Aster Novi-belgii Research Articles

First Report of Golovinomyces cichoracearum as the Causal Agent of Powdery Mildew on Symphyotrichum novi-belgii (Synonym Aster novi-belgii) in Denmark.

Symphyotrichum novi-belgii (L.) G.L. Nesom (synonym Aster novi-belgii L.) is an autumn flowering perennial used in gardens and as a cut flower. During the last 20 years, it has been developed as a potted plant, thereby increasing its economic importance. In Denmark, 7 to 8 million S. novi-belgii plants are produced annually, making it one of the 10 most popular potted plant crops ( http://floradania.dk/index.php?id=165 ). In general, S. novi-belgii is a healthy plant, but it can be severely attacked by powdery mildew both in greenhouse production and outdoors, and diseased plants have been observed in most parts of the country. Infected plants show typical symptoms: leaf surfaces become covered with white mycelium and as the disease progresses infected leaves turn yellow and die. Powdery mildew is regarded the main disease problem in S. novi-belgii and it causes problems year round in greenhouse production. Normally, the disease is controlled by fungicides, but once out of the production system, symptom development in the retail trade will reduce the plant's appeal to customers to a degree that prevents sales. The powdery mildew identified in this study was collected in a small research field at Aarslev, Denmark in September 2004. Since collection, the pathogen has been maintained in a greenhouse on S. novi-belgii and it has been used for disease resistance screening. However, lack of proper identification of the causal agent has hindered the development of powdery mildew resistant cultivars. To identify the pathogen, the internal transcribed spacer region (ITS) of the rDNA was amplified using primers ITS1 and ITS4 (2) and sequenced. The resulting sequence was deposited in GenBank (Accession No. HM769725). BLASTn analysis of the 598-bp fragment showed 99% identity to Golovinomyces cichoracearum (DC.) V.P. Heluta from Rudbeckia laciniata L. (Accession No. AB077622). The powdery mildew colonies were slightly pink with barrel-shaped, hyaline conidia borne in chains of three to four. The length of the conidia was 30 ± 4 μm and the width was 13 ± 1 μm (n = 105). Foot cells of the conidiophores were 101 ± 16 μm long and 12 ± 5 μm wide (n = 50) with a slight constriction at the base. Chasmothecia were not observed. These morphological characteristics confirmed the identification as G. cichoracearum (1). To fulfill Koch's postulates, 10 healthy S. novi-belgii 'Victoria Fanny' plants were inoculated in an inoculation tower by shaking infected S. novi-belgii plants over the tower, resulting in a spore density of 47 spores/mm2 on the leaf surface. The infected plants were placed in a growth chamber with 16 h of light (200 μmol·m-2·s-1) and day and night temperatures of 20 and 15°C, respectively. Symptoms developed on all plants after 11 days. Colony morphology on the leaves and the morphological characteristics were as described above. Conidia were washed off the leaves, DNA extracted, and the ITS was amplified by PCR. The resulting PCR product was sequenced and was identical to HM769725. To our knowledge, this is the first report of G. cichoracearum on S. novi-belgii in Denmark.

Ozone Sensitivity of 28 Plant Selections Exposed to Ozone Under Controlled Conditions

Ambient, ground-level ozone is the most important air pollutant affecting vegetation in the US. However, ozone-sensitive bioindicators need to be identified for use in field surveys to detect ozone-induced symptoms. To identify such bioindicators, 28 plant selections were exposed to ozone within greenhouse chambers during 2003 and 2004. Plants most sensitive to ozone included Asclepias incarnata (swamp milkweed), Asclepias syriaca (common milkweed), Cephalanthus occidentalis (buttonbush), Platanus occidentalis (American sycamore), Salix × cotteti (Bankers dwarf willow), Salix lucida (shining willow), Salix nigra (black willow), Salix sericea (silky willow), and Symphoricarpos albus (snowberry). Plants moderately sensitive included Aster novaeangliae (New England aster), Monarda didyma (bee-balm), Rhus aromatica (aromatic sumac), Salix discolor (pussy willow), Salix exigua (sandbar willow), Salix purpurea (basket willow), Sambucus ebulus (European dwarf elderberry), and Symphoricarpos spp. (mixture of “snowberries”). Plants more tolerant to ozone included Aster macrophyllus (bigleaf aster), Aster novibelgii (New York aster), Cercis canadensis (redbud), Populus maximowizii × trichocarpa (hybrid poplar), Rudbeckia laciniata (cutleaf, or tall green-headed coneflower), Salix amygdaloides (peach-leaved willow), Salix eriocephala (diamond willow), Sambucus canadensis (American elder), Sambucus nigra (European elder), Symphoricarpos orbiculatus (coralberry), and Viburnum trilobum (highbush-cranberry). The incidence and severity of ozone-induced symptoms varied with species, ozone concentration, and length of exposure. Pigmented adaxial leaf surface stipple, bifacial necrosis, and premature defoliation were common foliar symptoms induced by ozone; leaf reddening, bronzing, and chlorosis occurred less frequently. Species that produced classic ozone-induced stipple in this study may serve as useful bioindicators in field surveys to confirm that ozone injury occurs in many parts of the country. Such findings may have a positive impact on establishing more stringent air-quality standards to protect vegetation and the environment.

A comparison of two North-American asters invading in central Europe

Perennial North-American asters have become common in central Europe since the 17th century when they started to be cultivated as ornamental plants. Today, they are widely spreading especially in alluvial sites in lowlands. Two of the most common aster species, Aster lanceolatus and Aster novi-belgii, were investigated for their generative reproduction, including seed production and germination, and vegetative propagation (growth of rhizomes). Experimental sites with and without competition from the surrounding vegetation were used to test for differences between the species. Germination experiments showed that the asters produced a relatively high number of viable and easily dispersed seeds, which often germinated immediately after ripening and usually did not require any special treatment. Some aster clones produced more than 100 new rosettes from one initial rosette within a year. Apparently, asters are able to form large polycorms in a relatively short time. However, their rapid vegetative spread can be reduced by competition from established vegetation.

Evaluating vase life and tissue structure of some compositae (Asteraceae) species

The vase life of cut flowers and effects of various chemicals was examined with the help of a pulse treatment. According to the results using of chemicals (preservatives, disinfectants as well as blocking of synthesis of ethylene) is ineffective if it is used after seeding This shows the great importance of harvesting time.
 Using 8-HQS or l-MCP + 8-HQS proved to be the best for vase life in most of the samples. Using these materials did not prevent the appearance of air bubbles in the stems and absorption could be observed continuously.
 To examine the tissue structure reaction of chemicals stems were stained with toluidin-blue, and high of absorption was measured. It was found that in cases, when absorption was bad, small air bubbles blocked the xylem vessels.
 All the species examined (Aster linosyris, Achillea collina, Aster novi-belgii, Inula britannica, Solidago canadensis, Inula ensifolia, Senecio jacobea) show similar reactions to chemicals because they are the members of the same family.

Flower induction in seedlings of Aster novi-belgii and selection before and after vegetative propagation

Bolting and flowering of Aster novi-belgii seedlings as well as correlations between characteristics within seedling populations and between seedlings and their vegetatively propagated offspring were investigated in order to improve breeding efficiency. In seedlings of A. novi-belgii, flower induction was observed without vernalization. Seedlings initially formed a rosette, but bolting was a prerequisite for development of a normal flowering shoot. Bolting was promoted by long photoperiods as compared to short days. The shortest time from sowing to anthesis was recorded when plants were grown under long photoperiods until the main stem was at least 5 cm long, and then moved to short photoperiods. A large variation in time to anthesis, plant height, branching ability, and flower size and color was found among the seedlings within all crosses. Magnitude and significance of correlations between some characteristics varied among crosses. The more consistent correlations seem mainly to be due to natural courses of plant growth and development. High correlations between seedling characteristics and their vegetatively propagated offspring were only found for flower hue. Lower, but significant correlations were found for flower color intensity, plant height and branching ability. There were no significant correlations for the time-to-anthesis between the two groups of plants.

Chemical Growth Retardants for Height Control of Pot Asters

, then averaged), height (pot rim to the top of the plant), and days from potting to flowering were recorded. Data were tested using analy- sis of variance by general linear model proce- dures (SAS Institute, Cary, N.C.). Signifi- cantly different means were separated by least significant differences at P ≤ 0.05. Foliar applications of daminozide at 5000 mgliter -1 had the greatest effect on plant height for both cultivars, with plant height 29% and 24% shorter, respectively, than the nontreated plants (Table 1). With paclobutrazol at 160 mgliter -1 , plants also were 22% and 14% shorter than nontreated plants for 'Butterfly Blue' and 'Purple Monarch', respectively. The effectiveness of uniconazole varied by culti- var, with a rate of ≥10 mgliter -1 controlling plant height of 'Purple Monarch' by ≥10%. Asters (Aster novi-belgii L.) are hardy pe- rennials that can reach ≈140 cm tall (Bailey and Bailey, 1976) and bloom naturally in the late summer and fall. For greenhouse- produced pot asters, plants receive long days for 3 to 4 weeks after potting to promote vegetative development and increase plant size. During the vegetative phase, the plants may become elongated and disproportional to pot size, making them less attractive to the consumer. The only recommendation avail- able to growers to control plant height is to apply several foliar sprays of butanedioic acid mono (2,2-dimethylhydrazide) (daminozide) at 1000 to 5000 mgliter -1

PERENNIAL GARDEN ASTER PRODUCTION IN NORTHWEST ARKANSAS

Success of European research and marketing efforts on perennial garden asters prompted American nurserymen to introduce (Aster novi-belgii and Aster ericoides) for fall bedding plant sales in the United States. This research investigated the feasibility of asters for outdoor production in Northwest, AR. and examined general cultural practices for growing asters in this region. Variety, fertilization and pruning trials with 15 cultivars of perennial aster were conducted at Fayetteville, AR. in 1992. Six varieties demonstrated retail market potential based on appearance and growth habit. Plants produced from rooted cuttings established 6 June in 3.78-liter containers were of high market quality in 8-12 weeks. A conventional resin-coated slow release fertilizer plus 500 ppm N weekly or conventional slow release product plus 180 ppm N constant feed, produced better growth than the slow release fertilizer used alone. Of 9 pruning regimes, results showed a significant difference in plant height and width by treatment across varieties. The differences among treatments were consistent for each variety. Pruning had no significant effect on bloom date or duration of bloom.

Response of a Typha marsh community to draining, flooding, and seasonal burning

A Typha marsh community was subjected to draining and seasonal burning treatments to control the growth of emergent aquatics. Treatments resulted in an increase in total number of species after 3 years. Cover and frequency of Aster novi-belgii, Lycopus uniflorus, Epilobium watsonii, Brachythecium salebrosum, Pleurozium schreberi, and Cladonia cristatella increased appreciably on the drained side whereas those of Carex spp., Lysimachia terrestris, Epilobium palustre, Pellia epiphylla, Sphagnum squarrosum, Drepanocladus exannulatus, and Helodium blandowii increased on the flooded side. Draining plus summer burning produced the lowest cover, stem density, plant height, and stem base diameter of Typha. An attempt was made to interpret the effects of disturbance on the natural paludification process that leads to the development of patches of fen within the marsh.

Quantifying a within-lake gradient of wave energy in Gillfillan Lake, Nova Scotia

The zonation patterns of shoreline plants vary greatly within lakes and exposure to waves may be an important cause of this variation. The principal objective of this study was to find a method for ranking lakeshores from low to high exposure. Two methods for ranking were tried. The first was simply the percent of the substrate composed of silt and clay and the second was calculated based on fetch values from aerial photographs and wind data from a nearby weather station. Field data were collected from 30 points chosen at random along the shoreline of Gillfillan Lake in Yarmouth County, Nova Scotia. Each was sampled for the proportion of silt and clay in the substrate and the zone widths occupied by shoreline plants. Exposure values were calculated for all 30 points, using 16 different methods of calculation. The proportion of silt and clay in the substrate was negatively correlated with exposure, whichever method of calculation was used. Principal components analysis was then used to summarize the zonation patterns of 64 plant species. The positions of transects on the first principal component (PC1, 18.7% of variation) were not correlated with any measure of exposure; they appear to reflect two types of glacial till found in Gillfillan Lake. The positions of transects on PC2 and PC3 (12.9 and 9.6% of the variation, respectively) were strongly correlated with the percent of the substrate consisting of silt and clay but not significantly with the calculated exposure measure. Thus percent silt and clay is a more appropriate axis for gradient analysis of zonation patterns. Species such as Calamagrostis canadensis, Carex stricto, and Pontederia cordata had zone widths which were negatively correlated with exposure, whereas the widths of the zones occupied by Aster novi-belgii, Agrostis perennans, and Aster tradescanti were positively correlated with exposure. While exposure affects the zonation patterns of some species, these patterns are apparently superimposed upon those produced by different types of glacial till.