Bacterial Blight of Soybeans

Universitat Bremen

Bacterial Blight of Soybeans


Bacterial blight, caused by Pseudomonas syringae pv. glycinea (Coeper) Young et. al., is the most common bacterial disease of soybean. It was identified in Nebraska as early as 1906. P. syringae pv. glycinea can be further divided into pathogenic races based on the symptoms they elicit on various cultivars. The bacterium overwinters in crop residue and in seed. Disease development is favored by cool, wet weather (frequent rain or dew). Primary infection occurs when bacterial cells are windborne or rain splashed from residue on the soil surface to leaves and enter the host tissue through stomata. Free water on the leaf surface is necessary for infection to occur. Primary infection of cotyledons may also occur via infected seed. Once the bacterium has entered the host it produces a toxin which inhibits chlorophyll production. Secondary spread of the bacterium occurs when infected and noninfected leaves rub together during cultivation and via windblown and rain splashed. Seed is infected through pod infections during the season or by contact with infected material during harvest or storage. Infection may occur at any time during the growing season but is most common at midseason and continues until arrested by hot, dry weather.

Symptoms


Infections occurring early in the growing season are characterized by brown lesions on the margin of cotyledons. These lesions enlarge, turn dark brown and affected tissue collapses. Infected seedlings are stunted and may die if the growing point becomes infected. Lesions occurring at midseason are most common on leaves but may also be found on petioles, stems and pods. Leaf lesions begin as small, water-soaked, angular spots. These spots turn yellow then begin to enlarge. At this point they turn brown or black as tissue dies. Large spots are surrounded by a water-soaked margin of active infection and a yellow halo. Strong winds may cause the large areas of infected leaf tissue to tear, giving the plant a tattered appearance. Premature defoliation also occurs on heavily infected plants. Petiole and stem lesions are large and dark. Pod lesions begin as water-soaked spots that enlarge and coalesce becoming dark with age. Infected seed exhibits a wide range of symptoms. Seed may appear healthy or be so heavily colonized by the bacterium that slimy growth covers the seed. Symptom development may continue in storage where seed maintains its healthy appearance, becomes shriveled or discolored, or develops lesions that are raised or sunken.

Plant Health Management

References

Highlighted Area

Bacterial blight is the most commonly occurring bacterial disease of soybeans. However, significant yield loss is seldom seen under natural infection. The real economic loss associated with this disease is in the area of seed production.

ncidences greater than 90% may occur in some seed lots with no visible symptoms. Seed exported to the European Community (EC) must be tested for the pathogen in accordance with phytosanitary regulations. Testing can be time consuming and costly since laboratory tests (culturing of the pathogen) are required.

Useful Links

Caveat

This description is presented for information only and no endorsement is intented for products listed, nor criticism meant for products not mentioned. Always consult the product label before bying and using any pesticide.

Material contained on the Links from the page are the responsibility of the linked page's author(s).

Questions, Comments, Complaints and Complements?

This page was drafted by: Jane Christensen, Department of Plant Pathology, University of Nebraska-Lincoln

Disease images were provided by: Dr. David Wysong, Department of Plant Pathology, University of Nebraska-Lincoln

This page is maintained by:

Dr. J.E. Partridge, Department of Plant Pathology, University of Nebraska-Lincoln

jpartridge1@unl.edu Home Page

Copyright (C) 2003 J.E. Partridge, University of Nebraska-Lincoln. All Rights Reserved.