ISHS Acta Horticulturae 704: X International Workshop on Fireblight
BIOCHEMICAL ANALYSES OF POMACEOUS STIGMA EXUDATES AND RELEVANCE TO BIOLOGICAL CONTROL OF FIRE BLIGHT |
| Author: | P.L. Pusey |
| Keywords: | Malus, Pyrus, Erwinia amylovora, apple, pear, crab apple |
| Abstract:
Microbial antagonism toward Erwinia amylovora on stigmas of pear and apple flowers has been widely demonstrated. Since knowledge of the chemical environment on stigmas could advance the selection and use of antagonists, stigma exudates from different pomaceous cultivars and ages were analyzed for sugars and amino acids. Flowers were collected in groups of 50, and one-by-one, their stigmas were submerged and sonicated in the same aliquot of 600 μl water. Pollen and macromolecules were removed by centrifugation and filtration. Sugars were converted to trimethylsilyl derivatives and analyzed by GC. Amino acids were converted to fluorescent derivatives using o-phthaldialdehyde and separated by HPLC. The predominant sugars were glucose and fructose; predominant amino acids were asparagine, glutamine, proline and serine. A liquid medium was developed with these compounds to evaluate antagonist-pathogen interactions. The stigma-based medium was placed in microplates, 250 μl/well, then inoculated with selected bacterial antagonists 24 h prior to inoculation with E. amylovora. The same antagonist strains were applied to stigmas of detached crab apple flowers 24 h in advance of the pathogen. Differences among antagonists according to their effect on the size of pathogen populations in the artificial medium were similar to the differences indicated in tests with flowers. The stigma-based medium will likely be modified as we learn more about the chemistry of apple and pear stigma exudates. It remains to be proven whether the medium is more predictive of antagonist performance on flowers than other artificial media used for this purpose. | |
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