Inoculum availability and seasonal survival of Potebniamyces pyri in pear orchards

Potebniamyces pyri (anamorph Phacidiopycnis piri) is the causal agent of Phacidiopycnis rot, a postharvest disease of pear fruit (Pyrus communis). Infections of pear fruit by P. pyri occur in the orchard, and symptoms develop after harvest during storage or in the market. P. pyri also is the cause of a canker and twig dieback disease of pear trees. To determine inoculum availability of P. pyri, dead bark and dead fruit spurs were periodically collected in two commercial ‘d’Anjou’ pear orchards and examined for the presence and viability of fruiting bodies of P. pyri. To determine seasonal survival of P. pyri, 2-year-old twigs of ‘d’Anjou’ pear in a research orchard were inoculated approximately monthly over 2 years with P. pyri and monitored for canker development. Inoculated twigs were removed from the trees 6 months post inoculation and examined for formation, viability of pycnidia of P. pyri, and reisolation of the pathogen. In both commercial orchards, all sampled trees were infected by P. pyri; viable pycnidia of P. pyri were observed on 42–78 % of the sampled bark and 5–32 % of the sampled fruit spurs; and viable conidia were observed at all sampling times during the fruit growing season. Apothecia of P. pyri also were observed on sampled dead bark and fruit spurs, but at a frequency ranging from 0 % to 19 %. P. pyri was recovered from inoculated twigs 6 months after inoculation at all sampling times during the 2-year study, but recovery frequency varied. P. pyri formed pycnidia on most cold-injured and inoculated twigs. The results suggest that: i) the conidial state of P. pyri is the main type of inoculum in pear orchards in the region; ii) viable inoculum of P. pyri for potential fruit infections is available during the pear fruit-growing season; iii) P. pyri can form pycnidia on cankers of twigs infected by the fungus at different seasons during the year; and iv) P. pyri can survive as mycelium in diseased pear twigs year round in the orchard.