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Journal American Rhododendron Society

Current Editor:
Dr. Glen Jamieson ars.editor@gmail.com


Volume 14, Number 4
October 1960

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The Use of Artificial Lighting In The Breeding of Rhododendrons
Robert L. Ticknor and Paul F. Bobula**
Aurora, Oregon
** Work done at Waltham Field Station of University of Massachusetts

Plants grown under artificial light. Plants grown under normal day length.
   Fig. 33.  Plants grown under artificial light.
   Left R. 'Catalgla' x R. astrocalyx two
   years from seed, in the middle
   R. catawbiense compacta x (R. 'Fabia' x
   R. 'Cunningham's White') one year from
   seed, and on right. R. brachycarpum
   montanum
x R. decorum one year from
   seed.
   Fig. 34.  Plants grown under normal day
   length. Left R. 'Catalgla' x R. astrocalyx
   two years from seed, in the middle
   R. catawbiense compacta x (R. 'Fabia' x
   R. 'Cunningham's White') one year from
   seed, and on the right R. brachycarpum
   montanum
x R. decorum one year from
   seed.

        Rhododendrons, like many other woody plants, take five to seven years to flower from seed. A means of reducing this time period would be very helpful in a breeding program where often the second or F-2 generation is the true goal. This is particularly true where hybridization will be between species. The first generation will often be intermediate in character between the parental types. In the second generation segregation may occur so that the desirable characteristics of both species will be found in one plant.
        Davidson1 and Doorenbos2 have reported that the rate of growth of rhododendrons can be accelerated by the use of lighting at night. The accompanying illustrations show the results of lighting with 100 watt bulbs three feet apart from 10 P.M. to 6 A.M. (Fig. 33). Plants in the left picture have been growing in a cold frame (Fig. 34) while the plants in the right picture have been growing under lights in the greenhouse at 60 F. night temperature. The plants are as follows: on the left in each picture R. 'Catalgla' X R. astrocalyx two years from seed, in the middle R. catawbiense compacta X (R. 'Fabia' X R. 'Cunningham's White') one year from seed, and on the right R. brachycarpum montanum X R. decorum one year from seed.
        The plant of R. 'Catalgla' X R. astrocalyx, which was just through blooming had been grown in a cold frame the first summer. The other plants were grown continuously under artificial light from 10 P.M. to 6 A.M. and present an even greater contrast in plant size.
        The use of artificial light appears to be very promising as a tool to induce early flowering. More work needs to be done to determine the critical levels of lighting to induce flowering and to determine the costs involved.

1 Davidson, H. and C. L. Hammer, Photoperiodic Responses of Selected Woody Ornamental Shrubs, Mich. Agricultural Exper. Sta. Quarterly Bulletin 40, No. 2:327-343.
2. Doorenbos, J., 1955, Shortening The Breeding Cycle of Rhododendron, Euphytica 4:141-146


Volume 14, Number 4
October 1960

DLA Ejournal Home | QBARS Home | Table of Contents for this issue | Search JARS and other ejournals