Co-Authors:
Wallerstein, I., Department of Ornamental Horticulture, Agricultural Research Organization, The Volcani Center, P.O. Box 6, Bet Dagan, 50250, Israel
Hackett, W.P., Department of Horticultural Science, Landscape Architecture, University of Minnesota, St Paul, MN, United States
Abstract:
Mature-phase Hedera helix L. plants were subjected to different environmental conditions in growth chambers in order to determine the factors ensuring the maintenance of a strictly vegetative growth with foliar leaf production. At a temperature of 24‘C and at a light flux of 20, 000 lux (300 pE m~m-2s-1) photosynthetically active radiation (PAR), inflorescence initiation was inhibited under both long days (LD) and short days (SD); however, in about 50% of the plants the meristems became quiescent for a short period. During later development, these meristems, as well as those of the remaining 50% of the plants, became unstable resulting in plants with distichous phy llotaxis and other juvenile characteristics. At 21 "C and at the same light flux, a high percentage of the plants became quiescent or formed at least some scale-type leaves. When relative humidity (R.H.) was maintained at 100%, the proportion of quiescent plants was lower than at ambient humidity (50-70% R.H.). At 24“C and under SD, the degree of instability and quiescence of the meristems was dependent on light flux. A low light flux promoted meristem instability as reflected by the appearance of distichous phyllotaxis. A high light flux (30, 000 lux, 450 pE m-2s-1PAR) promoted the activity and stability of the meristems, as reflected by the continued production of foliar leaves in a spiral phyllotactic pattern. At a low light flux (10, 000 lux, 150 pE m-2s-1PAR) and at 27"C, meristems became unstable in 100% of the plants, which resulted in distichous phyllotaxis and other juvenile characteristics. These results demonstrate that environmental conditions can be manipulated so as to maintain mature characteristics or induce juvenile characteristics in H. helix plants. Although the size and shape of the meristems changed during growth and in relation to phase instability, it was not possible to conclude whether the reduction in meristem size preceded or followed the change to distichous phyllotaxis. © 1989 Taylor & Francis Group, LLC.
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