Hybrid poplar clones with Populus maximowiczii parentage demonstrate postoviposition antibiosis to Cryptorhynchus lapathi (Coleoptera: Curculionidae)

Damage caused by the poplar-and-willow borer, Cryptorhynchus lapathi (L.) (Coleoptera: Curculionidae), is reported to vary among hybrid poplar clones. We evaluated oviposition preferences and larval success in four hybrid poplars on potted and field-planted trees. Oviposition occurred somewhat less frequently and abundantly on two clones with Populus maximowiczii Henry parentage in field-planted and potted trees, and significantly fewer larvae survived to adulthood on those clones. No adults emerged from field-planted NM 6 (Populus nigra L. x P. maximowiczii) and four emerged from TM 256-28 (Populus trichocarpa Torrey & Gray x P. maximowiczii) on which male-female pairs of C. lapathi had been caged. In contrast, 50 and 140 adults emerged over the same 2-yr period from two susceptible clones (n = 20), TD 52-226 (P. trichocarpa x Populus deltoides Bartram ex Marshall) and TN 302-9 (P. trichocarpa x P. nigra), respectively. Thus, resistance expressed by clones with P. maximowiczii parentage partially involves decreased levels of oviposition, but more significantly, antibiosis in resistant clones prevents the development of larvae, probably in early spring.     

Differential susceptibility of poplar hybrids to the aphid Chaitophorus leucomelas (Homoptera: Aphididae)

After its recent introduction to Chile, the aphid Chaitophorus leucomelas Koch is becoming a serious pest affecting commercial poplar, Populus spp., plantations. The pattern of natural infestation of C. leucomelas among poplar hybrids with different pedigrees and the aphid intrinsic rate of increase (r(m)), of C. leucomelas were assessed in the field. In most of the hybrids, aphid abundance peaked in March (late summer). Among 12 types of poplar crosses, [(P. trichocarpa Torr. & Gray x P. deltoides Bartram ex Marshall) x (P. trichocarpa x P. deltoides)] and [(P. trichocarpa x P. maximowiczii Henry) x P. maximowiczii] showed the highest and lowest aphid densities, respectively. A trend to find more aphids in branch bases was apparent. The intrinsic rate of C. leucomelas increase was higher in [(P. trichocarpa x P. deltoides) x P. deltoides] hybrids, and lower in [(P. trichocarpa x P. maximowiczii) x P. trichocarpa] hybrids. Aphid density and performance were higher in hybrids with P. deltoides parentage, whereas hybrids with P. maximowiczii parentage showed lower aphid densities and performance. Hybrids with P. nigra L. parentage, namely, [P. trichocarpa x P. nigra], also had high aphid density, but aphid performance was lower compared with hybrids with P. deltoides parentage. These results suggest that among poplar hybrids studied, susceptibility to C. leucomelas is inherited through P. deltoides, whereas resistance seems to be inherited through P. maximowiczii. Thus, P. maximowiczii hybrids are recommended for commercial or ornamental planting programs in zones where there is a high risk of aphid infestation.     

Restriction fragment length polymorphisms of a chloroplast photosystem II gene from poplar and their use for species identification.

In a total DNA library from the poplar clone Beaupré (Populus trichocarpa x P. deltoides) one DNA clone was found to identify restriction site polymorphisms in different poplar species. This clone represents a cpDNA gene that shows close homology to a photosystem II gene of pea and spinach coding for the D2 protein and the 44 kDa reaction centre. In Southern blot analysis this probe identified interspecific restriction site variation among the different poplar species; intraspecific variation was not detectable. As the chloroplast genome is maternally inherited in poplars this cpDNA probe was used for identification of P. nigra or P. deltoides as the seed parents of F1 hybrid trees in natural stands of western Germany.     

Microsatellite DNA fingerprinting, differentiation, and genetic relationships of clones, cultivars, and varieties of six poplar species from three sections of the genus Populus.

Accurate identification of Populus clones and cultivars is essential for effective selection, breeding, and genetic resource management programs. The unit of cultivation and breeding in poplars is a clone, and individual cultivars are normally represented by a single clone. Microsatellite DNA markers of 10 simple sequence repeat loci were used for genetic fingerprinting and differentiation of 96 clones/cultivars and varieties belonging to six Populus species (P. deltoides, P. nigra, P. balsamifera, P. trichocarpa, P. grandidentata, and P maximowiczii) from three sections of the genus. All 96 clones/cultivars could be uniquely fingerprinted based on their single- or multilocus microsatellite genotypes. The five P. grandidentata clones could be differentiated based on their single-locus genotypes, while six clones of P. trichocarpa and 11 clones of P. maximowiczii could be identified by their two-locus genotypes. Twenty clones of P. deltoides and 25 clones of P. nigra could be differentiated by their multilocus genotypes employing three loci, and 29 clones of P. balsamifera required the use of multilocus genotypes at five loci for their genetic fingerprinting and differentiation. The loci PTR3, PTR5, and PTR7 were found to be the most informative for genetic fingerprinting and differentiation of the clones. The mean number of alleles per locus ranged from 2.9 in P. trichocarpa or P. grandidentata to 6.0 in P. balsamifera and 11.2 in 96 clones of the six species. The mean number of observed genotypes per locus ranged from 2.4 in P. grandidentata to 7.4 in P. balsamifera and 19.6 in 96 clones of the six species. The mean number of unique genotypes per locus ranged from 1.3 in P. grandidentata to 3.9 in P. deltoides and 8.8 in 96 clones of the six species. The power of discrimination of the microsatellite DNA markers in the 96 clones ranged from 0.726 for PTR4 to 0.939 for PTR7, with a mean of 0.832 over the 10 simple sequence repeat loci. Clones/cultivars from the same species showed higher microsatellite DNA similarities than the clones from the different species. A UPGMA cluster plot constructed from the microsatellite genotypic similarities separated the 96 clones into six major groups corresponding to their species. Populus nigra var. italica clones were genetically differentiated from the P. nigra var. nigra clones. Microsatellite DNA markers could be useful in genetic fingerprinting, identification, classification, certification, and registration of clones, clultivars, and varieties as well as genetic resource management and protection of plant breeders' rights in Populus.     

Molecular analysis of natural populations of Populus nigra L intermingled with cultivated hybrids

In this study six simple sequence repeats (SSR or microsatellites) were selected for their ability to fingerprint a total of 60 commercial clones of Populus deltoides Marsh. and Populus x canadensis Moench (typically derived from crosses between Populus nigra L and P. deltoides) and to characterize a natural population of P. nigra growing along the Ticino river in the North of Italy. Out of six SSRs used, four microsatellite loci were found to have alleles which were species-specific to P. deltoides and could therefore be used as markers for introgression of P. deltoides into P. nigra. In the studied region hybrid poplars and P. deltoides commercial clones are cultivated as monoclonal stands close to the area where black poplar has its natural habitat. SSR analysis was performed to investigate whether there was evidence of introgression between the natural population and the monoclonal plantations of hybrids and P. deltoides clones cultivated in the surrounding area. Three stages of the natural population were analysed: a group of old trees about a hundred years old, a younger population (aged 2-30 years) and the seedlings of three females of this population. Alleles specific to P. deltoides were detected only in the old cohort of the natural population, while no introgression was observed in the younger individuals and their progenies. These results were also confirmed by isozyme analysis of loci PGI-B, PGM and LAP-A, which were previously identified as diagnostic for P. nigra, P. deltoides and P.xcanadensis.     

Influence of poplar clones on fertility life-table parameters of Chaitophorus leucomelas (Hemiptera: Aphididae)

The aphid Chaitophorus leucomelas Koch (Hemiptera: Aphididae) is one of the most important pests of poplar (Populus spp.) plantations in Iran. In this study, development, reproduction, and life history of the aphid were assessed on 11 poplar clones; belong to three species, Populus nigra L., Populus deltoides Bartram ex Marshall, and Populus. euramericana Guinier. The experiments were carried out under controlled conditions at 24 +/- 1 degrees C, 50-60% RH, and a photoperiod of 12:12 (L:D) h. The developmental time at immature stage ranged from 10 to 12 d. Nymphs reproduced per female were ranged from 49 to 98 nymphs on Populus deltoides var. missoriensis and P. deltoides 72/51, respectively. The intrinsic rate of natural increase (r(m)) varied from 0.176 to 0.264 d(-1) among poplar clones. The r(m) values of the aphids were adversely affected in P. euramericana 242 in comparison with P. nigra 56/72 and P. nigra 63/135. In addition, the jackknife estimates of net reproductive rate (R0) indicated the presence of resistance among poplar clones. R0 ranged from 16.48 on P. nigra var. betulifoli to 47.53 on P. nigra 63/135. Mean generation times (T) was last 17.56 d on P. euramericana 242 to 14.51 d on P. deltoides 69/55. However, doubling time (DT) was 3.87 d on P. euramericana var. grandis to 2.63 d on P. nigra 63/135. The finite rate of increase (lambda) was 1.192 on resistant clone (P. euramericana 242) and 1.302 on susceptible clone (P. nigra 63/135). These results indicate that variation in life-table parameters could be an important component of variation in resistance to C. leucomelas in poplar.     

Screening hybrid poplar clones for susceptibility to Cryptorhynchus lapathi (Coleoptera: Curculionidae)

The poplar-and-willow borer, Cryptorhynchus lapathi (L.) (Coleoptera: Curculionidae), is a wood-boring pest of economic importance in irrigated hybrid poplar (Populus spp.) farms in eastern Washington and Oregon. There is no practical insecticide control tactic against either the larval or adult stage of C. lapathi. To assess variability in C. lapathi toward clone preference, we initiated a no-choice study on 180 caged trees that consisted of five clones in a randomized complete block design. C. lapathi was significantly more successful at establishing a population in two clones with Populus trichocarpa X P. deltoides (TxD) parentage (female x male) than in either of two clones with P. deltoides x P. nigra (DxN) parentage (female x male), or a single clone with P. deltoides x P. maximowiczii (DxM) parentage (female X male). There were no significant differences in the rate of weevil development among infested clones, with the exception of DxM trees. Larvae in DxM clones developed on average to the fourth size grouping and those in the two TxD clones developed on average to the fifth size grouping, and this difference was significant. These results corroborate our general damage surveys conducted in the field. Our findings provide growers with the option to choose less susceptible varieties when replanting.     

Dense genetic linkage maps of three Populus species (Populus deltoides, P. nigra and P. trichocarpa) based on AFLP and microsatellite markers

Populus deltoides, P. nigra, and P. trichocarpa are the most important species for poplar breeding programs worldwide. In addition, Populus has become a model for fundamental research on trees. Linkage maps were constructed for these three species by analyzing progeny of two controlled crosses sharing the same female parent, Populus deltoides cv. S9-2 x P. nigra cv. Ghoy and P. deltoides cv. S9-2 x P. trichocarpa cv. V24. The two-way pseudotestcross mapping strategy was used to construct the maps. Amplified fragment length polymorphism (AFLP) markers that segregated 1:1 were used to form the four parental maps. Microsatellites and sequence-tagged sites were used to align homoeologous groups between the maps and to merge linkage groups within the individual maps. Linkage analysis and alignment of the homoeologous groups resulted in 566 markers distributed over 19 groups for P. deltoides covering 86% of the genome, 339 markers distributed over 19 groups for P. trichocarpa covering 73%, and 369 markers distributed over 28 groups for P. nigra covering 61%. Several tests for randomness showed that the AFLP markers were randomly distributed over the genome.     

Chloroplast DNA variation in Populus. II. Interspecific restriction fragment polymorphisms and genetic relationships among Populus deltoides,P. nigra,P. maximowiczii,and P. x canadensis

Restriction fragment analysis was conducted to determine interspecific chloroplast DNA (cpDNA) variation and genetic relationships among Populus deltoides, P. nigra, P. x canadensis (P. deltoides x P. nigra), and P. maximowiczii. Total cellular DNAs of these poplars were digested with 16 restriction endonucleases, and Southern blots of the restriction digests were probed with six different cloned cpDNA fragments from Petunia. P. deltoides, P. nigra, and P. maximowiczii each had a distinct chloroplast genome, separated by many restriction-site and restriction-fragment-length mutations, predominantly in the large single-copy region of the genome. P. x canadensis shared the same cpDNA restriction fragment patterns as P. deltoides var. deltoides. P. nigra was most diverged from P. deltoides, and P. deltoides showed close cpDNA relationships to P. maximowiczii. Nucleotide substitutions per site in cpDNA were 0.0036 between P. deltoides and P. maximowiczii, 0.0071 between P. nigra and P. maximowiczii, and 0.0077 between P. deltoides and P. nigra. We suggest that P. nigra should be classified in a new separate section, the Nigrae.     

Microsatellite DNA and RAPD fingerprinting,identification and genetic relationships of hybrid poplar (<Emphasis Type="Italic">Populus x canadensis</Emphasis>) cultivars

Microsatellite DNA markers of ten SSR loci and 248 RAPD loci (resolved by 26 RAPD primers) were used for DNA fingerprinting and differentiation of 17 widely grown Populus x canadensis syn. Populus x euramericana (interspecific Populus deltoides x Populus nigra hybrids) cultivars ("Baden 431", "Blanc du Poitou", "Canada Blanc", "Dorskamp 925", "Eugenei", "Gelrica", "Grandis", "Heidemij", "I-55/56", "I-132/56", "I-214", "Jacometti", "Ostia", "Regenerata", "Robusta", "Steckby" and "Zurich 03/3"), and determination of their genetic interrelationships. Informativeness of microsatellite and RAPD markers was also evaluated in comparison with allozyme markers for clone/cultivar identification in P. x canadensis. High microsatellite DNA and RAPD genetic diversity was observed in the sampled cultivars. All of the 17 P. x canadensis cultivars could be differentiated by their multilocus genotypes at four SSR loci, and were heterozygous for their parental species-specific alleles at the PTR6 SSR locus. Except for "Canada Blanc" and "Ostia", which had identical RAPD patterns, all cultivars could also be differentiated by RAPD fingerprints produced by each of the two RAPD primers, OPA07 and OPB15. For microsatellites, the mean number of alleles, polymorphic information content, observed heterozygosity, observed number of genotypes and the number of cultivars with unique genotypes per locus was 5.2, 0.64, 0.67, 5.7 and 2.2, respectively. For RAPD markers, the number of haplotypes per locus, and the number of cultivars with unique RAPD profiles per locus were 1.06 and 0.72, respectively. Overall, microsatellite DNA markers were the most informative for DNA fingerprinting of P. x canadensis cultivars. On the per locus basis, microsatellites were about six-times more informative than RAPD markers and about nine-times more informative than allozyme markers. However, on the per primer basis, RAPD markers were more informative. The UPGMA cluster plots separated the 17 cultivars into two major groups based on their microsatellite genotypic similarities, and into three major groups based on their RAPD fragment similarities. Both the microsatellite and RAPD data suggest that the cultivars "Baden 431", "Heidemij", "Robusta" and "Steckby" are genetically closely related. The inter-cultivar genetic relationships from microsatellite DNA and RAPD markers were consistent with those observed from allozyme markers, and were in general agreement with their speculated origin. Microsatellite DNA and RAPD markers could be used for clone and cultivar identification, varietal control and registration, and stock handling in P. x canadensis.     

Detection of a variable number of ribosomal DNA loci by fluorescent in situ hybridization in Populus species

Fluorescent in situ hybridization (FISH) was applied to related Populus species (2n = 19) in order to detect rDNA loci. An interspecific variability in the number of hybridization sites was revealed using as probe an homologous 25S clone from Populus deltoides. The application of image analysis methods to measure fluorescence intensity of the hybridization signals has enabled us to characterize major and minor loci in the 18S-5.8S-25S rDNA. We identified one pair of such rDNA clusters in Populus alba; two pairs, one major and one minor, in both Populus nigra and P. deltoides; and three pairs in Populus balsamifera, (two major and one minor) and Populus euroamericana (one major and two minor). FISH results are in agreement with those based on RFLP analysis. The pBG13 probe containing 5S sequence from flax detected two separate clusters corresponding to the two size classes of units that coexist within 5S rDNA of most Populus species. Key words : Populus spp., fluorescent in situ hybridization, FISH, rDNA variability, image analysis.     

Evaluation of Populus and Salix continuously irrigated with landfill leachate I. Genotype-specific elemental phytoremediation

There is a need for the identification and selection of specific tree genotypes that can sequester elements from contaminated soils, with elevated rates of uptake. We irrigated Populus (DN17, DN182, DN34, NM2, NM6) and Salix (94003, 94012, S287, S566, SX61) genotypes planted in large soil-filled containers with landfill leachate or municipal water and tested for differences in inorganic element concentrations (P, K, Ca, Mg, S, Zn, B, Mn, Fe, Cu, Al, Na, and Cl) in the leaves, stems, and roots. Trees were irrigated with leachate or water during the final 12 wk of the 18-wk study. Genotype-specific uptake existed. For genera, tissue concentrations exhibited four responses. First, Populus had the greatest uptake of P, K, S, Cu, and Cl. Second, Salix exhibited the greatest uptake of Zn, B, Fe, and Al. Third, Salix had greater concentrations of Ca and Mg in leaves, while Populus had greater concentrations in stems and roots. Fourth, Populus had greater concentrations of Mn and Na in leaves and stems, while Salix had greater concentrations in roots. Populus deltoides x P. nigra clones exhibited better overall phytoremediation than the P. nigra x P. maximowiczii genotypes tested. Phytoremediation for S. purpurea clones 94003 and 94012 was generally less than for other Salix genotypes. Overall, concentrations of elements in the leaves, stems, and roots corroborated those in the plant-sciences literature. Uptake was dependent upon the specific genotype for most elements. Our results corroborated the need for further testing and selecting of specific clones for various phytoremediation needs, while providing a baseline for future researchers developing additional studies and resource managers conducting on-site remediation.     

rDNA cloning and rapid hybrid identification inPopulus spp. (Salicaceae)

Ribosomal DNA genes fromP. deltoides have been cloned and specific sequences of the 25 S and 18 S rDNA region, labelled by digoxigenin, have been used to determine the rDNA structure ofPopulus tremula, P. fremontii, P. maximowiczii, P. yunnanensis, P. nigra, P. wislizenii, P. alba. The restriction maps of the coding region appeared to be similar among the examined species and with those ofP. deltoides andP. trichocarpa, reported in a previous paper. Inter- and intraspecific variation in rDNA repeat unit length have been revealed after EcoRI digestions. SstI and XbaI restriction sites have been found at different positions in the IGS of some species. The polymorphic fragments generated by SstI digestion allowed the identification of the hybrid origin of some genotypes. The number of rDNA genes in the genome ofP. deltoides has been estimated to be about 2 000 copies. Finally, the usefulness of these studies inPopulus spp. taxonomy and forestry genetics is discussed.Ribosomal RNA gene structure in somePopulus spp. (Salicaceae) and their hybrids 2.     

Divergence in the ovipositional behavior of the Papilio glaucus group

This study contrasts the ovipositional profiles of four members of the Papilio glaucus group, P. glaucus , P. multicaudatus , P. canadensis , and P. rutulus. We used seven choice oviposition bioassays containing leaves from hosts in seven plant families utilized by members of the P. glaucus group. Specifically, we contrast the overall ovipositional profiles of these species and their acceptance of a host in a novel plant family ( Populus tremuloides : Salicaceae) and a host in a putatively ancestral host plant family ( Liriodendron tulipifera : Magnoliaceae). Significant differences were observed between the ovipositional profiles of P. glaucus and P. multicaudatus relative to each other and to P. canadensis and P. rutulus. In contrast, no significant differences were observed between the ovipositional profiles of P. canadensis and P. rutulus , which were also the only species that accepted P. tremuloides. Unlike the acceptance of P. tremuloides , the acceptance of L. tulipifera was present throughout the group despite the inability of the larvae of most species in the group to utilize this host. These results support the prediction of the "hierarchical threshold model" that ancestral host plants are likely to be retained in the ovipositional hierarchy while novel hosts should only be accepted by derived populations.     

Evaluating the tolerance of young hybrid poplar trees to recycled waters high in salinity and boron

The successful adoption of water recycling strategies in many arid regions will require crops able to tolerate poor-quality waters. We evaluated different clones for salt and boron (B) tolerance within each of seven genetically distinct genomic groups (e.g., deltoides, deltoides x nigra, trichocarpa x deltoides, trichocarpa x deltoides x maximowizcii, trichocarpa x deltoides x nigra, trichocarpa x nigra, trichocarpa x maximowizcii). During each evaluation period, different clones within each of the groups were irrigated with high sodium chloride (NaCl) salinity (i.e., 10-30 dS m(-1)) and B (i.e., 10 mg L(-1)) water up to a maximum of 150 days, for a 4-year testing period under micro-field plot conditions. Excessive accumulation (up to 6%) of chloride (Cl) likely caused toxicity symptoms (necrosis of the leaves) observed in the less tolerant clones, while leaf B concentrations rarely exceeded 300 mg kg(-1) DM in any clone. Increased soil salinity likely hindered the uptake of B by the clones. Our results show that a wide range of selected Populus clones, of parentage trichocarpa x nigra, followed by deltoides x nigra show potential salt and B tolerance as young trees to recycled waters high in salinity and B.     

Chloroplast DNA variation in Populus. III. Novel chloroplast DNA variants in natural Populus x canadensis hybrids

A rare phenomenon of the occurrence of novel non-parental chloroplast DNA (cpDNA) variants in natural sexual interspecific hybrids between Populus deltoides var deltoides and P. nigra, P. x canadensis is described. Restriction fragment variation of cpDNA in 17 P. x canadensis cultivars was examined and compared with that of representative samples of P. deltoides and P. nigra using 83 combinations of 16 restriction enzymes and six Petunia hybrida cpDNA probes. Twelve cultivars had one to five novel non-parental cpDNA fragments in the chloroplast genome region homologous to the 9.0-kb PstI cpDNA fragment of Petunia from the large single-copy region.     

杨树派间不同种的遗传密码子使用频率分析

遗传密码子的简并性特征造成了不同物种使用的密码子存在偏爱性。了解不同物种的密码子使用特点,可以为外源基因导入过程中的基因改造提供依据,从而实现外源基因的高效表达。杨树是世界上广泛栽培的重要造林树种之一,已经成为林木基因工程研究的模式植物。本研究采用高频密码子分析法,对美洲山杨P.tremuloides,毛白杨P.tomentosa,美洲黑杨P.deltoids和毛果杨P.trichocarpa 4种杨树的蛋白质编码基因序列(CDS)进行了分析,计算出了杨树同义密码子相对使用频率(RFSC),确定了4种杨树的高频率密码子,发现虽然不同种类的杨树密码子使用上有一些差别,但是偏爱密码子的差别却很小,共性的密码子占绝大多数。仅有Pro,Thr和Cys等少数几个氨基酸的偏爱密码子有差别。这种“共性”提示我们,用不同种的杨树中任何一种杨树的偏爱密码子所设计的外源基因在其他杨树中也可以使用。     

Molecular genetic analysis of black poplar (Populus nigra L.) along Dutch rivers

The genetic structure of remaining black poplar ( Populus nigra ) trees on the banks of the Dutch Rhine branches was investigated using the AFLP technique. In total, 143 trees, including one P. deltoides and some P. x euramericana , were analysed using six AFLP primer combinations which generated 319 polymorphic bands. The AFLP patterns showed that some of the trees sampled as P. nigra were clearly different. These deviating patterns were also observed for the P. deltoides tree and all trees already identified as hybrid P. x euramericana . Hybrids between the two species are morphologically sometimes difficult to distinguish from the species itself. Two important possible source populations for recolonization of the riverbanks of the river Rhine, consisting of mature flowering P. nigra trees, appeared to consist of only a few genotypes each. In contrast, young black poplar trees growing alone or in small groups downstream of the possible source populations appeared to be predominantly generatively derived because no clones of mature trees were found among them. Therefore vegetative propagation seems a very local strategy whereas colonization of new areas appears to occur through generative propagation. Whether the genetic diversity within these black poplars is sufficient for recolonization of river banks and survival of the metapopulation is a question for further research.