VIEW ARTICLE

Ecology and Epidemiology

The Role of Salinity in the Development of Phytophthora Root Rot of Citrus. N. S. Blaker, Former graduate student, Department of Plant Pathology, University of California, Davis 95616, Present address: Department of Vegetable Crops, University of California, Davis 95616; J. D. MacDonald, associate professor, Department of Plant Pathology, University of California, Davis 95616. Phytopathology 76:970-975. Accepted for publication 9 April 1986. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/Phyto-76-970.

A field survey of the Coachella Valley, CA, indicated that root rot of citrus, caused by Phytophthora parasitica, increased with increasing soil salinity. When rootstock seedlings were grown hydroponically in the greenhouse and exposed briefly to high levels of salinity (EC = 22 dS/m) before inoculation, those of the sweet orange cultivar Pineapple were predisposed to severe root rot, whereas those of the citrange cultivar Troyer were unaffected. However, Troyer seedlings grown for 9 wk in soil salinized to an EC_e of 3-4 dS/m and infested with P. parasitica had 30% of their total root length decayed by Phytophthora, whereas plants in infested nonsaline soil had only 10% decay. Similar results were obtained with Pineapple sweet orange seedlings at even lower levels of soil salinity. Total root growth and production of new roots by Troyer seedlings was greatly inhibited in saline soil. The results suggest that reduced root growth, as well as predisposition, may contribute to the severe root rot observed under saline field conditions.