Inoculum sources of the post-harvest pathogens Neofabraea spp. and Cadophora spp. in Dutch apple and pear orchards

Post-harvest diseases of apple and pear cause significant economic losses during long storage. Quiescent infections by fungal
pathogens such as Neofabraea alba, N. perennans, Neonectria galligena, Phytophthora spp., Alternaria spp., Fusarium spp.,
Cadophora spp. and Stemphylium vesicarium can occur in Dutch orchards and lead to post-harvest fruit rots in storage.
Knowledge on the occurrence of the different post-harvest diseases and their epidemiology is very limited. The objective of the
study was to identify the inoculum sources of main post-harvest pathogens and to gain insight into their population dynamics.
Samples of various necrotic residues and tree parts were collected in 10 apple and 10 pear orchards during the growing season
2012 monthly from May until September and in December from 4 replicate plots in each orchard. Species-specific primers and
probes were developed for N. alba, N. perennans and C. luteo-olivacea. TaqMan-PCR assays were used to quantify the amount
of DNA of each of the three pathogens in the environmental samples from the orchards.
N. perennans was found only in few samples whereas N. alba and C. luteo-olivacea were abundantly present on necrotic tissues
of apple and pear such as mummies, cankers and dead leaves. Interestingly, these pathogens were also found in varying
amounts on necrotic tissues of other plant species present on the orchard floors such as various weeds and grasses. The
concentration of pathogen DNA in the various substrate types varied during the growing season. Population dynamics also
differed between individual orchards indicating that orchard characteristics and management strategies may influence the
development of the pathogen populations.
The new knowledge on the major inoculum sources of fruit rot pathogens in apple and pear orchards is essential for the
development of preventative sanitation measures which reduce the risk of pre-harvest infections by the pathogens followed by
post-harvest losses. The inoculum load can be reduced by physical removal of the sources, enhancing decomposition or
application of competitive biological control agents. The new knowledge on the variation of populations dynamics between but
also within orchards can be used to identify major factors affecting pathogen survival and multiplication during the growing
season.