Degree Type

Dissertation

Date of Award

1985

Degree Name

Doctor of Philosophy

Department

Plant Pathology and Microbiology

Abstract

Studies on the microflora in the air of a seed germination laboratory indicated that the highest numbers of airborne spores as measured with a Burkard spore trap occurred during working hours. When measured on a monthly basis, spore counts were greatest in winter months, when approximately 90% of all corn and soybean samples were tested. Qualitative measurements on the Andersen air sampler showed that Aspergillus flavus was the most prevalent fungus found, with A. niger and Penicillium sp. occurring in trace amounts. A significant correlation was obtained between spore counts on the day the tests were prepared and the degree of fungal growth on germination tests (r = 0.68). Germination values were negatively correlated with the amount of fungal growth (r = -0.83). Air in the laboratory and seed were identified as significant sources of these fungi, but not water and/or substrates. The quality of the seed per se might also affect contamination;Isolates of Aspergillus flavus, A. niger, Penicillium sp. and Rhizopus sp. when applied to germination tests had no effect on corn, whether it was treated with Captan or untreated, regardless of substrate. Penicillium oxalicum, A. flavus, A. niger and Rhizopus sp. caused significant reduction of soybean germinations in Kimpak and paper towels, but not on sand. Aspergillus flavus and A. niger were associated with increased cotyledonary decay, A. niger with glassy (translucent) hypocotyls and Penicillium sp. with stubby roots. According to the Rules of the Association of Official Seed Analysts, these malformations could be interpreted as abnormals in soybean germination tests. The described effects were more pronounced in poorer quality seeds and were reduced by Captan seed treatment. When inoculated onto seeds before aging, all fungi reduced germination by at least 50% after an accelerated aging period of 72 hours at 41C and 100% relative humidity. Captan and Nystatin, however, reduced fungal contaminants and increased germination.

DOI

https://doi.org/10.31274/rtd-180813-5682

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/

Copyright Owner

Sarah A. H. Olembo

Language

en

Proquest ID

AAI8514427

File Format

application/pdf

File Size

172 pages

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