Harvest And Postharvest Techniques To Prevent Bacterial Soft Rot

Harvest And Postharvest Techniques To Prevent Bacterial Soft Rot

Bacterial Soft Rot


Producing a healthy crop obviously is of the utmost importance to vegetable growers, and among the key factors necessary to get quality produce to market is the care taken from harvest to packing.

One problem experienced by growers of tomatoes, potatoes, and others is the postharvest attack of the bacterium Erwinia sp., known otherwise as bacterial soft rot. Soft rot can become a serious issue, particularly when care is not taken to prevent bruising, etc. during harvest and proper postharvest food safety practices are not adhered to in packing areas.
In addition to proper postharvest handling, having the adequate levels of nutrients in the plants while they are growing in the field — especially calcium — is important for reducing the effects of this bacteria. It is reported that in warm, humid climates, bacteria can affect the inside of stems and the epidermis.

One of the first crops attacked by bacterial soft rot is tomatoes. Four species of bacteria are known to cause infection. In addition to tomatoes, the bacterium has been reported on other crops as well, such as potatoes, peppers, carrot, lettuce, cabbage, and onion.

Soft Rot Symptoms

Many symptoms will help growers identify soft rot in their fields. Specifically, infected fruit show soft, odiferous lesions. The spots are small, sunken areas that are watery in appearance. These injuries range from a light to slightly darker color and are related to the natural openings or wounds in the fruit. There may be a characteristic discharge coming from the wound that is made up of millions of bacteria.

Erwinia can affect roots and stems, causing darkening of the tissues. The bacteria in potatoes is called blackleg, and can cause plant death.

Survival Of The Pathogens

What makes soft rot critical to control is that bacteria can survive on vegetables in various parts of the plants and also has the ability to live in low populations in the soil and water.

It is important to note that this strain cannot penetrate the plant; it
can only enter through a previously sustained wound or natural opening in the tissues. During handling, if bruises and wounds occur, and if the water is not disinfected well, the pathogens can enter the fruit.

In potatoes, the main source of inoculum is from the seed tuber, machinery that has been in the field, and irrigation water. The bacteria is active when conditions are favorable for pathogen growth and development — excess moisture, poor aeration, damaged tissues, and a high presence of inoculum.

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Russell Owings says:

No company has a single “silver bullet” to eliminate plant and human health pathogens on fruits and vegetables; however, growers and packers armed with a “silver clip” can successfully control pathogens and produce a quality product. Years ago this process was call the Hurdle Approach. I am pleased to find in this article the mention of potential cross contamination from irrigation water and farming equipment. One of the first hurdles to be considered prior to planting is treating the soil to control soil pathogens. A second hurdle is to treat irrigation water. The third hurdle should be to clean and sanitize filed equipment and transportation vehicles to prevent cross contamination from field to field and field to packing house. Once produce enters the packing house there are a number of antimicrobial hurdles to consider. For example, hydro coolers, wash tanks, spray bars and fogging units can be antimicrobial hurdles. A final hurdle that grower and packers cannot control is the consumer washing the produce prior to use. Field to fork hurdles are necessary to assure high quality and safe vegetables. Russell

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