VIEW ARTICLE

Physiology and Biochemistry

Analysis of Photosynthesis in Resistant and Susceptible Alfalfa Clones Infected with Verticillium albo-atrum. B. W. Pennypacker, Doctoral candidate, Department of Plant Pathology, The Pennsylvania State University, University Park, PA 16802; D. P. Knievel(2), K. T. Leath(3), E. J. Pell(4), and R. R. Hill, Jr.(5). (2)Associate professor of crop physiology, The Pennsylvania State University, University Park, PA 16802; (3)Research plant pathologist, USDA-ARS, The U.S. Regional Pasture Research Laboratory, University Park, PA 16802; (4)Professor of plant pathology, The Pennsylvania State University, University Park, PA 16802; (5)Research agronomist, USDA-ARS, The U.S. Regional Pasture Research Laboratory, University Park, PA 16802. Phytopathology 80:1300-1306. Accepted for publication 14 June 1990. 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, 1990. DOI: 10.1094/Phyto-80-1300.

The effect of Verticillium albo-atrum on net photosynthesis, stomatal conductance, stomatal limitation of photosynthesis, and the activitity of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) was determined for a resistant and a susceptible alfalfa clone through A/Ci (net photosynthesis vs. internal CO₂) response curve analysis. In addition, leaf protein was extracted, and the activity and amount of totally activated Rubisco were determined by ¹⁴CO₂ assimilation and gel electrophoresis. No significant reductions in net photosynthesis, Rubisco activity, or stomatal conductance, or increases in stomatal limitation of photosynthesis were detected in the infected resistant clone by either in vivo or in vitro methods. Net photosynthesis, Rubisco activity, and stomatal conductance were reduced significantly in the infected susceptible clone, but stomatal limitation of net photosynthesis was not affected. There was a significant reduction in both the total activity and amount of Rubisco in the infected susceptible clone. The lack of effect of reduced stomatal conductance on net photosynthesis coupled with the reduction in amount and activity of Rubisco support the conclusion that the reduction in net photosynthesis in the infected susceptible clone was due to the reduction in Rubisco activity.