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Paul E. Cappiello

For nearly 30 years, the Univ. of Maine has been conducting woody ornamental plant performance evaluations. While there are a number of focus collections under evaluation, the Rhododendron collection is one of the central features of the program. This report offers performance data for more than 100 specimens grown at the Lyle E. Littletield Ornamentals Trial Garden on the campus of the Univ. of Maine. Winter survival, folk disease rating, fall foliage color and effectiveness, and flowering dates are included.

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Stephen L. Krebs and Michael D. Wilson

Bruce Briggs for supplying hundreds of micropropagated rhododendrons. Anne Dorrance generously provided fresh cultures of P. cinnamomi and reviewed an earlier draft of this paper. Don Whitney assisted with the greenhouse work.

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Mohamed S. Elmongy, Xiuyun Wang, Hong Zhou, and Yiping Xia

Azalea plants, which belong to the genus Rhododendron L. (family Ericaceae ), are some of the most popular ornamental shrubs worldwide. The in vitro production of Rhododendron plants is becoming commercially significant ( Eeckhaut et al., 2010

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Ryan N. Contreras, Thomas G. Ranney, Susana R. Milla-Lewis, and G. Craig Yencho

Rhododendron L. is an extremely diverse genus with eight subgenera and more than 1000 species ( Chamberlain et al., 1996 ). This diversity, combined with broad crossability, has led to the development of more than 28,000 cultivars registered

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Thomas G. Ranney, Frank A. Blazich, and Stuart L. Warren

The research was funded in part by the North Carolina Agricultural Research Service (NCARS) and the Research Foundation of the American Rhododendron Society. Use of trade names in this publication does not imp] y endorsement by the NCARS of products

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Mark H. Brand and Richard Kiyomoto

Storrs Agricultural Experiment Station scientific contribution 1834. This work was supported in part by funds made available through the Holden Arboretum, Mentor, Ohio, and the Connecticut Chapter of the American Rhododendron Society. The

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Jessica D. Lubell and Mark H. Brand

Elepidote rhododendrons are important landscape plants because of showy flowers and bold evergreen foliage. The most common flower colors are lavender, pink, and white, but red flower color is highly sought after. Only some elepidote rhododendrons

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Ryan N. Contreras, Thomas G. Ranney, and Shyamalrau P. Tallury

Rhododendrons and azaleas ( Rhododendron L.) are among the most widely grown ornamental plants in the world. There are over 1000 species recognized in eight subgenera ( Chamberlain et al., 1996 ). Species within subgenera readily hybridize and

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S.L. Krebs

Root rot caused by the soil-borne pathogen Phytophthora cinnamomi is one of the deadliest and most costly diseases in rhododendron culture. Unfortunately, the majority of cultivars appear to be susceptible to this fungus. Host resistance does occur, but it represents a tolerance of rather than immunity from the disease. A breeding program has been initiated to develop a broader array of root rot resistant cultivars and to determine the genetic basis for resistance. Greenhouse inoculations and screenings of 48 contemporary cultivars yielded seven clones with moderate to high levels of resistance to P. cinnamomi. Protocols for evaluation at the seedling stage were developed in order to screen large breeding populations of about 200 seedlings per cross. Root rot tolerance appears to have low-moderate heritability in these rhododendron populations. Groups of progeny with one resistant parent had a slower mortality rate and higher survivorship (avg. 10%) after 2 months of disease pressure than crosses in which both parents were susceptible (0 survivorship). A recurrent selection strategy is planned to increase the frequency of alleles for resistance in breeding populations of rhododendrons.

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Rajeev Arora and Lisa J. Rowland

study using deciduous azalea ( Rhododendron L.) to examine the effect of genotypic or ecotypic biogeography on midwinter-hardiness and dehardening kinetics. Nine azalea genotypes (species and varieties) were used in this study that represented eight