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R.N. Trigiano, M.T. Windham and W.T. Witte

Powdery mildew (Microsphaera pulchra) of flowering dogwood (Cornus florida L.) has become a significant problem of trees in nursery production as well as in the landscapes and forests of the eastern United States. The disease significantly reduces growth and berry production by older established trees and may contribute to the inability of younger trees (liners) in production to survive winter dormancy. Disease resistance in named cultivars is limited to partial resistance found in `Cherokee Brave'—all other cultivars are extremely susceptible. Until now, the only disease control measure was to establish an expensive, labor-intensive, preventive fungicide program. We examined >22,000 seedlings and identified 20 that were extremely resistant to powdery mildew. Three trees with white bracts were selected from the 20 and released as patent-pending cultivars. `Karen's Appalachian Blush' has long, non-overlapping, pink fringed bracts with a delicate appearance. `Kay's Appalachian Mist' has creamy white, slightly overlapping bracts with deeply pigmented clefts. `Jean's Appalachian Snow' has large, strongly overlapping bracts with non-pigmented clefts. The three powdery mildew-resistant cultivars will be entered into an existing breeding program with `Appalachian Spring', a cultivar released by the Tennessee Agriculture Experiment Station and resistant to dogwood anthracnose, in an attempt to produce trees that are resistant to both diseases.

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M.T. Windham, W.T. Witte and R.N. Trigiano

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G. Caetano-Anollés, R.N. Trigiano and M.T. Windham

Fifty-one isolates of Discula destructiva obtained from various Cornus species were evaluated using arbitrary signatures from amplification profiles (ASAP). ASAP analysis is based on dual-step arbitrary primer-based amplification procedure that produces “fingerprints of fingerprints” and in many instances increases detection of polymorphic DNA. This novel technique was able to distinguish groups of isolates from the northeast, middle and southeast range of the disease as well as western United States and Canada. The data supports the contention of recent and independent introduction of the disease on both east and west coasts, a genetic “bottleneck” that has limited diversity of the pathogen, and directionality of introduction of disease from coastal ports-of-entry to interior populations of C. florida and C. nuttalli.

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M.T. Windham, E.T. Graham, W.T. Witte, J.L. Knighten and R.N. Trigiano

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W.T. Witte, M.T. Windham, R.J. Sauve and P.C. Flanagan

Fifty-five accessions of commercially available crape myrtle cultivars were established with 10 single-plant replications during Fall 1993 and Spring 1994. Drip irrigation began on a regular basis May 1994 and plants were fertilized regularly. In contrast to the 1994 growing season with heavy powdery mildew infestation, little powdery mildew occurred in 1995. Mean growth index (GI = centimeter height + centimeter mean width) was calculated for each cultivar in Fall 1994 and 1995. Fastest growth occurred in `Tuskegee' and `Biloxi' (GI = 276, 246, respectively), followed by a group including `Tonto', `Comanche', `Choctaw', `Hardy Lavender', `Natchez', `Potomac', and `Tuscarora' (GI = 185 to 227). Slowest growth occurred in the group including `Pecos', `Seminole', `Baton Rouge', `Petite Orchid', `Bourbon Street', `Cherokee', `Monink Pink', `Moned Red', `Delta Blush', `Low Flame', `New Orleans', `Monow', and `World's Fair' (GI = 5 to 53). Data will be presented on powdery mildew ratings and physiological injury sustained during Winter 1995–96.

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W.T. Witte, M.T. Windham, R.J. Sauve and P.C. Flanagan

Sixty accessions of commercially available lilac cultivars were planted May 1994 and immediately placed under drip irrigation and fertilized regularly. Powdery mildew appeared in July 1994 and was rated on a scale of 0 (healthy) to 5 (totally mildewed) in July, August, and September. Mean growth index (GI = cm height + cm mean width) was calculated for each cultivar in Fall 1994 and 1995. Fastest growth (GI = 75 to 45 respectively) occurred in the group including chinensis `Rothomagensis', meyeri `Dwarf Korean', reticulata `Ivory Silk', prestoniae `Isabella', `Mrs. Harvey Bickle', `Excel', `Katherine Havemeyer', `Mme. F. Morel', `Silver King', `Leon Gambetta', `Mount Baker', and microphylla `Superba'. Data will be presented on powdery mildew ratings for the 1995 season.

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M.T. Windham, W.T. Witte, R.J. Sauve and P.C. Flanagan

Fifty-five cultivars of crapemyrtle were established in a cultivar trial with 10 single-plant replications during Fall 1993 and Spring 1994. Drip irrigation began on a regular basis on 18 May 1994 and plants were fertilized regularly. Powdery mildew appeared in July, and within 2 to 3 weeks maximum levels of infection occurred. Plants were rated using a scale of 0 (healthy) to 5 (totally mildewed). In the group of seven cultivars, most heavily infected (>2.8 rating), `Byers Wonderful White' was worst (4.1), followed by `Royalty', `Pink Lace', `Prairie Lace', `Petite Plum', `Firebird', and `Christmastime'. There were 21 cultivars with no mildew (0.0). Many of these were USDA–NA hybrids but also included `Hope', `Bourbon Street', `Glendora White', `Petite Snow', `Centennial Spirit', and `Hardy Lavender'. A few USDA–NA hybrids had slight mildew: `Potomac', `Powhatan', `Catawba', `Seminole', `Biloxi', and `Hopi' (<10% of foliage mildewed).

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M.T. Windham, W.T. Witte, R.J. Sauve and P.C. Flanagan

Eighty-one oak taxa were established at the Nursery Crops Research Station in McMinnville, Tenn., in Fall 1993 and Spring 1994. Drip irrigation was applied as needed beginning 18 May 1994 and plants were fertilized regularly. Powdery mildew began to appear in July on some taxa. Each plant was rated on a scale where 0 = healthy plant and 5 = totally mildewed. Height and caliper were recorded in Fall 1994 and the 1994 growth increment calculated. Quercus robur fastigiata was most severely affected by powdery mildew (4.1), followed by a group of six taxa, including douglasii, oglethorpensis, macrocarpa, virginiana, prinus, and aliena (2.3–1.4). There were slight amounts of mildew on 26 taxa and 48 taxa were mildew-free. Growth increment in height and caliper will also be presented.

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M.T. Windham, W.T. Witte, R.J. Sauve and P.C. Flanagan

Sixty cultivars of lilac obtained from two commercial nurseries were planted 18 May 1994 and immediately placed under drip irrigation and fertilized regularly. Powdery mildew appeared in July. Each plant was rated in July, August, and September for powdery mildew on a scale of 1 (healthy) to 5 (totally mildewed). There were 22 cultivars in the most resistant group (0–1.8) in July, 13 in August (0–1.0), and 11 in September (0–1.0). Mildew-free were: `Miss Kim', `Royalty', `Palibin', `Summer Snow', `White Summers', `Minuet', `Ivory Silk', `Anna Amhof', `Donald Wyman', but these were not significantly different from `James MacFarlane' and `Superba' (<10%of plant mildewed). Data on growth will also be presented.

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R.N. Trigiano, K.M. Kaveriappa, S.E. Schlarbaum, M.T. Windham and W. Witte

DNA amplification fingerprinting (DAF) was Used to characterize both parents (different cultivars) in breeding experiments with Cornus florida. Putative hybrids were fingerprinted and true crosses identified by finding unique male parent products in amplification profiles. Both manual and honey bee mediated pollinations successfully produced hybrid seed. Axillary buds from seedlings were used to initiate proliferating shoot cultures on woody plant medium with 4.5 μm BA. Initiation and development of adventitious roots were dependent on IBA (4.1 μm), sucrose (0–2%), and agar (0.2–0.6%) concentrations. About 40–50% of the microshoots produced roots and were acclimatized to greenhouse conditions. Cultures have been maintained without loss of regeneration potential for over 2 years. Clonal material can be reentered into the breeding program or used to evaluate horticultural characteristics in different environments and locales.