Date of Award

1988

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biological Sciences

First Advisor

Meredith Blackwell

Second Advisor

Keith Clay

Abstract

This study was designed to investigate host specificity of the fungus Balansia cyperi Edg. on Cyperus rotundus L. (purple nutsedge) and to determine the effect of fungus presence on the biology and ecology of the sedge. Isolates of epiphytic Balansias from C. rotundus and C. virens had similar cultural characters, conidium morphology, and extracellular enzyme activity in artificial culture. However, B. cyperi from C. rotundus had a faster growth rate, greater conidium production, and higher temperature optimum than did the isolate from C. virens. Artificial infection of C. rotundus by B. cyperi from C. rotundus was far more successful than infection by the isolate from C. virens. These results suggest that host specificity may exist. Evidence obtained in this study indicates that purple nutsedge gains three selective advantages from fungus infection. Non-choice and preference feeding experiments conducted in the laboratory showed that larval weight and to a lesser extent larval growth rate were significantly reduced when the fall armyworm was fed leaves from B.cyperi-infected purple nutsedge as compared to uninfected leaves; larvae also preferred uninfected leaves. Therefore one advantage is reduced herbivory on uninfected plants. A second advantage of infection to the sedge is escape from other infection. This is indicated by growth inhibition of fungi isolated from C. rotundus by B. cyperi mycelium, culture medium, and infected leaf extracts. Growth in culture of potentially pathogenic fungi was statistically reduced in the presence of extracts from infected sedges as compared to uninfected sedges. In greenhouse studies epiphyte infection accounted for increased vegetative growth--the third advantage. Vegetative shoot number and total dry weight were significantly greater while inflorescence number in infected plants decreases as compared to uninfected plants. Infected plants produced more, but smaller tubers than uninfected plants. Thus, the ecological status of the association between B. cyperi and purple nutsedge appears to be mutualistic.

Pages

165

Share

COinS