Leaf spot resistance in sweet and sour cherries

Background. Cherry leaf spot (caused by the fungus Coccomyces hiemalis Higg.) has been one of the most harmful diseases of stone fruits for many years. The increasing genetic homogeneity of plant forms used in breeding promotes the acceleration of the pathogen’s adaptive microevolution and the overcoming of previously effective resistance genes. The structure of C. hiemalis populations from Krasnodar Territory in terms of their virulence to a set of differentiators and the effectiveness of new leaf spot resistance donors were studied.

Materials and methods. The polymorphism in three populations of the fungus was assessed by the frequencies of virulence phenotypes which were identified using six differentiators. The resistance of new distant hybrids to 50 monopustular isolates was assessed in laboratory experiments.

Results and conclusions. Five phenotypes of the fungus, differing in virulence to six cherry genotypes, were identified. An increase was observed in the frequencies of virulence phenotypes capable of strongly affecting donors used in breeding for resistance. Five hybrids are proposed to expand the genetic diversity of sour and sweet cherry cultivars resistant to C. hiemalis: 3-61-4-139, 3-39-5-47, 3-107-6-28, AI 5 B-D-2-4-27, and 3-76. They are protected by the leaf spot resistance genes that have been transferred from Prunus serrulata Lindl. The alleles of the resistance genes in these plants are not identical to the resistance alleles in the genotypes Seyanets No. 1, Mutant 561, ‘Almaz’, Kusumkent 8, Vetrovoe 11 (P. kurilensis Miyabe), and BG-35 (P. sargentii Rehd.), all used in breeding. Seedling 3-20-5-23 (P. serrulata × Northstar) was not resistant to a number of C. hiemalis clones. It is assumed that this genotype and Vetrovoe 11 (P. kurilensis) are protected by identical alleles of resistance genes, which differ from the alleles present in the five new hybrid forms.

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