Blueberry disorders and diseases
Customers are willing to purchase healthy fruits, meaning fruits free of diseases, and disorders. Furthermore, blueberries must not only look appetizing from the outside, but also be fresh inside. There are dozens of different diseases and disorders, which are not always easy to recognize. A good diagnosis is important. By recognizing the symptoms of a disease or disorder, it can be linked to the cause. After which, measures can be taken to prevent the disease or disorder from happening again in the future.
Frequently occurring disorders and diseases
Dehydrated blueberries shrivel. Photo by WUR
Blueberries have a thin and soft skin, which makes them susceptible to water loss. A relative humidity between 90-95% during storage can minimize water loss. Water loss is also a major cause of firmness loss during storage, besides cell-wall degradation related processes. Blueberries are best kept cool, at a high relative humidity, and can also be stored under controlled atmosphere (CA) to extend their shelf-life.
Shrivelling can also be apparent on blueberries attacked by “mummy berry” disease, caused by fungi during the growth of the fruit. Those berries have to be pick out of the batch at harvest and have nothing to do with water loss due to low relative humidity.
Mechanical harvest of blueberries is a main cause of bruising. Photo by TFoxFoto/Shutterstock.com
BruisingA main cause of bruising is mechanical harvesting. Mechanical harvesting is more common toward the end of the season, when blueberry sales prices are reduced and blueberries are destined for processing. Since secondary diseases may develop on bruises, bruised blueberries should be removed from post-harvest chains.
Mealiness is correlated with firmness, which can be measured with a penetrometer. Photo by WUR
MealinessMealiness or grainy blueberries, while still edible, are always a deception to the consumers. Rather than juicy, the blueberry has a mealy, floury or grainy texture. Causes may be diverse, including cultivar, growth conditions and maturity. It currently cannot be cured by postharvest management.
Mouldy blueberries. Photo by kellyreekolibry/Shutterstock.com
MouldOne of the most common moulds found on blueberries is Botrytis or grey mould. The mycelium is grey and fluffy. Actions during growth in the field can reduce its presence. Botrytis may also remain latent until the fruit softens or by entering the fruit through damages such as bruises. Although, cooler temperature will not stop the growth of Botrytis, it will significantly slow it down and extend the shelf-life of the blueberry.
Antracnose in a petri dish. Photo by BENPOL/Shutterstock.com
Antracnose rotBlueberries infected by fungi causing anthracnose can be recognised by sunken-brown lesions or by the growth of orange mycelium. The optimum temperature for anthracnose development is 20-27 °C. If the supply chain is maintained at a low temperature, the chances for anthracnose development are very low as the fungi causing it are relatively inactive below 15 °C. Infected berries should be taken out of the food chain.
Truck with CA cover at the rear door. Photo by WUR
CA-related disordersBlueberries can be stored under CA conditions to extend the shelf-life also during shipment; a generally safe condition is 10% CO2 and 11% O2. Note that the optimal settings will depend on several factors such as storage temperature, variety and location. Deviation from the recommended values can result in off-flavours and brown discoloration.