To reveal the genetic mechanisms behind drought tolerance, we attempted to identify the drought-responsive genes in Populus tremula var. davidiana (Dode) C.K. Schneid. and eight other species of Populus. Nine drought-responsive genes were assayed by single nucleotide polymorphism (SNP) genotyping using TaqMan probe-based real-time PCR. A total of 346 SNPs were found from the 101 sequences of the nine genes. Among them, 57 primers were selected for SNP genotyping and haplotype determination. For the SNP genotyping, 56 assays were applicable to section Leuce Duby, 53 to section Aigeiros Duby, 50 to Populus maximowiczii Henry, and 52 to Populus simonii Carrière. The expectation maximization algorithm was implemented to determine haplotypes among species and sections. A total of 78 haploid types were estimated from nine drought-responsive gene loci, and the average number of haploid types per locus was 8.67. The analysis of genetic diversity revealed that P. tremula var. davidiana had substantial levels of genetic variation for the nine drought-responsive genes, which was higher than the eight other species. The means of observed number of alleles (NA) and heterozygosity (Ho) were 5.33 and 0.6609, respectively. Analysis of the genetic differentiation of P. tremula var. davidiana showed that 7.52% of genetic variation was among populations and the remaining was within a population.

Pinus densiflora f. multicaulis is a rare and unusual form of genus Pinus. It has excellent ornamental values due to many trunks from its root collar, and produces female, male, and bisexual strobili on thes ame tree. However, there is limited study whether the bisexual strobili are functional, mature lateral conesproduce filled seeds, and the seeds from the mature lateral cones germinate and grow as well as those frommature apical cones. The structure of apical female, and lateral male and bisexual strobili were analyzed in an open-pollination-progeny population. The strobili were photographed to obtain external, cross-section, and radial-section images using a 45× stereoscopic microscope. Radial sections of strobili were imaged using scanning electron microscopy. Characteristics of apical and lateral cones and seeds were surveyedby cone analysis and germination test. P. densiflora f. multicaulis developed typical female strobili apically,and ordinary male and bisexual strobili laterally. Additionally, female strobili developed laterally whereas the male strobili were normally located. The mature lateral female strobili had the same structure as the apical female. In the mature bisexual strobili, the proportion of male and female tissue was unequal. The cones developed from lateral female strobili showed highly significant differences in the length, width, and weight, being shorter (32.7%), narrower (26.9%), and lighter (59.8%) than those from apical female strobili. Both types produced filled seeds and seedlings, and well significant positive correlations were found among characteristics of seeds from apical and lateral female strobili. The initial seed germination rate of the seeds from apical female strobili was higher than that of seeds from lateral female strobili, but the difference decreased over time. The viability and spatial distribution of the female and male tissue of bisporangiate cones, and their frequent occurrence suggests a common mechanism for the production of bisporangiate structures in seed plants.

The genus Populus is one of the important tree species in Korean peninsula and many other countries in the world. It represents the model species of forest genomics because it grows fast and reproduces rapidly. In this reason, their genetic characteristics have been well studied and the whole genome has been sequenced completely in some species. However, cytogenetic study of the genus Populus has been limited. In the present study, karyotypes of Korean aspen (P. tremula var. davidiana), Silver poplar (P. alba) and their two hybrids, Suwon aspen (P. tremula var. glandulosa) and Hyun aspen (P. alba × P. tremula var. glandulsa) were analyzed by means of the fluorescence in situ hybridization (FISH). Root samples were collected from mature trees in the demonstration forest, located at Suwon, Kyonggi province in South Korea. The fresh root cells were examined by DAPI (4',6-diamidino-2-phenylindole) staining and FISH using 45S rDNA and 5S rDNA probes. As the results, the chromosome compositions of all species were the same as 2n = 38. The karyotype formulas of Korean aspen, Silver poplar, Suwon aspen and Hyun aspen were 28m + 6sm + 4st (2sat), 26m + 10sm (2sat) + 2st, 26m + 12sm (2sat) and 28m + 10sm (2sat), respectively. The four species had one pair of 45S rDNA site and one pair of 5S rDNA site in common with FISH karyotypes. The similarity of FISH karyotypes among four species indicated close genetic relationship and coexistence of their interspecific hybrids. This research will provide genetic information on cytogenetic research of Populus and genetic mapping that can be applied to the breeding program of Populus in the near future.

No abstract

No abstract