VIEW ARTICLE

Host Colonization and Polygalacturonase Production by Two Tracheomycotic Fungi. Harry W. Mussell, Graduate Research Assistant, Department of Botany and Plant Pathology, Purdue University, Lafayette, Indiana 47907, Present address of senior author: Boyce Thompson Institute for Plant Research, Inc., Yonkers, New York 10701; Ralph J. Green, Jr., Professor, Department of Botany and Plant Pathology, Purdue University, Lafayette, Indiana 47907. Phytopathology 60:192-195. Accepted for publication 7 August 1969. DOI: 10.1094/Phyto-60-192.

Verticillium albo-atrum and Fusarium oxysporum f. sp. lycopersici produced polygalacturonase within stems of susceptible tomato and cotton, and polygalacturonase activity correlated well with the onset and development of disease symptoms. Although the test fungi were recovered from inoculated, resistant tomato stem sections, polygalacturonase activity and disease symptoms were either absent or much lower than in the susceptible tomato. Polygalacturonase production by the virulent T-1 cotton isolate of V. albo-atrum was much higher than by the less virulent SS-4 isolate both in vitro and in susceptible cotton stem sections. Polygalacturonase activity and the occurrence of disease symptoms in all susceptible host-pathogen combinations investigated, coupled with the absence of both polygalacturonase activity and symptom development in all resistant combinations, suggests that polygalacturonases have a role in the pathogenesis by these fungi. Persistence of these fungi in resistant stem sections in the absence of both polygalacturonase production and symptom expression supports this idea, and indicates that resistant host tissues may regulate polygalacturonase production by these fungi.