The paper presents the results of a long-term test of eight scab-immune apple varieties of domestic and foreign breeding under the conditions of North Caucasus region of Russia. The study was aimed at improving the assortment of apple trees in the Southern region of Russia on the basis of a comprehensive assessment of promising varieties of domestic and foreign breeding. The study objects included scab-immune apple varieties (Malus x domestica Borkh.) of various ecological and genetic origin: Carmen, Nika, Orphey and Margo (North Caucasian Federal Scientific Center of Horticulture, Viticulture, Wine-making together with Nationwide Research Institute for Horticultural Breeding, Russia), Mikhsan and Zarya Stavropoliya (Stavropol Experimental Horticulture Station together with Nationwide Research Institute for Horticultural Breeding, Russia), Modi (Italy), Florina (France). The common and up-to-date breeding programs and techniques developed with the assistance of Nationwide Research Institute for Horticultural Breeding were applied. Based on the long-term results of ecological testing of new scab-immune apple varieties of different origins under the conditions of the Republic of North Ossetia-Alania and Krasnodar Krai, the most valuable varieties for industrial use and for breeding process were identified. The following varieties were identified as promising for industrial use and breeding: varieties with a late flowering time – Margo and Orphey; varieties with a high average flowering score (4.5–5.0 points): Carmen, Modi, Orphey, Nika, Florina, Margo. It was found that all investigated varieties of apple trees can be attributed to the annual fruit-bearing; the periodicity of fruiting varied within 22.6–28.8 %. In 2020, in the conditions of North Ossetia-Alania the maximum yield was observed for the following scab-immune varieties: Margo (24.1 t/ha) and Modi (25.2 t/ha) on rootstock СK2; Mikhsan (19.2 t/ha) and Nika (20.6 t/ha) on rootstock MM106. In order to improve the assortment of the Southern region of Russia and to create modern intensive orchards, new varieties of apple of domestic breeding were recommended: Margo, Nika, Orphey and Modi (foreign breeding), which have high productivity, immunity to scab (based on Rvi-6 gene), better commerciality and a long period of fruit storage.

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The results of a long-term ecological testing of 12 apple varieties of domestic and foreign selection in the Republic of North Ossetia-Alania are presented. The biological features of fruiting of representatives of the genus Malus in a southern region of Russia were studied with the purpose of identifying the most valuable varieties in terms of a set of indicators for further breeding and production. According to the conducted long-term observations (2012–2019), the following varieties with compact small-sized crowns (volume of 1.48-2.09 m3) were identified: Zolotaya Korona, Lyubimoe Dutovoj, Sunrise and Red Chiff. Among summer triploid varieties, the variety of Soyuz was selected according to the yield factor (total yield was 159.2 t/ha, which was 56.5 t/ha higher than the control). The varieties of early winter and winter ripening period with a high total (198.3–299.2 t/ha) and average (33.05–49.87 t/ha) yield were determined: Ligol, Zolotaya Korona, Lyubimoe Dutovoj, Alanskoe and Pinova. It was established that the varieties of Alanskoe, Zolotaya Korona, Lyubimoe Dutovoj, Sunrise and Pinova exhibit high productivity indicators, with the specific productivity of the crown volume being 17.00–21.87 kg/m3. It was revealed that the fruits of all studied foreign and domestic apple varieties grown under favourable conditions of the region meet modern requirements in terms of diameter (65–75 + mm) and average weight (200–220 g). Among the most promising varieties for breeding and production were found to be Liberty, Zolotaya Korona and Lyubimoe Dutovoj with large fruit (214.5–237.8 g), as well as Soyuz, Ligol, Alanskoe and Prikubanskoe with very large fruit (289.3–330.2 g). It is concluded that the apple varieties of regional selection (Alanskoe, Zolotaya Korona, Lyubimoe Dutovoj, Soyuz) and foreign selection (Sunrise and Pinova) can be recommended when breeding varieties with the required set of valuable agrobiological propertites, as well as when creating intensive industrial plantings and obtaining high-quality domestic fruit products.