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Beet vascular necrosis
Beet vascular necrosis and rot is a soft rot disease caused by the bacterium ''Pectobacterium carotovorum'' subsp. ''betavasculorum'', which has also been known as ''Pectobacterium betavasculorum'' and ''Erwinia carotovora'' subsp. ''betavasculorum''.〔 It was classified in the genus ''Erwinia'' until genetic evidence suggested that it belongs to its own group, however, the name Erwinia is still in use. As such, the disease is sometimes called Erwinia rot today. It is a very destructive disease that has been reported across the United States as well as in Egypt. Symptoms include wilting and black streaks on the leaves and petioles. It is usually not fatal to the plant, but in severe cases the beets will become hollowed and unmarketable. The bacteria is a generalist species which rots beets and other plants by secreting digestive enzymes that break down the cell wall and parenchyma tissues.〔 The bacteria thrive in warm and wet conditions, but cannot survive long in fallow soil.〔〔 However, it is able to persist for long periods of time in the rhizosphere of weeds and non-host crops.〔〔 While it is difficult to eradicate, there are cultural practices that can be used to control the spread of the disease, such as avoiding injury to the plants and reducing or eliminating application of nitrogen fertilizer.
== Hosts ==
Fodder beets, sugar beets and fodder-sugar crosses are all susceptible to infection by ''Pectobacterium carotovorum'' subsp. ''betavasculorum''. Today most beet cultivars are resistant to the pathogen, however, isolates vary geographically, and some cultivars of beets are only resistant to specific isolates of bacteria. For example, the cultivar USH11 demonstrates resistance to both Montana and California isolates, whereas Beta 4430 is highly susceptible to the Montana isolates but resistant to the California isolate. Other cultivars resistant to California isolates of ''Pectobacterium caratovorum'' subsp. ''betavasculorum'' include Beta 4776R, Beta 4430R and Beta 4035R, but HH50 has been found to be susceptible.〔
Breeding for resistance to other diseases such as beet yellows virus without also selecting for vascular necrosis resistance can leave cultivars susceptible to the pathogen. For example, the use of USH9A and H9B in California’s San Joaquin valley is thought to have led to an epiphytotic (severe) outbreak of disease in the early 1970s. This was likely because of the limited gene pool used when selecting strongly for resistance to beet yellows virus. Further information on resistant cultivars can be found in the section Management.
In addition to beets, ''Pectobacterium carotovara'' subsp. ''betavasculorum'' can also infect tomato, potato, carrots, sweet potato, radish, sunflower, artichokes, squash, cucumber and chrysanthemum.〔〔〔〔 Other subspecies of ''Pectobacterium carotovora'' can also be pathogenic to beets. ''Erwinia carotovara'' subsp. ''atroseptica'' is a bacterial soft rot pathogen that is responsible for the disease Blackleg of Potato (''Solanum tuberosum''), and variants of this bacterium can cause root rot in sugarbeets,. This subspecies also has a wide host-range. ''Erwinia carotovora'' var. ''atroseptica'' has been detected in the rhizosphere of native vegetation and on weed species such as ''Lupinus blumerii'' and ''Amaranthus palmeri'' (pigweed).〔 It is thought that the source of inoculums survives on these non-host plants in areas in which it is endemic as well as in the rhizosphere of other crops such as wheat and corn〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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