Call number: LD2668 .T4 1979 T73 / Master of Science

Tree-ring chronologies from ten mixed conifer stands in the Colorado Front Ranges and New Mexico Sangre de Cristo Mountains were used to reconstruct timing, duration, and radial growth impacts of past outbreaks of western spruce budworm, Choristoneura occidentalis Freeman. Graphical and statistical comparisons of tree-ring chronologies from host and non-host tree species, in conjunction with Forest Service records of outbreaks during the twentieth century, revealed that outbreaks were identifiable only in the host chronologies as sharply reduced growth periods. These comparisons also showed that host and non-host tree-ring chronologies were generally similar between outbreaks and that both were responding in a similar manner to climatic variation. A study of defoliation and insect population data that was available for the New Mexico stands demonstrated that host radial growth from 1978 to 1983 was highly correlated with budworm activity. The non-host chronologies from each stand were used to correct the host chronologies for climatic and other non-budworm environmental variations by a differencing procedure. The corrected chronologies were then used to estimate the dates and radial growth effects of past budworm outbreaks. Tree-ring characteristics of twentieth century documented outbreaks were used as criteria for inferring the occurrence of outbreaks in previous centuries. At least nine periods of increased budworm activity were identified in the region from 1700 to 1983. The mean duration of reduced growth periods caused by known and inferred budworm outbreaks was 12.6 years, and the mean interval between initial years of successive outbreaks was 34.9 years. The mean maximum radial growth loss was 50 percent of expected growth, and the mean periodic growth loss was 21.6 percent. There was an unusually long period of reduced budworm activity in the first few decades of the twentieth century, and since that time outbreaks have been markedly more synchronous between stands. Increased synchroneity of outbreaks in the latter half of the twentieth century suggests that areal extent of outbreaks has increased. This phenomenon may be due to changes in the age structure and species composition of forests following harvesting and fire suppression in the late nineteenth and early twentieth centuries.

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Erwinia strains from several geographic regions and several hosts were evaluated for virulence, sensitivity to siderophores produced by Pseudomonas fluorescens (Pf) and bacteriocins produced by Erwinia, and for the presence of plasmids. Selection of virulent strains of Erwinia for use in plant breeding programs for resistance to disease might be based upon quantitative characters which are correlated with disease severity rather than the biochemical reactions used to distinguish Erwinia carotovora subspecies. Quantitative assays for motility, polygalacturonate degradation, potato tuber infection, and tuber decay revealed that motility was correlated with infection (r = 0.83, p = 0.01) and polygalacturonate degradation with decay (r = 0.84, p = 0.01) of potato tubers. Siderophores produced by Pf and bacteriocins produced by Erwinia yielded variable results in bioassays against the Erwinia strains studied. Six of the 12 strains of Erwinia tested were resistant to Pf siderophores. The growth inhibition of sensitive strains was bacteriostatic and reversible by addition of iron (Fe II or Fe III) to the culture medium. Additionally, only one strain of Erwinia was sensitive to the bacteriocins produced by the other 12 strains. The resistance of Erwinia strains to Pf siderophores and Erwinia bacteriocins severely limits the potential for widespread application of these agents in biological control of Erwinia. Bacteriocin-like structures were detected in culture extracts of all 12 Erwinia strains studied. The presence of bacteriocins is indirect evidence that these strains harbor plasmids. Bacteriocin-coding plasmids may be the source of genetic and phenotypic variability demonstrated by the erwinias. The status and value of subspecific classification of Erwinia carotovora may therefore require re-evaluation.

published_or_final_version / Botany / Master / Master of Science