This article includes a list of references, related reading, or external links, but its sources remain unclear because it lacks inline citations .(December 2011) |
Bacterial soft rots are caused by several types of bacteria, but most commonly by species of gram-negative bacteria, Erwinia , Pectobacterium , and Pseudomonas . It is a destructive disease of fruits, vegetables, and ornamentals found worldwide, and affects genera from nearly all the plant families. The bacteria mainly attack the fleshy storage organs of their hosts (tubers, corms, bulbs, and rhizomes), but they also affect succulent buds, stems, and petiole tissues. With the aid of special enzymes, the plant is turned into a liquid mush in order for the bacteria to consume the plant cell's nutrients. Disease spread can be caused by simple physical interaction between infected and healthy tissues during storage or transit. The disease can also be spread by insects. Control of the disease is not always very effective, but sanitary practices in production, storing, and processing are something that can be done in order to slow the spread of the disease and protect yields.
There are a variety of hosts including but not limited to; banana, beans, cabbage, carrot, cassava, coffee, corn, cotton, onion, other crucifers, pepper, potato, sweet potato and tomato. Pandanus conoideus and karuka ( Pandanus julianettii ) get bacterial soft rot and necrosis on the leaves from Pectobacterium carotovorum subsp. carotovorum. [1] For each host there are different symptoms displayed. Most symptoms are along the lines of watery and soft decay of the tissue. Cabbage and crucifers' symptoms start where the tissue makes contact with the soil. Often there is a change in color and in the case of a carrot, the whole taproot can be decayed leaving just the epidermis. Sweet potatoes show clear lesions that grow rapidly leaving a recognizable watery and soft, oozy tissue where only the peel remains intact.
Potatoes experience a cream to tan colored tuber that becomes very soft and watery. A characteristic black border separates the diseased area and the healthy tissue. Only when the secondary organism invades the infected tissue does that decay become slimy with a foul odor. Like the carrot, the whole tuber can be consumed leaving just the epidermis in the soil. The foliage becomes weak and chlorotic with upward turned leaves and lesions on the stem. The stem also rots and becomes mushy with its colorless or brown lesions. [2] [3] [4] [5]
Soft rots are characterized by their distinct maceration of hosts' cell walls with pectolytic enzymes, and subsequent digestion of the intracellular fluid as the bacteria grows. But little is known about the pathogen's interaction with its host at earlier stages when it is still attaching to, and growing within the host with no symptoms present. In fact, the bacteria may develop large populations within a plant before any symptoms can be seen. No one knows exactly why the bacteria have this dormant stage, or what factors influence the bacteria's virulence, but the research is being done.
There are many ways in which a plant can become infected by a bacterial soft rot. They can be host to the bacteria either by being infected as seed, or from direct inoculation into wounds or natural openings (stomata or lenticels) in mature plants, which is most common. But, when a plant is infected and the conditions are favorable, the bacteria immediately begin feeding on liquids released from injured cells and start replicating. As they replicate they release more and more pectolytic enzymes that degrade and break down cell walls. And, because of the high turgor pressure within the cells, this maceration effectively causes the cells to explode and die providing more food for the bacteria.
As they gorge on intracellular fluid, the bacteria continue to multiply and move into the intercellular spaces, with their cell-wall-degrading enzymes ahead of them preparing the plant tissues for digestion. Often the epidermis is left unscathed, keeping the rotten flesh contained within until a crack allows the ooze to leak out and infect others around it.
When the plant organs are harvested and placed into storage, those that are infected will automatically infect the others placed with it. When certain insects are present, the eggs laid over the stored vegetables will be invaded by the bacteria, becoming host and transporter, able to infect others as they grow. The bacteria then overwinters within the plant tissues, insect hosts, or in the soil and lay dormant until the conditions are right again to reproduce. If the infected storage organs are being used to propagate the plant, or if infected seed was produced, then when spring comes the bacteria will begin to grow just as its host does. Also in the spring, the contaminated insect eggs hatch into larvae and begin to cause infection within the host plant. The larvae then become adults, leave its infected host, and move on to unknowingly inoculate more plants to start the cycle over again.
Growth of the bacteria is possible between 32–90 °F, with the most ideal conditions between 70–80 °F. Post-harvest storage and transportation is difficult for tropical and other warm environments when the air is not properly ventilated during these processes. Higher temperatures and high humidity are ideal growing conditions for the bacteria making ventilation a big priority when trying to combat this disease.
There are very few things that can be done to control the spread of bacterial soft rots, and the most effective of them have to do with simply keeping sanitary growing practices.
Storage warehouses should be removed of all plant debris, and the walls and floors disinfected with either formaldehyde or copper sulfate between harvests. Injury to plant tissues should be avoided as much as possible, and the humidity and temperature of the storage facility should be kept low using an adequate ventilation system. These procedures have proven themselves to be very effective in the control of storage soft rot of potato in Wisconsin.
It also helps if plants are planted in well-drained soils, at intervals appropriate for adequate ventilation between plants. Few varieties are resistant to the disease and none are immune, so rotating susceptible plants with non-susceptible ones like cereals is a practice positive to limiting soft rot infection.
The control of specific insect vectors is also a good way of controlling disease spread in the field and in storage. Soil and foliage insecticide treatment helps controls the bugs that frequently cause wounds and disseminate the bacteria.
Due to its wide range of hosts, bacterial soft rot devastates many significant crops both in the field and in storage all over the world. Almost all fresh vegetables are subject to infection by bacterial soft rots. But, it is not just the vegetables that are susceptible; in the tropics, soft rot develops on important crops like corn, cassava, and banana even while still in the field. Specifically, soft rot of potatoes can cause a huge decrease in yield, and is the most serious bacterial disease that potatoes are exposed to. For a grower of potatoes, there is a possibility that 100% of a whole season's yield could be destroyed due to insufficient conditions in a storage facility. In turn this impacts customers with reduced quantities of produce for sale, a reduction in quality, and an increase in expense. All in all, bacterial soft rots cause a greater loss of produce than any other bacterial disease known.
The bacteria, Erwinia carotovora or Pectobacterium carotovorum , is gram-negative, anaerobic, rod-shaped and named after the carrot it was first isolated from. Found mostly in tropical, warm regions of the world. Because the organism is spread in so many ways, there is speculation that it was introduced to water through aerosols and runoff into water bodies. Specifically this could have happened through dumping potatoes that were infected and disposed of.
Fire blight, also written fireblight, is a contagious disease affecting apples, pears, and some other members of the family Rosaceae. It is a serious concern to apple and pear producers. Under optimal conditions, it can destroy an entire orchard in a single growing season.
Erwinia is a genus of Enterobacterales bacteria containing mostly plant pathogenic species which was named for the famous plant pathologist, Erwin Frink Smith. It contains Gram-negative bacteria related to Escherichia coli, Shigella, Salmonella, and Yersinia. They are primarily rod-shaped bacteria.
A leaf spot is a limited, discoloured, diseased area of a leaf that is caused by fungal, bacterial or viral plant diseases, or by injuries from nematodes, insects, environmental factors, toxicity or herbicides. These discoloured spots or lesions often have a centre of necrosis. Symptoms can overlap across causal agents, however differing signs and symptoms of certain pathogens can lead to the diagnosis of the type of leaf spot disease. Prolonged wet and humid conditions promote leaf spot disease and most pathogens are spread by wind, splashing rain or irrigation that carry the disease to other leaves.
Stewart's wilt is a bacterial disease of corn caused by the bacterium Pantoea stewartii. The disease is also known as bacterial wilt or bacterial leaf blight and has been shown to be quite problematic in sweet corn. The causal organism is a facultatively anaerobic, gram-negative, rod-shaped bacterium. The disease is endemic in the mid-Atlantic and Ohio River Valley regions and in the southern portion of the Corn Belt. Stewart's Wilt causes minor reductions in field corn yield, despite common occurrence, because most hybrids grown in the Midwest have adequate resistance. However, the disease can be problematic in seed production because many countries have restrictions on maize seed from areas where the Stewart's Wilt occurs.
Dickeya dadantii is a gram-negative bacillus that belongs to the family Pectobacteriaceae. It was formerly known as Erwinia chrysanthemi but was reassigned as Dickeya dadantii in 2005. Members of this family are facultative anaerobes, able to ferment sugars to lactic acid, have nitrate reductase, but lack oxidases. Even though many clinical pathogens are part of the order Enterobacterales, most members of this family are plant pathogens. D. dadantii is a motile, nonsporing, straight rod-shaped cell with rounded ends, much like the other members of the genus, Dickeya. Cells range in size from 0.8 to 3.2 μm by 0.5 to 0.8 μm and are surrounded by numerous flagella (peritrichous).
Clavibacter michiganensis is an aerobic non-sporulating Gram-positive plant pathogenic actinomycete of the genus Clavibacter. Clavibacter michiganensis has several subspecies. Clavibacter michiganensis subsp. michiganensis causes substantial economic losses worldwide by damaging tomatoes and potatoes.
Phytophthora erythroseptica—also known as pink rot along with several other species of Phytophthora—is a plant pathogen. It infects potatoes causing their tubers to turn pink and damages leaves. It also infects tulips (Tulipa) damaging their leaves and shoots.
Pectobacterium carotovorum is a bacterium of the family Pectobacteriaceae; it used to be a member of the genus Erwinia.
Helminthosporium solani is a fungal plant pathogen responsible for the plant disease known as silver scurf. Silver scurf is a blemish disease, meaning the effect it has on tubers is mostly cosmetic and affects "fresh market, processing and seed tuber potatoes." There are some reports of it affecting development, meaning growth and tuber yield. This is caused by light brown lesions, which in turn change the permeability of tuber skin and then it causes tuber shrinkage and water loss, which finally causes weight loss. The disease has become economically important because silver scurf affected potatoes for processing and direct consumption have been rejected by the industry. The disease cycle can be divided into two stages: field and storage. It is mainly a seed borne disease and the primary source of inoculum is mainly infected potato seed tubers. Symptoms develop and worsen in storage because the conditions are conducive to sporulation. The ideal conditions for the spread of this disease are high temperatures and high humidity. There are also many cultural practices that favor spread and development. There are multiple ways to help control the disease.
Ditylenchus destructor is a plant pathogenic nematode commonly known as the potato rot nematode. Other common names include the iris nematode, the potato tuber eelworm and the potato tuber nematode. It is an endoparasitic, migratory nematode commonly found in areas such as the United States, Europe, central Asia and Southern Africa.
Bacterial wilt is a complex of diseases that occur in plants such as Cucurbitaceae and Solanaceae and are caused by the pathogens Erwinia tracheiphila, a gram-negative bacterium, or Curtobacterium flaccumfaciens pv. flaccumfaciens, a gram-positive bacterium. Cucumber and melon plants are most susceptible, but squash, pumpkins, and gourds may also become infected.
Rhizopus soft rot is a disease of the sweet potato. It is one of the most common to affect the sweet potato, happening during packing and shipping. The disease causes a watery soft rot of the internal portion of the storage root. Strategies to manage the disease include the development of resistant varieties, curing through the use of heat and humidity, and application of decay control products.
Phalaenopsis bellina is an orchid endemic to Borneo. It is one of 75 species of Phalaenopsis and one of the most commonly cultivated species in the genus.
A wilt disease is any number of diseases that affect the vascular system of plants. Attacks by fungi, bacteria, and nematodes can cause rapid killing of plants, large tree branches or even entire trees.
Black rot, caused by the bacterium Xanthomonas campestris pv. campestris (Xcc), is considered the most important and most destructive disease of crucifers, infecting all cultivated varieties of brassicas worldwide. This disease was first described by botanist and entomologist Harrison Garman in Lexington, Kentucky, US in 1889. Since then, it has been found in nearly every country in which vegetable brassicas are commercially cultivated.
Dickeya solani is a bacterium that causes blackleg and soft rot in potato crops. Its symptoms are often indistinguishable from those caused by Pectobacterium but is more virulent, causing disease from lower levels of inoculum and spreading through the plant more effectively.
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.
Blackleg is a plant disease of potato caused by pectolytic bacteria that can result in stunting, wilting, chlorosis of leaves, necrosis of several tissues, a decline in yield, and at times the death of the potato plant. The term "blackleg" originates from the typical blackening and decay of the lower stem portion, or "leg", of the plant.
Erwinia papayae is a bacteria species causing bacterial crown rot, or bacterial canker, a noteworthy and grave disease of papaya.
Clavibacter sepedonicus is a species of bacteria in the genus Clavibacter. C. sepedonicus is a high-profile alien plant pathogen of A2 Quarantine status affecting only potatoes. It causes a disease in potatoes known as 'ring rot' due to the way it rots vascular tissue inside potato tubers It is present in parts of Europe but is under statutory control under 'Council Directive 93/85/EEC' of 4 October 1993 on the control of potato ring rot. This means that if an outbreak occurs, the outbreak must be controlled and if possible the disease has to be eradicated. If necessary, prohibitions are put into place to prevent further spread.