Genetic variation and interspecific hybridization among natural populations of zoysiagrasses detected by RFLP analyses of chloroplast and nuclear DNA.

Genetic variations among 17 accessions of zoysiagrasses collected from natural populations in Japan were investigated by RFLP analyses of chloroplast DNA (cpDNA) and nuclear DNA. These accessions were classified into five species based on morphological characteristics: Zoysia japonica, Z. matrella, Z. tenuifolia, Z. sinica, and Z. macrostachya. On the basis of eight kinds of RFLPs in cpDNAs detected across accessions, six chloroplast genome types (types A-F) were identified. Although type-A cpDNA was shared by five accessions of japonica and four accessions of matrella, derivative cpDNAs of type A, which each arose by a mutation, were identified in one accession of japonica (type B) and in two accessions of matrella (type C). One accession of japonica which showed spikelets similar to those of shapes macrostachya, contained type-F cpDNA as did sinica and macrostachya. The two accessions of tenuifolia each showed a specific cpDNA type, i.e. types D and E. Genetic relationships among the 17 accessions were investigated by the RFLP analyses of nuclear DNA with 20 genomic and gene probes. A dendrogram constructed with genetic distances calculated from the RFLP patterns indicated four major groups among them. Six accessions of japonica comprised one group, whereas the one accession of japonica possessing the type-F cpDNA was clustered with macrostachya and sinica. Four accessions of matrella with type A cpDNA constituted another group in the dendrogram, showing a closer relationship to the japonica accessions than to the other two accessions of matrella. The remaining two accessions of matrella and tenuifolia accessions were grouped together. These data indicate that zoysiagrasses distributed in Japan harbor highly genetic variations, and that interspecific hybridization has occurred in natural populations.