Characteristics of immune and scab-resistant apple cultivars

Summer and autumn ripening cultivars

Growing apple cultivars with genetic resistance to scab allows for a significant reduction in the pesticide load on the orchard and lowers the costs associated with purchasing fungicides. Summer and autumn cultivars provide an early product turnover and allow sales of fresh apples to begin as early as mid-summer. Such apple trees are optimally suited for intensive orchards in southern regions, which are focused on quick sales during the holiday season.

• Onset of fruiting for Topaz apple: 1st year
• Annual yield of Liberty cultivar: from 20.0 to 30.0 t/ha
• Maximum fruit weight of Persikovoie cultivar: 250 g
• Storage duration of GoldRush fruits: up to 7 months

Redfree is a late-summer cultivar, zoned for the North Caucasus region since 2000, with fruit harvesting beginning at the end of July. Thanks to the Vf gene, the trees are completely immune to scab, resistant to powdery mildew, and also exhibit winter hardiness and drought tolerance above average. This medium-sized cultivar with a broadly pyramidal canopy is characterized by precocity and annual fruiting. The round fruits, weighing 120–140 g, have an attractive reddish-burgundy blush, firm sweet-and-sour flesh, and can be stored for up to 30 days.

Prima is a late-summer or autumn cultivar, included in the register for the North Caucasus region since 1996. Fruit harvesting takes place at the end of August, and their storage period is 2 months. Relatively vigorous trees with an obovate canopy are characterized by high precocity and biennial bearing with good overall yield. The cultivar is completely immune to scab. The round and often asymmetric fruits are covered with a blurred striped red blush, and the tender light-cream flesh has a pleasant sweet-and-sour taste.

Liberty is a dessert cultivar of American breeding, ripening at the end of September and zoned for the North Caucasus region since 2000. Relatively vigorous trees with a spreading canopy are resistant to scab and slightly affected by powdery mildew. Average precocity allows for the first harvest 4 years after planting with an annual productivity in the range of 20.0–30.0 t/ha. The medium-sized fruits have a light green color with a fresh scarlet blush, and mixed fruiting is distributed on spurs and last year's shoots. During storage, the apples acquire a light yellow tint and keep until January.

Winter and late-winter ripening cultivars

Winter immune cultivars allow farms to preserve the harvest for half a year and sell it during the period of maximum prices. They have high keeping quality in cold storage conditions and are resistant to major storage pathogens. Introducing such cultivars into the crop rotation reduces the costs of plant protection at the end of the growing season.

Florina is a table cultivar of French breeding (1977), zoned for the North Caucasus region since 2000 and specifically for the Krasnodar Territory since 2003. Its fruits are distinguished by outstanding keeping quality and can be stored in cold storage chambers until May. Medium-sized trees possess average winter hardiness, high and low biennial bearing, and resistance to scab. Smooth, round-shaped fruits weighing 140 g (maximum up to 160 g) are covered with a bluish-red blush with large whitish-gray dots.

Persikovoie is a dessert cultivar of domestic breeding for the early winter consumption period, zoned for the North Caucasus region since 2002. The trees show high winter hardiness, resistance to heat, drought, and major fungal diseases. The yield of this cultivar is very high and regular, and the fruits are large — 220 g on average, with a maximum weight of up to 250 g. The fruit flesh is yellowish-cream, semi-oily, juicy, and fine-grained.

Granny Smith is a late-winter table cultivar of Australian breeding, zoned for the North Caucasus region since 2006. The trees have sufficient winter hardiness for southern conditions, average drought tolerance, and provide annual high yields. Large, uniform green fruits are valued for their firm, juicy flesh with a mild aroma, although the fruits do not have a pronounced peel scent. The cultivar shows relative resistance to a complex of diseases:

• scab;
• powdery mildew;
• fruit rot.

GoldRush is a winter cultivar obtained in 1980, which is characterized by precocity and regular fruiting on medium-sized trees with a compact canopy. Fruits with an average weight of 130 g (maximum up to 145 g) have a firm yellow skin with an intense red blush. The apples are distinguished by juicy cream flesh with a good taste and can be stored in the refrigerator for up to 7 months. The trees are completely immune to scab and have average resistance to powdery mildew.

Topaz is a late-winter cultivar of Czech breeding (1984), belonging to spur-type cultivars. Low-growing trees with a compact, low-volume canopy form fruit primarily on annual growth, and fruit harvesting in the orchard is carried out in September. The cultivar is moderately resistant to powdery mildew and slightly susceptible to scab; meanwhile, the yellow-green apples with a solid blush are stored in the refrigerator for 6 to 7 months.

Imrus. Obtained at the All-Russian Research Institute of Fruit Crop Breeding fruit crops. Promising (Isachkin, Vorobyov, 2003). Winter consumption period; fruits are stored until March. Winter hardiness is above average. Immune to all five races of scab (Vf resistance gene). Yield and precocity are high. Dessert type.

Trees are medium-sized, with a rounded, sparse canopy. Fruits are of medium to above-average size, 125 g, maximum 190 g, of medium uniformity, oblate-round-conical in shape, slightly ribbed.

The skin of the fruit is smooth, oily, shiny, greenish-yellow with a diffused, striped, and streaky crimson blush on half of the fruit's surface. The flesh is creamy, firm, and juicy. The taste is good, sweet and sour.

Figure 12 – Tree (a) and fruits (b) of the Topaz apple cultivar

Enterprise. Obtained in 1982, promising. A cultivar for winter consumption. Immune to scab, has the Vf resistance gene, moderately resistant to powdery mildew. The cultivar is precocious, with regular fruiting.

Trees are vigorous, with a spreading canopy. The fruits have the following characteristics:

• Size: large (maximum 190 g);
• Shape: oblate-round, slightly ribbed;
• Skin: firm, smooth, shiny, bright red;
• Flesh: creamy, firm, juicy;
• Taste: good, with a "rich" aroma.

Figure 13 – Tree (a) and fruits (b) of the Imrus apple cultivar Figure 14 – Tree (a) and fruits (b) of the Enterprise apple cultivar

Apples are stored in a refrigerator at a temperature of 1 °С for about 6 months. The fruits are used both fresh and for processing.

The results of the evaluation of the resistance of the described apple cultivars to certain abiotic stressors are presented in the following text.