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Inhibitory and Lytic Effects of a Nonionic Surfactant on Various Asexual Stages in the Life Cycle of Pythium and Phytophthora Species. M. E. Stanghellini, Professor, Department of Plant Pathology, University of Arizona, Tucson 85721; J. A. Tomlinson, Senior virologist, National Vegetable Research Station, Wellesbourne, Warwick, England, CV35 9EF. Phytopathology 77:112-114. Accepted for publication 14 July 1986. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/Phyto-77-112.

Zoospores of Pythium aphanidermatum, P. dissotocum, P. intermedium, P. tracheiphilum, and Phytophthora nicotianae ceased motility and lysed within 1 min after placement in a solution containing 20 Μg of Agral per milliliter. Zoospores of the same species, with the exception of P. tracheiphilum, remained motile for 14 hr or more in the absence of Agral. Solutions containing 20 Μg of Agral per milliliter were also totally inhibitory to vesicle formation and zoospore production by the four species of Pythium and to zoospore production by Phytophthora nicotianae. Vesicles were formed by all Pythium spp. except P. intermedium in solutions containing 15 Μg of Agral per milliliter. All vesicles of P. aphanidermatum and P. dissotocum and most of those of P. tracheiphilum, however, lysed within 10 min after formation. The lytic effect on both vesicles and zoospores indicates that the mode of action of Agral resides in disruption of the integrity and / or permeability of the plasma membrane of fungus structures lacking a cell wall. Agral had little or no effect on mycelial growth or direct germination of encysted zoospores and sporangia of the same fungi. The potential use of Agral for controlling root diseases caused by species of Pythium and Phytophthora that rely on zoospores for plant-to-plant spread is discussed.