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  • Author or Editor: David J. Norman x
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In field crops the origin and movement of bacterial inoculum is difficult to determine due to inadequate means of distinguishing strains of bacteria. In this study the introduction, establishment, and spread of Xanthomonas campestris pv. dieffenbachiae (McCulloch and Pirone) Dye into anthurium fields were examined by monitoring the distribution of serologically distinct strains recovered from propagation benches and production fields. One thousand Anthurium andraeanum Lind. plants were indexed for X. c. pv. dieffenbachiae and 962 were later introduced into a production field. Strains recovered from the propagative stock were serotyped using a panel of 10 monoclonal antibodies and serotypes were compared to serotypes of strains already prevalent in the production field. Four distinct serotypes were identified which were not characteristic of strains already prevalent in the production field. Two biotypes of X. c. pv. dieffenbachia were also identified, based on their ability to hydrolyze starch. Sensitivity to 500 ppm streptomycin sulfate also was used to characterize strains associated with introduced propagative stock. Of 248 strains isolated from field plants, 39% were streptomycin resistant, whereas none of the strains isolated from introduced cuttings at the initial indexing were resistant. Over a 3-year period, strains with serotypes associated with the propagation material became established in the field, but spread to other cultivars was limited. This paper demonstrates the utility of serological methods for epidemiological studies.

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This study is the first report of using titanium dioxide (TiO2) to control Xanthomonas bacterial blight on geranium and leaf spot on poinsettia. Potted zonal geranium ‘Patriot Bright Violet’ and poinsettia ‘Snowcap’ were grown in a greenhouse and treated with a foliar spray of TiO2 at 25 and 75 mm, respectively, twice. Titanium-treated and control geranium plants were inoculated with Xanthomonas hortorum pv. pelargonii and poinsettias were inoculated with Xanthomonas axonopodis pv. poinsettiicola. The experiment was repeated once. The numbers of lesions on geranium leaves sprayed with TiO2 at 25 and 75 mm were 53% and 67%, respectively, less than in control plants in the first trial, but there were no significant differences among treatments in the second trial. Results on poinsettia, however, showed significant decrease in lesion numbers in both trials. Plants treated with TiO2 at 25 and 75 mm showed 85% and 93% reduction in lesions, respectively, in the first trial and 87% and 92% reduction in lesions in the second trial. No symptoms of phytotoxicity were observed. This study suggests that TiO2 has potential as an alternative to currently labeled products for controlling Xanthomonas bacterial blight in geranium and leaf spot on poinsettia.

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Abstract

The radiant fractions of four currently available orchard heaters (spot, large cone, return stack and auto clean stack) were determined under orchard conditions using observed surface temperatures, emissivity and the Stefan-Boltzmann Law. The contribution of the flame extending above the spot heater stack to its total radiant output was determined. Stack surface temperatures increased with burning rate on the large cone, return stack and auto clean stack heaters but decreased on the spot heater. The position of the highest temperature was near the bottom of the large cone, return stack and auto clean stack heaters and near the top of the spot heater. Surface temperatures were lower in general on the spot heater than on the other three heaters. The radiant fractions of the large cone, return stack and auto clean stack heaters were greater than 20% and relatively constant with burning rate. Even though the flame contribution is purposely overestimated the radiant fraction of the spot heater was less than 16%. For low wind speeds under which most orchard heating occurs the effect of wind speed on the radiant fraction was negligible.

Open Access

Dieffenbachia Schott is an important ornamental foliage plant genus. A total of 30 species has been recognized, but most cultivars come from or are related to a single species, D. maculata (Lodd.) G. Don. At least 11 of the cultivars are sports or somaclonal variants. As a result, the potential lack of genetic diversity in cultivated Dieffenbachia has become a concern. However, no research has been conducted to determine the genetic relatedness of the cultivars. This study analyzed the genetic similarity of 42 Dieffenbachia cultivars using amplified fragment length polymorphism (AFLP) markers. Six primer sets, selected from an initial screening of 48, generated a total of 453 scorable AFLP fragments of which 323 (71%) are polymorphic. All cultivars were clearly differentiated by their AFLP fingerprints. A dendrogram was constructed using the unweighted pair-group method of arithmetic averages, and principal coordinated analysis was carried out to show multiple dimensions of the distribution of the cultivars. The 42 cultivars were divided into three clusters; clusters I and II comprise 18 and 23 cultivars, respectively. Jaccard's similarity coefficients for cultivars in the clusters I and II varied from 0.44 to 0.95 and 0.41 to 0.87, respectively. These results indicate that broadening the genetic variability in the Dieffenbachia gene pool is needed, but the genetic similarity of many cultivars is not as close as previously thought. Additionally, Jaccard's similarity coefficients between most sports or somaclonal variants and their parents were 0.73 or lower, suggesting that accumulation of somatic mutations through tissue culture may play a role in the increased variation between some sports or variants and their parents.

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Abstract

Spatial and temporal components of the turbulent heat flux above a heated orchard are discussed. Direct measurements of the temporal component of the turbulent flux at 2 locations are reported. Drag anemometry and fine-wire thermocouples provided measurements of u, v, w, and T at 30 Hz. About 10% of the energy provided by heating escaped the crop zone by the temporal flux. Variation in the flux measured at a given location was caused by changes in wind speed and direction, and heater proximity.

Open Access

Sixty-one cultivars of geraniums, including zonal, regal, ivy, and scented, were tested for susceptibility to three strains of Ralstonia solanacearum: a race 1, biovar 1 (R1B1) strain P597 isolated from tomato in Florida, a R1B1 strain P673 obtained from pothos originated from Costa Rica, and a race 3, biovar 2 (R3B2) strain UW551 isolated from geranium imported from Kenya. These three strains represent populations of R. solanacearum found in the United States or imported with infected plant propagative material. A genomic comparison of the geranium cultivars was also done using amplified fragment length polymorphisms. Both R1B1 strains were more virulent than the R3B2 strain, producing wilt symptoms on most cultivars of zonal, regal, and ivy types. Variation in susceptibility of geranium cultivars to the two R1B1 strains was observed. The R3B2 strain UW551 had a much more restricted host range and was not able to infect most regal geranium cultivars when applied as a soil drench. Many of the scented cultivars were found to be resistant to all three strains of R. solanacearum when tested using the drench inoculation method. However, most scented cultivars were found to be susceptible when plants were wound-inoculated. The greatest variation in type of resistance was observed between the scented geranium cultivars and specific strains of R. solanacearum.

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Gibberellins (GAs) are phytohormones that regulate plant height and flowering time in plants. Plants with reduced GA or disrupted in GA signaling exhibit a dwarf phenotype. DELLA proteins are transcriptional repressors that attenuate GA-mediated promotion of plant growth. Alleles in which the eponymous DELLA motif in these proteins is disrupted result in constitutive repression of GA signaling and a dominantly inherited dwarf phenotype. We found that the dwarf Helianthus annuus (sunflower) cultivar Sunspot is hyposensitive to GA3 as compared with the tall cultivar Mammoth Grey. Sequencing of the HaDella1 gene indicates that ‘Sunspot’ has a single nucleotide polymorphism resulting in a missense mutation in the DELLA motif as compared with ‘Mammoth Grey’ and the reference sequence. Helianthus annuus has five genes encoding DELLA proteins, including HaDella1. We propose that the DELLA motif alteration in the HaDella1 gene results in a dominant mutation in ‘Sunspot’ and is the cause of its dwarf phenotype.

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