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D.J. Norman, R.J. Henny and J.M.F. Yuen

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.

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D.J. Norman, J.M.F. Yuen and R.J. Henny

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.

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D.J. Norman, J.M.F. Yuen and R.J. Henny

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.

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D.J. Norman, R.J. Henny, J.M.F. Yuen and T.A. Mellich

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.

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David J. Norman, Qi Huang, Jeanne M.F. Yuen, Arianna Mangravita-Novo and Drew Byrne

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.