NPIPM:Bacterial pustule on soybean

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Compiled by: Buyung Hadi, from the materials by: Loren Giesler and Dean Malvick

Contents

Causal Organism

Bacterial pustule is caused by the bacterium Xanthomonas axonopodis pv. glycines.

Symptoms and Signs

Early symptoms consist of small, pale green spots with raised centers on leaves in the mid- to upper canopy. As the disease progresses, small brown-colored pustules form in the middle of the spots and the spots turn yellow. The spots may merge, forming large irregularly yellowing lesions. Bacterial pustule symptoms are easily confused with soybean rust pustules. Soybean rustpustules have circular openings at the top as gateways for spore spread. Bacterial pustules do not have this feature although under microscope bacterial pustules may appear to have crack openings on their surfaces. Bacterial pustule lesions are sometimes confused with the lesions caused by bacterial leaf blight. Bacterial leaf blight lesions appear water-soaked while the lesions of bacterial pustule do not. As in other bacterial diseases, if a soybean leaf with lesions due to bacterial pustule is cut and submerged in water, bacteria will stream out of the infected tissue.

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Photo by , , Bugwood.org
Image needed: Bacterial pustule on whole soybean leaf
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Image needed: Bacterial pustule on whole soybean leaf
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Photo by Paul Bachi, University of Kentucky Research and Education Center, Bugwood.org
A close up of bacterial pustules. The spots range in size from small flecks to larger necrotic areas. The center of the spots have a raised pustule on the lower leaf surface which can appear similar to structures seen with Asian soybean rust.
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A close up of bacterial pustules. The spots range in size from small flecks to larger necrotic areas. The center of the spots have a raised pustule on the lower leaf surface which can appear similar to structures seen with Asian soybean rust.
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Photo by , , Bugwood.org
Image needed: The circular opening on soybean rust pustule
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Image needed: The circular opening on soybean rust pustule
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Photo by , , Bugwood.org
Image needed: The crack opening of bacterial pustule
View in Bugwood Image Database
Image needed: The crack opening of bacterial pustule
5368282
Photo by Paul Bachi, University of Kentucky Research and Education Center, Bugwood.org
The whitish strands oozing out of cut soybean leaf with bacterial pustule are called bacterial streaming, a sign of bacterial disease
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The whitish strands oozing out of cut soybean leaf with bacterial pustule are called bacterial streaming, a sign of bacterial disease

Disease Impacts

Bacterial pustule rarely cause defoliation and yield loss.

Life Cycle and Epidemiology

Similar to bacterial leaf blight pathogen, X. axonopodis survives the winter on crop residue in the field. Plant infection occurs when infected crop residue on soil surface is dislodged by the wind or rain splash onto healthy plants. Leaf wetness is required for infection to occur. Thus, field cultivation while the leaves are wet (e.g. from previous rain) may also blow infected crop residue onto healthy soybean tissues and promote new infection. Unlike bacterial leaf blight pathogen, X. axonopodis development is not hampered by high temperatures. In fact, the optimum temperature for bacterial pustule pathogen ranges between 86-92˚F. In the field, this ability to thrive in high temperatures translates into continuous disease development in wet summers. Bacterial pustule pathogen may infect soybean seeds .

Management Approaches

Scouting is recommended between R1 through R6 of soybean developmental stages. Resistant varieties and pathogen-free seeds should be used to manage bacterial pustule. Crop rotation and plowing the field before planting also help to reduce field inoculum level of the pathogenic bacterium. Try to avoid cultivation when the leaves are wet.

Online Resources

University of Nebraska

University of Minnesota

Plant Health Initiative

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