Inoculum availability and seasonal survival of Potebniamyces pyri in pear orchards

Authors: Xiao, Chang-Lin; BOAL, R.J. - Washington State University

Submitted to: European Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/2013
Publication Date: 11/1/2013
Citation: Xiao, C., Boal, R. 2013. Inoculum availability and seasonal survival of Potebniamyces pyri in pear orchards. European Journal of Plant Pathology. 137:535-543.

Interpretive Summary: Phacidiopycnis rot caused by the fungus Potebniamyces pyri (asexual state Phacidiopycnis piri) is a recently reported postharvest fruit rot disease of pear in the United States. 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. Previous studies indicated that P. pyri can infect pear fruit at different times during the fruit growing season in the orchard, thus, availability of viable inoculum of P. pyri in pear orchards is important to potential infection by the fungus that leads to Phacidiopycnis rot of fruit during storage or in the market. In this study, we monitored the availability of Potebniamyces inoculum in commercial pear orchards in two years and found that viable spores of the fungus are available during the fruit growing season. We also found that the fungus can survive year around on pear twigs inoculated with the fungus. Our results suggest that inoculum is not a limiting factor for infection of pear fruit by P. pyri.

Technical Abstract: 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, 10 dead bark and 10 dead fruit spurs were periodically collected during the fruit-growing season from each of 10 selected trees at each sampling time in two ‘d’Anjou’ pear orchards. Samples were examined for the presence and viability of fruiting bodies of P. pyri. To determine seasonal survival of P. pyri in infected twigs, 2-year-old twigs in a research orchard were inoculated approximately monthly 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 orchards, all sampled trees were infected by P. pyri; viable pycnidia of P. pyri were observed on 42 to 78% of the sampled bark and 5 to 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 low 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 the conidial state of P. pyri is the main type of inoculum in pear orchards in the region; that viable inoculum of P. pyri for potential fruit infections is available during the pear fruit-growing season; that P. pyri can form pycnidia on cankers of twigs infected by the fungus at different seasons during the year; and that P. pyri can survive as mycelium in diseased pear twigs year round in the orchard.