The bacteria that cause bacterial spot are called xanthomonads. Some bacterial spot lesions initially have a whitish appearance, similar to a bacterial canker lesion.īacteria enter the plant through natural openings (stomates and hydathodes) or wounds caused by wind-driven soil, insects or mechanical damage (handling, wind whipping, high pressure sprayers). Figure 4: Bacterial spot lesions on foliage and young bacterial spot lesions on fruit. Figure 3: Bacterial spot lesions on tomato fruit and under sepals. In the field, spread by equipment or workers is probably of lesser importance than it is in the greenhouse, unless wounds are being opened up at the same time, as in a pruning operation or when plants are injured by a cultivator. The bacteria are spread primarily by splashing water and wind-driven rain or mists produced during storms. Like the bacterial speck pathogen, they also may be present on volunteer tomato plants and on the surfaces of contaminated equipment (farm machinery, racks, greenhouse structures, tools). The major sources of infection for these bacteria are thought to be seed and infected crop debris. Bacterial spot lesions may increase in size to 4-6 mm in diameter and become brown, greasy-looking and sometimes scabby. In contrast, bacterial canker fruit lesions retain their white halo. As the fruit ages, the white halos disappear. The lesions also may have a white halo, similar to the bird's-eye spotting seen with bacterial canker. On fruit, the first symptoms are small, dark brown-to-black, raised spots. Lesions on pedicels may cause flower abortion, resulting in lost yield and split sets of fruit.įruit lesions are initiated only on green fruit, most likely because infection occurs through fruit hairs, which are present only on immature fruit. Figure 2: Tomato plant showing defoliation and fruit symptoms due to bacterial spot. Diane Cuppels, Agriculture and Agri-Food Canada. Figure 1: Bacterial spot lesions on tomato leaves. When spots are numerous, foliage turns yellow and eventually dies, leading to defoliation of the lower portion of the plant. Infected leaves may develop a scorched appearance. The lesions tend to concentrate on the leaf edges and tip and may increase in size to a diameter of 3-5 mm. Initial leaf symptoms are small, circular-to-irregular, dark lesions, which may be surrounded by a yellow halo. It is difficult to reliably distinguish bacterial spot from bacterial speck based on visual symptoms, especially in the early stages. The bacterial spot pathogen may produce lesions on all aboveground parts of the plant - leaves, stems, flowers and fruit. Optimum growth temperature ranges for bacterial pathogens of tomato DiseaseĬlavibacter michiganensis subsp. The pathogens multiply much more slowly outside this optimum range. Each pathogen has a particular temperature range, in which it is at its peak rate of growth and infection (see Table 1). Wet conditions in the plant canopy due to rain, fog, dew, high humidity or irrigation give the bacteria a suitable environment for growth. The pathogensīacterial pathogens need moisture to multiply. Seed suppliers, transplant growers, field growers, processors, researchers, extension specialists and crop advisors all have a part to play. Management of tomato bacterial diseases must focus on prevention and must start well before transplanting. Processors also face the risk of falling short of their packing goals. Depending on the product being produced, bacterial disease may result in lower solids, increased costs, slower factory operations and reduced peeled recovery for the processors. Processing growers also face the risk of increased tare penalties and the possibility of not meeting their contracted tonnage. Secondary rots can also develop.īoth fresh-market and processing growers may incur higher sorting costs due to fruit lesions. Defoliation exposes the fruit, resulting in sunscald and poor colour. When present, fruit lesions disfigure and reduce the marketability of both fresh-market and processing fruit (especially in whole-pack or diced product) and interfere with peeling. However, when conditions are optimal for bacterial disease, losses in marketable yield can be up to 60% in some fields.ĭamage from these diseases may range from a light spotting of the foliage to almost complete defoliation of the plant, with corresponding impacts on photosynthesis and production potential. In Ontario, bacterial disease is present at some level every season, though not always at destructive levels. bacterial canker, caused by Clavibacter michiganensis subsp.bacterial speck, caused by Pseudomonas syringae pv.bacterial spot, caused by Xanthomonas campestris pv.Three bacterial diseases are common in Ontario tomato fields:
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