Relationship Between Endophyte Infestation Level of Tall Fescue Seed Lots and Rhizoctonia zeae Seedling Disease. K. D. Gwinn, Assistant Professor, Department of Entomology and Plant Pathology, University of Tennessee, P.O. Box 1071, Knoxville 37901-1071. A. M. Gavin, Research Associate, Department of Entomology and Plant Pathology, University of Tennessee, P.O. Box 1071, Knoxville 37901-1071. Plant Dis. 76:911-914. Accepted for publication 8 April 1992. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/PD-76-0911.

The objective of this research was to define the relationship between endophyte (Acremonium coenophialum) infestation level of tall fescue (Festuca arundinacea) seed lots and a seedling disease caused by Rhizoctonia zeae. Seeds were planted in soilless medium or medium amended with R. zeae cultures, and number of seedlings per three 5.0-cm cores was determined. In a preliminary experiment, percentage of loss (61%) was greater for Forager (a low-endophyte cultivar) than for a Kentucky 31 seed lot with an 85% endophyte infestation level (32%). In subsequent experiments, Kentucky 31 seed lots with either 0 or 85% endophyte infestation level were used to determine if high percentage of loss in Forager was due to the lack of endophyte infection or to cultivar differences. For two R. zeae isolates, the number of seedlings was significantly higher in controls than in R. zeae treatments. Interactions between endophyte level and treatment were significantly different for both isolates. Additional seed lots were used to determine the nature of the relationship between endophyte infestation level and seedling loss. The relationship between endophyte level and seedling number was linear for both R. zeae treatments and controls (P = 0.0615).