical and methodological basis for grape breeding for immunity is the theory of co-evolution of the host plant and the parasite, put forward by N. I. Vavilov and further developed in the works of P. M. Zhukovsky, D. D. Verderevsky, A. M. Negrul, N. I. Guzun, P. N. Nedov, K. A. Voytovich, L. Ya. Golodriga, and others. According to this theory, the centers of plant species formation simultaneously serve as centers for the formation of races of their parasites.

Host plants in their homeland show exceptional variability. However, this property is equally inherent in pathogenic microorganisms and harmful insects. If a plant forms new and newer forms, the harmful organism also forms new races. As a result of natural selection against such a background, the least affected forms are identified and accumulated in the process of evolution.

D. D. Verderevsky formulated the hypothesis of complex resistance, according to which the appearance of pathogenic microorganisms and grape pests (causative agents of downy mildew, powdery mildew, gray mold; phylloxera) in nature did not occur simultaneously. Most likely, in the process of evolution of American grape species, they were initially attacked by one of the pathogens or pests. Under the influence of natural selection, all susceptible forms perished, and only those that possessed tolerance or full immunity survived. Later, within the resistant populations, an attack by a second pathogen or pest occurred, and in the process of the evolutionary struggle against a natural severe infectious background, resistance to this pathogen or pest was also formed. Even later, immunity to a third pathogen (pest) was formed in the same way. Ultimately, all this led to the emergence of grape forms possessing complex resistance to the most dangerous pathogens and pests. Based on this theory, a method of stepwise grape breeding for complex resistance has been developed.

The primary method for breeding cultivars with complex resistance is interspecific hybridization. At its initial stage, hybrids were obtained — direct producers that possess resistance but produce low-quality harvests. Some of them spread to areas where European-Asian grapes suffer from frost, fungal diseases, and phylloxera.

Certain hybrids — direct producers are still cultivated in some countries:

• Isabella, Lydia, Zolotoy Luch (in the USSR);
• Muscat Saint Vallier and Pierrelle (in France).

In many hybrids (Seyve-Villard and Seibel) currently grown in southern France and other countries, more than 80 years of complex backcrossing and multi-way crossing have made it possible to combine the genomes and specific chromosomal blocks of four, five, or more species. Some of these hybrids possess resistance to frost, downy mildew, powdery mildew, and are tolerant to the root form of phylloxera.

Using complex interspecific hybrids as initial parental forms in crosses with Vitis vinifera cultivars of superior quality, Soviet breeders and immunologists obtained new valuable cultivars combining resistance to pests and diseases with high harvest quality. Three new cultivars have been regionalized (Moldova, Yubileyny Magaracha, Podarok Magaracha), and more than fifty cultivars are undergoing State variety trials.

It has been established that resistance factors are generally inherited according to more complex patterns. Since economic traits and resistance traits have a polygenic basis, it is rational to conduct breeding work on a large scale, which will increase its effectiveness.

The leading breeding method for frost and winter hardiness is interspecific hybridization. Vitis amurensis and complex hybrids derived from crosses between American species serve as the primary donors of resistance to low temperatures.

Based on the results of hybridological analysis of several tens of thousands of grape seedlings, Soviet breeders reached a very important conclusion that a single hybrid organism can combine traits of increased resistance to low temperatures with good harvest quality.

The widest spectrum of variability for frost and winter hardiness traits occurs in those crossing combinations where V. vinifera grape cultivars introduced into crossing with Amur grapes and complex Seibel and Seyve-Villard hybrids are represented by the eco-geographical group of the Black Sea basin.

Recent studies have established that V. amurensis possesses broad polymorphism. I. N. Martynova (1981) identified 3 ecotypes of this species:

• northern (at the latitude of Khabarovsk);
• southern (at the latitude of Vladivostok);
• Chinese.

The Chinese ecotype is of greatest interest for breeding, as it possesses not only high frost resistance but also higher yield and is distinguished by larger clusters and berries. Hybrids obtained with its participation are characterized by superior economic traits.

New cultivars of Amur-European origin that have received the greatest recognition and distribution include: Saperavi Severny, Fioletovy Ranny, Golubok, Stepnyak, Megrabur, Tsvetochny, and others. However, interspecific hybrids obtained with the participation of Amur grapes are susceptible to the root form of phylloxera and fungal diseases.

Another way to obtain grape cultivars resistant to low temperatures by the hybridization method is to perform crosses within V. vinifera between cultivars possessing increased frost resistance. The properties of increased frost and winter hardiness in individual hybrid grape seedlings obtained within V. vinifera manifest due to the wide polymorphism of this species. One of the positive aspects of the method is a higher guarantee of obtaining seedlings with high harvest quality in the hybrid progeny.

This breeding method is most promising for developing new cultivars intended for southern viticulture zones. For these zones, it is sufficient to increase the frost resistance of new cultivars by a few degrees. Conversely, cultivars obtained with the participation of V. amurensis in southern zones lose their frost and winter hardiness due to an easier exit from dormancy during winters with frequent thaws, often suffering from minor cold snaps. Using the method of inter-cultivar crosses within V. vinifera, the cultivars Adisi, Echmiadzini, Gladzori, Sipan, and others were obtained in Armenia.

An original and effective method for breeding frost-resistant grape cultivars with a shortened growing season and increased sugar accumulation intensity was developed and proposed at the Timiryazev Agricultural Academy (TSKhA) by K. P. Skunyin. Hybrid seed obtained from interspecific crosses were sown in open ground in the Moscow region, where environmental conditions for grape cultivation are extreme.

During the cultivation of the seedlings, strict selection for survival was conducted based on traits of high resistance to low temperatures and a short growing season. The surviving seedlings were subjected to selection for harvest quality under greenhouse conditions in Moscow and in open ground in the southern zones of our country (Armenia, Dagestan, Uzbekistan). The use of this breeding method allowed for the production of new valuable grape cultivars: Burmunk, Moskovsky Ustoychivy, Muscat Skunyin, and others.

The most dangerous pest of vineyards, brought from America to Europe more than 100 years ago, is phylloxera, which originates from the regions of the USA located east of the Rocky Mountains.

According to modern concepts, the damage caused by phylloxera to the root system of V. vinifera cultivars involves 2 consecutive processes:

• primary — direct damage to roots by phylloxera;
• secondary — invasion of the damaged sites by pathogens causing root rot, including certain species of the genera Gliocladium, Fusarium, and Cylindrocarpon, as well as bacteria of the genera Pseudomonas and Bacillus.

According to P. N. Nedov (1977), the degree of damage caused by pathogenic microorganisms depends on the mechanical composition of the soil. In sandy soils, they are absent or their quantity is very insignificant.

In global practice, the solution to the problem of phylloxera control through breeding is carried out in two directions:

• developing and selecting rootstock immune and highly resistant to phylloxera with good affinity for grafting non-resistant European-Asian grapevine cultivars onto them;
• developing high-quality table and wine grape cultivars complexly resistant to phylloxera and fungal diseases through hybridization for own-rooted culture.

The second approach is the most promising, as it solves the problem of phylloxera control most radically.

Donors of phylloxera resistance in breeding include a group of American species, among which V. rotundifolia possesses complete immunity to phylloxera. However, its involvement in crossing with V. vinifera cultivars is difficult due to the imbalance in the chromosome number of these species. Nevertheless, research has been launched to develop a method for overcoming these difficulties, resulting in the production of DRX hybrids, which can be used to obtain hybrids with V. vinifera.

Donors of high resistance to phylloxera include the American species: V. vulpina (= V. riparia), V. rupestris, and V. cinerea.

Of great value as source material are the interspecific hybrids of Seibel and Seyve-Villard, on the basis of which a number of new cultivars have been obtained at the NPO "Vierul," the All-Union Research Institute of Viticulture and Enology "Magarach," and other scientific institutions, characterized by simultaneous resistance to phylloxera and root rot with good quality of grape products. In the opinion of I. N. Nedov, V. vinifera does not possess genes for resistance to phylloxera, but it does have genes for resistance to the root rot process, which provide tolerance when damaged by phylloxera. This makes it possible to identify cultivars suitable for own-rooted culture with good economic traits.

There are more such cultivars in the ecological-geographical group of the Black Sea basin than in other groups. In addition to direct practical use, they are highly valuable as source material for breeding.