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ROLE OF AMINO ACIDS IN BIOLOGICAL CONTROL OF ERWINIA AMYLOVORA BY ERWINIA HERBICOLA
M.J. HATTINGH, S.V. BEER AND J.R. RUNDLE
Department of Plant Pathology Cornell University Ithaca, NY 14853 USA
Previous studies have indicated that fire blight, caused by Erwinia
amylovora, can be controlled by spraying apple blossoms with suspensions of
E. herbicola. The most acceptable hypothesis to explain the mechanism of
suppression involves depletion of organic nitrogen compounds in plant
tissue by ~. herbicola. To explore this hypothesis further, utilization of
single amino acids by 8 strains of E. amylovora and 7 strains of
E. herbicola was determined in vitro. In general, strains of both species
utilized L-alanine, a-aminobutyric acid, L-asparagine, L-aspartic acid,
L-citrulline, L-glutamic acid, L-glutamine, and L-histidine. L-arginine,
L-cysteine, L-ornithine, L-phenylalanine, L-proline, L-serine, and
L-tryptophane were used by some or all of the E. herbicola strains. None
of the strains tested utilized B-alanine, glycine, L-isoleucine,
L-leucine, L-lysine, L-methionine, L-threonine, L-valine, DL-pipecolic acid
or amino-cyclopropane. Thus,~. herbicola utilizes a wider range of amino
acids than~. amylovora.
Direct evidence for the role of amino acids in biological control was
sought by adding selected compounds to immature pear fruit and to apple
blossoms which were treated with E. amylovora and~. herbicola. L-alanine
applied to immature pear fruit tissue partially prevented ~. herbicola
strain l12Y (utilizes L-alanine poorly) from protecting fruit from
infection by ~. amylovora 107 (utilizes L-alanine effectively). E.
herbicola 252 (utilizes L-proline) suspended in water or in L-proline was
equally effective in reducing populations of ~. amylovora 273 (does not
utilize L-proline) on apple blossoms and infection of flowers. However,
L-proline applied alone was as effective as the antagonist in reducing
infection. Although competition for a single amino acid could not be
E. L. Civerolo et al. (eds.), Plant pathogenic bacteria© Martinus Nijhoff Publishers, Dordrecht 1987
demonstrated on apple blossoms, !. herbicola and !. amylovora appear to
occupy the same site on blossoms. Antagonistic!. herbicola colonizes
stigmas, and this apparently prevents or reduces infection by!.
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amylovora. In the absence of pollinating insects, the well-protected apple
nectaries ace probably not colonized effectively by the antagonist.