Post Harvest diseases and Disorders : Agrilearner

Postharvest diseases of fruit crops:

Fruit crops are attacked by a wide range of microorganisms in the postharvest phase.
Actual disease only occurs when the attacking pathogen starts to actively grow in the host. Diseases are loosely classified according to their signs and symptoms.
Signs are visible growths of the causal agents, and symptoms the discernible responses produced by the host.
Postharvest diseases are caused primarily by microscopic bacteria and fungi, with fungi the most important causal agent in fruit crops.
Fungi are further subdivided into classes and are described as lower fungi, characterized by the production of sporangia which give rise to numerous sporangiospores, or higher fungi, described as ascomycetes, deuteromycetes, and basidiomycetes. (Post Harvest)

Agri Exam Important 10000 Agriculture MCQ

Pre-Harvest Factors That Influence Post-Harvest Diseases

Weather: Weather affects many factors related to plant diseases, from the amount of inoculum that overwinters successfully to the amount of pesticide residue that remains on the crop at harvest. Abundant inoculum and favorable conditions for infection during the season often result in heavy infection by the time the produce is harvested. For example, conidia of the fungus that causes bull‟s-eye rot are rain dispersed from cankers and infected bark to fruit especially if rainfall is prolonged near harvest time, causing rotten fruit in cold storage several months later.

Physiological condition: Condition of produce at harvest determines how long the crop can be safely stored. For example, apples are picked slightly immature to ensure that they can be stored safely for several months. The onset of ripening and senescence in various fruits renders them more susceptible to infection by pathogens. On the other hand, fruits can be made less prone to decay by management of crop nutrition. (Post Harvest)

Fungicide Sprays: Certain pre-harvest sprays are known to reduce decay in storage. Several studies have been done on the effectiveness of pre-harvest ziram water inactivates chlorine, and levels of chlorine must be constantly monitored. Recently, in precisely controlled tests in water or as foam, chlorine dioxide was found to be effective against common postharvest decay fungi on fruit packinghouse surfaces.

Postharvest Treatments: Products used for postharvest decay control should only be used after the following critical points are considered:

Type of pathogen involved in the decay.

1. Location of the pathogen in the produce.

2. Best time for application of the treatment.

3. Maturity of the host. (Post Harvest)

4. Environment during storage, transportation and marketing of produce.

Specific materials are selected based on these conditions and fall into either chemical or biological categories listed below.

Fungicide treatments: Several fungicides are presently used as postharvest treatments for control of a wide spectrum of decay-causing microorganisms. However, when compared to preharvest pest control products the number is very small.

For example, intensive and continuous use of fungicides for control of blue and green mold on citrus has led to resistance by the causal pathogens of these diseases. Chemical treatments that are presently used are thiabendazole, dichloran, and imazalil. However, resistance to (Post Harvest)thiabendazole and imazalil is widespread and their use as effective materials is declining.

Temperature and relative humidity: Proper management of temperature is so critical to postharvest disease control that all other treatments can be considered as supplements to refrigeration. Fruit rot fungi generally grow optimally at 20 to 25 0C and can be conveniently divided into those with a growth minimum of 5 to 10 0C or -6 to 0 0C . Fungi with a minimum growth temperature below -2 0C cannot be completely stopped by refrigeration without freezing fruit. High temperature may be used to control postharvest decay on crops that are injured by low temperatures such as mango and papaya. (Post Harvest)

Heating of pears at temperatures from 21 to 38 0C for 1 to 7 days reduced postharvest decay. Decay in „Golden Delicious‟ apples was reduced by exposure to 38 0C for 4 days and virtually eliminated when treated after inoculation.