Influence of Time Intervals Among Wounding, Inoculation, and Incubation on Stem Blight of Geranium Caused by Botrytis cinerea. M. K. Hausbeck, Former Graduate Research Assistant, Department of Plant Pathology, The Pennsylvania State University, University Park 16802. S. P. Pennypacker, Associate Professor, Department of Plant Pathology, The Pennsylvania State University, University Park 16802. Plant Dis. 75:1168-1172. Accepted for publication 8 May 1991. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/PD-75-1168.

All stems of geranium (Pelargonium × hortorum) stock plants inoculated with Botrytis cinerea and incubated in a dew chamber under conditions conducive for disease development within 12 hr of excising cuttings (stem wounding) became blighted. Disease incidence maxima were 38 and 29% when plants were inoculated 1 and 3 days, respectively, after stem wounding and placed in an environment of low relative humidity (RH < 60%) before incubation in a dew chamber. The area under the incidence of stem blight disease progress curve (AUDPC) revealed a minimum of 1 day in an environment of low RH between stem wounding and subsequent inoculation and incubation in a dew chamber was necessary to significantly limit stem blight incidence. When averaged, at least 94% of the stems became blighted when plants were exposed to an environment of low RH for 1 day after inoculation, before incubation in a dew chamber. When plants were inoculated and subjected to an environment of low RH for 3, 5, and 7 days before incubation in a dew chamber, an average of 69, 85, and 50% of the stems, respectively, became blighted. According to the AUDPC data, when inoculated plants were placed in an environment of low RH for a minimum of 1 day before incubation in a dew chamber, stem blight incidence was significantly limited. The AUDPC data indicated that the longer inoculated plants were maintained in an environment of low RH before incubation in a dew chamber, the lower the stem blight incidence.