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Activity of Juniper Diffusates on Spores of Phomopsis juniperovora. Ronald W. Pero, Research Assistant, University of Rhode Island, Kingston 02881, Present address of senior author: Postdoctorate Appointee, Department of Plant Pathology, North Carolina State University, Raleigh 27607; Frank L. Howard, Professor of Plant Pathology, University of Rhode Island, Kingston 02881. Phytopathology 60:491-495. Accepted for publication 17 October 1969. DOI: 10.1094/Phyto-60-491.

Juniperus virginiana and J. chinensis ‘Keteleeri’ foliage immersed in water yield diffusible substances that affect spore germination. Concentrations similar to those that occur in drops of water on J. virginiana leaves stimulate germination and germ tube elongation of Phomopsis juniperovora spores. The solutes from Keteleeri foliage exposed to water for an equal period have no significant stimulatory effect on P. juniperovora spores, but if the diffusate from Keteleeri is concentrated 10 to 40 times, then P. juniperovora spores are stimulated. Keteleeri is resistant to P. juniperovora infection; J. virginiana is susceptible. Two active components were isolated, potassium as K2SO4 and an unsaturated carboxylic acid. The carboxylic acid had ultraviolet absorption maxima of 212 and 262 mµ in distilled water, an equivalent wt of 105.69, a melting point of 164-166 C (unc.), and an elemental composition of carbon 47%, hydrogen 9%, and oxygen 44%. Potassium above 1,250 ppm in a 5:1 ratio with sodium stimulated J. juniperovora spores to germinate. The carboxylic acid was approximately 16 times more active, causing stimulation of spores above 77 ppm. Potassium was found in all juniper diffusates analyzed, whereas the carboxylic acid was found only in foliar diffusate from actively growing, 7-year-old J. virginiana.