Genetic analysis of Eutypa strains from California supports the presence of two pathogenic species

Eutypa dieback is a perennial canker disease that adversely affects grape ( Vitis vinifera) production throughout the world. The causal agent has been known as either Eutypa armeniacae or E. lata, and it has been unclear wheth er the two taxa are separate species. We analyzed 115 isolates of Eutypa an d conspecific strains, including 106 from California, using amplified fragm ent length polymorphism (AFLP) and sequence analysis of the ribosomal DNA ( rDNA) internal transcribed spacer (ITS) sequence. Strains from cultivated p lant species exhibited an average genetic distance of 0.34, as calculated b y the DICE coefficient (NTSYS-pc software). An unweighted pair-group method with arithmetic averages dendrogram revealed a genetically distinct (dista nce of 0.73) group of Eutypa strains from valley oak (Quercus lobata) and m adrone (Arbutus menziesii) and a strain from grape. Analysis of rDNA ITS se quences strongly supported the genetically distinct cluster detected in the AFLP data. Combined data indicated the presence of two species of Eutypa ( E, armeniacae and E. lata) in our sample population. However, both Eutypa s pecies were capable of infecting native and cultivated hosts, suggesting th e potential for native tree species to serve as inoculum sources for grape infection in California. Further investigations of E. armeniacae and E, lat a would contribute to the development of a successful disease management st rategy.