Abstract
Background Neonectria ditissima is one of the most important fungal pathogens of apple trees, where it causes fruit tree canker. Information about the amount and partitioning of genetic variation of this fungus could be helpful for improving orchard management strategies and for breeding apple cultivars with high levels of genetically determined resistance. In this study single-spore Neonectria isolates originating from both the same and from different perithecia, apple cultivars and apple orchards in Sweden and Belgium, were evaluated for AFLP- and SSR-based genetic similarity and for mating system.ResultsSeven SSR loci produced a total of 31 alleles with an average of 4 alleles per locus, while 11 AFLP primer combinations produced an average of 35 fragments per primer combination and 71 % polymorphic fragments. An AFLP-based analysis of molecular variance (AMOVA) revealed that 89 % of the variation was found within orchards and 11 % between orchards. Genetic similarity among the studied isolates was illustrated with a principal coordinate analyseis (PCoA) and a dendrogram. AFLP-based Jaccard’s similarity coefficients were the highest when single-ascospore isolates obtained from the same perithecium were compared, medium-high for isolates from different perithecia on the same tree, and lowest when isolates from different trees were compared.ConclusionsBased on the results of PCoA and AMOVA analysis, isolates from the same or geographically close orchards did not group together. Since AFLP profiles differed also when single-ascospore isolates from the same perithecium were compared, the mating system of N. ditissima is most likely heterothallic.
Highlights
Neonectria ditissima is one of the most important fungal pathogens of apple trees, where it causes fruit tree canker
Correct species determination was ascertained by observation of colony morphology and by Polymerase chain reaction (PCR) amplification of DNA samples using species-specific primers previously developed for N. ditissima [13]
These results suggest that the fungal populations occurring on apple were less variable than the single population occurring on black birch
Summary
Neonectria ditissima is one of the most important fungal pathogens of apple trees, where it causes fruit tree canker. Tul.) Samuels & Rossman, previously known as Neonectria galligena (Bres.) Rossman & Samuels, causes cankers on a wide range of trees and shrubs including apple (Malus) and pear (Pyrus). This pathogen can damage the woody tissue of infected trees substantially, and render fruit production unprofitable in certain areas [5]. Apple canker is mainly associated with mild and wet conditions, and climate has an important impact on the geographic distribution of the pathogen [6].
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