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Protease Production During Pathogenesis of Bacterial Leaf Spot of Alfalfa and by Xanthomonas alfalfae In Vitro. M. Narahari Reddy, Former Graduate Research Assistant, Kansas State University, Manhattan 66502, The senior author is now a postdoctoral fellow in Biochemistry, University of Wisconsin, Madison 53706; D. L. Stuteville(2), and E. L. Sorensen(3). (2)(3)Associate Professor of Plant Pathology, and Research Agronomist, Crops Research Division, ARS, USDA, respectively, Kansas State University, Manhattan 66502. Phytopathology 61:361-365. Accepted for publication 16 October 1970. DOI: 10.1094/Phyto-61-361.

Xanthomonas alfalfa produced an extracellular protease which liberated Congo Red from Congocoll, hydrolyzed gelatin, and clotted milk. The enzyme was most active at pH 8.0. Dialysis and EDTA reduced activity. Co++, Zn++, Mn++, and Fe++ increased protease activity, whereas Hg++, Fe+++, Cu++, cyanide, and mercaptoethanol reduced it. Protease activity was about 20 times greater in extracts from susceptible inoculated plants than in extracts from noninoculated control plants. Broths prepared from susceptible and resistant alfalfa plants supported nearly equal bacterial growth, but protease activity was greater in broth from the susceptible plants.