The identification, distribution and spread of dogwood anthracnose in Michigan (Discula destructiva, Cornus florida)

Dogwood anthracnose, caused by the fungal pathogen Discula destructiva , has led to wide spread mortality of the native flowering dogwood tree, Cornus florida. Since its initial identification in the 1970s, D. destructiva has spread throughout much of the range of C. florida, but only one county in Michigan was identified as infected in 1993. The objectives of this study were to determine the distribution of dogwood anthracnose in Michigan forests, design species-specific PCR primers for detection of D. destructiva, and survey imported flowering dogwood stock in Michigan nurseries by microscopic and PCR methods. A total of 52 long-term monitoring plots recorded using global positioning systems (GPS) were developed during surveys for dogwood anthracnose in Michigan. Dogwood anthracnose was found at 13 sites in 7 counties in Michigan. PCR primers DdF and DdR targeted the internal transcribed spacer (ITS) region of rDNA, amplifying a 460 by fragment of DNA. PCR primers for DdF and DdR were found to amplify DNA from both D. destructiva and D. fraxinae. A survey of five Michigan nurseries in 2001 examined 342 newly arrived C. florida and C. kousa trees from ten out-of-state nurseries. Analysis of twig samples from nursery trees by microscopic methods yielded an infection rate of 10.23%, with infections occurring in 8 of 10 out-of-state nurseries and all five Michigan nurseries. PCR of nursery samples using DdF and DdR detected infected trees in 2 of 10 out-of-state nurseries and 2 of 5 Michigan nurseries, for a 4.39% infection rate.