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Ontogenetic Predisposition of Tomato Foliage to Race O of Phytopthora infestans. L. J. Dowley, Senior Research Officer, Plant Pathology and Entomology Department, The Agricultural Institute, Carlow, Ireland; D. G. Routley(2), and L. C. Peirce(3). (2)(3)Professors of Plant Science, respectively, Plant Science Department, University of New Hampshire, Durham, NH 03824. Phytopathology 65:1422-1424. Accepted for publication 7 July 1975. DOI: 10.1094/Phyto-65-1422.

Seven resistant and six susceptible tomato lines were tested for reaction to Phytophthora infestans (tomato race O) at five dates, 43 to 99 days after planting, and three leaf positions, using detached leaves and standard inoculum concentrations. Lines showed greatest susceptibility in the youngest plants. Resistance in resistant plants increased with maturity. Susceptible lines were least susceptible at an intermediate stage of growth, after which susceptibility tended to increase slightly. Lower leaves of a given plant were most susceptible and the upper leaves were most resistant.

Additional keywords: physiological plant age, epidemiology, chronological plant age.