Blackwell Publishing Journal Backfiles 1879-2005
Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
An enzyme-linked immunosorbent assay (ELISA) was standardized for detecting Xanthomonas campestris pv. undulosa (Xcu) in plant tissues. Antiserum prepared against somatic antigens of Xcu reacted with cells of pathovars undulosa, cerealis, translucens and phleipratensis, but not with other bacterial species belonging to the genera Xanthomonas, Pseudomonas, Agrobacterium, Clavibacter, and Erwinia. The lower limit of detection of pure cultures was 5 × 103 cfu/ml. A semi-selective enrichment broth (SSEB) improved the recovery of Xcu in cultures mixed with contaminating bacteria commonly found on wheat seeds. In ELISA tests the enriched samples gave two- to three-fold increases in A405nm readings when viable cells of Xcu were present. By enrichment, X. campestris pathovars undulosa, cerealis, translucens and phleipratensis were detected in samples that originally had less than 5 × 102 cfu/ml. Semi-selective enrichment combined with ELISA (SSEB-ELISA) allowed for determination of the percentages of infestation of wheat seed lots. Potential seedling infection (PSI) of naturally infested wheat seed lots was obtained by growing seed samples in the greenhouse under conditions optimal for disease development. Three methods were evaluated for their capacity to estimate the PSI: ELISA, combined SSEB and ELISA, and direct plating onto semi-selective XTS agar. Percentages of seed infestation determined by combined SSEB and ELISA resulted in a highly significant correlation with the PSI (r = 0·87, P× 005), whereas determinations made by ELISA or direct plating onto XTS did not significantly correlate with the PSI determined in the greenhouse. This test may constitute a convenient tool for fast initial screening of wheat seed lots in wheat certification programmes.
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