Reinforced evidence on partial compatibility between Pinus sylvestris and Pinus mugo and on maternal inheritance of chloroplast DNA in the Pinus mugo × Pinus sylvestris cross

The crossability relationship between Scots pine (Pinus sylvestris L.) and mountain dwarf pine (Pinus mugo Turra) was tested under field conditions using an artificial pollination approach. There was partial compatibility between the parental species, as evidenced by the amount of filled seeds in their reciprocal crossings and in control variants from self-pollination, controlled intraspecific outcrossing and open pollination of mother trees. The crossability degree in P. sylvestris × P. mugo was characterised by the index 0.15, and the reciprocal crossing by the index 0.18. Crossability of P. sylvestris and P. mugo with their putative hybrid individuals was much higher; the number of filled seeds was comparable with that of the control variants. The reciprocal crossings of P. sylvestris and P. mugo species were highlighted by the opposite inheritance of their chloroplast DNA (cpDNA). The paternal cpDNA inheritance in P. sylvestris × P. mugo and maternal cpDNA inheritance in P. mugo × P. sylvestris was repeatedly confirmed using the cpDNA trnV-trnH/HinfI marker as well as the newly developed partial cpDNA trnV-trnH/AseI marker. The nature of the latter is described in terms of the nucleotide sequence.

Chloroplast DNA variation and inheritance in waxflowers (Myrtaceae)

A study of chloroplast DNA variation and inheritance in waxflowers (Myrtaceae) was undertaken as a basis for validating parentage in putative, juvenile hybrid plants and in naturally occurring hybrids. Polymerase chain reaction amplification of three chloroplast DNA regions, followed by restriction of the amplified products, was used to identify restriction fragment length polymorphisms (RFLP) in 18 Chamelaucium uncinatum and C.�megalopetalum genotypes. Five cpDNA haplotypes were observed within the two species studied. In C.�uncinatum, three site mutations and one length mutation were observed, corresponding to three cpDNA haplotypes; and in C. megalopetalum, two cpDNA haplotypes were observed.Chloroplast DNA (cpDNA) inheritance was studied in 17 intraspecific and 33 interspecific hybrids by using the cpDNA polymorphisms between the female and the male parents. Maternal cpDNA inheritance was observed in all cases, as in most angiosperms. These results support a 95.5% probability of maternal cpDNA inheritance in waxflowers at the 90% confidence level.The method has been used to identify maternal parents of naturally occurring hybrids in our waxflower breeding program. It may also be applied to the study of the evolution of natural populations and, in this study, indicates distinct lines of evolution for individual populations of the two species.

Ubiquity of the St chloroplast genome in St-containing Triticeae polyploids

Interspecific hybridization occurs between Tritceae species in the grass family (Poaceae) giving rise to allopolyploid species. To examine bias in cytoplasmic DNA inheritance in these hybridizations, the sequence of the 3' end of the chloroplast ndhF gene was compared among 29 allopolyploid Triticeae species containing the St nuclear genome in combination with the H, I, Ns, P, W, Y, and Xm nuclear genomes. These ndhF sequences were also compared with those from diploid or allotetraploid Triticeae species having the H, I, Ns, P, W, St, and Xm genomes. The cpDNA sequences were highly similar among diploid, allotetraploid, allohexaploid, and allooctoploid Triticeae accessions containing the St nuclear genome, with 0-6-nucleotide (nt) substitutions (0-0.8%) occurring between pairs of species. Neighbor-joining analysis of the sequences showed that the ndhF DNA sequences from species containing the St nuclear genome formed a strongly supported clade. The data indicated a strong preference for cpDNA inheritance from the St nuclear genome-containing parent in hybridizations between Triticeae species. This preference was independent of the presence of the H, I, Ns, P, W, and Xm nuclear genomes, the geographic distribution of the species, and the mode of reproduction. The data suggests that hybridizations having the St-containing parent as the female may be more successful.Key words: interspecies hybridization, cytoplasmic inheritance.