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Disease Detection and Losses

Relationships of Infection by Cercospora zebrina to Seed Production and Seed Quality of Subterranean Clover. R. G. Pratt, Research plant pathologist, Forage Research Unit, Agricultural Research Service, U.S. Department of Agriculture, P.O. Box 5367, Mississippi State, MS 39762; Phytopathology 79:209-213. Accepted for publication 29 August 1988. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1989. DOI: 10.1094/Phyto-79-209.

The potential for Cercospora zebrina to reduce seed production and affect seed quality of subterranean clover was evaluated in the field during four growing seasons. Cultivar Woogenellup was grown in plots from September to May of each year. Infection of foliage by C. zebrina was initiated by applying infested debris to plots in late winter. Control plots received autoclaved debris. Burrs (seed heads) were harvested each spring and counted. Seed were threshed, counted, weighed, measured volumetrically, and evaluated by a standard germination test. Over all years, plots infested with C. zebrina had 16-31% fewer burrs and 18-33% fewer seed than control plots (differences significant as P < 0.01) with no significant year x treatment interactions. Seed weight and size were reduced 6-24 and 5-21%, respectively, in infested plots as compared to controls, and year x treatment interactions were significant. Seed from control and infested plots did not differ significantly in frequencies of normal or abnormal germination, hard seed, embryo dormancy, or dead seed. Disease progress and flower production were compared during 2 yr. Rapid increase of foliar symptoms did not occur until 1-2 wk after peak flowering, and flowering was significantly reduced in infested plots only at those times. These results indicate that foliar infection by C. zebrina will significantly reduce seed production and seed quality of subterranean clover within or over years. It is unlikely, however, that the disease will eliminate seed production entirely during any one year for Woogenellup or earlier maturing cultivars when grown in climates similar to that of north Mississippi.