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= Cranberry Fruit Rot =

Background
Cranberry fruit rot describes a disease complex of multiple disease-causing agents affecting American cranberry (Vaccinium macrocarpon). Cranberry fruit rot (CFR) can be categorized into field rot (rot occurring while growing and before harvest) and storage rot (occurring any time after harvest)1. The importance of field rot and fruit rot depends on how the cranberries will be processed after harvest. Cranberries immediately processed after harvest focus on preventing field rot while fresh market cranberries must prevent storage rot1. There are 10-15 fungal pathogens known to cause cranberry fruit rot diseases, some active in only field rot, storage rot, or both2. The majority of pathogens are ascomycetes, with the rest being deutermycetes2. There is no known bacterial pathogen to play a role in cranberry fruit rot or any major disease on cranberry, potentially due to the low pH conditions on the cranberry fruit3.

Host and Symptoms
In cranberries, the fruit rot pathogens can infect before or after harvest. The symptoms of a rot are related to a general softening and deterioration of the cranberry, which occur both in the field and in storage1. Each specific rot disease that make up the CFR disease complex are caused by specific pathogens (Table 1). An example is the field rot cotton ball caused by Monilinia oxycocci, common in Wisconsin, while bitter rot caused by Glomerella cingulate occurs generally in Massachusetts4. However, these pathogens have been shown to not be entirely specific to their areas5. These symptoms can often resemble other forms of fruit deterioration such as sunscald, hail, and physiological breakdown1.

Disease Cycles
Due to the complexity and number of fungal pathogens involved in cranberry fruit rot, the specific disease cycles have yet to be fully studied. Researchers believe almost every fruit rot pathogen completes a disease cycle every 1-3 years2. Researchers however have hypothesized 3 potential disease cycles taken by the pathogens1. These 3 disease cycles rely heavily on leaves or stems, either debris or living, mainly because all berries are harvested1.

Type 1. Fungal inoculum overwinters in plant debris in the soil surface. In the spring, the fungi produce fruiting bodies and infect developing plants. The main infection occurs when flowers bloom and during the early parts of fruit development.

Type 2. Fungi persist in living leaves then infect as the plant develops fruit while leaves drop.

Type 3. Fungal inoculum overwinter in plant debris and infect during cranberry harvest. When the floodwater is released during harvest, spores are dispersed and infect through potential wounds from equipment.

Management
The management of cranberry fruit rot can be complicated and varies due to the number of pathogens and the temporal aspect of fruit rot. Fungicides applied during the projected times of infection and on potential areas, such as flowers and after fruit set, are effective at deterring fruit rot. Due to the number of pathogens, general fungicides such as chlorothalonil, instead of specific-targeting fungicides, are more effective2. However, fungicides can reduce fruit quality and fruit set in some cases, thus their use is often limited2. Harvest can also play a role in reducing the risk of pathogens. Wet harvest using floodwater, although quicker and easier, can spread pathogens, which would increase chances of storage rot6. Dry harvests can cause more damage to vines and take longer, but can reduce disease spread and decrease the potential of storage rot6. Depending on the final use of cranberries, each harvest type can be beneficial. Sanding, a process where sand is laid on the field to stimulate root growth from the harvested cranberries, could actually may play a role in covering up plant debris with inoculum, which may decrease the chances of field and storage rot2. Resistance and biological controls have proved difficult to validate due to the disease complex being composed of different fungal pathogens2.