Symptoms first appear as watery spots on the underside of the leaves. When seeds are severely infected, they shrink and when planted, they do not germinate properly, and those that germinate will appear weak. On white dry bean seeds, butter yellow or brown spots can be seen throughout the seed coat. After some rainfall, or heavy mist or lengthy overhead irrigation, the lesions on pods become covered in bacteria. The sizes and shapes of the lesions differ. Pod symptoms consist of lesions that are generally circular, slightly sunken, and dark red-brown. Bacteria from infested material act as a source for new infections on healthy plants and healthy plant tissues. When the bacteria have severely infected the plant, the leaves die out and the dead leaves remain attached to the plants even at maturity. The lesions enlarge and join together, making the plant appear as if it has been burnt. These watersoaked spots become dry (necrotic lesion) and are often surrounded by a small zone of lemon yellow tissue ( Photo 1). The symptoms associated with common bacterial blight first appear as small water soaked spots on the underside of the leaves. In addition seeds look unattractive with less chance of germinating or growing properly when planted. It must be said that these symptoms deny the plant maximum generation and usage of the all-important nutrients that plants require. ![]() Once inside the plant tissue, the bacteria start feeding and cause visible damage (symptoms) to the plant. They also penetrate a host plant through wounds and natural openings on a plant. The three diseases mainly affect the foliage and pods (including the seeds) and are all seed-borne. phaseolicola (Psp), and bacterial brown spot, caused by Pseudomonas syringae pv. phaseoli (Xap) (Smith), halo bacterial blight, caused by Pseudomonas savastanoi pv. The most important bacterial diseases of dry beans in South Africa are common bacterial blight, caused by Xanthomonas axonopodis pv. Some very small microscopic organisms called bacteria, among other organisms, cause diseases and brings about a negative impact on yield and profitability. However, seeds usually do not show symptoms.HANGWANI MUEDI AND DEIDRE FOURIE, ARC-GRAIN CROPS INSTITUTEĭry beans are one of the most affordable high protein sources in the world, but its production is not without hassles. Lesions can also occur on the pods causing the seeds to become shriveled and discolored. Generally young leaves are most susceptible to blight infection. Eventually the lesions will fall out of the leaf and the foliage will appear ragged. A yellowish-green "halo" will appear around the edge of water soaked tissue that surrounds the lesions. The centers of the spots will turn a dark reddish-brown and dry out. ![]() Symptoms in later growth stages include angular lesions, which begin as small yellow to brown spots on the leaves. Young plants may be stunted and if the infection reaches the growing point, they may die. Disease Symptomsīrown spots on the margins of the cotyledons characterize plants infected early in the growing season. Bacteria can also be spread to uninfected leaves when they rub against infected ones during cultivation, rain, and wind. Seedlings may be infected through infected seed.īacteria that enter the host produce a toxin, which prevents chlorophyll production. ![]() In order for infection to occur, the leaf surface must be wet. The bacteria enter the plants through stomata and wounds on leaves. Initial infection of soybeans occurs when wind or splashing water droplets from plant residue on the soil surface to the leaves carry bacterial cells. Bacterial blight ( Pseudomonas savastanoi) of soybeans is typically an early season disease, which over winters in the field on plant residue.
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