Publication Date


Document Type


First Advisor

Toth, Ronald

Degree Name

M.S. (Master of Science)

Legacy Department

Department of Biological Sciences


Corn--Diseases and pests; Mycorrhizas


Recent studies have suggested that a relationship exists between percent mycorrhizal infection and yield in corn, Zea mays. In low phosphorus soil there is an increase in mycorrhizal infection causing a corresponding increase in phosphorus uptake and yield. Conversely, high phosphorous soil has been shown to decrease mycorrhizal colonization. Zea mays grown in the Midwestern United States has been found to be heavily infected despite high soil phosphorus fertilities. This imbalance is thought to reduce yield through mycorrhizal inefficiency; i.e., host plant photosynthates are removed by the fungus without the benefit of enhanced phosphorus uptake in the plant. In order to determine the colonization level providing mycorrhizal efficiency, the relationship between differences in percent colonization and the corresponding differences in yield needs to be addressed. This can only be accomplished using inbreds of Zea mays demonstrating variability in percent colonization by the same endophyte. Two inbreds of Zea mays, one a high colonizer and one a low colonizer, were grown in both high and low phosphorus soil with and without fungal inoculum. Yield determinations, as shoot dry weight, were made and analyzed in a ratio format to cancel out any differences between the inbreds other than those of the mycorrhizal association. Under high phosphorus conditions there was a disadvantage to being mycorrhizal, as expected. Under low phosphorus conditions there was a disadvantage to being mycorrhizal but less of a disadvantage to being more mycorrhizal. This apparent contradiction may be explained by soil phosphorus levels not being low enough for a mycorrhizal advantage. However, if a plant must be mycorrhizal there is, apparently, less of a disadvantage in having enhanced phosphorus uptake and carbohydrate drain associated with high mycorrhizal formers as opposed to having a decrease in carbohydrate drain and phosphorus uptake found in low mycorrhizal formers. High colonizing plants were found to be more efficient at low phosphorus levels, as expected. Low colonizing plants were more efficient at high soil phosphorus levels. Evidently there is a greater advantage from the reduction in photosynthate diversion found in high phosphorus soils than there would be from the increased nutrient uptake expected in low phosphorus soil.


Bibliography: pages [22]-25.


vi, 25 pages




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