ABSTRACT
Powdery mildew (Sphaerotheca macularis Mag. (syn. Podosphaera aphanis Wallr.)) is a dangerous disease of strawberry (Fragaria L.). The resistance of strawberry to powdery mildew is controlled polygenically. Several genetic loci with a large contribution to disease resistance have been identified in various strawberry varieties. Diagnostic DNA markers have been developed for QTL 08 To-f. They showed a high level of reliable gene detection in mapping populations. The purpose of this study was assessment of a strawberry genetic collection for resistance to powdery mildew and identification of promising strawberry forms for breeding for resistance to S. macularis. The objects of the study were wild species of the genus Fragaria L., varieties and selected seedlings of strawberry (Fragaria × ananassa Duch.) created in the I.V. Michurin Federal Scientific Center, and strawberry varieties introduced from various ecological and geographical regions. To identify QTL 08 To-f, DNA markers IB535110 and IB533828 were used. Locus 08 To-f was detected in 23.2 % of the analyzed strawberry genotypes, including wild species F. moschata and F. orientalis, strawberry varieties of Russian breeding (Bylinnaya and Sudarushka) and foreign breeding (Florence, Korona, Malwina, Ostara, Polka and Red Gauntlet). The correlation between the presence of markers IB535110 and IB533828 and phenotypic resistance (powdery mildew effect on strawberry plants is absent) was 0.649. The determination coefficient (R2 ) showing the contribution of the studied locus to the manifestation of the trait was 0.421, that is, in 42.1 % of cases resistance was explained by the presence of QTL 08 To-f, and in 57.9 % of cases, by other genetic factors. All strawberry genotypes with locus 08 To-f were characterized by high field resistance to S. macularis in the conditions of Michurinsk, Tambov region. Thus, locus 08 To-f is promising for conferring resistance on local powdery mildew races, and markers IB535110 and IB533828 can be used in marker-assisted breeding programs to create powdery mildewresistant strawberry genotypes.
ABSTRACT
Fruit aroma is an important consumer attribute of strawberry varieties. The key volatile compounds of the aromatic complex of strawberry fruit are mesifurane (fruity and caramel aromas) and γ-decalactone (fruity, sweet, or peachy aroma). The mesifurane content in strawberry fruit is controlled by the FaOMT gene, which is mapped to the distal region of the long arm of chromosome VII-F.1. The γ-decalactone content in strawberry fruit is controlled by the FaFAD1 gene, mapped to the distal region of the long arm of chromosome III-2. Identification of forms carrying genes for fruit flavor volatiles is an important step in breeding varieties with fragrant fruit. The use of molecular markers allows highly reliable detection of target gene alleles in a genome at early developmental stages. This study involves molecular genotyping of Fragaria L. varieties for the FaOMT and FaFAD1 genes, analysis of polymorphism of the loci in question, and identification of genotypes valuable for breeding. The objects of our study were wild species of the genus Fragaria L. and strawberry varieties (Fragaria × ananassa Duch.) of different ecological and geographic origins. To assess the allelic states of the FaOMT gene, the codominant marker FaOMT-SI/NO was used, and for the FaFAD1 gene, the dominant marker FaFAD1. The functional allele of the FaOMT gene (FaOMT+) in the heterozygous state (FaOMT+FaOMT- genotype) was detected in 34.9 % of the accessions tested. The functional allele of the FaOMT gene in the homozygous state (FaOMT+FaOMT+ genotype) was detected in 51.2 % of the accessions. The homozygous state of the inactive allele (FaOMT-FaOMT- genotype) was detected in 13.9 % of the studied strawberry accessions. The FaFAD1 gene was identified in 25.6 % of the analyzed collection of strawberry genotypes, including the wild species F. orientalis Los., F. moschata Duch., F. ovalis Rydb. The combination of functional alleles of the FaOMT and FaFAD1 genes was detected in 16.3 % of the analyzed forms. The wild species F. orientalis Los. and F. moschata Duch. and strawberry variety Red Gauntlet combine the functional allele of the FaFAD1 gene with the homozygous state of the active allele of the FaOMT gene; therefore, we recommend them as promising sources of high contents of mesifurane and γ-decactone in fruit in breeding programs for fruit aroma.
