Graduate Thesis Or Dissertation
 

The disease cycle of side rot of pear, caused by Phialophora malorum

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  • Potential sources of inoculum of Phialophora malorum were investigated. P. malorum was found to be a soil-borne fungus whose role as a postharvest pathogen of pear is dependent upon passive dispersal with infested soil. P. malorum survived in soil under a wide range of conditions, with greatest survival in cool, moderately dry soil of nearneutral pH. P. malorum was not a primary colonizer of fallen fruit on orchard soil, but propagule numbers increased subsequent to fruit decay by other microorganisms. Cankers were induced when P. malorum was inoculated into injured bark of pear trees. However, cankers were nonperrenating, and P. malorum was not recovered from cankered tissue for more than one season. The fungus also survived saprophytically on the bark of pear trees, but dispersal of inoculum from infested bark to fruit or other areas of bark on the same trees was not observed. Inoculation of fruit and redistribution of inoculum from infested to previously uninfested fruit in packinghouse immersion dump tank solutions was demonstrated. Infection took place at fruit wounds. Spore penetration into wounds was influenced by wound diameter and hydrostatic pressure during immersion dumping. Infection via intact lenticels could not be induced. Results suggest that sanitation to avoid contamination of packinghouse immersion tanks with orchard soil may reduce disease incidence. As a weak competitor in colonizing pear tissue, P. malorum appears vulnerable to control through enhancement of fruit resistance or biological control.
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