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Effect of Infection by Verticicladiella wagenerii on the Physiology of Pinus ponderosa. J. A. Helms, School of Forestry and Conservation and Department of Plant Pathology, University of California, Berkeley 94720; F. W. Cobb, Jr.(2), and H. S. Whitney(3). (2)(3)Department of Fisheries and Forestry, Edmonton, Alberta, Canada. Phytopathology 61:920-925. Accepted for publication 23 February 1971. DOI: 10.1094/Phyto-61-920.

The effects of Verticicladiella wagenerii infection on host tree physiology were studied on ponderosa pine seedlings growing under field conditions. The study was carried out at an elevation of 1,300 m in the Sierra Nevada Mountains of California from July to October 1969. Data analyzed were obtained at approximately 2-week intervals during the noon period from 1100-1300 hr. Despite soil temperature reaching 24 C during the summer, approximately 80% of all seedlings inoculated became infected. One month after inoculation, dramatic decreases in net photosynthesis and transpiration occurred in diseased seedlings together with marked increases in foliar water stress and closure of stomates despite the absence of visual symptoms. No real differences in dark respiration were observed. These effects continued until the end of the study when most of the inoculated seedlings had died. These findings elucidate some of the fungus-host interactions of the root stain disease, which is commonly observed in parts of the mixed conifer forests in California. The importance of the fungus is discussed, particularly from the standpoint of its predisposing trees to bark beetle attack.

Additional keywords: respiration ratios.