COMPARISON OF GENETIC DIVERSITY IN THE CHESTNUT BLIGHT FUNGUS, CRYPHONECTRIA (ENDOTHIA) PARASITICA, FROM CHINA AND THE UNITED-STATES

Cryphonectria (Endothia) parasitica was introduced into the U.S. from China and/or Japan approximately 90-100 years ago. We tested the null hypothesis that the introduced population in the U.S. and the ancestral population in Asia are similar in their genetic diversity. We compared genetic diversity in a sample of 16 isolates of C. parasitica from China to a sample of 16 isolates from the U.S. using restriction fragment length polymorphisms. DNA from each isolate digested with either the restriction endonucleases EcoR I or Pst I was probed with 17 randomly selected plasmid probes from a DNA library from C. parasitica, two additional single-copy probes known to detect polymorphisms in the U.S., and a DNA fingerprinting probe. Among the 17 random probes, six were monomorphic for both samples; three probes hybridized to repetitive sequences and were not used for comparing genetic diversity. Eight random probes were polymorphic in the Chinese sample, compared to only two in the U.S. Average gene diversity was 0.22 for China but only 0.08 for the U.S.; the average number of restriction patterns per probe was 2.5 in China and 1-5 in the U.S. Thus, the Chinese sample was more genetically diverse than the U.S. when probed with the random plasmids. There were 12 multilocus haplotypes determined by the random probes among the 16 Chinese isolates compared to nine in the U.S. sample (six of these nine were determined by one highly variable probe that hybridized to three loci). These results are consistent with what would be expected in a population founded by a small number of individuals. Results from the additional single-copy probes gave mixed results. An unexpected result was that the DNA fingerprinting probe showed greater variability among the U.S. isolates than among the Chinese isolates. We currently have no explanation for this last result.