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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.
Abstract
A model that computes orchard foliage temperature distributions in a heated orchard is described. The energy balance for individual foliage elements is computed, considering thermal radiation from the environment, plus the radiative and convective effects of an array of orchard heaters. The model is used to analyze various heater configurations and densities, and to determine rates of fuel consumption required for frost protection. The results indicate that radiative heating of the foliage by the heaters is as important as convective heating of the air, even though only one-fifth of the fuel contributes to radiation emission. Further, results suggest several simple passive methods for increasing the efficiency of orchard heating.
One cut-flower and 14 pot anthurium cultivars were screened for resistance to anthurium blight by spraying four isolates of Xanthomonas campestris pv. dieffenbachiae (McCulloch and Pirone) Dye onto leaf surfaces in replicated experiments. Varying degrees of resistance were observed among the 15 cultivars tested. The pot cultivars Julia and Gemini were the most resistant, while the cut-flower cultivar Hearts Desire was the most susceptible. Each cultivar displayed different degrees of resistance to individual isolates of the pathogen. The results of this research permit the selection of clones with greater resistance for use in breeding and also create a baseline for comparing resistance of newly developed cultivars.
Twenty commonly grown Dieffenbachia cultivars were tested for their resistance to diseases affecting production caused by the following bacterial and fungal pathogens: Xanthomonas campestris pv. dieffenbachiae (McCulloch and Pirone) Dye, Erwinia chrysanthemi Burk, Fusarium solani Sacc, and Myrothecium roridum Tode ex Fr. Two isolates of each pathogen were used to compare heterogenic pathogen populations to the relatively homogenetic asexually produced cultivars. Cultivars having horizontal resistance toward tested pathogens could then easily be identified. The cultivars Camille, Compacta, and Parachute showed the broadest horizontal resistance, with resistance toward three of the four pathogen groups tested. Disease resistance identified in this research permits the selection of plants to be used in breeding, and also creates a baseline to compare resistance of newly developed cultivars.
Twenty-two spathiphyllum cultivars were evaluated for resistance to Cylindrocladium root rot (CRR). Four isolates of the fungus Cylindrocladium spathiphylli Shoult., El-Gholl & Alf. were selected from two different locations each in Florida and Hawaii. Spores of isolates were applied as a soil drench in replicated experiments using a randomized complete block design. The most severe symptoms were those produced by C. spathiphylli isolates from Hawaii. None of the spathiphyllum cultivars tested were highly resistant to CRR although resistance among the cultivars was observed. The cultivars Chris and Textura were the most promising cultivars, having fairly uniform resistance to the four isolates of C. spathiphylli. The cultivars Cupido, Daniel, Frederik, Jetty, and Vanessa were moderately resistant when combined data from all tests were analyzed. Results from this research permit the selection of more resistant breeding lines and also creates a baseline against which resistance of newly developed cultivars can be compared.
Syngonium `White Butterfly', growing in 1.6-L pots and treated in August with a single GA3 spray at 250 to 2000 mg·L–1, flowered within 86 days. Mean flower number increased with GA3 concentration. Flowers were normal in appearance and were fertile. Chemical name used: gibberellic acid (GA3).
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.
Commercially grown cultivars of Syngonium (Araceae) are very susceptible to Myrothecium leaf spot (incited by Myrothecium roridum Tode ex Fr.). Therefore, cultivation of Syngonium requires rigorous sanitation and frequent applications of fungicides for disease control. The goal of this research was to identify species and noncultivated accessions of Syngonium resistant to Myrothecium leaf spot. Five commercial cultivars and 30 accessions, comprising 16 different Syngonium species, were screened for resistance to M. roridum. All five commercial cultivars were susceptible to M. roridum. However, seven species (S. neglectum, S. wendlandii, S. dodsonianum, S. erythrophyllum, S. chiapense, S. dodsonianum, and S. angustatum) showed the highest resistance, as did two noncultivated accessions of S. podophyllum. The information on disease resistance for these species and accessions will be useful in future breeding work.
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.