Date of Award

Winter 1983

Project Type

Dissertation

Program or Major

Botany and Plant Pathology

Degree Name

Doctor of Philosophy

Abstract

A multifaceted program which examined several aspects of the host-pathogen interaction was conducted. Investigations were conducted in the following areas:

Developmental Anatomy of Wound Response in Current Year Shoots. Shoots wounded in mid-June developed a suberized necrophylactic periderm (NP) within two weeks. Both diffuse and delimited wound responses were observed. Normal xylem and phloem production was replaced by parenchymatous tissue in samples exhibiting a diffuse wound response. Within four weeks, NP acted as a center for, and instigated, premature exophylactic periderm development. Formation of gum cysts in the xylem and an accumulation of calcium oxalate crystals in cortical cells was also observed.

Developmental Anatomy of Cytospora Canker During Initial Canker Formation. Changes occurring in response to wounding and wounding plus inoculation were monitored over a one year period. Gum ducts were produced in the xylem to form a barrier zone in both treatments. NP formed at a faster rate in uninoculated samples. In addition, wound periderms in inoculated samples were poorly delimited and weakly suberized. Barriers in both the bark and xylem of inoculated samples were penetrated by the mass action of wedges of mycelia. Callus tissue in inoculated samples differentiated slowly and multiple attempts to comparmentalize infection were ineffective.

Interaction Between Cytospora and Host-Phenolic Compounds in Dormant Peach Trees. The presence of Cytospora in host tissues played a significant role, over and above the wounding response, in establishing levels of host phenolic compounds. Cytospora had the ability to break down host-phenolic compounds. Levels of phenol increased in advance of the fungus to restrict the pathogen.

Effect of Crop Load on Growth and Susceptibility to Cytospora. Deblossomed trees attained a greater average leaf area and a greater increase in both trunk and one-year old twig diameter. Highest levels of total resources were attained in twigs of deblossomed trees. The difference in these parameters was associated with canker elongation rates. Deblossomed trees had significantly slower rates of canker development.

Seasonal Variation in Cambial Electrical Resistance and Its Relation to Growth. A strong correlation between cambial electrical resistance (CER) and individual cultivars and the onset of dormancy was established. CER was a reliable indicator of growth within and between cultivars.

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