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Semiselective Agar Medium for Isolation of Clavibacter michiganense subsp. michiganense from Tomato Seed. M. Fatmi, Department of Plant, Soil, and Entomological Sciences, University of Idaho, Moscow 83843, Present address: Institut Agronomique et Veterinaire Hassan II, Complexe Horticole deAgadir B.P. 438, Agadir, Morocco; N. W. Schaad, Department of Plant, Soil, and Entomological Sciences, University of Idaho, Moscow 83843. Phytopathology 78:121-126. Accepted for publication 14 August 1987. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/Phyto-78-121.

A semiselective agar medium was developed for isolating Clavibacter michiganense subsp. michiganense, the causal agent of bacterial canker of tomato, from tomato seed. The new medium, designated SCM (semiselective medium for C. michiganense), contained sucrose, mono-and dipotassium phosphate, magnesium sulfate, yeast extract, nicotinic acid, boric acid, nalidixic acid, potassium tellurite, and cycloheximide. Recovery of 34 strains of C. michiganense on SCM in comparison to nutrient broth yeast extract (NBY) medium ranged from 85 to 132%, and more than 98% of the recoverable tomato seed saprophytic bacteria growing on NBY did not grow on SCM. SCM was quantitatively and qualitatively superior to other selective media for C. michiganense. Extracting seed by blending for 10-15 min in a commercial laboratory blender resulted in an increase of 100% or more over washing seeds in a flask at 4 C for 72 hr. A single contaminated seed containing as few as 50 colony-forming units of C. michiganense was detectable in samples of 10,000 seeds.

Additional keywords: bacteria.