Submitted to: Canadian Journal of Forest Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/12/2004
Publication Date: 12/25/2004
Citation: Chen, J., Tauer, C.G., Bai, G., Huang, Y., Payton, M.E., Holley, A.G. 2004. Bidirectional introgression between pinus taeda and pinus echinata: evidence from morphological and molecular data. Canadian Journal of Forest Research. 34:2508-2516. Interpretive Summary: Loblolly and shortleaf pine are important tree species in the southeast United States. The hybrids derived from the two species are more resistant to several diseases. It is important to distinguish the hybrid from both parental species and understand the direction of introgression. In this study, a sympatric population from central Arkansas was used. DNA markers identified 10 putative hybrids from the 80 trees sampled. Two putative hybrids were similar to loblolly pine, and eight hybrids were similar to the shortleaf pine. These results suggested that some of the putative hybrids were likely derived from early-generation of backcross with either shortleaf or loblolly pine as the recurrent parent within the studied population.
Technical Abstract: The frequency of mature hybrids, including post-F1 individuals, between loblolly (Pinus taeda L.) and shortleaf pine (Pinus echinata Mill.), detectable with a codominant nuclear marker, was studied in a sympatric population from central Arkansas. The direction of introgression was also examined. The marker revealed 10 putative hybrids from the 80 trees sampled. PCR-RFLP analysis of their rbcL gene showed two of the putative hybrids (HL) share loblolly pine chloroplast DNA, and eight (HS) share the shortleaf pine chloroplast DNA. The two putative HL hybrids were morphologically similar to loblolly pine, and the eight putative HS hybrids were morphologically similar to shortleaf pine. Utilizing microsatellite data, Nei's measure of genetic identity showed the putative HL hybrids to be similar to loblolly pine, and the putative HS hybrids as being similar to shortleaf pine. An inferred tree of the individuals, using simple sequence repeat data and the neighbor-joining method, also suggested that some of the putative hybrids were not F1 individuals. Principle component analysis of the morphological characters groups the HL trees with loblolly pine and the HS trees with shortleaf pine. These results suggest bidirectional introgression occurred within the study population, and some of the putative hybrids were likely derived from early-generation backcross(es) with either shortleaf or loblolly pine.