How do plants get blight?
10877790#2
Research has shown that "Pantoea agglomerans" can serve as a plant pathogen competitor for the management of plant diseases. Fire blight, a plant disease caused by bacterium "Erwinia amylovora," is commonly found in pear and apple crops. After coming in contact with "Erwinia amylovora", "Pantoea agglomerans" produces antibiotic properties that are toxic to the fire blight-inducing bacterium. It has been identified that it is possible that habitat modification or exclusion may also play a role in the effectiveness of the antibiosis of the fire blight biological control.
Pantoea agglomerans
10207944#4
To continue, the symptoms of this bacterial blight include spots and lesions on leaves, and rot of floral buds and flowers. The floral symptoms undergo changes throughout the seasons that ultimately end in the floral bud dying and falling off. These symptoms are found initially as brown and sunken spots on the green sepals of the vine that enclose the flower buds. The result is the flower buds begin to rot when unopened. If the buds do open and yield a yellow-orange color, rather than white, the flower turns brown rather quickly and dies. In addition, the anthers or male sexual parts of the flower can be destroyed in this disease causing an incomplete retraction of sepals. Regarding the leaves, symptoms are visible in later spring and are found on the lower leaves first. The lesions created are angular and gray on the lower leaves, and the lesions are surrounded with a yellow halo on the upper leaves. These lesions turn brown and can be a site for a secondary infection by a fungus or some other pathogen. All of this leads to abnormal fruit development on diseased plants which can create an economic problem for the grower. Fruit development is the largest economical concern when referring to this pathogen. Yield loss can become very high, reaching over 90% in orchards that have symptoms of this pathogen. When no symptoms are present, however, the plant is healthy and fruit development is normal. It is stated that it is very rare to find normal fruit development on plants with symptoms of bacterial blight showing how detrimental this disease and pathogen is.
Pseudomonas viridiflava
11471480#0
"Phomopsis obscurans" is a common fungus found in strawberry plants, which causes the disease of leaf blight. Common symptoms caused by the pathogen begin as small circular reddish-purple spots and enlarge to form V-shaped lesions that follow the vasculature of the plant’s leaves. Although the fungus infects leaves early in the growing season when the plants are beginning to develop, leaf blight symptoms are most apparent on older plants towards the end of the growing season. The disease can weaken strawberry plants through the destruction of foliage, which results in reduced yields. In years highly favorable for disease development, leaf blight can ultimately lead to the death of the strawberry plants. A favorable environment for the growth and development of the "Phomopsis obscurans" pathogen is that of high temperature, high inoculum density, a long period of exposure to moisture, and immature host tissue. In the case of disease management, a conjunction of cultural practices is the most effective way of reducing the infection.
Phomopsis obscurans
48225529#4
Bacterial blight of soybeans can enter leaves through wounds or natural openings such as stomata. After gaining entrance to the host leaves, "Pseudomonas syringae pv. glycinea" multiplies in the leaf intercellular fluid. The pathogen must then overcome the plants defenses. "Pseudomonas syringae pv. glycinea" accomplishes this by using the type three secretion system to inject a variety of pathogenicity effector proteins (Hrp proteins) into the plant cell cytoplasm. These proteins act by interfering with effector-triggered immunity and producing phytohormones/toxins that suppress plant defenses. The expression of these virulence factors depends on the environmental conditions at the time of infection (see "environment section). Furthermore, expression of virulence factors will only take place when a sufficiently large population of bacteria is present, which is determined through quorum sensing. When successful, the common symptoms of bacterial blight will be seen, with the main effect on the plant being a reduction in photosynthetic leaf area. Generally, the amount of photosynthetic area lost is not enough to impede plant growth. As the plant continues to grow it overcomes the loss of photosynthetic area and reduction in yield, if there is any, is negligible.
Bacterial blight of soybean
35944071#5
The spores remain viable for five years in fallen boxwood leaves, and are dispersed by wind and rain over short distances. Since they are sticky the spores may also be spread by birds, animals, and contaminated clothing and footwear. The most common mode of transmitting the blight is by the introduction of asymptomatic plants, or plants treated with fungicide (which can mask the disease) to unaffected areas. Warm and humid conditions facilitate its spread. The fungus does not need a wound to infect a plant, but it does require high humidity or free water.
Boxwood blight
23063231#91
Sheath blight, caused by the fungus "Rhizoctonia solani", is one of the deadlier diseases of rice. Up to 50% of southern United States rice could be infected with sheath blight each year. Unlike most infections it does not produce spores and instead must be spread from contact through plants, rainwater, or the soil. It is a resilient disease that can survive for years in the soil even when there is no rice crop present. Symptoms include lesions on the sheath of the plant, which feed off the nutrients within the plant. These lesions give rise to brown fungus balls which, if the plant dies from nutrient starvation, fall to the ground. The following season, heavy rains may allow the balls to float to other plants, which they can then infect. Primary yield loss is therefore attributable to plant death and lower yields from the surviving plants due to the nutrient loss. Yield losses can be as high as 42%. Research data has demonstrated that one application of azocystrobin at panicle differentiation can control sheath blight for almost the entire season.
Fungicide use in the United States
244847#10
Spraying plants with streptomycin or injecting plants with oxytetracycline can prevent new infections. The widespread use of streptomycin spray has led to antibiotic resistance in some areas, such as California and Washington. Certain biological controls consisting of beneficial bacteria or yeast can also prevent fire blight from infecting new trees. The only effective treatment for plants already infected is to prune off the affected branches and remove them from the area. Plants or trees should be inspected routinely for the appearance of new infections. The rest of the plant can be saved if the blighted wood is removed before the infection spreads to the roots. There is no known cure; prevention is the key.
Fire blight
67741#18
Current efforts are under way by the Forest Health Initiative to use modern breeding techniques and genetic engineering to create resistant tree strains, with contributions from SUNY College of Environmental Science and Forestry, Penn State, the University of Georgia, and the US Forest Service. One of the most successful methods of breeding is to create a back cross of a resistant species (such as one from China or Japan) and American chestnut. Researchers identified 2 or 3 genes that allow for blight resistance, and are focusing on giving the American chestnut hybrids only those genes from the Chinese or Japanese chestnut. The two species are first bred to create a 50/50 hybrid. After three back crosses with American chestnut, the remaining genome is approximate 1/16 that of the resistant tree, and 15/16 American. The strategy is to select blight-resistance genes during the back crossing, while preserving the more wild-type traits of American chestnut as the dominant phenotype. Thus, the newly bred hybrid chestnut trees should reach the same heights as the original American chestnut. Many of these 15/16 American chestnut hybrids have been planted along the East Coast, including in the Jefferson National Forest and on the Flight 93 National Memorial. Some of these sites have had researchers check on the saplings that have been planted to see their survival rate. For the hybrids to do well, they need areas with decent drainage and abundant sunlight. Meeting these needs can be hard to do, so not all restoration areas have been successful with hybrid survival.
Chestnut blight
67741#19
Plant pathologists, Drs. William Powell and Charles Maynard, working at the State University of New York College of Environmental Science and Forestry, have developed American chestnuts which have full blight resistance. Full resistance was attained by introducing a wheat gene coding for the enzyme oxalate oxidase into the American chestnut genome. This enzyme breaks down the oxalic acid secreted by the fungus into carbon dioxide and hydrogen peroxide. Early studies on hypovirulence showed that less virulent strains of the chestnut blight produced less oxalic acid when attacking the cambium. The transgenic trees have blight resistance either equal to or surpassing that of Chinese chestnuts. In 2013, SUNY ESF had over 100 individual events being tested, with more than 400 slated to be in the field or in the lab for various assay tests in the next several years and more than 1,000 trees growing in several field sites in 2014. Government approval will be required before returning any of these blight resistant trees to the wild. The New York Botanical Garden has planted several of the transgenic trees for public display.
Chestnut blight
37386971#6
Other methods include starting with disease free plants, buying cultivars that are less susceptible to raspberry spur blight such as Brandywine, Killarney, Latham and Newburgh, and avoiding cultivars that have greater susceptibility such as Royalty, Titan, Canby, Skeena, Willamette, Reveille, and Sentry. Willamette readily infects with spur blight but is tolerant to the disease and still produces satisfactory yields.
Raspberry spur blight