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Resistance to pear decline phytoplasma and its relationship to pathogen overwintering, host response and foliar symptoms

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Title: Resistance to pear decline phytoplasma and its relationship to pathogen overwintering, host response and foliar symptoms
Author: Kaviani, Mina
Department: Department of Plant Agriculture
Program: Plant Agriculture
Advisor: Hunter, DavidGoodwin, Paul
Abstract: Pear Decline (PD) phytoplasma populations were measured using quantitative real-time PCR over a year in non-symptomatic pear trees (HW620 as scion) on the rootstocks, OH×F87 (PD resistant), OH×F69 (PD susceptible) and Bartlett (PD susceptible), growing in the Niagara region (Ontario, Canada). Seasonal patterns of PD populations were not greatly altered by the rootstock. Maximum populations occurred during late summer for leaves and shoots, and minimums during mid-winter for shoots and early spring for leaves, whereas maximum populations in roots were in mid-winter and minimums in mid-spring. PD populations for each month were typically less in leaves than in shoots, but both were much less than in roots. Regardless of tissue type, PD populations were lowest with OH×F87, then higher with OH×F69 and highest with Bartlett rootstock indicating that rootstock resistance affects PD populations in scion tissues. PD phytoplasma populations and expression patterns of six pear genes were also compared between leaves, shoots and roots of non-infected and PD-infected pear trees showing symptoms of leaf curling (selection 9328-1) or leaf reddening (selection 8824-1). The only significant differences in PD populations were higher numbers in roots of selection 9328-1 than 8824-1. More genes had significantly higher expression in PD-infected than non-infected tissues for selection 8824-1 than 9328-1 indicating stronger host responses. A comparison of PD-infected selection 8824-1 to 9328-1 showed greater up-regulation of genes in selection 8824-1 for sucrose synthase in leaves, acid invertase in leaves and roots, alcohol dehydrogenase in shoots, chitinase in all tissues, and phloem protein in roots, whereas greater up-regulation in PD-infected selection 9328-1 than 8824-1 was observed only in shoots for sucrose synthase, acid invertase and phenylalanine ammonia-lyase. Up-regulation of sucrose synthase and acid invertase could be associated to localized changes in sugars, while up-regulation of alcohol dehydrogenase, chitinase class III, phenylalanine ammonia-lyase and phloem protein2 could be part of triggered immunity. The results indicate that leaf reddening may be due to greater triggered immunity in selection 8824-1 resulting in an accumulation of anthocyanins, while leaf curling in selection 9328-1 may be due to water stress because of more dysfunctional phloem.
URI: http://hdl.handle.net/10214/8397
Date: 2014-08
Rights: Attribution-NonCommercial-NoDerivs 2.5 Canada
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Attribution-NonCommercial-NoDerivs 2.5 Canada Except where otherwise noted, this item's license is described as Attribution-NonCommercial-NoDerivs 2.5 Canada