Báo cáo lâm nghiệp: "Experimental control in Weigela japonica of flower initiatiob"

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Experimental control of flower initiation in Weigela japonica M. Bodson (IRSIA), Universite de Liege, Institut de Botanique, B22, Centre de Physiologie Vegetale Appliqu6e Sart Tilman, B-4000 Li6ge, Belgium Introduction unknown and may be related to physio- logical conditions internal to the bud (Romberger, 1963; Crabbe, 1984). One Most of the experimental work on the may thus suspect that the floral transition mechanisms controlling flowering are of woody species is controlled by specific reported for herbaceous annuals for which mechanisms not found in photoperiodic floral transition is under photoperiodic annuals. A study has been started with control. Experimentation with these spe- woody ornamental, Weigela japonica, to a cies has the of emphasized importance consider some aspects of this question. the leaf system for the perception of the Results are reported on the effect of a proper photoperiod and made clear that pruning treatment on the floral response of the leaf processes resulting in the synthe- resting axillary buds. Two points were sis of the flowering stimulus are a major investigated: 1) the floral response with control point of the floral transition (Zee- regard to the age of the buds located at a vaart, 1976; Bernier, 1988). similar node position; and 2) the floral re- Several characteristics are specific to sponse at a single time of pruning applied the floral transition of woody perennials. at different node positions on the same For most woody species of the temperate axis. zone: 1) flowers are initiated on resting axillary buds; 2) there is a long rest period between flower initiation and anthesis; 3) there is no direct control of flower initia- Materials and Methods tion by the daylength, while vegetative growth may be under strong photoperiodic The rooted Plants propagated by cuttings. control (Nitsch, 1957); and 4) the floral were first potted in leaf mould in 7-cm cuttings were response is localized to certain buds pots. After 3 wk, they were transplanted clay (Jackson and Sweet, 1972; Buban and into peat moss (TKS Oldenburg, Germany) , 2 Faust, 1982). The causes of this localiza- pinched so as to keep 2 leaf pairs and their and respective axillary buds. Such a plant will de- tion of the floral response are still largely
velop 4 axillary shoots. The zero time was arbitrarly fixed at the time of pinching. The plants were kept in 16-h LD, under fluorescent tubes (cool white, 4300°K, ACEC, Charleroi, Belgium), at a constant temperature of 20°C and relative humidity of 60%. The light flux at the top of the canopy was 250 ¡lEom-. 1 os- 2 Under these conditions, all the axillary buds from intact plants remained vegetative for up to 150 d. Results reported here concern only those buds located at the node just below the pruning zone. Results as leafy shoots and the percentage In the first experiment, ramifications of dif- tially of buds developing as reproductive axes ferent ages were pruned so as to keep 3 increased with the position of the buds. nodes. For an early pruning, realized after The optimum was observed for buds lo- 40 d of growth, all buds developed as cated at the axil of node 3. leafy shoots (Table I). When 90-d old rami- fications were pruned, 80% of the buds developed as reproductive axes and the floral response decreased for later pruning Conclusions times. In the second experiment, the pruning These results show that: specific 1) at treatments were applied to 90-d old a time, all the axillary buds located along the shoots and carried out so as to keep a ramification did not have a similar capacity variable number of nodes (from 1 to 4). to initiate flowers in response to a pruning The type of development of the axillary treatment; and 2) there optimal buds depended upon their position on the was an for buds at a specific location on timing shoot (Table II). The buds located at the the ramification to respond to a treatment base of the ramification developed essen- promoting flowering. These observations suggest that the control of flowering is at least partially located within the bud. This control could be related to morphological or biochemical properties of certain com- ponents of the bud specific to its physio- logical age and/or linked to the relation of the bud to the other growth centers of the plant. An anatomical description of the bud with regard to its organogenetic activity is presently under investigation to detect and localize within the bud the histological modifications specifically involved in the floral transition.
Jackson D.J. & Sweet G.B. (1972) Flower initia- References tion in temperate woody plants. Hortic. Abstr. 42, 9-24 Bernier G. (1988) The control of floral evocation Nitsch J.P. (1957) Photoperiodism in woody and morphogenesis. Annu. Rev. Plant Physiol. Proc. Am. Soc. Hortic. Sci. 70, 526-544 plants. 9 39. 175-219 Buban T. & Faust M. (1982) Flower bud induc- Romberger J.A. (1963) Meristems, growth and tion in apple trees: internal control and differen- development in woody plants. US Department tiation. Hortic. Rev. 4, 174-203 of Agriculture, Tec:hnical Bull. no. 1293, pp. 214 4 Crabbe J.J. (1984) Vegetative vigor control over Zeevaart J.A.D. (1976) Physiology of flower for- location and fate of flower buds in fruit trees. mation. Annu. Rev. Plant Physiol. 27, 321-348 Acta Hortic. 149, 55-63