The primary postharvest decay pathogens on cherries are fungi (molds). Their spores (fungal inoculum) are prevalent in the orchard, contaminating fruit surface, leaves, soil and agricultural tools. The fungal inoculum arrives into the pack-house with the harvested fruit, on its surface, in disease fruits, on contaminated tools and bins and with orchard litter.
When the fruit comes in contact with other fruit, with leaves, branches, insects, on the tree, or during handling and packing, micro- and macroscopic cuts, bruises and wounds occur that serve as entry points for the fungal spores. As a result, a fruit may become diseased in the orchard and spread the disease to other fruits throughout the supply chain.
Frequently encountered pathogens and the diseases they cause:
Alternaria rot is caused by fungal species in the group Alternaria. This fungus is cosmopolitan and overwinters in orchard litter. It infects via wounds, yielding a dark brown circular spot that may increase to produce a lesion where concentric circles of spores can be seen (Fig. 1). Alternaria is suppressed by low temperatures, therefore holding temp. of nearly 0oC should suppress its development. Storage in modified atmospheres at 10% CO2 also demonstrated disease reduction.
Gray mold rot is a serious disease on many fruits and vegetables during postharvest. The disease is the outcome of infection by the fungus Botrytis cinerea, which may infect the fruit directly or utilize wounds. The disease produces a watery tissue covered by a fleecy mass of grey-brown spores (Fig. 2).
Blue mold rot is the outcome of infection by the fungus Penicillium expansum. The fungus infect primarily via wounds. The initial symptoms appear as small circular spots, but as disease progresses, the fungus produce enzymes that breakdown the tissue and the fruit becomes soft and flaccid. The fungus is easily recognized by the blue-green velvety sporulation surrounded by white expanding mycelium (Figure 3).
Brown rot is incited by species in the fungal group Minilinia spp., primarily Monilinia fructicula. The pathogen infects blossoms in the orchard, unripen and ripen fruit. Monilinia spp. can infect fruit directly without the need for wound, or utilize wounds, bruises, cuts and splits to colonize the fruit and cause disease. Cherry fruits diseased with brown rot initially demonstrate brown, powdery sporulation. Then, the fruit shrivels to become a "mummy" (Figure 4). Diseased fruit usually fall onto the ground and the pathogen overwinters in the mummified remnants, which serve as sources of inoculum for the next season.
Cladosporium rot is considered a distinctive disease in cherry. This rot is the outcome of infection by the fungus Cladosporium herbarum. The fungus is a common mold frequently found in orchards. It infects fruits through breaks in the skin, causing a hard and dry decayed tissue with a gray-black discoloration.
Rhizopus rot is caused by the fungus Rhizopus spp., which is one of the most severe postharvest diseases of cherries (Figure 5). The pathogen infects most commonly after harvest and needs an open wound for penetration. The fungus will not develop below 7°C and can be managed by holding the cherries at a temp. close to 0°C.
Good Agriculture Practices in a nutshell
During the season:
- Monitor nutrient application to keep trees healthy and reduce susceptibility to disease.
- Control insects that may serve as disease vectors.
- Develop a master sanitation plan and apply sanitation practices:
- Remove and eradicate litter that may serve as sources of inoculum.
- Scout for diseased branches, leaves and injured, split or bruised fruits on the ground and on trees, remove and eradicate.
- Sanitize working tools periodically with approved surface sanitizers.
- Utilize approved fungicides following producer's recommendations when needed.
- Prune trees to increase air flow.
During harvest and postharvest:
- At all times fruit should be handled with care to limit bruising and injury.
- Dispose of cracked, injured or infested fruit.
- Utilize sanitation practices to prevent infestation of healthy fruit by:
- Cleaning bins from dirt, soil, and litter and sterilizing before usage.
- Periodically sanitize hand pruners and knives used during harvest.
- Surface-sanitize storage facility and packing-line equipment, keeping Good Manufacturing Practices for optimum food safety.
- Monitor workers hygiene.
- Wash fruit with approved sanitizers followed by potable water wash.
- Hydro-cool cherry cultivars, which are insensitive to the process, as soon as possible.
- Store at temp. close to 0°C.
- Do not store cull in proximity to healthy undamaged fruit.
For more information:
Ms. Andy Swersky
+972-4-9872131
[email protected]
www.stepac.com