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Effects of Temperature and Relative Humidity on Germination, Growth, and Sporulation of Zygophiala jamaicensis. C. M. Ocamb-Basu, Department of Plant Pathology, North Carolina State University, Raleigh 27695-7616; T. B. Sutton, Department of Plant Pathology, North Carolina State University, Raleigh 27695-7616. Phytopathology 78:100-103. Accepted for publication 15 July 1987. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/Phyto-78-100.

In vitro studies of Zygophiala jamaicensis, the cause of flyspeck on apple, demonstrated that conidia germinated more rapidly and over a wider temperature range than did ascospores. Some conidia germinated at 20 to 28 C after 2 hr, but no ascospores germinated until 4 hr had elapsed. Ascospores germinated at temperatures from 16 to 28 C, whereas conidia germinated at 8 to 28 C. Conidia required relative humidity of 96.2% or greater for germination, whereas ascospores had a higher minimum relative humidity threshold (>96.2%) for germination. Mycelial growth of Z. jamaicensis occurred from 12 to 28 C, with an optimum of 16 to 24 C. Production of conidia occurred from 12 to 24 C and was greatest at 16 and 20 C. Relative humidity of 96.2% or greater was necessary for mycelial growth and sporulation. It is hypothesized that the higher relative humidity requirement of Z. jamaicensis limits its development in the orchard compared to that of Gloeodes pomigena (the cause of sooty blotch).