Calosphaeria canker of sweet cherry caused by Calosphaeria pulchella in California and South Australia

Abstract

California is the second largest sweet cherry producer in the United States with annual revenues up to $200 million. The South Australian cherry industry generates about 10% of Australia's overall production with approximately 1,500 metric tons of cherries produced yearly. In California, perennial canker diseases and subsequent branch dieback are responsible for extensive damage throughout sweet cherry orchards, reducing annual yields and tree longevity. Surveys of cherry orchards and isolation work were conducted in California to identify the main canker-causing agents. Calosphaeria pulchella was the main fungus isolated from cankers, followed by Eutypa lata and Leucostoma persoonii, respectively. Preliminary surveys in cherry orchards in South Australia documented C. pulchella and L. persoonii in cankers. The pathogenicity of C. pulchella in sweet cherry was confirmed following field inoculations of 2- to 3-year-old branches. C. pulchella was able to infect healthy wood and produce cankers with as much virulence as E. lata or L. persoonii. Spore trapping studies were conducted in two sweet cherry orchards in California to investigate the seasonal abundance of C. pulchella spores. Experiments showed that rain and sprinkler irrigation were important factors for aerial dissemination. Finally, this study illustrates the symptoms and signs of the new disease Calosphaeria canker.