DIFFERENTIATION OF MYCOSPHAERELLA-DEARNESSII BY CULTURAL CHARACTERS AND RAPD ANALYSIS

Isolates of Mycosphaerella dearnessii, the causal agent of brown spot needle blight of pine, were collected from the northern and southern U nited States and China and analyzed for differences in cultural morpho logy, growth rate, conidial germination at various temperatures, and r andomly applied polymorphic DNA (RAPD) markers. Differences in cultura l morphology and conidial germination were detected between the northe rn U.S. isolates and the other sources, but not between the southern U .S, isolates and Chinese isolates. Molecular polymorphisms (RAPDs) wer e also detected among 43 isolates from the United States and China. No rthern U.S. isolates composed a distinct ''northern group,'' while sou thern U.S. and Chinese isolates composed a related ''southern group.'' Results of this study support the existence of races within Mycosphae rella dearnessii. The southern United States appears to be the origin of the current Chinese population, as suggested by the dendrograms gen erated using the molecular data.