Halo Blight of Beans

Halo Blight of Beans


Halo blight occurs world wide wherever beans are grown. In the United States, yield losses as high as 43 % have been reported. The disease is caused by Halo Blight of Beans (Burkholder) Young et. al. The bacterium is quite variable in nature which has made the development of resistant varieties difficult. It can survive as both a parasite and/or an epiphyte on plant tissue. P. syringae pv. phaseolicola also produces a phytotoxin call phaseolotoxin. All species of common bean (Phaseolus vulgaris) are hosts of the bacterium but the most susceptible types are snap, red kidney, cranberry and yellow eye field beans. Lima and scarlet runner beans and kudzu vine are also hosts of the pathogen. The bacterium overwinters in and on seed and in plant debris on the soil surface. Inoculum from contaminated seed is the main source of primary inoculum in areas where bacteria in debris cannot survive cold winter temperatures. Bacteria contaminated seed are usually present in low numbers per given seed lot but disease development and spread can occur so quickly that even a very low number (one in 16,000 seeds) can result in a severe outbreak. Seedling produced from infected seed provide primary inoculum. They main exhibit no symptoms initially but main be heavily loaded with bacterial cells. The disease cycle begins when bacteria are carried in wind blown rain from infected cotyledons to new plants. Bacteria may also be rain splashed of carried on soil particles from infected debris. Infection and disease development are favored by cool to moderate temperatures and wet conditions. A layer of free water is necessary for infection to occur. The bacteria enter the plant via natural openings (stomata and hydathodes) and wounds. Once inside the plant the bacterium can spread through the xylem to other areas. Secondary spread, on individual plants or to other plants, occurs when bacteria produced in lesions on aerial plant parts are disseminated. Secondary inoculum is spread by a number of means including, wind blown rain, plant to plant contact, irrigation water, animals, insects, and field workers. Seed becomes infected via the vascular system or by pod infection.

  • Symptoms


    Symptoms produced by an infection of P. syringae pv. phaseolicola are variable depending on the age of the plant and whether the infection is local or systemic. Seedlings grown from infected seed develop rotted cotyledons and chlorotic primary leaves. If young plants have small water-soaked lesions on their primary leaves the inoculum source was contaminated plant debris on the soil surface. The presence of such spots is the most characteristic of these disease be it on seedling or older plants. The water-soaked spots appear as tiny pin pricks on the lower leaf surface they eventually turn brown and are surrounded by a broad yellow-green halo when temperatures are optimum. The halo is present at temperatures of 75-83oF and absent above that range. These lesions do not enlarge but when large numbers are present with accompanying halos, leaves may have a overall chlorotic appearance. Systemically infected older plants are characterized by leaves with dark green tissue around the veins and yellow tissue between the veins. Pod lesions are similar to leaf lesions when they are young. The lesions appear as necrotic pin pricks. However they are not surrounded by a halo and they do enlarge with age. Another characteristic of pod lesions is the presence of white bacterial exudate in the center of the lesion.

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    Caveat

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

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

    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

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    This page is authored and maintained by:
    Dr. J.E. Partridge, Department of Plant Pathology, University of Nebraska-Lincoln

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