Improved control of Colletotrichum acutatum in strawberry and sweet cherry

Colletotrichum acutatum is an important fungal pathogen in many crops worldwide. In the Nordic countries it is of particular importance in strawberry and cherry where it causes blackspot and bitter rot, respectively. The disease usually appears very late in the season in sweet cherry, even after harvest, with negative implications for marketing. In 2002 to 2004 blackspot had a severe outbreak at the Elite plant station and in many certified strawberry plant nurseries in Norway. C. acutatum may be found ei ther symptomatically or asymptomatically on a wide spectre of hosts and on weeds, but there is limited knowledge about possible movement of the fungus between plant species. Food authorities are responsible of testing for C. acutatum in certified strawber ry plant material, but no such testing is required in production of sweet cherry trees. The officially recommended test method in Norway and EU is time consuming. We want to develop a quick and reliable PCR based diagnostic tool that can be used on both s trawberry and cherry. Even if not required by the authorities, the Elite plant station and three nurseries producing sweet cherry trees want to produce grafting material and trees of sweet cherry with minimal risk of contamination by C. acutatum. We furth er want to use the diagnostic tool to test commercial cherry plantings for presence of the disease and thus to optimise control measures and avoid unnecessary use of fungicides where the disease is absent. To lower the risk of contaminating disease free n ew crops of strawberry and sweet cherry, we want to explore the possible movement of C. acutatum between hosts and to study long time survivability of the fungus in plant debris. This knowledge is very important for food authorities that enforce legislati ve measures and for certified plant producers and strawberry or sweet cherry growers when planning crop rotation. Management strategies to avoid C. acutatum will be developed based on results from the project.