Friday, 6 September 2019

Bacterial (Soft Rot) Disease in Potato Plants

Bacterial (Soft Rot) Disease in Potato Plants poster

The article gives info about potatoes bacterial soft rot caused by bacterial pathogen carotovora  Pectobacterium chrysanthemi and cause potato disease. Erwinia carotovora pv. carotovora, E. chrysanthemi, and Pseudomonas fluorescens. Bacteria E. carotovora PV. carotovora and P. fluorescens cause the most common and most destructive soft rots. Erwinia caratovora pv. atroseptica, E. Karatovora P.V. The reason for the blackness of the potato can be considered a colder temperature version. carotovora potato is mostly limited. Erwinia crescent affects many hosts and causes soft rot of tropical plants, while they are still growing in the area. Soft-rot bacteria can develop and are active at temperatures ranging from 5 to 35 ° C. They are killed at about 50 ° C.


Soft rot on tubers first appears as small, tannish, water-soaked spots on the surface. These spots rapidly Enmedium and the tissue decomposes in a soft, blister-like area on the surface of the tuber. Often, a slimy or watery substance oozes from breaks in the blister. The blister margin is darker than the tuber skin. Soft rot often follows bruising and is first white to cream-colored.

After exposure to air, it becomes brown to black. The boundary between the disintegrated and the sound tissue is sharp. It is nearly odorless at the stage. As secondary rot occurs, the rot becomes very foul-smelling. The rot typically progresses to the point of a chalky white, foul-smelling mass. Soft rot symptoms on the foliage include weak, chlorotic (yellowed) plants with margins of leaflets curled upward. Stem lesions are usually light brown and can be colorless, but not black. Stems will root and become very mushy. Tuber rot will occur as a point of infections often on an eye but can be generalized on the tuber.

Development of Disease

Soft decay bacteria survive in infected fleshy organisms, on farms, in debris, in roots or in other parts of host plants, in ponds, and in organisms used for storage in water irrigation, occasionally in the soil, and in the pupae of several insects. The disease first appears on plants grown from infected seed pieces. Some tubers, rhizomes, and bulbs become infected with sores after forming in the soil. The inoculation of bacteria into fleshy organs and their further dissemination in storage and in the field are facilitated greatly by insects.  Bacteria soft-rot can live in all stages of the insect. Moreover, the bodies of the insect larvae become contaminated with bacteria when they crawl about on rotting seed pieces, carry them to healthy plants, and put them into wounds where they can cause the disease.  Plants are resistant to soft rot and can prevent its growth by forming wound-cork layers, maggots destroy wounds that form early from cork, and soft rot continues to spread.

When bacteria enter a soft-decaying wound, they pre-feed and multiply on the fluids left by the broken cells on the wound surface. They produce increasing amounts of pectolytic enzymes that break down the pectic substances of the middle lamella and bring about the stabilization of tissues. Due to the high osmotic pressure of the macerated tissue, water from the cells diffuses into intercellular locations; As a result, cells plasmolyze, collapse and die. Bacteria continue to move and to multiply in the intercellular spaces, while their enzymes advance ahead of them and prepare the tissues for invasion. The tissue is softened by invasion and is converted into a hideous mass consisting of innumerable bacteria floating in liquefied materials.

The epidermis of most tissues is not attacked by the bacteria; however, cracks are usually present, and the slimy mass extrudes through them into the soil or in storage, where it comes into contact with other fleshy organs, which are subsequently infected.

Disease Cycle

Potato soft rot is caused by the bacterium Erwinia carotovora subsp. carotovora, a common soil resident. Bacteria are present on all tubers and are associated with many kinds of plants. Infections in the field are favored by high soil moisture and high temperatures. Other factors include anaerobic conditions, Enmediumd lenticels, and invasion by other pathogens. Bacteria enter lenticels, growth cracks, or any injury. During and after harvest, soft rot is favored by immature tubers, adverse temperatures (pulp temperatures above 21°C at harvest), mechanical damage, and free water on tuber surfaces.

Disease cycle of bacterial soft rot diagram

Figure. Disease cycle of bacterial soft rot 

This bacterium can grow between the temperatures of 0°C and 32°C, with optimal growth between 21°C and 27°C. Bacterial soft rot occurs on a wide range of crops and is one of the most severe postharvest diseases of potatoes worldwide. Loss may occur during storage, transit, or marketing. All potato varieties are susceptible. Contamination of potato tubers occurs anytime they come into contact with the bacterium, most commonly during harvest, handling, or washing. The bacterium invades the potato tuber chiefly through wounds. Most of the soft rot infections are in tissues that have been weakened, invaded, or killed by pathogens or by mechanical means. Soft rot in tubers is favored by immaturity, wounding, invasion by other pathogens, warm tuber and storage temperatures, free water, and low oxygen conditions. Tubers harvested at temperatures above 27°C can be predisposed to soft rot. Decay can be retarded by temperatures less than 10°C; the lower the temperature, the better. Immature tubers are susceptible to harvester related injury and bacterial infection. Suberizing seed and treatment with fungicide is a tactic to reduce the risk of other seed infections that could lead to a soft rot breakdown of the seed.

Disease Management

Although symptoms of bacterial soft rot do not begin in the field, control of bacterial soft rot does begin in the field. Other diseases that produce tuber lesions need to be controlled. Consider these suggestions:
  • Delaying harvest until the skin has set reduces tuber injuries. This will reduce the entry points for the pathogen.
  • At harvest, watch tuber-handling practices, and ensure good sanitary procedures to reduce the spread of bacteria. Harvesting during wet, muddy conditions generally leads to an increase in bacterial soft rot in storage.
  • Properly suberize potatoes to ensure wound healing and reduce the infection sites for the pathogen.
  • Leave potatoes a minimum of 7 days after the vines are totally dead to encourage skin set and reduce bruising.
  • Eliminate as much soil as possible before the tubers are stored, as the soil can restrict air movement.
  • If harvesting wet potatoes ventilate continually until the potatoes are dry.
  • Isolate and keep problematic potato lots in a separate bin.
  • Check the pile temperature at regular intervals. Early detection aids in control, thereby reducing loss. If elevated pile temperatures are detected, consider hot-spot fans. These 1/3- to 1/2-horsepower fans are about 16–18 in. in diameter. When run continuously for up to several weeks, these hot-spot fans can stop storage breakdown.
  • Minimizing potato bruising, avoiding harvesting during wet conditioa1ns, and placing the potatoes into a disinfected storage are three easy, cheap, and effective control practices to reduce loss in storage from soft rot.
  • Avoid washing seed or potatoes before storage unless absolutely necessary. This is a desperate salvage operation. Potatoes that have soft rot should be removed before storing and during packing. After washing, potatoes should be dry before shipping. Tubers need to be protected from bruises, excessive heat, or cold during harvest and transport.
  • Use high-quality seed. Split applications of water-soluble calcium applied at 100–200 lb/ acre during bulking has been shown to reduce infection and severity of soft rot. Harvest mature tubers with well-set skins and avoid mechanical injury.
  • Avoid excessive soil moisture before harvest to reduce lenticel infection.
  • Use clean water to wash potatoes and avoid water films on tuber surfaces during storage.
  • Postharvest curing and storage temperatures can be critical components of soft rot management. Specific temperature recommendations vary depending on the level of decay evident at packing and the market destiny of the potatoes (i.e., processing, fresh market, or long-term storage).


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