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Recognition and Detection in Seed of the Xanthomonas Pathogens That Cause Cereal Leaf Streak Using rDNA Spacer Sequences and Polymerase Chain Reaction. M. Maes, Research Station for Plant Pathology, Ministry of Agriculture, B. Van Gansberghelaan 96, 9820 Merelbeke, Belgium; P. Garbeva, and O. Kamoen. Research Station for Plant Pathology, Ministry of Agriculture, B. Van Gansberghelaan 96, 9820 Merelbeke, Belgium. Phytopathology 86:63-69. Accepted for publication 14 September 1995. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/Phyto-86-63.

Two short DNA sequences, situated in the spacer segment between the 16S and 23S rRNA genes and flanking an alanine-tRNA gene, varied among four xanthomonads. Polymerase chain reaction (PCR) primers designed to exploit this variability amplified a 139-bp fragment from strains of five leaf streak pathogens of cereals, Xanthomonas campestris pvs. cerealis, hordei, secalis, translucens, and undulosa, and five X. campestris pathovars pathogenic on forage grasses, X. campestris pvs. arrhenatheri, graminis, phlei, phleipratensis, and poae. These primers did not amplify DNA from 52 other bacteria, including other xanthomonads. PCR specificity was largely determined by one primer site, which is located in a 57-bp sequence present only in the rDNA spacer of DNA homology group I strains. Amplification of extracts of 2 seed lots known to be contaminated with a translucent leaf streak pathogen produced the specific 139-bp PCR fragment; 4 of 27 additional seed lots with unknown levels of leaf streak pathogens were positive for this amplified fragment. The assays proved to be fast and relatively sensitive (2 103 CFU/g of seed), indicating the technique might be useful for detecting pathogens in seed.