Origin, genetic diversity and population structure of Nectria coccinea var. faginata in North America

Genetic similarity of Nectria coccinea var. faginata (NCF) from the northea stern USA to other Nectria taxa was investigated using RFLPs of ribosomal ( r) DNA, mitochondrial (mt) DNA, and anonymous nuclear (n) DNA to determine whether NCF is native or was introduced into North America. Mitochondrial a nd nDNA restriction fragments were cloned from NCF for use as probes. Genet ic relatedness was assessed using neighbor-joining analyses of restriction sites mapped within each probed region. NCF was more similar to N, coccinea var. coccinea isolates from Europe (NCCE) than to N. coccinea var. coccine a isolates from North America (NCCA) in all probed regions. NCCA. isolates were highly dissimilar among themselves and did not form a single group. Se veral probes did not hybridize to two of the NCCA isolates, indicating thei r lack of similarity to NCF. Nectria galligena (NG) isolates, collected in northeastern USA, were distinct from NCF in all probed regions, forming its own cluster in neighbor-joining analysis. Haplotype diversity and nucleoti de diversity within populations, estimated from restriction site data, were markedly greater in NG than in NCF. Genetic similarity of NCF to NCCE, lac k of similarity of NCF to North American taxa, and the limited diversity of NCF populations compared to a North American NG population strongly suppor t the hypothesis that NCF was introduced into North America from Europe.