Dissertation
Biology and Epidemiology of Phacidiopycnis Washingtonensis on Apple
Doctor of Philosophy (PhD), Washington State University
01/2013
Handle:
https://hdl.handle.net/2376/5067
Abstract
Phacidiopycnis washingtonensis was first described in 2005 and is the cause of speck rot, a new postharvest fruit rot disease of apple and a twig dieback and canker disease of crabapple in eastern Washington. Since then, P. washingtonensis has also been reported on Pacific madrone in western Washington. The goal of this study was to estimate the population genetic structure of the fungus and study its various epidemiological aspects.
Fifty-eight unique haplotypes among the populations were identified using eight microsatellite markers developed in this study. Genetic differentiation was not observed between populations from apple and Pacific madrone. However, high genetic diversity was observed within subpopulations from different geographic locations. Overall, the P. washingtonensis population in Washington State appeared to be largely asexual with high genotypic flow. Isolates are capable of infecting both apple and Pacific madrone irrespective of their host of origin.
Fruit inoculation was carried out to understand infection courts and timing of fruit infection in the field in relation to postharvest rots in storage. Speck rot developed during cold storage on fruit inoculated at any given time during the growing season. The incidence of total speck rot in storage increased as the inoculation time approached harvest. Histological studies revealed that infection occurring through micro cracks on pedicel and sepal surface, but colonization was restricted to cuticular and epidermal layers.
Two separate studies were conducted to understand the seasonal susceptibility of apple twigs, seasonal survival of P. wahsingtonensis and availability of inoculum in the orchard. Twigs were most susceptible to infection during spring to early summer. Cold predisposition prior to inoculation facilitated infection and production of pycnidia on twigs. Viable pycnidia were detected on inoculated twigs at all sampling times.
Symptoms of speck rot are similar to those of Sphaeropsis rot caused by Sphaeropsis pyriputrescens and gray mold caused by Botrytis cinerea. Accurate diagnosis of these diseases is important during fruit inspection, particularly for fruit destined for export. qPCR based assays were successfully developed to differentiate the three diseases and to detect latent infections in symptomless fruit that were pre-inoculated in the orchard.
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Details
- Title
- Biology and Epidemiology of Phacidiopycnis Washingtonensis on Apple
- Creators
- Parama Sikdar
- Contributors
- Mark Mazzola (Advisor)Chang-Lin Xiao (Advisor)Tobin Peever (Committee Member)Patricia Okubara (Committee Member)
- Awarding Institution
- Washington State University
- Academic Unit
- Plant Pathology, Department of
- Theses and Dissertations
- Doctor of Philosophy (PhD), Washington State University
- Number of pages
- 152
- Identifiers
- 99900581739101842
- Language
- English
- Resource Type
- Dissertation