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Lognormal Distribution of Bacterial Populations in the Rhizosphere. J. E. Loper, Former graduate research assistant, Department of Plant Pathology, University of California, Berkeley 94720, Present address of senior author: Chevron Chemical Co., 940 Hensley Street, Richmond, CA 94804; T. V. Suslow(2), and M. N. Schroth(3). (2)Staff scientist, Advanced Genetic Sciences, Berkeley, CA; (3)Professor, Department of Plant Pathology, University of California, Berkeley 94720. Phytopathology 74:1454-1460. Accepted for publication 26 June 1984. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/Phyto-74-1454.

Rhizosphere bacterial populations were estimated on 43 sets of up to 60 entire root systems of young greenhouse and field-grown plants (potato, sugar beet, barley, tomato, or radish). Total aerobic bacterial populations, total fluorescent bacterial populations, and populations of inoculated plant growth-promoting strains of Pseudomonas putida or P. fluorescens generally approximated a lognormal distribution as determined by several graphic and statistical tests of normality (Rankit diagrams, Shapiro-Wilk tests, and Kolmogorov tests). Total bacterial populations and populations of fluorescent pseudomonads varied by a factor of 10 to 50 within a given set of root systems. Seed piece or seed populations of inoculated rhizobacterial strains A1 or SH5 varied by a factor of 4- 34, respectively, whereas rhizosphere populations of these strains on potato or sugar beet varied by a factor of 100- 1,000. Populations of these inoculated strains of Pseudomonas on seed or seed pieces also approximated a lognormal distribution.