Association of a Spiroplasma with Brittle Root of Horseradish

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Abstract
Brittle root (BR) horseradish from Illinois [USA] was consistently distinguished from healthy horseradish by the dark discoloration of phloem tissue of the root of affected plants and also by the reaction of stained (Dienes'' stain) phloem of leaf or root. Mycoplasma-like organisms were observed by EM in ultrathin sections of BR horseradish phloem, but not in phloem of healthy plants. A helical, motile, wall-free spiroplasma was isolated in 36 of 36 attempts from surface-sterilized leaves and roots of diseased horseradish. No spiroplasma was isolated from healthy horseradish obtained from Illinois and California. The spiroplasma isolated (HR-101) from horseradish was triple cloned and deposited at the American type Culture Collection (ATCC 33451). The HR-101 spiroplasma isolate resembled Spiroplasma citri in morphology, ultrastructure and serology. Optimum temperature for the growth of the organism was 31.degree. C. The organism also grew at 22, 25, 38 and 34.degree. C, but not at 19 and 40.degree. C. Growth of the HR-101 isolated required serum and was inhibited by digitonin. The organism can hydrolyze arginine. In serological tests by growth inhibition and deformation, the spiroplasma isolates from diseased horseradish were indistinguishable from S. citri. The spiroplasma in BR horseradish was effectively detected by enzyme-linked immunosorbent assay (ELISA) conducted with our antisera prepared against the HR-101 isolate or S. citri. Positive ELISA reaction also was obtained with extracts from stubborn-diseased citrus by using HR-101 spiroplasma antiserum.

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