Chrysanthemum Plants Research Articles

Increased damage by western flower thrips Frankliniella occidentalis in chrysanthemum intercropped with subterranean clover

AbstractSuppressive effects of intercropping on Frankliniella occidentalis (Pergande) infestations have been reported in several crops. However, this study demonstrates that in year‐round chrysanthemum, Dendranthema grandiflora Tzvelev, undersowing with subterranean clover, Trifolium subterraneum L., results in an increased thrips feeding damage. In a pot experiment, performed with chrysanthemum plants (cultivars Reagan and Tiger) grown with or without subterranean clover, significantly more leaves with silver and growth damage were found in the chrysanthemum plants with subterranean clover in comparison with the monocropped chrysanthemum plants. Similarly, the degree of deformation of leaf perimeter and leaf surface was higher in the top leaves of the intercropped chrysanthemum plant. In the soil experiment (only performed with Tiger and plants were grown in the soil in the greenhouse) intercropped chrysanthemum plants suffered a higher feeding damage as well. Analysis of the relation between silver or growth damage and the thrips pressure demonstrates that at similar thrips pressure in the intercropped chrysanthemum plants suffered significantly more damage. The higher thrips pressure in the intercropped chrysanthemum only explains the differences in damage partly. Changes in the reaction of chrysanthemum plants to thrips feeding or in the behaviour of the thrips, mediated by the presence of the non‐host crop, are discussed. Our explanation is that chrysanthemum plants grown with clover are more susceptible to thrips feeding than monocropped plants. We conclude that undersowing with clover does not contribute to reduce damage by F. occidentalis in year‐round chrysanthemum. Also, the influence of crop diversification on a pest cannot be foreseen until the specific characteristics of each individual crop – pest system are studied.

The role of pre‐ and post‐imaginal experience in the host‐finding and oviposition behaviour of the cabbage moth

SummaryThe influence of pre‐ and post‐imaginal experience on the orientation, landing, and oviposition of the female cabbage moth, Mamestra brassicae (L.) (Lepidoptera: Noctuidae) was studied in a wind tunnel. The results of experiments on the influence of pre‐imaginal experience do not support the Hopkins host selection hypothesis because the females’ responses to host plants were not affected by the plant species used for feeding the larvae. The females were initially attracted to and landed on chrysanthemum whether or not they were fed on this plant species. In addition, the oviposition preference for cabbage plants was not changed by the larval feeding regimen. Imaginal experience influenced the females’ subsequent orientation/landing responses: exposure of the females to chrysanthemum plants for 5 min decreased their subsequent responses to this species, but subsequent responses to cabbage were not changed when the females were exposed to cabbage plants. Overnight exposure of females to a chrysanthemum or cabbage plant decreased the subsequent orientation/landing on the same species offered in non‐choice tests. A similar effect was observed in responses to chrysanthemum plants after overnight contact, and possibly to cabbage plants, in the two‐choice tests. Overnight exposure to cabbage or chrysanthemum had no effect on subsequent oviposition: females from both treatments oviposited more often on cabbage.

The number of bacteria in the rhizosphere during plant development: relating colony-forming units to different reference units

The number of bacteria was determined during the growth of chrysanthemum plants on young (tip) and old (base) root parts. We assessed if the same conclusions could be drawn on the dynamics of bacterial populations during plant development when different reference units were used to express the bacterial counts. The results indicated that the total number of bacteria on the base decreased significantly during plant development, when expressed per root length, per root fresh weight or per root surface. The number of bacteria on the tip only decreased significantly when expressed per root length. Using the unit of dry weight of adhering soil, contradictory results were obtained for both base and tip; in general, the number of bacteria increased significantly during plant development. Thus, different reference units may lead to different conclusions. Root surface seemed to be the best unit to use, but the use of this unit requires time-consuming measurements. Regression analyses indicated that the reference unit "root surface" was highly correlated with root fresh weight (R2=93%). Thus, once this relation is determined, the less time-consuming unit can be measured in the experimental work. To analyse the data, the colony-forming units should be expressed per root surface. Besides bacterial numbers during plant development, we assessed whether the bacterial populations collected showed different growth rates on agar plates. The growth rates of bacteria from the tip and base and different development stages of the plants showed differences, indicating differences in the metabolic state of the collected populations.

The effects of crop density on plant growth and variability in cut-flower chrysanthemum (Chrysanthemum morifolium Ramat.)

SummaryThe effects of crop density on chrysanthemum plant yield and variability were studied using two cultivars, Snowdon and Delta, in four experiments (spring, summer, autumn and winter) using fan design layouts of gradually increasing space per plant. Average total fresh weight per plant varied greatly between experiments, but empirical linear regression relationships showed that changes in space per plant gave near proportional changes in weight per plant over the whole range of densities sampled. This suggests that the density responses were essentially mediated by the available light per plant. A simple three-parameter model was developed incorporating the accumulated light integral and this gave an excellent fit to data in all four experiments. The fresh weight of flowers per plant was allometrically related to ``productive'' plant weight which was defined as total plant weight minus a fixed weight not contributing to flower production. The relationships showed that the proportional partitioning of fresh weight to the flowers differed between the cultivars and varied between the experiments, being greatest under conditions of an increasing daily light integral (spring) and least under conditions of a declining daily light integral (autumn). The log coefficient of variation of total fresh weight per plant was found to increase with increase in plant density and was greatest under winter conditions. The log coefficient of variation of `Snowdon' was generally greater than that of `Delta' at harvest, although at planting the two were similar. Polynomial regression relationships between average fresh weight and the log coefficient of variation obtained when data from all four experiments were pooled, suggested that competition for light was a primary determinant of variation. Increasing density was associated with progressively slower flowering and this trend was most pronounced in `Delta' and in the autumn and winter experiments. Stems were generally reduced in length at high density but this was not always the case. The development of a simple model to predict average stem weights and grade-outs for given spacings at particular times of year is discussed.

Growth Response and Carbohydrate Status of Gibberellin-treated Spectral Filter-grown Chrysanthemum Plants

Interest in the use of non- (or less) chemical methods to reduce the height of ornamental crops has increased tremendously. Manipulation of greenhouse light quality is one alternative for plant growth regulation. We have shown that eliminating far-red light from the greenhouse environment with liquid CuSO4 spectral filters is effective in reducing the height of a wide range of plants though plant carbohydrate status is also altered under CuSO4 filter. In previous studies, application of GA3 reversed both the reduction of plant height and carbohydrate status of CuSO4 spectral filter grown plants. It has been proposed that GAs enhance the activity of the enzyme sucrose phosphate synthase to regulate carbohydrate levels. In the present study the role of exogenously applied GA19, GA1, and GA3 in overcoming the reduction of plant height and carbohydrate levels was investigated. Chrysanthemum plants were treated weekly for 4 weeks with saturating doses of GA19, GA1 and GA3 (25 μg) or the growth retardants paclobutrazol and prohexadione. GA1 was also applied with paclobutrazol and prohexadione to assess whether response to GAs is altered under CuSO4 filter. GA1 and GA3 promoted growth similarly under control or CuSO4 filter. GA19 was least effective in promoting growth under CuSO4 filter. In summary, these results suggest that gibberellin physiology is altered under spectral filters with the conversion of GA19 a possible point of regulation. The correlation between the carbohydrate status and the growth of the plants will be discussed.

Response of western flower thrips, Frankliniella occidentals and its predator Amblyseius cucumeris to chrysanthemum volatiles in olfactometer and greenhouse trials

In olfactometer assays, the predatory mite Amblyseius ciicumeris (Oudemans) recorded a significantly higher response to volatiles from chrysanthemum, Denranthemct morifolium plants infested with western flower thrips (WFT), Frankliniella occidentalis (Pergande) than to volatiles from healthy plants. This increased attraction was attributed to the presence of higher amounts of Germacrene-D in WFT-infested plants. In choice experiments using synthetic volatiles, the predator remained longer in the olfactometer treated with 50 ng Germacrene-D and made many entries at 500 mg. Preferential attraction of WFT to healthy chrysanthemum flower buds was observed, and attributed to the significantly higher amounts of (E)-β-farnesene found in the buds compared to leaves and open flowers. This attraction peaked at 100 ng/μl (E)-β-famesene. In greenhouse experiments, blue sticky traps with 500 ng (E)-β-farnesene or 1000 mg p-anisaldehyde attracted 32.3% and 27.5% more WFT than the untreated controls, respectively. The prospects of using Germacrene-D in improving the attraction of A.cucumeris to whole chrysanthemum plants and (E)-β-farnesene in monitoring WFT, are discussed.

Light Quality Regulation of Gene Expression in Chrysanthemum

A major part of Clemson light quality research program focuses on understanding the mechanisms of plant growth alteration under spectral filters. We have extended this research to understand the molecular basis for plant height control by spectral filters. From the whole plant research we have found that gibberellins (GA) play a key role in height control under spectral filters. However, it is not clear whether an alteration of endogenous gibberellin levels or a change in sensitivity to gibberellins is causing the observed effects. Since gibberellins are a key hormone in cell expansion and flower development, an understanding of gibberellin regulation and metabolism under spectral filters is critical for the control of height and flowering of plants grown under these filters. For the molecular study, we have selected the gene that code for enzyme GA 20-oxidase, one of the key enzymes involved in producing functional GAs in the mevalonic acid pathway. GA 20-oxidase is thought to be a site of regulation of GA synthesis by the environment. We are currently studying the regulation of the expression of this gene by light quality using Northern analysis. Results from temporal and tissue specific regulation of chrysanthemum plants grown under CuSO4 filters will be presented.

Pot soil air composition in conditions of high soil moisture and its influence on chrysanthemum growth

Chrysanthemums were grown in 15.2 cm standard pots in a heavy mix of clay loam soil+sphagnum peat moss (2:1). A fine texture mix was used to accentuate undesirable gas profiles in the soil. Soil air was analyzed at five depths in the soil profile. In one set of tests, water was applied to the top of the pot at a matrix potential in the center of the soil profile of −5 kPa. The average gas concentrations in soil air in the top and bottom fifths of soil were for O 2—20.0 and 14.5%, for CO 2—0.8 and 2.4%, and for C 2H 4—0 and 0.08 μl dm −3. Smooth concentration gradients of each gas occurred from top to bottom of the soil profile. The composition of soil air changed greatly during the drying cycle. At soil moisture tensions of −0.7, −2.5, and −5 kPa in the center of the soil profile, the gas concentrations in the lowest fifth of soil were for O 2—9.6, 15.3, and 20.3%, and for CO 2—4.5, 3.5, and 0.6%, respectively. Thus, soil atmospheric conditions for plant growth were poorest immediately after watering and continuously improved up to the time of watering. When pots of chrysanthemum were watered by capillary action from mats, the average concentration of gases in soil air in the lowest fifth of soil were 5.8% O 2, 3.6% CO 2, and 0.38 μl dm −3 C 2H 4. This gas profile was less desirable for growth than the profile found in top-watered pots. Unlike the situation in top-watered pots, the gas concentrations in mat-watered pots were stable. Roots in top-watered pots were restricted to the upper two thirds of the soil ball, and were distributed evenly in the inner part of the soil and at the periphery. Roots of mat-watered plants developed further down the vertical periphery of the pot than roots of top-watered plants, but they did not grow inside the ball. Chrysanthemum plants were grown through a hole in the side wall of each of five 3.9 cm tall by 15.2 cm diameter plastic rings stacked vertically and separated by stainless steel screens that allowed for passage of water but not roots. Water was applied to the top of these cylinder stacks. The largest plants developed in the top ring with progressively smaller plants at lower depths. Plants in the lower two rings developed interveinal chlorosis and did not reach commercial size.

Characterization and host range evaluation of Pseudomonas viridiflava from melon, blite, tomato, chrysanthemum and eggplant

The fluorescent bacterium Pseudomonas viridiflava (Burkholder) Dowson was identified as the causal agent of bacterial leaf blight of melon, tomato, blite, eggplant and of pith necrosis of chrysanthemum plants. Koch's postulates were fulfilled on greenhouse-grown or on potted plants under controlled environmental conditions. Twenty seven cultivated and one weed species, when artificially inoculated, were found to be susceptible to a strain of the bacterium isolated from cucumber. In cross-inoculation tests on potted plants, each strain induced the disease symptoms, independently of the host of origin. To our knowledge, melon and blite have not been previously reported as natural hosts of P. viridiflava. Also this is the first record of the bacterium as a foliar pathogen of melon, tomato, eggplant and blite and as a stem pathogen of chrysanthemum in Greece.

Degradation of dimethoate in chrysanthemums and soil.

Chrysanthemum (Chrysanthemum Morifolium Tzvel) is an important medical herb that is widely planted in China. It can not only cure some diseases as a traditional medicine but may be a useful health protective ingredient. It is usually processed into dry flower or health beverage to go on the market. Aphids (Aphids gossypii Glover and Pyrethrmyzus sanborni Gilletti) and stem borers (Phytoecia rufiventris Gautier) are two important pests that damage Chrysanthemum plants and affect the yield of Chrysanthemum flowers. Dimethoate, O,O-dimethyl-S-(Nmethylcarbamoyl-methyl)phosphorodithioate, is a broad-spectrum systemic insecticide used on many crops world-wide. It is also widely used to protect chrysanthemums from Aphids (Aphis gossypii Glover and Pyrethrmyzus sanborni Gilletti) and stem borer (Phytoecia rufiventris Gautier) in China currently. Because high residues of dimethoate will affect human health, degradation and residues of dimethoate in crops, fruits and vegetables have been brought to people’s attention. Lee and Westcott (1981) described the rapid degradation of dimethoate in wheat leaves. MacNeil et al.( 1975) studied the persistence of dimethoate and dimethoxan on cherries and found the half life in sweet and sour cherries was 6.6 and 4.69 days. Zwick et al.( 1977) also determined the residues of dimethoate and dimethoxon on sweet cherries and found the half life degraded residues was 3.5 to 4 days. Woodham et al. (1974a, 1974b) designed several experiments for searching the effect of different application on persistence of dimethoate and its oxygen in citrus and showed higher residues by the aid of ultra low volume spray than conventional high volume spray. Yutaka Iwata et al. (1981) reported half life of dimethoate in citrus leaves was 3.6 days. Steller and Brand (1974) reported half life of dimethoate in grapes was 6.8-7.0 days. Ferreira et al. (1987) studied residues of dimethoate and omethoate in peaches and apples and described only in the case of apples with seven applications, mean residues of dimethoate exceeded 1 ppm at the end of the preharvest interval (14 days). Szeto et al. (1985) reported that after application of dimethoate, the residues in asparagus decreased by about 90% in 7 days. There is, however, no report on dimethoate residues in chrysanthemum flowers to be published. To determine dimethoate residues in chrysanthemum products and keep

A New Method of Applying Imidacloprid to Potted Plants for Controlling Aphids and Whiteflies

The effectiveness of two application methods of the insecticide imidacloprid in controlling 1) melon aphids (Aphis gossypii Glover) on `Nob Hill' chrysanthemum (Dendranthema ×grandiflora Ramat) plants and 2) silverleaf whitefly (Bemisia argentifolii Bellows & Perring) on `Freedom Red' poinsettia (Euphorbia pulcherrima Wild.) were compared. Plants were grown in containers with their interior covered by a mixture of flat latex paint plus several concentrations of imidacloprid (0, 10, 21, 42, and 88 mg·L−1), or treated with a granular application of the insecticide (1% a.i.) according to label recommendations. All imidacloprid treatments effectively reduced aphid survival for at least 8 weeks. The two most effective treatments were the granular application (10 mg a.i.) and the 88-mg·L−1 treatment (0.26 mg a.i). All imidacloprid treatments effectively reduced whitefly nymph survival. The 42- and 88-mg·L−1 treatment and the granular application (1% a.i.) were equally effective in reducing nymph numbers in lower poinsettia leaves. None of the plants given treatments with paint exhibited any phytotoxicity symptoms. These results suggest the possibility of a new application method for systemic chemicals with the potential of reducing the release of chemicals to the environment. Paint and imidacloprid mixes are not described in any product label and cannot be legally used by growers. Chemical name used: 1-[(6-chloro-3-pyrimidil)-N-nitro-2-imidazolidinimine (imidacloprid)

Is stem extension determined by DIF or by absolute day and night temperatures?

Plants of tomato and chrysanthemum were grown in 24 combinations of day temperature (DT) and night temperature (NT) ranging from 12 to 32°C. Internodes about 1 mm in length were identified and their length recorded after 10 days of growth. For neither species could the extension growth in 10 days be related to the difference between DT and NT (DIF). Extension growth in tomato could largely be accounted for by linear DT effects, with linear NT and quadratic DT and NT effects having a smaller influence; the quadratic model accounted for over 93% of the total variance. The optimum temperature for extension growth was rather higher for DT than for NT so that increase in DT over the full temperature range, and increase in NT up to about 24°C, resulted in increased extension growth. DT had a similarly large influence on internode extension in chrysanthemum, but NT had relatively less effect than in tomato; the quadratic model accounted for over 87% of variance. It is concluded that extension growth in these two species responded to the absolute day and night temperatures rather than to DIF.

The pattern of14C-assimilate distribution in chrysanthemum cv. Red Delano with particular reference to branch interrelations

SummaryThe physiological organization of pinched plants of chrysanthemum was investigated by following the pattern of 14C-assimilate allocation from individual leaves on the main stem and uppermost branch, and from selected branches. In vegetative plants almost all of the assimilate imported by a developing branch was obtained from its subtending leaf and the three uppermost branches became virtually independent components of the plant within three weeks from pinching. The root system was the major sink for assimilate exported by main stem leaves and branches. Only a very small proportion of assimilate was distributed generally throughout the shoot and there was evidence that this followed a sectorial pattern. There was no interbranch exchange of assimilate. In flowering plants the flowers were the major sink for assimilate produced within the flowering branch. The results are discussed in relation to competition for assimilate between various plant components and in terms of the physiological status of b...

DETECTION OF A NOVEL TOSPOVIRUS IN CHRYSANTHEMUM

Up to 1994, tomato spotted wilt virus (TSWV) was the only tospovirus species reported in chrysanthemum (Dendranthema morifolium) in the Netherlands. Since then, however, occasionally an aberrant tospovirus was found in this ornamental. The virus evoked symptoms similar to those caused by TSWV, i.e. mild to severe stem necrosis, wilting of leaves and stems, and chlorotic and/or necrotic spots and rings on some of the leaves. The virus was isolated from different cultivars grown in different greenhouses. Test plants mechanically inoculated with this virus, produced symptoms that resemble those caused by TSWV. The most obvious differences were observed in Datura stramonium, in which only the tospovirus from chrysanthemum evoked stem necrosis and in Physalis floridana, in which systemic symptoms were caused by TSWV but not by the chrysanthemum virus. The symptoms produced on Citrullus lanatus ‘Dulzura’, Nicotiana occidentalis-P1 and Phaseolus vulgaris ‘Dubbele Witte zonder draad’ and ‘Pinto’ differ slightly from those caused by TSWV. Lycopersicum esculentum appeared to be less susceptible for this virus than for TSWV. Electron-microscopic studies revealed the presence of tospovirus-like particles in infected plants. In ELISA, however, the tospovirus from chrysanthemum did not react with antisera to the nucleocapsid protein of TSWV, neither to those of Impatiens necrotic spot virus, watermelon silver mottle virus and a tospovirus isolated from iris, respectively. Based on these results it is concluded that the tospovirus from chrysanthemum is a distinct virus that does not belong to any of the established serogroups. Sofar, in each greenhouse in which the first infection of this novel virus was found, chrysanthemum plants were derived from mother plants in Brazil, suggesting that the virus is endemic in South America.

CARBOHYDRATE STATUS OF CUSO4 SPECTRAL FILTER-GROWN CHRYSANTHEMUM PLANTS

The response of `Bright Golden Anne' chrysanthemum plants grown under CuSO4 spectral filters to exogenous GA3 application was evaluated to determine the relationship between gibberellins (GAs) and carbohydrate levels. The CuSO4 filters removed far red (FR) wavelengths of light and increased red: far red (R:FR), blue: far red (B:FR), blue: red (B:R) ratios, and phytochrome photoequilibrium (Ø) values of transmitted light compared to water (control) filter. Plant height, internode length, and leaf and stem dry weights were significantly reduced by light passing through CuSO4 filters in spring and summer seasons. Weekly applications of exogenous GA3 reversed the reduction in height and internode length induced by CuSO4 filters. Plants grown under CuSO4 filters responded more to exogenous GA3 application with respect to height and internode length, suggesting that the sensitivity to GA was not lowered. Light passing through CuSO4 filters reduced the carbohydrate levels, but the response varied with the season. Weekly GA3 application increased the carbohydrate levels, but did not totally reverse the reduction in carbohydrate levels under the CuSO4 filters. Although GA3 application increased the carbohydrate levels partially in CuSO4 filter-grown plants, the inhibition of GAs may not be solely responsible for reduction of carbohydrate levels under CuSO4 filters, showing that exogenous GAs and carbohydrate levels are not well correlated under CuSO4 spectral filters.

Painted Containers: A New Method for Imidacloprid Application

The effectiveness of two methods of application of the insecticide imidacloprid in controlling 1) aphids (Brachycaudus helichrysi) on Chrysanthemum plants, Dendranthema ×grandiflora (Ramat) (cv. Nob Hill) and 2) whitefly (Bemisia argentifolii) on poinsettia, Euphorbia pulcherrima (Wild.) (cv. Freedom Red) were compared. Plants were grown in containers with their interior covered by a mixture of flat latex paint and several concentrations of imidacloprid (0, 10, 21, 42, and 88 mg·L–1), or treated with a granular application of the insecticide (1% a.i.) according to label recommendations. All imidacloprid treatments were effective in reducing aphid survival after 8 weeks. The two most effective treatments were: granular (1% a.i.) and 88 mg·L–1 with an average of 0.2 aphid per plant as opposed to 50.4 aphids per plant for the control. The 42-mg·L–1 treatment had an aphid survival rate 1.6 aphids per plant. All imidacloprid treatments were effective in reducing white fly larvae. The 42 and 88 mg·L–1 and the granular (1% a.i.) were equally effective in reducing larvae numbers in lower poinsettia leaves: 0.5, 1.9, 0.9 larvae/2.5 cm leaf disk, respectively, while the control treatment had 62.9. None of the plants given treatments with paint showed any sign of phytotoxicity. These results suggest the possibility of a new application method for systemic chemicals with the potential of reducing or eliminating Worker Protection Standard (WPS) Restricted Entry Intervals (REI) and reducing the release of chemicals to the environment. Chemical name used: 1-[(6-Chloro-3-pyrimidil)]-N-nitro-2-imidazolidinimine.

Painted Containers: A New Method for Paclobutrazol Application

The effectiveness of two application methods of the growth regulator paclobutrazol on the growth of Chrysanthemum plants, Dendranthema ×grandiflora (Ramat) (cv. `Fina' and `Cream Dana') were compared. Plants were grown in containers with their interior covered by a mixture of flat latex paint and several concentrations of paclobutrazol (0, 5, 10, 20, 40, 80, 100, 150, 160, and 200 mg·L–1) or were treated with a soil drench of the growth regulator according to label recommendations (59 ml/container of paclobutrazol solution at 4 mg·L–1). Plants grown in containers with the paint–paclobutrazol mix at concentrations >80 mg·L–1 were shorter than plants given the control and paint only treatments but taller than plants given the drench treatment. Increasing paclobutrazol concentrations in paint from 100 to 150 and 200 mg·L–1 did not produce proportionately shorter plants. Paint alone had no effect on growth and development. Plants subject to growth regulator treatments appeared greener than the control plants. None of the plants given treatments with paint with or without paclobutrazol showed any sign of phytotoxicity. These results suggest the possibility of a new application method for systemic chemicals with the potential of reducing or eliminating worker protection standard restricted entry intervals and reducing the release of chemicals to the environment. Chemical name used: beta-[(4-chlorophenyl)methyl]-α-(1,1-dimethyl)-1H-1,2,4,-triazole-1-ethanol (paclobutrazol).

Ethylene + GA3 Sprays for Delaying Flower Bud Initiation in Chrysanthemum (Dendranthema grandiflora Tzvelv.) Stock Plants

Our objective was to determine whether repeated applications of 2-chloroethylphosphonic acid (ethephon) + gibberellic acid (GA3) to stock chrysanthemum plants that are day-neutral for flower bud initiation would increase the number of quality cuttings. Across five cultivars, there were no significant differences between controls and plants receiving 250 ppm ethephon in the total number of cuttings per plant. The percentage of cuttings with crown buds was greater for cuttings from controls than for ethephon-treated plants. Applying 500 ppm ethephon significantly reduced the number of cuttings. We conclude that chrysanthemum clones day-neutral for flower bud initiation and development with low long-day leaf number could be selected to form a 4 to 5 week production group.

Chrysanthemum Stem Necrosis Caused by a Possible Novel Tospovirus

AbstractNecrotic lesions surrounded by yellow areas on leaves followed by stem necrosis were observed on chrysanthemum plants cultivated in Atibaia, Sào Paulo State, Brazil. The host range, in vitro properties and particle morphology of the causal virus were typical of a Tospovirus. Serological studies demonstrated that the virus differed from tomato spotted wilt. tomato chlorotic spot, groundnut ringspot and inpatiens necrotic spot Tospoviruses. The virus isolate is thus possibly a representativeof a new serogroup of a new virus.

Biolistic transformation of chrysanthemum with the nucleocapsid gene of tomato spotted wilt virus

In vitro regeneration and biolistic transformation procedures were developed for several commercial chrysanthemum Dendranthema grandiflora Tzvelev, syn. Chrysanthemum morifolium Ramat. cultivars using leaf and stem explants. Studies on the effect of several growth regulators and kanamycin on chrysanthemum regeneration were conducted, and a step-wise procedure to optimize kanamycin selection and recovery of transgenic plants was developed. A population of putative transformed chrysanthemum plants cvs. Blush, Dark Bronze Charm, Iridon, and Tara, was obtained after bombardment with tungsten microprojectiles coated with the binary plasmid pBIN19 containing the nucleocapsid (N) gene of tomato spotted wilt virus (TSWV) and the marker gene neomycin phosphotransferase (NPT II). PCR analysis of 82 putative transgenic plants selected on kanamycin indicated that the majority of the lines (89%) were transformed and contained both genes (71%). However, some transgenic lines contained only one of the genes: either the NPT II (15%) or the TSWV (N) gene (14%). Southern blot analysis on selected transgenic lines confirmed the integration of the TSWV (N) gene into the chrysanthemum genome. These results demonstrate the development of an efficient procedure to transfer genetic material into the chrysanthemum genome and selectively regenerate transgenic chrysanthemum plants at frequencies higher than previously reported.