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Etiology

Race 3 of Phytophthora parasitica var. nicotianae. John L. McIntyre, Assistant Plant Pathologist, The Connecticut Agricultural Experiment Station, New Haven, CT 06504; G. S. Taylor, Plant Pathologist, The Connecticut Agricultural Experiment Station, Windsor, CT 06095. Phytopathology 68:35-38. Accepted for publication 15 July 1977. Copyright © 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-35.

Connecticut (CT) isolates of Phytophthora parasitica var. nicotianae cause typical black shank symptoms on tobacco and have similar morphology to isolates of races 0 and 1. It differs, however, in that the symptom response of the differential tobacco Nicotiana nesophila to CT is similar to that caused by race 1, but on cultivar 1071 the symptom response is similar to that caused by race 0. Tobacco cultivar A23, which is resistant to race 2, is susceptible to CT, and cultivar L8 is moderately susceptible to CT. After 5 days of growth in liquid culture, the dry weight of CT mycelia is 50% less than that of races 0 or 1. Races 0 or 1 cause the pH of culture broth to change from 7.2 to about 5.3 but in broth cultures of CT pH remains essentially unchanged. On an agar medium containing sucrose and 2,3,5-triphenyl tetrazolium chloride (TTZ), the TTZ is reduced by races 0 and 1 but not by CT. Isolates of CT qualify as a new race, race 3, of P. parasitica var. nicotianae.