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Joseph Postman, Gayle Volk and Herb Aldwinckle

generated by crossing a highly disease resistant with a highly susceptible parent often identifies loci containing resistance genes ( Pierantoni et al., 2007 ), but disease evaluations using highly diverse germplasm collections are vital to the discovery of

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Nathalie Delhomez, Odile Carisse, Michel Lareau and Shahrokh Khanizadeh

Seventeen strawberry (Fragaria ×ananassa Duchesne) cultivars and six selections were tested under greenhouse conditions for susceptibility to leaf spot induced by Mycosphaerella fragariae (Tul.) Lindau. The level of susceptibility was evaluated based on maximum disease severity and area under the disease progress curve (AUDPC). The 23 genotypes were ranked based on AUDPC and grouped according to their susceptibility. Cluster analysis for AUDPC gave four groups corresponding to low, moderate, high, and very high susceptibility to leaf spot. `Annapolis', `Chambly', `Glooscap', `Redcoat', and `Veestar' consistently showed a low level of susceptibility. The selections SJ89700-1 and SJ8518-11 and `Tribute' showed a very high level of susceptibility, and the remaining cultivars were grouped as either moderately or highly susceptible.

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Lisa W. Alexander, Anthony L. Witcher and Fulya Baysal-Gurel

Witchhazel (Hamamelis sp.) cultivars are now available in an array of forms and flower colors, including several native, pollinator-friendly cultivars. However, little is known about response of witchhazel cultivars to powdery mildew (Podosphaera biuncinata) or the growth and flowering characteristics of witchhazel cultivars in a nursery field production setting. To provide growth, flowering, and disease incidence data to nursery growers, a cultivar trial including 23 cultivars of witchhazel representing five species was planted Apr. 2016 in McMinnville, TN. Plant growth, flowering density, length of bloom, and foliar disease incidence were evaluated over three growing seasons between May 2016 and Oct. 2018. ‘Zuccariniana’ japanese witchhazel (H. japonica) and ‘Sunglow’ common witchhazel (H. virginiana) showed the greatest height increase during the trial, and ‘Sunglow’ also added the most width during the trial. Cultivars with negative height or width growth included Sweet Sunshine chinese witchhazel (H. mollis) and hybrid witchhazels (H. ×intermedia) Aphrodite, Twilight, and Barmstedt Gold. Ten of the 23 cultivars experienced winter injury in the form of stem necrosis. Root crown sprouts were observed for all cultivars at least once during the trial. ‘Wisely Supreme’ chinese witchhazel had the longest bloom period, followed by ‘Westerstede’ and ‘Twilight’ hybrid witchhazels, whereas ‘Quasimodo’ vernal witchhazel (H. vernalis) had the greatest density of flowers. The hybrid witchhazel cultivars Aphrodite, Nina, and Arnold Promise and the common witchhazel cultivars Green Thumb and Sunglow were resistant to powdery mildew under trial conditions in all 3 years. ‘Twilight’ and ‘Barmstedt Gold’ hybrid witchhazel, ‘Little Suzie’ common witchhazel, ‘Wisley Supreme’ chinese witchhazel, and ‘Shibamichi Red’ japanese witchhazel were moderately resistant to powdery mildew.

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Ana B. Monteagudo, A. Paula Rodiño, Margarita Lema, María De la Fuente, Marta Santalla, Antonio M. De Ron and Shree P. Singh

Vegetable Seeds Co. for greenhouse and laboratory facilities for disease evaluations and to Carl Strausbaugh, Stephen Love and Krishna Mohan for reviewing the manuscript.

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John A. Juvik, M.A. Rouf Mian and Andrea J. Faber

–Champaign. We sincerely thank Jerald Pataky for providing his guidance in the disease evaluations and the northern leaf blight inoculum. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper

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Martin L. Kaps, Marilyn B. Odneal and James F. Moore

Wine and table grape vineyards were planted at Mountain Grove in 1985. Twenty-seven wine and 10 table grape cultivars were evaluated in respective 12 and 18 vine plots, replicated five times. Vineyard management practices were single curtain cordon training, dormant season balance pruning, protective spray program according to Missouri recommendations, grass sod row middles with preemergence herbicide applied underneath the trellis, and fertilization according to soil and petiole analysis. Cluster thinning and shoot positioning were done as needed. Productivity data was measured yearly and included: pruning weight, yield, cluster and berry weights, and juice °Brix, titratable acidity, and pH. Disease evaluation data was also taken on these cultivars. Based on these data and current market trends, two wine grape cultivar groups were identified: recommended, `Catawba', `Cayuga White', `Chambourcin', `Norton', `Seyval blanc', `Vidal blanc', and `Vignoles'; not recommended, `Aurore', `Baco noir', `Bellandais', `Chancellor', `Chelois', `Couderc noir', `DeChaunac', `Delaware', `Horizon', `LaCrosse', `Leon Millot', `Marechal Foch', `Melody', `Missouri Riesling', `Niagara', `Rayon d'Or', `Rougeon', `Ventura', `Villard noir', and `Vivant'. Three table grape cultivar groups were identified: recommended, `Mars' and `Reliance'; recommended for limited planting, `Canadice', `Vanessa', and `Vinered'; and not recommended, `Challenger', `Einset', `Festivee', `Himrod' and `Venus'. This information is used by growers to make cultivar decisions and also serves as a benchmark for comparing new grape germplasm coming into the state.

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M.T. Mmbaga and E.C. Nnodu

Cornelian cherry (Cornus mas L.) has been free of disease and pest problems until recently when a bacterial leaf blight caused by Pseudomonas syringae was reported. Since its first observation in middle Tennessee in 1999, the disease has become endemic in the nursery where it was first discovered. The objective of this study was to assess the disease, evaluate factors that favor disease development, and develop disease management strategies. Cool temperatures of 20 to 24 °C (day) and 10 to 15 °C (night) were most favorable to the disease and young leaves were highly susceptible while mature leaves were resistant to infection. Leaf wounding increased the susceptibility of leaves and mature leaves developed infection at 28 °C, temperature at which nonwounded leaves were completely resistant to infection. Results from this study also showed that plant propagation from seemingly healthy branches of infected plants may have perpetuated the disease at the nursery. Six chemicals—Phyton-27 (copper sulfate), Camelot (copper salt of fatty acids), Agri-Mycin 17 (streptomycin), Kocide 101 (copper hydroxide), Basicop (elemental copper 53%), and, Bordeaux mixture (cupric sulfate + lime) were evaluated for disease control. Phyton-27, and Agri-Mycin—were most effective and reduced disease severity to 10% of foliage showing disease symptoms. Information from this study will be useful in designing effective disease management strategies.

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Fahrettin Goktepe, Zhanao Deng, Brent K. Harbaugh, Teresa Seijo and Natalia A. Peres

Caladiums, widely used in containers and landscapes as ornamental plants for their bright colorful leaves, are generally forced or grown from tubers. Commercial production of these tubers in central Florida is through dividing “seed” tubers and growing them in fields. Tuber quality is therefore of critical importance to success in container forcing, landscape use, and tuber production. Fusarium tuber rot (Fusarium solani) has been recognized as the most-destructive disease that affects caladium tuber quality. There is anecdotal evidence from growers indicating the existence of resistance in commercial caladium cultivars. To identify and confirm the source of fusarium tuber rot resistance in caladium, F. solani isolates have been collected from rotting tubers grown under different soil conditions and from different locations. The pathogenecity of these isolates has been tested through artificial inoculation of fresh harvested and/or stored tubers, and a number of highly virulent isolates have been identified. These isolates have been used to refine inoculation and disease evaluation techniques. Two techniques, spraying a conidial suspension onto fresh cut surfaces and inserting Fusarium-infested carnation leaf segments into artificial wounds, have proven to yield consistent resistance/susceptibility ratings among cultivars of known difference in resistance to fusarium tuber rot. Appropriate incubation temperatures and humidity seem to be very critical for disease development and evaluation. The two techniques have been used to evaluate 35 cultivars. Several cultivars, including `Candidum', showed a high level of resistance to fusarium tuber rot, and may be good breeding parent for developing new resistant cultivars.

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Joseph L. Smilanick

the subject of that chapter. Methods described include classical ones, such as inoculation, pathogen culture media, microscopy, and disease evaluation tests, as well as molecular and biochemical techniques, such as enzyme activity assays, antibody

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Nahla V. Bassil and Gayle M. Volk

speaker, Joseph Postman, related how “Standardized plant disease evaluations will enhance resistance gene discovery.” He emphasized the value of using standardized numerical ratings and reference cultivars to record resistant and tolerant individuals. Jay