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Document Type

Thesis - University Access Only

Award Date


Degree Name

Master of Science (MS)

Department / School

Plant Pathology

First Advisor

Martin L. Carson


A closely related set of field corn inbreds (Zea mavs L.) crossed to two inbred testers (LH39 and W117) were evaluated for tolerance and resistance to leaf freckles and wilt (LFW) caused by Clavibacter michiganense subsp. nebraskense, Stewart's bacterial wilt (SBW) caused by Erwinia stewartii and northern corn leaf blight (NCLB) caused by Exserohilum turcicum during the 1987 and 1988 planting seasons. Reactions to the three diseases were significantly correlated in both years. The mean percent yield losses due to LFW in both years were 10.9 and 19.6 and the maximum yield loss in each year was 31.8 and 56.1%, respectively. The mean yield losses associated with SBW were 8.1 and 12.8% and the maximum loss in each year was 21.9 and 38.2%, respectively. The mean yield losses attributed to the effects of NCLB in 1987 and 1988 were 4.1 and 2.0% and the maximum levels of yield losses were 28.1 and 28.3%, respectively. Percent yield losses due to LFW and SBW and their disease severity ratings were correlated in 1987-1988. Correlations between percent yield loss due to NCLB and its disease severity ratings in 1987 were significant at the 0.01 level of probability but, the relationship was not significant in 1988. Yield losses associated with the two bacterial diseases in 1987 were significantly correlated, but neither was correlated with losses due to NCLB. No significant relationship between yield losses due to any of the diseases was found in 1988. Relationships between tillering ability, disease reaction and yield losses associated with the diseases in 1987 were not significant. However, negative significant correlations were found between tillers per plant and SBW ratings and yield loss due to NCLB in 1988. Tolerance was-observed to operate in each pathosystem but was very unstable. Resistance accounted for most of the reduced yield losses in these studies and was observed to be consistently expressed across both years. Tolerance was observed to be pathogen specific; it operated only in one pathosystem at a time. However, a few cases were noticed where it operated in more than one pathosystem. The variability in the relative degree of tolerance in this study suggests that it would be difficult to incorporate into breeding programs.

Library of Congress Subject Headings

Corn -- Growth

Corn -- Breeding

Corn -- Yields



Number of Pages



South Dakota State University