Fibulorhizoctonia psychrophila, causal agent of lenticel spot in pome fruit, rarely detected in Dutch pear and apple orchards

Fibulorhizoctonia psychrophila causes lenticel spot in stored pome fruit. A Dutch survey revealed that damage can be observed regularly in individual lots at low incidence to occasionally incidences above 25% after storage for five months or longer under specific controlled atmosphere storage conditions. The source of inoculum of the psychrophilic pathogen is not known. A species-specific TaqMan PCR assay was developed to quantify the pathogen DNA in orchard litter considered as potential inoculum source. 2008 samples of various litter types such as dead leaves, fallen fruits and mummies and necrotic tissues of grasses and weeds, collected in 2009-2012 in ten apple and twenty pear orchards, were analyzed. Although other fruit rot pathogens such as Neofabraea alba, Cadophora luteo-olivacea and Stemphylium vesicarium were detected in the samples at high incidences in earlier studies, F. psychrophila was only detected in three samples. The results show that F. psychrophila is not ubiquitously present in Dutch orchards at traceable concentrations. The main sources of the disease remain unknown. Possibly, the pathogen is present on storage bins or dust in storage facilities.