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922 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. herbicola utilizes a wider range of amino acids 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 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

[Current Plant Science and Biotechnology in Agriculture] Plant Pathogenic Bacteria Volume 4 || Role of Amino Acids in Biological Control of Erwinia Amylovora by Erwinia Herbicola

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Page 1: [Current Plant Science and Biotechnology in Agriculture] Plant Pathogenic Bacteria Volume 4 || Role of Amino Acids in Biological Control of Erwinia Amylovora by Erwinia Herbicola

922

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

Page 2: [Current Plant Science and Biotechnology in Agriculture] Plant Pathogenic Bacteria Volume 4 || Role of Amino Acids in Biological Control of Erwinia Amylovora by Erwinia Herbicola

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!.

923

amylovora. In the absence of pollinating insects, the well-protected apple

nectaries ace probably not colonized effectively by the antagonist.