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Disease Detection and Losses

Foliar Diseases Alter Carbohydrate and Protein Levels in Leaves of Alfalfa and Orchardgrass. A. Mainer, Former Graduate Assistant, Department of Plant Pathology, The Pennsylvania State University, U.S. Regional Pasture Research Laboratory, University Park, PA 16802, Present address of senior author: Centro Regional de Investigaciones Agrarias, Apartado 10, La Coruña, Spain; K. T. Leath, Research Plant Pathologist, Science and Education Administration, Federal Research, U.S. Department of Agriculture (also Assoc. Prof. of Plant Pathology, The Pennsylvania State University), U.S. Regional Pasture Research Laboratory, University Park, PA 16802. Phytopathology 68:1252-1255. Accepted for publication 6 March 1978. Copyright © 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-1252.

The percentage of crude protein (CP), total nonstructural carbohydrate (TNC), and dry matter (DM) levels were investigated with alfalfa and orchardgrass infected with Phoma medicaginis and Stagonospora arenaria, respectively. In alfalfa, the TNC and CP were decreased and the DM increased when the infection severity level was greater than 80%. Crude protein was significantly reduced in orchardgrass leaves at the 20% disease level, TNC at the 50% disease level, and DM was increased at all levels of disease. Crude protein was higher in healthy new growth from diseased alfalfa plants than CP in regrowth from healthy plants. In bulk-harvested orchardgrass the TNC percentage, TNC yield, and DM yield were reduced. We concluded that foliar diseases reduced the TNC and CP of both alfalfa and orchardgrass leaf tissues sufficiently to adversely affect the quality of the forage and that the loss of TNC was greater than that of CP.