Biomedical subjects

O P Rajora

Publications and source records attributed to O P Rajora.

8 recordsLinked to original sources

PubMed2006

Impacts of forest fragmentation on the mating system and genetic diversity of white spruce (Picea glauca) at the landscape level.

We studied the mating system of white spruce (Picea glauca) in a landscape fragmented by agriculture in northern Ontario, Canada. We sampled 23 stands that ranged in size from 1 to >500 trees isolated by 250-3000 m from the nearest other stand. Six polymorphic allozyme loci from four enzyme systems were used to genotype approximately 10 000 embryos from 104 families. We detected no allele frequency heterogeneity in the pollen pool among stands or families (Phi(FT)=-0.025). Overall, estimates of outcrossing were high (t(m)=94% and mean t(s)=91%) but significantly different from unity. Bi-parental inbreeding (t(m)-t(s)=3.2%) was low but significantly different from zero. Allozyme-based outcrossing estimates did not differ significantly among three stand-size classes (SSCs): small (<10 trees), medium (10-100 trees) and large (> or =100 trees). The number of effective pollen donors was high in all SSCs, but was significantly lower in small stands (N(ep)=62.5) than in medium-sized and large stands (both N(ep)=143). The primary selfing rate was significantly higher in medium stands than in large stands. We found no significant difference in genetic diversity measures in the filial (seed) population among SSCs. Overall, these results indicate that white spruce stands in this fragmented landscape are resistant to genetic diversity losses, primarily through high pollen-mediated gene-flow and early selection against inbred embryos. We discuss the importance of using seed data, in conjunction with genetic data, to evaluate the impacts of fragmentation on natural populations.

Canada↗

PubMed2005

Intraspecific and interspecific genetic and phylogenetic relationships in the genus Populus based on AFLP markers.

Although Populus has become the model genus for molecular genetics and genomics research on forest trees, genetic and phylogenetic relationships within this genus have not yet been comprehensively studied at the molecular level. By using 151 AFLP (AFLP is a registered trademark of Keygene) markers, 178 accessions belonging to 25 poplar species and three interspecific hybrids were analyzed, using three accessions belonging to two willow species as outgroups. The genetic and phylogenetic relationships were generally consistent with the known taxonomy, although notable exceptions were observed. A dendrogram as well as a single most parsimonious tree, ordered the Populus sections from the oldest Leuce to the latest Aigeiros, a pattern consistent with their known evolutionary relationships. A close relationship between Populus deltoides of the Aigeiros section and species of the Tacamahaca section was observed and, with the exception of Populus wilsonii, between the species of the Leucoides, Tacamahaca, and Aigeiros sections. Populus nigra was clearly separated from its consectional P. deltoides, and should be classified separately from P. deltoides. The AFLP profiles pointed out to the lack of divergence between some species and revealed that some accessions corresponded with interspecific hybrids. This molecular study provides useful information about genetic relationships among several Populus species and, together with morphological descriptions and crossability, it may help review and update systematic classification within the Populus genus.

Cluster Analysis↗

PubMed2002

Genetic diversity impacts of forest fires, forest harvesting, and alternative reforestation practices in black spruce (Picea mariana).

Benchmarks were established for genetic diversity inherent in natural mature populations, and genetic diversity impacts of forest fires, clearcut harvesting and alternative natural and artificial silvicultural regeneration practices were determined in black spruce (Picea mariana). Allozymes of 32 loci were used to determine and compare genetic diversity and genetic relationships of adjacent or nearby four stand types: post-fire natural mature (FNM), post-fire natural young (FNR), post-harvest natural young (HNR) and post-harvest plantation (PLT), of black spruce at each of the four study sites located in two ecoregions in Manitoba: Ecoregion 90-Lac Seul Upland (Eastern) and Ecoregion 158 - Mid-Boreal Lowland (Northern). Both allelic- and genotypic-based genetic diversity parameters, as well as latent genetic potential, were determined. Black spruce populations showed typical moderate to high levels of allozyme genetic diversity. The mean genetic diversity parameters over the 16 black spruce populations sampled were as follows: percent loci polymorphic - 67%, mean number of alleles per locus - 2.52, effective number of alleles per locus - 1.70, observed heterozygosity - 0.222, expected heterozygosity - 0.308, mean number of observed genotypes per locus - 3.65, mean number of expected genotypes per locus - 5.03, genotype additivity (observed) - 116.8, genotype additivity (expected) - 161, genotype multiplicity (observed) - 6.16 x 10(15), genotype multiplicity (expected) - 2.06 x 10(19) and latent genetic potential - 26.12. The four stand types (FNM, FNR, HNR and PLT) had comparable and statistically similar genetic diversity levels at each of the four study sites as well as overall. No significant differences in black spruce genetic diversity levels were observed between the two ecoregions in Manitoba, as well as between the post-fire and post-harvest regenerated stands. No particular order of genetic relatedness among the four stand types was observed. Black spruce populations showed some sort of site-related differentiation in their genetic constitution. Allelic heterogeneity and genetic distances among populations within stand types and among four stand types suggest that the genetic diversity was maintained at the landscape level in black spruce. The results of our study demonstrate that forest fires and currently used clearcut harvesting, and alternative natural and artificial silvicultural regeneration practices, do not adversely affect genetic diversity in black spruce, and that the genetic diversity effects of clearcut harvesting are not significantly different from those due to forest fires in black spruce.

Alleles↗

PubMed2002

Old-growth red spruce forests as reservoirs of genetic diversity and reproductive fitness.

Old-growth forests are assumed to be potential reservoirs of genetic diversity for the dominant tree species, yet there is little empirical evidence for this assumption. Our aim was to characterize the relationship of stand traits, such as age, height and stem diameter, with the genetic and reproductive status of old-growth and older second-growth stands of red spruce (Picea rubens Sarg.) in eastern Canada. We found strong relationships between height growth (a fitness trait) and measures of genetic diversity based on allozyme analyses in red spruce. The negative relationship between height and the proportion of rare alleles suggests that high proportions of these rare alleles may be deleterious to growth performance. Latent genetic potential, however, showed a significant and positive relationship with height. Stand age was not correlated to height, but was correlated to seedling progeny height. In late-successional species such as red spruce, age and size (e.g., height and stem diameter) relationships may be strongly influenced by local stand disturbance dynamics that determine availability of light, growing space, moisture and nutrients. In larger and older stands, age appeared to provide a good surrogate measure or indicator for genetic diversity and progeny height growth. However, in smaller and more isolated populations, these age and fitness relationships may be strongly influenced by the effects of inbreeding and genetic drift. Therefore, older populations or old-growth forests may represent superior seed sources, but only if they are also of sufficient size and structure (e.g., stem density and spatial family structure) to avoid the effects of inbreeding and genetic drift. Thus, larger and older forests appear to have an important evolutionary role as reservoirs of both genetic diversity and reproductive fitness. Given the rapid environmental changes anticipated (as a result of climate change, increasing population isolation through fragmentation, or following the introduction of exotic pests and diseases) these older populations of trees may have a valuable function in maintaining the adaptive potential of tree species.

Genetic Variation↗

PubMed2001

Isolation, characterization, inheritance and linkage of microsatellite DNA markers in white spruce (Picea glauca) and their usefulness in other spruce species.

Microsatellite DNA/simple-sequence-repeat (SSR) loci were identified, isolated and characterized in white spruce (Picea glauca) by screening both a non-enriched partial genomic library and a partial genomic library enriched for (AG/TC)n-containing clones. Inheritance and linkage of polymorphic SSR loci were determined in F1 progeny of four controlled crosses. We also assessed the compatibility and usefulness of the P. glauca microsatellite DNA markers in five other Picea species. Twenty-four microsatellites were identified by sequencing 32 clones selected from screens of 5,400 clones from the two libraries. The (AG/TC)n microsatellites were the most abundant in the non-enriched library. Eight microsatellite DNA loci were of the single-copy type, and six of these were polymorphic. A total of 87 alleles were detected at the six polymorphic SSR loci in 32 P. glauca individuals drawn from several populations. The number of alleles found at these six SSR loci ranged from 2 to 22, with an average of 14.5 alleles per locus, and the observed heterozygosity ranged from 0.48 to 0.91, with a mean of 0.66 per locus. Parents of the controlled crosses were polymorphic for five of the six polymorphic SSR loci. Microsatellite DNA variants at each of these five SSR loci followed a single-locus, codominant, Mendelian inheritance pattern. Joint two-locus segregation tests indicated complete linkage between PGL13 and PGL14, and no linkage between any of the remaining SSR loci. Each of the 32 P. glauca individuals examined had unique single or two-locus genotypes. With the exception of non-amplification of PGL12 in P. sitchensis, P. mariana, and P. abies and the monomorphic nature of PGL7 in P. mariana, primer pairs for all six polymorphic SSR loci successfully amplified specific fragments from genomic DNA and resolved polymorphic microsatellites of comparable sizes in P. engelmanni, P. sitchensis, P. mariana, P. rubens, and P. abies. The closely related species P. mariana and P. rubens, and P. glauca and P. sitchensiss could be distinguished by the PGL12 SSR marker. The microsatellite DNA markers developed and reported here could be used for assisting various genetics, breeding, biotechnology, tree forensics, genome mapping, conservation, restoration, and sustainable forest management programs in spruce species.

Base Sequence↗

PubMed2000

Microsatellite DNA analysis of genetic effects of harvesting in old-growth eastern white pine (Pinus strobus) in Ontario, Canada.

Microsatellite DNA markers from 13 simple sequence repeat (SSR) loci were used to compare genetic diversity between preharvest pristine and postharvest residual gene pools of two adjacent virgin, old-growth ( approximately 250 years) stands of eastern white pine (Pinus strobus L.) in Ontario. There was concurrence in genetic diversity changes in the postharvest gene pools of the two stands. The total and mean numbers of alleles detected in each stand were reduced by approximately 26% after tree density reductions of approximately 75%. Approximately 18 and 21% of the low-frequency (0. 25 > P > or = 0.01) alleles and 76 and 92% of the rare (P < 0.01) alleles were lost from residual stands A and B, respectively, after harvesting. Multilocus gametic diversity was reduced by 38 and 85% and genotype additivity by approximately 50% in the residual stands after harvesting. Latent genetic potential of each stand was reduced by approximately 40%. Although heterozygosity was reduced (1-5%) in the postharvest residual stands, the reductions were not substantial and not comparable to those using other genetic diversity measures. The reductions in genetic diversity measures were slightly higher than those theoretically expected in postbottleneck populations according to drift theory. In the absence of substantial gene migration that could ameliorate the genetic losses, the ability of the postharvest white pine gene pools to adapt to changing environmental and disease conditions may have been compromised. The microsatellite DNA results for genetic effects of harvesting in old-growth eastern white pine stands were similar to those that we reported earlier from allozyme analysis (Buchert et al. 1997). The results indicate that silvicultural practices should ensure that the gene pools of remaining pristine old-growth stands are reconstituted in the regenerating stands.

Alleles↗

PubMed2000

Microsatellite DNA markers in Populus tremuloides.

Markers for eight new microsatellite DNA or simple sequence repeat (SSR) loci were developed and characterized in trembling aspen (Populus tremuloides) from a partial genomic library. Informativeness of these microsatellite DNA markers was examined by determining polymorphisms in 38 P. tremuloides individuals. Inheritance of selected markers was tested in progenies of controlled crosses. Six characterized SSR loci were of dinucleotide repeats (two perfect and four imperfect), and one each of trinucleotide and tetranucleotide repeats. The monomorphic SSR locus (PTR15) was of a compound imperfect dinucleotide repeat. The primers of one highly polymorphic SSR locus (PTR7) amplified two loci, and alleles could not be assigned to a specific locus. At the other six polymorphic loci, 25 alleles were detected in 38 P. tremuloides individuals; the number of alleles ranged from 2 to 7, with an average of 4.2 alleles per locus, and the observed heterozygosity ranged from 0.05 to 0.61, with an average of 0.36 per locus. The two perfect dinucleotide and one trinucleotide microsatellite DNA loci were the most informative. Microsatellite DNA variants of four SSR loci characterized previously followed a single-locus Mendelian inheritance pattern, whereas those of PTR7 from the present study showed a two-locus Mendelian inheritance pattern in controlled crosses. The microsatellite DNA markers developed and reported here could be used for assisting various genetic, breeding, biotechnology, genome mapping, conservation, and sustainable forest management programs in poplars.

Alleles↗

PubMed1992

Maternal transmission of mitochondrial DNA in interspecific hybrids of Populus.

Restriction fragment analysis was conducted to investigate the mode of inheritance of mitochondrial (mt) DNA in F1 progeny of two P. deltoides x P. deltoides, three P. deltoides x P. nigra, and two P. deltoides x P. maximowiczii controlled crosses, and in Populus x canadensis by using 16 restriction endonucleases and two heterologous probes of cloned mtDNA fragments of maize. Five restriction fragment length polymorphisms (RFLPs) of mtDNA differentiated P. deltoides from P. nigra, whereas three RFLPs of mtDNA separated P. deltoides from P. maximowiczii. In all cases, F1 progeny of P. deltoides x P. nigra, and P. deltoides x P. maximowiczii, crosses had mtDNA restriction fragments of only their maternal P. deltoides parents. P. x canadensis had mtDNA restriction fragments of only P. deltoides. F1 progeny of intraspecific P. deltoides crosses also had the same mtDNA fragments as their maternal parent. The results clearly demonstrate uniparental-maternal inheritance of the mitochondrial genome in F1 interspecific hybrids of P. deltoides with P. nigra and P. maximowiczii.

Crosses, Genetic↗