VIEW ARTICLE

Ecology and Epidemiology

Colonization of the Rhizosphere by Biological Control Agents Applied to Seeds. W. L. Chao, Research associate, Department of Horticultural Sciences, Cornell University, New York State Agricultural Experiment Station, Geneva 14456, Current address: Department of Microbiology, Soochow University, Wai Shuang Hsi, Shih Lin, Taiwan, Republic of China; E. B. Nelson(2), G. E. Harman(3), and H. C. Hoch(4). (2)(3)Research associate, and professor, respectively, Department of Horticultural Sciences, Cornell University, New York State Agricultural Experiment Station, Geneva 14456, (2)Current address: Department of Plant Pathology, University of Arkansas, Fayetteville 72701; (4)Associate professor, Department of Plant Pathology, New York State Agricultural Experiment Station, Geneva 14456. Phytopathology 76:60-65. Accepted for publication 29 July 1985. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/Phyto-76-60.

The ability of various fungi and bacteria to move from inoculated seeds to developing roots was studied. Plant roots growing into soil-free moist chambers were not colonized by Trichoderma spp., but were colonized by Enterobacter cloacae. When roots were grown in sterile soil, Trichoderma harzianum was detected in the rhizosphere of the upper half of the roots, while E. cloacae colonized the entire rhizosphere. In untreated soil, none of the organisms studied (T. harzianum, T. koningii, Gliocladium virens, Penicillium funiculosum, E. cloacae, Pseudomonas fluorescens, P. putida, or another fluorescent Pseudomonas sp.) could be detected in the rhizosphere more than 3 cm below the planted seed. In autoclaved soil to which fungi were added, E. cloacae colonized roots well, while T. harzianum was inhibited. Conversely, in autoclaved soil to which soil bacteria were added, E. cloacae was inhibited, and T. harzianum grew well. Percolating water enhanced the downward movement of both bacterial and fungal propagules.