CHLOROPLAST DNA VARIATION IN POPULUS .1. INTRASPECIFIC RESTRICTION FRAGMENT DIVERSITY WITHIN POPULUS-DELTOIDES, P. NIGRA AND P. MAXIMOWICZII

We examined intraspecific chloroplast (cp) DNA variation within Populu s deltoides, P. nigra, and P. maximowiczii by restriction fragment ana lysis using 16 restriction endonucleases and six heterologous probes o f cloned Petunia cpDNA fragments. All three Populus species showed int raspecific cpDNA variation, which was intra- and inter-varietal in P. deltoides, intervarietal in P. nigra, and origin-specific in P. maximo wiczii. Two varieties of P. deltoides, var deltoides and var occidenta lis, showed distinct cp genomes/DNA. Three distinct cp genomes/DNA, se parated by a loss or gain of 1 EcoRV restriction site and/or 1 restric tion fragment length polymorphism (RFLP), were observed among the indi viduals of P. deltoides var deltoides. Within P. nigra, cpDNA of var i talica was distinct from that of vars nigra and plantierensis by one R FLP and by a loss or gain of one BamHI restriction site. Populus maxim owiczii clones of Chinese origin were separated from those of Japanese origin by a gain or loss of one ClaI restriction site in their cpDNA. The estimate of nucleotide substitutions per site in cpDNA was 0.07% between two varieties of P. deltoides, 0.05% between var italica and v ar nigra or plantierensis of P. nigra, and 0.01% between Japanese and Chinese accessions of P. maximowiczii.