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Pectic Enzymes Produced by Diplodia gossypina In Vitro and In Infected Cotton Bolls. Sy -ying C. Wang, Postdoctoral Fellow, Agricultural Experiment Station, Louisiana State University, Baton Rouge 70803; J. A. Pinckard, Professor, Agricultural Experiment Station, Louisiana State University, Baton Rouge 70803. Phytopathology 61:1118-1124. Accepted for publication 22 April 1971. DOI: 10.1094/Phyto-61-1118.

Culture filtrates of Diplodia gossypina grown in a pectin medium, extracts of Diplodia-diseased cotton boll tissues, and extracts of fungal mycelia from diseased cotton boll surfaces contained a pectin methylesterase, an exopolygalacturonase, and a polygalacturonate trans-eliminase with pH optima of 6.5, 4.5, and 9.0, respectively. Pectin methylesterase from culture filtrates was stimulated by K+, Na+, Ca++, Mg++, and Mn++, but inhibited by EDTA. Exopolygalacturonase from culture filtrates was stimulated by K+, Na+, Mg++, Mn++ , Zn++ , and Cu++ but slightly inhibited by EDTA and Ca++. Polygalacturonate trans-eliminase from all three sources was stimulated by Ca++; however, this enzyme obtained from diseased tissues was inhibited by Ca++ when the concentration was higher than 1.4 × 10^–3 m. Polygalacturonate trans-eliminase from culture filtrates was slightly stimulated by Na+ and Mg++, but inhibited by EDTA. All these enzymes were inductive; their activities were slightly reduced when 0.1% glucose was added to the medium for growth. Young cultures contained principally exopolygalacturonase. The activities of pectin methylesterase and polygalacturonate trans-eliminase increased to a maximum when mycelial growth was maximum. Exopolygalacturonase activity decreased, but pectin methylesterase and polygalacturonate trans-eliminase activities increased rapidly as cotton boll decay progressed. We conclude that exopolygalacturonase may play an important role in the early stages of infection, and that polygalacturonate trans-eliminase and pectin methylesterase become important in later stages of boll rot.