Date of Award:

5-1-2002

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Biology

Committee Chair(s)

Sherman V. Thomson

Committee

Sherman V. Thomson

Committee

Schuyler D. Seeley

Committee

Bradley Kropp

Abstract

Erwinia amylovora dissemination was studied by sampling apple and pear leaves before and after a precipitation event. All pear and apple experiments revealed similar trends for the temporal and spatial nature of E. amylovora. Rain dispersed the bacteria to leaves only a short distance from the infection and survived less than 24 hours on the leaf. An experiment was designed to determine leaf age susceptibility to inoculation by E. amylovora when leaves were subjected to injury types that simulated hail, wind-blown rain, and rain dispersal. Succulent leaves in the hail and rain dispersal treatments were more susceptible to infection than hardened off leaves. The hail treatment was the most susceptible for both leaf age classes. Wind-blown rain resulted in low infection levels, possibly due to a foliar apoptotic reaction. E. amylovora was transformed with a Green Fluorescent Protein (GFP) gene to monitor bacterial ingress into apple seedlings under greenhouse conditions. The youngest leaf was injured and inoculated simultaneously or injured followed by inoculation. The injured/inoculated portions of leaves were viewed using confocal microscopy at set times following treatment. E. amylovora was found around most injury margins and did not move through major vascular elements for at least 24 hours. E. amylovora was not exclusively associated with either the xylem or phloem. Bacteria from simultaneous injury and inoculation with E. amylovora moved a greater distance into the injured secondary vein compared to the other treatment. Streptomycin was selected for the experiment to control shoot blight. Jonathan apples were chosen and a subset of actively growing shoots within each tree were selected for injury and inoculation or non-injured and inoculated. Each tree differed in the timing of the streptomycin application. The results indicated that a single application of streptomycin 4 hours following the injury and inoculation reduced infections by 50%. A preventative application of streptomycin only slightly reduced infections for all treatments. The results showed that a streptomycin spray 24 hours post-injury does not provide control of shoot blight.

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