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Integrated Effects of Polygenic Resistance and a Protective Fungicide on Development of Potato Late Blight. W. E. Fry, Department of Plant Pathology, Cornell University, Ithaca, New York, 14853; Phytopathology 65:908-911. Accepted for publication 14 March 1975. DOI: 10.1094/Phyto-65-908.

The relative polygenic resistance to Phytophthora infestans in eight potato (Solanum tuberosum) cultivars was determined by calculating the apparent infection rate (r) for each cultivar in field plots. The effects on r of weekly applications of fungicide to Sebago (polygenically resistant) and Russet Rural (susceptible) were determined and related quantitatively to the effect of polygenic resistance. On the basis of reduction in r, the effect of greater polygenic resistance in Sebago than in Russet Rural was equivalent to approximately 0.5 kg fungicide (a.i.)/hectare applied weekly to Russet Rural.

Additional keywords: horizontal resistance, epidemic, pest management.