Scab (Venturia inaequalis (Cooke) G. Winter) lesion on some apple (Malus domestica Borkh.) varieties with Vf gene (Rvi 6) in Oryol region

Abstract. Research was carried out in 2022-2023 to monitor scab lesion on apple varieties in the conditions of the Oryol region, in the breeding gardens of the Russian Research Institute of Fruit Crop Breeding, VNIISPK. The purpose of the study is to evaluate degree of scab lesion and to determine the possibility of the appearance of 6 race of scab. Methods. We assessed 16 apple cultivars with the Vf gene previously known to be immune to scab and Malus Floribunda 821. The assessment was carried out under a natural infection. Scientific novelty. This paper reports scab infestation of a number of varieties with the Vf gene in the conditions of Central Russia (Oryol region). Results. Scab lesion was observed on such varieties with the Vf gene as ‘Bolotovskoye’, ‘Venyaminovskoye’, ‘Vostorg’, ‘Poeziya’, ‘Priokskoe’, ‘Pristsilla’, ‘Svezhest’’, ‘Solnyshko’, ‘Yubiley Moskvy’. At the same time, no scab damage was detected on the varieties with the Vf gene ‘Aleksandr Boyko’, ‘Vavilovskoe’, ‘Valyuta’, ‘Girlyanda’, ‘Ivanovskoe’, ‘Imrus’, and ‘Rozhdestvenskoe’. It is concluded that 6th scab race has appeared, that capable to overcome Vf gene. At the same time, there is currently no scab infection on the M. floribunda 821, which indicates the absence of the 7th scab race. It is important to note that at the moment, not all varieties with the Vf gene are affected by scab. Perhaps this is due to the presence of other resistance factors or the new scab race is not yet widespread enough. Possible strategies for breeding apple trees for long-term resistance are discussed, including other donors of resistance genes, gene pyramiding, as well as orchard management preventing the evolution of the pathogen.