Date of Award:

5-1-1982

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Biology

Department name when degree awarded

Life Sciences:Biology

Committee Chair(s)

Donald Davis

Committee

Donald Davis

Committee

Wade G. Dewey

Committee

B. Austin Haws

Committee

J. Clair Theurer

Abstract

This study was initiated to determine some of the biological and environmental factors affecting the expression of resistance in beet breeding lines to the sugarbeet root maggot. Findings will help to define the most appropriate conditions for testing and provide a better understanding of the mechanisms involved in resistance. Laboratory and field studies were conducted to (1) determine the effect of plant age, soil type, soil nutrition, and soil moisture on larval development and oviposition; (2) determine the effects of these conditions on the expression of resistance; and (3) search for possible morphological or physiological root characteristics related to plant resistance. Entries were two stable inbreds designated as resistant and susceptible based on previous field and laboratory studies, and two entries selected in a recurrent breeding program specifically for low and high damage. Plants were subjected either to natural fly populations in the field or artificially infested with eggs or flies in the laboratory. Larval survival, growth, and development were enhanced by older plants, clay loam soils, soil high in organic content, nitrogen and phosphorus fertilization, moderate to wet soil moisture, and on more susceptible entries. Preferred for oviposition were intermediate-aged plants, plants grown in sandy and silt loam soils, soil low in organic content, moderately moist soil, and susceptible entries. The expression of resistance was enhanced (in terms of larval survival and size) by infesting younger plants, particularly those in the 2- to 4-leaf growth stage. Resistance was also enhanced by growing plants in sandy loam soil. Resistance entries had a higher percentage of root tissue forming periderm and central vascular core. In addition, the resistance plants had a higher percentage of plants forming wound periderms both in response to maggot damaged and artificially damaged areas. Susceptible entries had a higher percentage of cambium, cortex, and vascular tissue outside the central vascular core. The most resistant entry appeared to show antibiosis, tolerance, and non-preference, while the most susceptible entry showed little or no indication of resistance.

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