VIEW ARTICLE

Resistance

Reaction of Cotyledons of Safflower Cultivars to Phytophthora drechsleri: Effect of Temperature and Inheritance. C. A. Thomas, Research Plant Pathologist, Applied Plant Pathology Laboratory, Plant Protection Institute, Agricultural Research Service, U.S. Department of Agriculture, Beltsville, MD 20705; R. F. Hill, Agricultural Research Technician, Applied Plant Pathology Laboratory, Plant Protection Institute, Agricultural Research Service, U.S. Department of Agriculture, Beltsville, MD 20705. Phytopathology 67:698-699. Accepted for publication 6 December 1976. Copyright © 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-698.

Cotyledons of 7-day-old safflower (Carthamus tinctorius) seedlings were wound-inoculated with a virulent isolate of Phytophthora drechsleri. Inoculated plants were held in a controlled environment with continuous light (13,988 lux) at 22, 26, 28, and 30 C for 10 days. Cotyledons of the cultivars Nebraska 10, both root and hypocotyl tissues susceptible to P. drechsleri, and Gila and US 10, roots resistant and hypocotyls susceptible, were susceptible at all temperatures. Cotyledons of VFR 1, root tissue resistant and hypocotyl tissue susceptible, and USB, both root and hypocotyl tissues resistant, were resistant at 22 and 26 C, showed intermediate symptoms at 28 C, and were susceptible at 30 C. The cotyledon reactions of the F₁, F₂, and BC₁ progenies derived from a VFR 1 × Nebraska 10 cross indicate that resistance at 22 C is conditioned by a single dominant factor.