Date of Award

1950

Degree Type

Thesis

Degree Name

Master of Science in Botany

Department

Botany

First Advisor

Frank L. Howard

Abstract

Eight isolates of Ceratostomella ulmi exhibiting distinctive cultural variations were assembled for comparative studies of physiological and pathogenic differences. These isolates originated from cultures taken from diseased trees in several geographical areas. The principal objectives of the investigation were to determine (a) the relationship of certain physiological variations among the eight isolates of C. ulmi to toxin production, (b) the extent or pathogenic specialization among C. ulmi isolates, and (c) the relationship between observed physiological variations and pathogenicity. It was thought that evidence so gained might not only materially aid in explaining why variations in pathogenicity among isolates occur in different geographical regions, but also be of value in determining the effectiveness a given therapeutant has in neutralizing toxin produced by a given isolate.

Two experimental methods were used to determine the effect varied pH values have on the rate and habit or growth of isolates of C. ulmi. The first method involved culturing the isolates on a solid nutrient medium buffered at three pH values (4.0, 6.0, and 8.0). In the second method the isolates were grown as shake cultures in a buffered (pH 4.0 and 8.0) and unbuffered (initial pH 5.2) liquid nutrient medium.

On a solid medium the most abundant mycelial growth was produced at pH 4.0. Mycelial growth was slower but good at pH 6.0. At pH 8.0 mycelial growth was poor.

When grown as shake cultures most or the isolates grew best in the nutrient medium series buffered initially at pH 8.0 (lowered to 7.1 by autoclaving). Two of the isolates produced their highest mycelial yields in the unbuffered medium series and one isolate grew best at pH 4.0. Considerable differences were noted in the rate at which the various isolates grew in shake cultures. The evidence provided by the experiments on growth responses indicates that isolates of C. ulmi may differ in their specific pH requirements.

In experiments designed to determine whether or not isolates differed in the capacity to elaborate a toxin in culture, the isolates were grown in shake cultures and the filtrates

were assayed for toxin by the use or succulent two to three week-old tomato cuttings. The highest toxin titres were produced in the medium buffered at pH 4.0. The lowest titres were generally produced in the medium initially buttered at pH 8.0.

The evidence provided indicates that the initial pH of the medium at the time of inoculation appears to be the critical feature in the relationship of pH to toxin elaboration.

The filtrates from shake cultures were also analyzed tor a polysaccharide fraction. All isolates growing in the pH 4.0 medium series failed to produce polysaccharide. Five of the isolates growing in the unbuttered medium series and tour in the pH 8.0 medium series formed trace to measureable amounts of polysaccharide.

The results from toxin titre determinations were compared with the results from the other physiological experiments to determine if relationships exist between toxin titre and mycelial growth, mycelial age and polysaccharide yield. There was no correlation between toxin titre and mycelial growth or between toxin titre and polysaccharide yield. Toxin titre appeared, however, to have a definite correlation with mycelial age.

Experimental tests revealed that some of the eight isolates were strong pathogens while others were moderate to weak pathogens. There were no non-pathogenic isolates.

Comparisons of pertinent data reported in the thesis gave no indication that a definite relationship existed between pathogenicity and toxin titre.

Exploratory histological studies were conducted or wood from normal and diseased seedlings and from cuttings treated with toxin. Tyloses and gum-like substances were observed in vessels in tissue sections from diseased and toxin treated wood. The affected vessels appeared to be largely restricted to the primary xylem and early secondary xylem.

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