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Inheritance of Powdery Mildew Resistance in Greenhouse-Grown Versus Field-Grown California Strawberry Progenies. M. D. Nelson, Department of Plant Pathology, University of California, Davis 95616; W. D. Gubler(2), and D. V. Shaw(3). (2)Department of Plant Pathology, University of California, Davis 95616; (3)Department of Pomology, University of California, Davis 95616. Phytopathology 85:421-424. Accepted for publication 29 December 1994. Copyright 1995 The American Phytopathological Society. DOI: 10.1094/Phyto-85-421.

Seedlings from 17 strawberry (Fragaria ananassa) progenies were evaluated for resistance to powdery mildew (Sphaerotheca macularis f. sp. fragariae) using controlled greenhouse inoculations and field trials with differing natural infection levels. Genetic differences contributed a large fraction of the phenotypic variance among individuals for both disease incidence (H2 = 0.440.71) and disease severity (H2 = 0.700.94) in all cases, but the variance attributable to breeding value for these traits varied substantially with infection level (h2 = 0.120.90). Likewise, genotypic and breeding value correlations for a single trait scored in different infection environments suggest that different genes may confer resistance with different levels of disease pressure. Greenhouse evaluations corresponded well with rankings obtained under high levels of field infection. However, evaluation of genetic potential only under conditions of extreme infection may ignore valuable components of partial resistance, and should not be used in isolation.