Isoenzyme variation and genetic structure in natural populations of shortleaf pine (Pinus echinata)

Abstract

Seed from 126 trees from populations representing 15 geographic locations covering much of the natural range of shortleaf pine (Pinus echinata Mill.) were analyzed using 23 enzyme systems covering 39 loci to determine patterns of genetic variation and structure. Populations were polymorphic (p) at 87.2% of the loci, had 2.18 alleles (A) per locus, and had 2.35 alleles per polymorphic locus (A p ). Mean expected heterozygosity (H e ) was 0.194 and mean observed heterozygosity (H o ) was 0.174. Western populations had a higher p, higher A, similar A p , and a higher H o and H e than eastern populations, in part because of six private alleles (alleles seen only in one population) in the west but only one in the east. Genetic structure analysis revealed interpopulation genetic variation at 9%, meaning 91% of the genetic variation in shortleaf pine resides within populations. Interpopulation gene flow was 2.56, indicating two or three allele migrations per generation, which is relatively high and explains the low interpopulation genetic variation in the species. There was no apparent relationship between geographic distance among populations and their genetic distance. Shortleaf pine populations exist in naturally outcrossing random-mating populations and have a relatively large amount of natural variability. Western populations are more diverse than their eastern counterparts.Résumé : Les auteurs ont déterminé les patrons de la variabilité génétique et sa structure chez le pin jaune (Pinus echinata Mill.) à partir de graines récoltées sur 126 arbres représentatifs de 15 localités géographiquement distinctes couvrant la plus grande partie de l'aire de distribution naturelle. Pour ce faire, la variation d'isoenzymes fut évaluée pour 23 systèmes enzymatiques représentatifs de 39 loci. En moyenne, les populations étaient polymorphes (p) pour 87,2% des loci. Elles affichaient 2,18 allèles par locus (A) et 2,35 allèles par locus polymorph (A p ). L'hétérozygotie moyenne espérée (H e ) atteignait une valeur de 0,194 alors que l'hétérozygotie moyenne observée (H o ) était de 0,174. Les populations de l'ouest affichaient des valeurs plus élevées que les populations de l'est pour les paramètres p, A, H o et H e , alors que le paramètre A p était similaire pour les deux groupes de populations. Ces résultats sont en partie attribuables à la présence de six allèles privées (présentes dans une seule population) dans l'ouest comparativement à une seule dans l'est. L'analyse de la structure génétique a révélé que 9% de la variabilité génétique était attribuable à la différenciation de populations, indiquant que 91% de la variabilité génétique se retrouvait au sein des populations chez le pin jaune. Le flux génique inter-population a été estimé à 2,56, indiquant ainsi qu'il y avait deux ou trois migrations d'allèles par génération. Cet estimé est relativement élevé et il explique la faible différenciation de populations observée chez cette espèce. Les auteurs n'ont pas observé de relation significative entre les distances géographiqu...

Paternal chloroplast inheritance patterns in pine hybrids detected with trnL–trnF intergenic region polymorphism

“…The trnL-trnF polymorphism should facilitate population genetic studies in other plant species. In this study, all of the nine putative hybrids identified by Raja et al (1997) from eight shortleaf pine populations have the shortleaf pine chloroplast profile. This was consistent with Edwards et al (1997) who reported paternal inheritance in natural loblolly × shortleaf pine hybrids.…”

“…Nine putative hybrids between shortleaf pine and loblolly pine, previously identified by Raja et al (1997) were also analyzed. Raja et al (1997), identified these putative hybrids based on the heterozygosity of one allozyme marker (IDH: Isocitrate dehydrogenase) reported by Huneycutt and Askew (1989) to be indicative of a hybrid between shortleaf and loblolly pine.…”

“…Raja et al (1997), identified these putative hybrids based on the heterozygosity of one allozyme marker (IDH: Isocitrate dehydrogenase) reported by Huneycutt and Askew (1989) to be indicative of a hybrid between shortleaf and loblolly pine.…”

Natural hybridization within seed sources of shortleaf pine (Pinus echinata Mill.) and loblolly pine (Pinus taeda L.)

“…The IDH locus will identify some of these, but not all, and an IDH heterozygote is not necessarily a hybrid. This suggests that earlier estimates of the level of hybridization between these two species by Chen et al (2004), Raja et al (1997), andEdwards et al (1997) are in question. The lack of F1s in the populations in this study, as explained below, might suggest this study's estimate of the level on hybridization is low.…”

“…About 0.05 g of needle tissue from each tree was ground in the same buffer used for the megagametophytes tissue. The protocol used for the IDH analysis followed that of Raja et al (1997).…”