A CHLOROPLAST DNA PHYLOGENY OF LILACS (SYRINGA, OLEACEAE) - PLASTOME GROUPS SHOW A STRONG CORRELATION WITH CROSSING GROUPS

Phylogenetic relationships and genomic compatibility were compared for 60 accessions of Syringa using chloroplast DNA (cpDNA) and nuclear ri bosomal DNA (rDNA) markers. A total of 669 cpDNA variants, 653 of whic h were potentially phylogenetically informative, was detected using 22 restriction enzymes. Phylogenetic analyses reveal four strongly suppo rted plastome groups that correspond to four genetically incompatible crossing groups. Relationships of the four plastome groups (I(II(LII,I V))) correlate well with the infrageneric classification except for se t. Syringa and Pinnatifoliae. Group I, which includes subg. Ligustrina , forms a basal lineage within Syringa. Group II includes ser. Syringa and Pinnatifoliae and the two series have high compatibility and low sequence divergence. Group III consists of three well-defined species groups of ser. Pubescentes. Group IV comprises all members of ser. Vil losae and has the lowest interspecific cpDNA sequence divergences. Com parison of cpDNA sequence divergence with crossability data indicates that hybrids have not been successfully generated between species with divergence greater than 0.7%. Hybrid barriers are strong among the fo ur major plastome groups, which have sequence divergence estimates ran ging from 1.096 to 1.962%. In contrast, fully fertile hybrids occur be tween species pairs with sequence divergence below 0.4%. Three regions of the plastome have length variants of greater than 100 bp, and thes e indels identify 12 different plastome types that correlate with phyl ogenetic trees produced from cpDNA restriction site data. Biparentally inherited nuclear rDNA and maternally inherited cpDNA length variants enable the identification of the specific parentage of several lilac hybrids.