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  • Author or Editor: J. Chen x
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Angular leaf spot is a common but rarely studied disease of muscadine grapes (Vitis rotundifolia Michx.) in the southeastern United States. During 1994 and 1995, we performed two field evaluations of angular leaf spot on 30 muscadine cultivars. Based on disease severity data, no cultivar was immune to angular leaf spot; however, `Albermarle', `Doreen', `Higgins', `Noble', `Regale', `Scuppernong', `Southland', and `Summit' showed high degrees of resistance. `Alachua', `Darlene', `Dixie Red', `GA-3-9-2', `Jane Bell', `Janet', `Jumbo', `Pam', and `Rosa' were susceptible.

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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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Eastern redbud (Cercis canadensis L.) is a commonly used small landscape tree. Compact growth, purple leaf color, and weeping architecture are three popular ornamental phenotypes. Inheritances of weeping architecture and purple leaves have been reported previously. Inheritance of compact growth habit and its genetic linkage with the weeping and purple leaf genes have not been reported. In the present research, the inheritance of compact growth derived from ‘Ace of Hearts’ was explored in the F1, F2, and reciprocal backcross families resulting from the controlled hybridization of ‘Ruby Falls’ (normal growth/weeping architecture/purple leaf) × ‘Ace of Hearts’ (compact growth/nonweeping architecture/green leaf). All 27 F1 individuals were nonweeping, green-leaved, and noncompact. A total of 572 F2 progeny were obtained, and subsequent analysis of segregation revealed a single recessive gene controlled compact growth habit. Analysis of reciprocal backcross families confirmed this result as well. Weeping architecture and purple leaf color were also controlled by single recessive genes, confirming findings presented in previous studies in another redbud family. No linkage between the three genes was detected. This research is the first to report the inheritance of compact growth in eastern redbud and confirms independent assortment between the compact, purple leaf, and weeping genes.

Open Access

ZZ (Zamioculcas zamiifolia), a member of the family Araceae, is emerging as an important foliage plant due to its aesthetic appearance, ability to tolerate low light and drought, and resistance to diseases and pests. However, little information is available regarding its propagation, production, and use. This report presents relevant botanical information and results of our four-year evaluation of this plant to the ornamental plant industry.

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A two-dimensional mathematical model was developed to describe the time course of root growth and its spatial distribution for container-grown plants, using chrysanthemum [Dendranthema ×grandiflorum (Ramat.) Kitamura] as the model system. Potential root growth was considered as consisting of several concurrent processes, including branching, extension, and death. Branching rate was assumed to be related sigmoidally to existing root weight density. Root growth extension rate was assumed to be proportional to the existing root weight density above some threshold root weight density in adjacent cells. The senescence rate of root weight density was assumed to be proportional to existing root mass. The effects of soil matric potential and temperature on root growth were quantified with an exponential function and the modified Arrhenius equation, respectively. The actual root growth rate was limited by the amount of carbohydrate supplied by the canopy to roots. Parameters in the model were estimated by fitting the model to experimental data using nonlinear regression. Required inputs into the model included initial root dry weight density distribution, soil temperature, and soil water potential data. Being a submodel of the whole-plant growth model, the supply of carbohydrates from canopy to roots was required; the total root weight incremental rate was used to represent this factor. Rather than linking to a complex whole-plant C balance model, the total root weight growth over time was described by a logistic equation. The model was validated by comparing the predicted results with independently measured data. The model described root growth dynamics and its spatial distribution well. A sensitivity analysis of modeled root weight density to the estimated parameters indicated that the model was more sensitive to carbohydrate supply parameters than to root growth distribution parameters.

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