Bacterial diseasesof tomatoes can be many of the most serious and destructive diseases impinging on both field- and greenhouse-grown crops. Under moist field conditions they can cause localized epidemics affecting young developing fruit; in the green house total crop losses can occur. The three bacterial diseases discussed allow me to share bacterial canker, bacterial speck, and bacterial spot. The 3rd disease can also cause serious damage of peppers.

Bacterial Canker

Bacterial canker is caused by Corynebacterium michiganense pv. michiganense. Although commonly intermittent in its occurrence, it’s so destructive in nature that vigilance should be exercised within the selection and handling of seed stocks, the preparation and control over greenhouse soil beds or bags, along with the selection and preparation of ground for field production. Bacterial canker is a vascular (systemic) and parenchymatal disease with a range of symptoms creating loss of photosynthetic area, wilting and premature death, and the production of unmarketable fruit. Early recognition of the disease, specifically in greenhouse crops, is important if the disease is to be contained. The organism is seedborne and can survive for brief periods in soil, green house structures, and gear and then for for a longer time in plant debris.

Symptoms

Plants at any phase of growth are inclined. Infected seedlings can be quickly killed, or they’ll produce weak, slower plants, or if conditions are unfavorable for disease progress, infected seedlings may develop into apparently healthy plants that fail to show disease symptoms until they are set in the field. In Ny the condition may not be observed until after the plants begin to blossom The early symptoms of the disease are wilting, curling of leaflets, and browning of leaves, often only on one side of the plant. As the leaves die, the petioles remain green and firmly attached to the stem. A cut through the stem shows yellowish brown discoloration of the vascular element.

Symptoms might be split into two types: superficial symptoms resulting from bacterial colonization of the surface tissues and systemic symptoms resulting from bacterial invasion of the vascular tissue. Necrotic leaf lesions up to 1/4 inch in diameter show up on top of the leaf surface of mature leaves, and in other cases circular, slightly raised white spots about 1/16 inch in diameter appear. Similar spots may also be noted on stems and petioles. Superficial symptoms on fruit may be observed at any age, but are usually seen first on green fruit 1/2-2 inches in diameter. White spots 1/8 inch in diameter develop on the most-exposed parts of the fruit. The spots have a dark brown center, which becomes raised, and are surrounded by a distinct white halo; they have been termed “bird’s-eye spots.”

 

Sometimes the spots lose the white halo and become necrotic, and may merge online websites.As plants mature, symptoms may be noted on leaves, stems, and inside fruits. Regions of leaves above the second or third truss may show dull green and water-soaked areas, which later appear desiccated and become necrotic. Wilting progresses before the entire leaflet dies. Close examination of stems reveals open cankers, from which the disease receives its name.Splitting of the stem lengthwise reveals reddish brown discoloration. The pith becomes granular to mealy and filled with cavities. Young green fruit cut in half often show discolored vascular bundles in surrounding tissue. Bacteria can happen on the seed coat in addition to within the embryo. Seedborne inoculum functions as one source of the bacterium.

Control

Bacterial canker is one of the most difficult tomato diseases to control. First, there is the problem of detecting infected plants, due to the wide variability of symptom expression. Second, the highly infectious nature of the disease, the number of sources of inoculum, and the absence of efficient chemicals for treatment mean that sanitation and preventive measures should be enforced.

1. Use only certified, disease-free seed from canker-free plants. Never save seed from a source known to have had bacterial canker. If it’s important to use noncertified seed or seed of unknown origin, make sure the seed has been extracted through the standard acetic acid extraction method or by the fermentation process. Make sure seed has not been prepared by centrifuge extraction, be responsible for high levels of seed contamination. Although the acid or fermentation treatment will eliminate seed coat contamination, it does not completely control embryonic infection. We do not suggest that growers save their own seed. However, if this sounds like necessary for special reasons, begin to see the section entitled “Tomato Seed Extraction and Treatment method.”
2. Plant only certified disease-free transplants which have been produced within vigorous examination program. It is generally not possible to differentiate between infected or healthy seedlings at the time of transplanting.
3. When the disease is suspected or confirmed in a greenhouse crop, aids to pollination and high-volume, high-pressure pesticide spraying should stop. These restrictions will decrease the risk of spread, especially when superficial symptoms are present . Remove diseased plants as soon as they are detected by cutting the plants off at the ground line and placing them in a plastic bag for disposal. At least several “healthy” plants on either side of the infected plants should also be removed. If the area of diseased plants is limited, there’s a pretty good possibility that the disease can be contained. Every effort should be made to isolate affected areas from the remaining crop. Hands, shoes, tools, and cropsupport wires should be disinfected. Hypochlorite, or laundry bleach, is not satisfactory as a greenhouse disinfectant. Quaternary ammonium compounds as used to disinfect potato storages are recommended. Refer to Cornell Recommendations for Commercial Vegetable Production for specifics. In the field, if bacterial canker becomes severe early in the growing season, fields ought to be plowed down to prevent spread to close by healthy fields. If affected plants are found through the crop, only 100 plants per acre ought to be removed in an attempt to restrict spread. Taking out more isn’t of benefit.
4. Green house seedbeds and soils must be sterilized to destroy the bacteria. Steam sterilization is preferred, but *methyl bromide is satisfactory if attention is paid to removing all debris. (Restricted use pesticides are identified by an asterisk, *.) In the field all plant debris should be plowed under, and impacted areas should be rotated out of tomatoes for at least three years. Weeds belonging to the Solanaceae family should be destroyed.
5. Fixed copper sprays might help in protecting healthful plants, particularly if only superficial signs and symptoms are present.

Bacterial Speck

Bacterial speck is brought on by Pseudomonas syringae pv. tomato. Although this disease continues to be known since the early 1930s, it did not result in serious losses until the winter tomato crop of 1977-78 in southern Florida and in 1978 in southern implant fields and in northern production places that some infected transplants were shipped inadvertently. Cool, moist ecological conditions led to the development of the disease, which has now established itself as a major production problem in northern producing states.

Signs and symptoms

The foliar signs and symptoms of speck consist of small (1/8-1/4 in.) black lesions, often having a discrete yellow halo .The lesions of bacterial spot are similar, but tend to have a greasy appearance, whereas the ones from speck don’t. Speck appears to curl the leaves more severely than spot. Both diseases affect flowers. Lesions on stems and petioles cannot be distinguished. Bacterial speck and spot tend to be more clearly classified by symptom development around the fruit. Bacterial speck lesions are slightly raised, but they are usually much smaller (1/16 in.) compared to those of bacterial spot. Bacterial speck lesions are extremely superficial and don’t crack or become scaly as in microbial spot.

Epidemiology

A much better knowledge of the epidemiology of bacterial speck is essential for developing control measures. The question may be asked why this disease, which has been around for many years, has now moved to the forefront of tomato production. Research from different sections of the country offers several explanations. Circumstantial evidence suggests that the recent introduction of the bacterial speck organism into transplant production fields in southern Georgia originated on commercial seed. If seeds are harvested by either the acetic acid extraction method or by the fermentation process, the threat of seedborne inoculum is greatly reduced. It is not known if the seed grown in Georgia was removed through the more controversial centrifugation method.

A cool (below 70° F or 21° C) and moist (high relative humidity and prolonged period of free moisture) growing season in 1978 contributed to the outbreak of bacterial speck in southern transplants. Although these conditions are exceptional in the south, they represent typical growing conditions in the north, when young transplants are set out in spring. Research has shown that with appropriate temperature and leaf wetness plants harboring a low resident bacterial population can show symptoms within as few as 3-5 days. In most cases in the field, symptoms can be expected in 6-10 days. This is significant in light of the finding thatthe bacterial speck pathogen can survive shipment and spread disease in the field even though no disease symptoms were present on the plants during shipment or at planting time. Similarly, fruits that develop during cool, moist weather early in the season can be severely infected. Use of scanning electron microscopy has shown that bacteria can be related to both glandular and nonglandular leaf hairs present on ovaries during anthesis (the period of flower expansion and stamen maturation).After anthesis the leaf hairs are gradually lost, leaving openings in the young fruit epidermis. These sites functions as areas for fruit an infection. Uninjured fruit are most susceptible to infection from anthesis until the fruit reach 1 1/4 inches in diameter.Another essential factor in the epidemiology of bacterial speck is the survival of the organisms in either soil or host debris and on native weeds. In California the leaves and roots of various weed and crop species maintained resident populations of bacterial speck virus. In Michigan survival of the bacterium in buried tomato leaf tissue at various soil depths advised that overwinter diseased tissue was another source of primary inoculum.Bacteria existed well before humans evolved, and bacterial diseases probably co-evolved with each species which unvoluntarily hosts them. Many bacterial diseases that we see today have been around for as long as we have, others may have developed later. In either case, for the longest time we were unaware of the reason for infectious diseases. Using the beginning of microbiology, bacterial bad bacteria became apparent.Some interesting websites describe the early developments:

•The highlights in the good reputation for microbiology.
•Ancient microbiological history.
•An overview of the the history of microbiology is a web of discoveries.

Known and newly-discovered bacteria could be blamed for new and old diseases. The most obvious diseases caused by bacteria are infectious diseases.Infectious diseases emerged and disappeared with time. Some stayed around, others disappeared to make a come-back, others were made extinct by human influence. The names might have changed, the diseases stayed the same. See this display about emerging and re-emieging infectious diseases.What do we know of the bacterial diseases that bothered our ancesters? Quite a few infectious diseases are known from historical times. Possibly the best known is The Black Death, or Plague, caused by Yersinia pestis. A special feature file is dedicted to the Plague only. Tuberculosis was a major killer in Europe in the past. Tuberculosis, in combination with HIV, still causes many deaths in Africa. Epidemics raged over countries: see this impressive list of past epidemics in the US, on which two diseases dominate that we don’t frequently encounter in that country anymore: Yellow fever and Measles (both of them are caused by viruses). For those interested there are more lists of Epidemics and Plagues. Epidemics didn’t stop at borders, followed trade routes and travellers or colonists, and could wipe out a considerabel proportion of inhabitants. The results were often devastating, and treatment was limited due to lack of edcuation. The big killers in the Americas were European diseases, often caused by viruses.

What kindled such epidemics? That will depend on the causative agent. Human-to-human contact is needed for many viruses to spread (be it Ebola or the common cold), fecal-oral contamination (most often drinking water contaminated with sewage) causes most enteric disease outbreaks including cholera, whereas insects (fleas or mosquitos) may be required for the spread of yet other diseases. Contrary to common believe, corpses are not a typical source of infection. Most post-catastrophic outbreaks are the result of lack of clean normal water.

Epidemics: a treatise about Benjamin Rush, Yellow Fever and the birth of modern medicine.

Infectious diseases within their historical context : plague, smallpox, cholera, typhoid, and typhus.

In some cases we can recognize various degrees of certainty which infection caused the death or suffering of famous people. Pharao Ramses I might have suffered from Ear infection and smallpox may have brought Ramses V, queen Mary II of England, and Louis XV of France together. Alexander the Great died of an infection of the lungs, possibly causes include Westnile Virus ; before him, his dear friend Hephaistion probably died of typhoid fever, based on the symptoms described of his death bed. Amadeus Mozart might have died of rheumatic fever which is caused by a prior infection). Several celebrities suffered from syphilus, such as the composer Franz Schubert, the writer Karen Blixen and the painter Vincent van Gogh. The condition might be lethal in pre-antibiotic days.

Clearly, epidemics aren’t something of history. We have new and old diseases to combat. But those massive killings known from historian times are no longer common in most parts of the world. This was mainly achieved by vaccination. Before vaccines might be developed, the organisms causing the disease needed to be identified and characterized. That was not an easy job for a number of diseases but very few discoverers received a Nobel Prize for his or her efforts. The exceptions are Nobel-laureate C. Nicolle with his pursuit of the organism causing typhus (now considered to be caused by Rickettsiae, not to be mistaken with typhoid, or enteric fever, caused by Salmonella typhi) (Nobel E museum). Plus Nobel-laureates B. Marshall and R. Warren, for their discovery of Helicobacter pylori.A few kinds of cancer are caused by microbiological infections, of which gastric cancer is associated with Helicobacter pylori. However, presence of these bacteria is not sufficent to cause cancer; multiple other factors play a role, too. For other bacteria, a potential role in causing specific cancers is less straight-forward.

In the old days, people warned eachother that a new ‘pest’ was coming. Sometimes people fled with fear, and the human movement helped spreading the disease even faster. Nowadays, we have better ways of treatment, especially for bacterial infections. But even more importantly: we have faster ways of communication. Although modern-day travels helps infectious diseases cross oceans at the speed of the aircraft it travels with, the warning can spread even faster: by internet. For example, the World Health Organisation publishes a disease outbreak alert. That way we can be warned and knowledgeable.

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