Populus Genotypes Research Articles

Range of Phytoplasma Concentrations in Various Plant Hosts as Determined by Competitive Polymerase Chain Reaction

ABSTRACT For competitive polymerase chain reaction (PCR), an internal standard DNA template was developed that consisted of a highly conserved, internally deleted 16S rDNA fragment of an aster yellows phytoplasma. The internal standard was calibrated using a quantified culture of Acholeplasma laidlawii. Serial dilutions of the internal standard and fixed amounts of target templates from infected plants were coamplified with the same primers, and the products obtained were quantified using an enzyme-linked immunosorbent assay procedure. Analysis of the data revealed that the phytoplasma concentration in the plants examined differed by a factor of about 4 x 10(6). Phytoplasma concentrations of 2.2 x 10(8) to 1.5 x 10(9) cells per g of tissue were identified in periwinkles infected with various phytoplasmas. High to moderate concentrations were detected in Malus domestica (apple) genotypes infected with the apple proliferation phytoplasma, Alnus glutinosa (alder) genotypes infected with the alder yellows phytoplasma, and most aster yellows-infected Populus (poplar) genotypes examined. Very low phytoplasma concentrations, ranging from 370 to 34,000 cells per g of tissue, were identified in proliferation-diseased apple trees on resistant rootstocks 4551 and 4608, yellows-diseased Quercus robur (oak) trees, and Carpinus betulus (hornbeam) trees. Such low concentrations, which corresponded to about 4 to 340 cells in the reaction mixture, could only be detected and quantified by nested PCR.

Diverse effects of overexpression of LEAFY and PTLF, a poplar (Populus) homolog of LEAFY/FLORICAULA, in transgenic poplar and Arabidopsis.

PTLF, the Populus trichocarpa homolog of LEAFY (LFY) and FLORICAULA, was cloned to assess its function in a dioecious tree species. In situ hybridization studies showed that the gene was expressed most strongly in developing inflorescences. Expression was also seen in leaf primordia and very young leaves, most notably in apical vegetative buds near inflorescences, but also in seedlings. Although ectopic expression of the PTLF cDNA in Arabidopsis accelerated flowering, only one of the many tested transgenic lines of Populus flowered precociously. The majority of trees within a population of 3-year-old transgenic hybrid Populus lines with PTLF constitutively expressed showed few differences when compared to controls. However, phenotypic effects on growth rate and crown development, but not flowering, were seen in some trees with strong PTLF expression and became manifest only as the trees aged. Competence to respond to overexpression of LFY varied widely among Populus genotypes, giving consistent early flowering in only a single male P. tremula x P. tremuloides hybrid and causing gender change in another hybrid genotype. PTLF activity appears to be subject to regulation that does not affect heterologously expressed LFY, and is dependent upon tree maturation. Both genes provide tools for probing the mechanisms of delayed competence to flower in woody plants.

Genetic transformation of Populus genotypes with different chimaeric gene constructs: transformation efficiency and molecular analysis

Aspen (Populus tremula) and hybrid aspen (P. tremula × P. tremuloides) were transformed with different gene constructs using two types of promoter. The aim was to determine the influence of the reporter gene rolC, controlled by promoters of viral or plant origin, on genetic and morphologic expression of different transgenic aspen clones. An improved transformation method using leaf discs was developed, by which putative transgenic plantlets were regenerated at high efficiencies (up to 34%) on kanamycin-containing medium. Transgenic aspen carrying the rolC gene from Agrobacterium rhizogenes under control of the cauliflower-35S-promoter are reduced in size with smaller leaves, whereas aspen transgenic for the same rolC gene, but under control of the light inducible rbcS promoter from potato, are only slightly reduced in size compared to untransformed controls. However, all clones carrying 35S-rolC and rbcS-rolC genes revealed light-green colouration of leaves when compared to untransformed aspen. Owing to this special feature, constructs were used in which expression of the rolC gene was inhibited by insertion of a transposable element, Ac, from maize. Transgenic aspen transformed with the 35S-Ac-rolC and rbcS-Ac-rolC genes were morphologically similar to untransformed aspen, but out of 54 independently regenerated 35S-Ac-rolC transgenic aspen clones, 30 clones showed light-green/dark green variegated leaves. In contrast, out of 19 independently transformed rbcS-Ac-rolC aspen clones, only two clones revealed light-green/dark green variegated leaves. The role of bacterial strains in transformation, and molecular genetics of transgenic aspen plants (including the function of the transposable element, Ac, in the aspen genome) are discussed

Stable transformation of Populus and incorporation of pest resistance by electric discharge particle acceleration

Three different target tissues (protoplast-derived cells, nodules, and stems) and two unrelated hybrid genotypes of Populus (P. alba x P. grandidentata 'Crandon' and P. nigra 'Betulifolia' x P. trichocarpa) have been stably transformed by electric discharge particle acceleration using a 18.7 kb plasmid containing NOS-NPT, CaMV 35S-GUS, and CaMV 35S-BT. Four transformed plants of one hybrid genotype, NC5339, containing all 3 genes were recovered and analyzed. Two expressed GUS and one was highly resistant to feeding by 2 lepidopteran pests (the forest tent caterpillar, Malacosoma disstria, and the gypsy moth, Lymantria dispar.) Pretreatment of the target tissues, fine-tuning of the bombardment parameters, and the use of a selection technique employing flooding of the target tissues were important for reliable recovery of transformed plants.

Whole-tree carbon and nitrogen partitioning in young hybrid poplars.

The effects of water, nitrogen (N), and genotype on whole-tree carbon and nitrogen partitioning were examined in two Populus genotypes grown from cuttings in large pots set in the ground. Four replicate trees from each genotype/water/N treatment combination were harvested in either August, September, or November of their first year of growth. Aboveground biomass was linearly related to total leaf area. Clones allocated photosynthate differently. Populus tristis x P. balsamifera cv. Tristis #1 produced 14.5 cm of fine roots (< 0.5 cm diameter) per cm(2) of foliage, whereas P. x euramericana cv. Eugenei only produced 4.0 cm of fine roots per cm(2) of foliage. The large diameter structural roots of Eugenei grew rapidly late in the growing season so that large-root biomass was 3.8 to 7.5 times greater in November than in mid-August. In both clones, the root system grew twice as fast as the stem and branches late in the year. During August, about 75% of total tree N was in the canopy, but at least 80% of the September N content was still present in November following leaf fall. The major site of N storage was the large diameter structural roots. Nitrogen concentrations in these roots doubled following bud set.

HPLC in the investigation of taxonomic problems. Classification of poplar genotypes

The RP-HPLC technique has been applied to the analysis of the flavonoid content of leaf extracts from various genotypes ofPopulus nigra andPopulus deltoides and from several of their hybrids. Two elution procedures different either as regards gradient program or the type of organic modifier used were checked to optimize the reliability of the results obtained. Before making any identification, the chromatographic profiles proved so typical of each species as to allow of their use as fingerprints in this type of taxonomic problem. Individual identifications were carried out by spiking real samples with known amounts of standard substances. The presence of flavonoid compounds previously identified was confirmed and a few new identifications were proposed.

Interaction of geographic isolates of Melampsora medusae and Populus: effect of temperature

Twelve isolates of the leaf rust pathogen Melampsora medusae Thüm., collected from six locations across the eastern U.S.A., were tested for their reaction on 18 poplar genotypes at two temperatures of incubation (16 and 26 °C). All isolates were recognized as distinct physiologic races, based on the qualitative and quantitative reaction of the isolates on the cultivars. Temperature was an important factor in determining the level and type of disease expression in most cultivar – isolate combinations. The results support the hypothesis that the physical environment may have an important role in the regulation of this "wild" pathosystem. The high degree of race specificity observed in the Populus genotypes and the polymorphism for virulence in the M. medusae population emphasize the importance of maintaining host diversity to manage this disease.

Bud Dormancy in Populus

This communication describes the photoperiod-temperature interaction which markedly affects bud dormancy in certain Populus genotypes. High temperatures qualitatively inhibit the normal short-day control of the onset of dormancy. This finding contrasts sharply with the general conclusion that light and temperature operate independently in the photo control of growth in woody plants (Downs 1962).