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Areas of Research on Rhododendrons & Azaleas of Interest to the ARS

Research Proposal Application Form

Grants Awarded in Previous Years

The research committee is interested in the following issues of both practical and theoretical value to rhododendron growers:
  • Physiological and genetic factors affecting tolerance of rhododendrons to heat, cold, drought, insects, and diseases.  Why are some rhododendrons more susceptible than others?  How do we use this information to breed more tolerant rhododendrons?
  • What can be done to counteract the intolerance of current rhododendrons to various adverse factors, such as powdery mildew and petal blight?  Are there chemical or biological control agents that are effective against these pathogens?  
  • Plant exploration in the U.S., the dissemination of new plant germplasm found, and the maintenance of such new germplasm.
  • Polyploidy and aneuploidy in hybrid rhododendrons; chromosome numbers (different from 2N=26) in Rhododendron species.

More generally, members of the society have identified a broader range of subjects as appropriate for ARS-funded research.  These follow:

Botanical Research:

  • Studies on the biosystematics of native American Rhododendron species, including the collection of superior clones and populations for distribution to the members through the Seed and Pollen Exchanges.
  • Support for the introduction of foreign species.
  • Translation of key botanical research publications on Rhododendron published in German, Japanese, etc.

Breeding Research:

  • Methods for screening and breeding for cold hardiness.
  • Breeding for heat tolerance.
  • Breeding for resistance to root weevils.
  • Breeding for improved fragrance.
  • Develop charts for interspecific compatibilities.
  • Techniques for improving the success of wide crosses and overcoming incompatibility systems.
  • Improved methods for crossing deciduous with evergreen azaleas.
  • Computer systems to handle all aspects of record-keeping for breeding programs, with wide applicability to a large number of amateur breeders.

Cultural Research:

  • Examination of pruning effects across various cultivars.
  • Develop a schedule and appropriate techniques to establish container-grown plants in soil.
  • Study the effects of dead heading (removal of spent blossoms and developing seed pods) on succeeding year's flowering.
  • Studies on growing rhododendrons and azaleas under competitive trees, such as pines, maples, dogwoods, tulip poplars, Douglas fir and madrona.
  • Pruning and other cultural methods for the rejuvenation of plants that are too large or rangy.
  • Low-cost growing media and weed control methods for container plants.
  • Cultural methods to set flower buds on very young plants.
  • Methods to protect plants from damage by extreme environmental conditions, such as hot, dry weather, extreme cold, etc.
  • Development of a sleeve to enclose stems to avert bark splitting.

Cytological and Genetical Research:

  • Studies on the inheritance of flower color and relationships between flower color and environmental adaptation.
  • Determination of chromosome numbers in species and cultivars, especially for deciduous azalea cultivars.
  • Studies on the inheritance of fragrance, indumentum, and truss size.
  • Production of haploids and/or polyploids.
  • Tests of tubulin antagonists and antimitotic chemicals for their ability to induce polyploidization.
  • Development of methods for in vitro selection of tissue cultures for resistance to diseases, pests, and extreme environmental conditions.
  • Evaluation of species and hybrids for flower color pigments, especially in sections of the genus not studied to date.

Fertilization Practices:

  • Develop safe, but effective fertilization schedules for both container-grown and field-grown plants.
  • Study the role of calcium on plant vigor.
  • Study the role of phosphorus in bud set and the effects of high phosphorus on chlorosis, and relationship to the pH of the soil.
  • Research on the influence of nitrogen on bud set.
  • Study the effects of fall fertilization.
  • Study the effects of alfalfa leaf meal and other fertilizer supplements on growth.
  • Study the role of soluble salts in soil or artificial media in relation to the predisposition of plants to diseases and pests.

Pest Control Research:

  • Develop reliable tests to screen seedlings for resistance to diseases such as root rot and to other pests.
  • Control of Phytophthora dieback.
  • Biological control of root weevils and borers, including the use of predaceous nematodes and insects.
  • Use of terpenes and related compounds to repel root weevils.
  • Methods for the long-term control of petal blight.
  • Control of galls on azaleas.
  • Studies on the cause, nature, and control of slow decline.
  • Identify cultivars sensitive to Cygon.
  • Control of Botryosphaeria dieback.
  • Control of powdery mildew, especially in deciduous azaleas.
  • Studies on the synergistic effects of anti-transpirants on pesticides.
  • Research on the effect of red spider mite and other debilitating pests or conditions on susceptibility to other diseases and pests.
  • Protection from feeding by rabbits, mice, moles, deer, etc.
  • Control of Armillaria mellea.

Physiological Research:

  • Chemical induction of hardiness and the practical applications of hardiness induction.
  • Cultural manipulations to improve fall hardening.
  • Prevention of fall flowering.
  • Physiological factors affecting bud set.
  • Determination of factors affecting fall hardening, mid-winter hardiness, and dehardening.
  • Determination of the physiological differences between easy-to-root and hard-to-root cultivars.
  • Correlation of leaf analysis with soil tests.
  • Interaction of fertility levels and light intensity on plant performance.
  • Techniques to break dormancy, especially in deciduous azaleas.
  • Physiological factors controlling root growth and practical applications in promoting extensive root growth.
  • Physiological factors affecting disease and pest resistance and possible application in the area of systemic immunization.
  • Studies on the effect of chlorinated and/or "hard" water on growth and plant health.

Propagation Research:

  • Research on dwarfing rootstocks.
  • General development of improved propagation techniques.
  • Research on seed dormancy in wild species, and techniques to overcome seed dormancy.
  • Development of optimal methods for seed handling and storage.
  • Home propagation of hard-to-root cultivars.
  • Studies on cutting propagation (including the effects of sugars, willow extract, growth regulators, soaking, and cutting collection date).
  • Effects of the temperature of the rooting medium on rooting success.
  • Bulletins, slide presentations, and video tapes demonstrating propagation methods.
  • Innovative methods for the control of bacterial and fungal contamination in Rhododendron tissue cultures.
  • Research on basal callusing and other undesired variants generated by tissue culture propagation.

Review Papers and Popular Publications:

  • Develop outlines of pest control methods and fertilizer applications for the average gardener.
  • Develop small, easy-to-read, "what to do" booklets on plant problems.
  • Prepare illustrated manuscripts on all aspects of the garden culture of rhododendrons and azaleas for particular sets of environmental conditions.
  • Develop plans for simple, but effective, structures for indoor growing of plants and seedlings.
  • Reprint out-of-print bulletins of interest to society membership.
  • Develop slide presentations and/or video tapes of general interest to society membership.

Other Areas of Research:

  • The Research Committee will consider original research proposals in areas other than those listed above, provided that the findings are directly applicable and of value to the membership of the Society.  However, the problems listed are those that were considered some time ago to be of highest priority and interest to the membership.

For additional information contact the Chairman of the ARS Research Committee:
Phone: 610-647-8870
Fax: 610-647-6664

American Rhododendron Society
Executive Director: P.O. Box 525,  Niagara Falls, NY 14304
Ph: 416-424-1942   Fax: 905-262-1999   E-Mail:
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