VIEW ARTICLE

Ecology and Epidemiology

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.