Sources of Neofabraea spp. and Cadophora spp. in Dutch apple and pear orchards


Abstract: Post-harvest diseases of apple and pear result in significant economic losses during long storage. Pathogens causing quiescent infections in the orchard leading to late post-harvest losses in The Netherlands are Neofabraea alba (Lenticel spot disease), N. perennans (Bull eye rot), Neonectria galligena (Nectria rot), Phytophthora spp., Alternaria spp., Fusarium spp., Cadophora spp. (Phialophora spp.) and Stemphylium vesicarium. Knowledge on the occurrence of the different post-harvest diseases and their epidemiology is very limited. The objectives of our project were to develop tools for the quantitative species-specific detection of pathogens in environmental samples; to study the population dynamics of pathogens in orchards; and to identify major inoculum sources of the different pathogens. Species-specific primers and probes have been developed for three main pathogens N. alba, N. perennans and Cadophora luteo-olivacea. The amount of DNA of each of the three pathogens can now be quantified in environmental samples using TaqMan-PCR assays. Samples of various necrotic plant residues and tree parts were collected in 10 apple and 10 pear orchards during the growing season 2012 to investigate their role as potential inoculum source. In all orchard samples were taken monthly from May until September and in December 2012 from 4 plots (replicates). Neofabraea alba and C. luteo-olivacea were found in all orchards whereas N. perennans occurred only occasionally. Neofabraea alba and C. luteo-olivacea were present on necrotic tissues of apple and pear such as mummies, cankers, and dead leaves. Interestingly, the pathogens were also found in varying amounts on necrotic tissues of other plant species present on the orchard floors. The concentration of pathogen DNA showed a differential pattern on different substrate types. Based on the new knowledge on major inoculum sources of the different pathogens, preventative measures will be developed to reduce the risk of late post-harvest losses.

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