The fungal pathogen Colletotrichum acutatum causes Blueberry Anthracnose (Ripe Rot) on pre and post harvest fruit of highbush blueberry. The disease occurrs in all blueberry production areas and has a great impact of reducing shelf life of fruits and having a poor quality of fresh fruits on the market.
Blueberrys are susceptible to the fungal pathogen. The berries don`t develop symptoms until they are mature or ripe. The first symptoms are seen near the end of the blossom on ripe fruits as dark, sunken areas. These infected area may shrivel with time. Within a few days bright salomon- orange coloured, wet spore masses are seen on these sunken areas. The sticky spore masses spread to other berries by rain, irrigation, splashing water, wind and contacts during harvest. The fungal pathogen infects all stages of the plant: leaves, buds, twigs and canes. New shoots and leaves may become blighted in the spring. Twigs are becoming infected by transferring spores from infected buds. Dark brown, canker- like lesions with fruit bodies develop on young canes.
The fungal pathogen overwinters in twigs and flower buds, spurs and trusses. In spring the fungus produce spores, which are dispersed by rain, irrigation and water- splashes. Infections occurr at a temperature optimum of 12- 27°C and a leaf wetness period of more than 12 hours. The fruit can be infected at any time, although infections are just visible (symptoms seen) when the fruit is mature. The fungus enters the fruit and remains dormant until the berry starts to ripen. At this time the fungus starts to colonize the infected area and produce enzymes with destroy the plant cell walls. These damaged cells loose their contents and integrity (symptoms are seen as sunken areas and shrivelled). Spent fruit trusses could be infected after harvest. In FieldClimate.com weak, moderate and severe Infection are calculated in dependance of the parameters temperature, leaf wetness and precipitation. Whenever 100 % of infection are reached the conditions for an weak/moderate or severe infection have been fullfilled.
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Gillett J.M., Schilder A. C. (2009): Environmental Requirements for Infection of Blueberry Fruit by Colletotricum acutatum. Proc. IxthIS on Vaccinium.