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Audrey I. Gerber, Karen I. Theron and Gerard Jacobs

Inflorescence initiation in Protea cv. Lady Di (P. magnifica Link × P. compacta R. Br.) occurs predominantly on the spring growth flush when it is subtended by one or more previous growth flushes. Mature, over-wintering leaves are essential for induction of flowering in `Lady Di', and are also crucial to the early stages of inflorescence initiation and differentiation. Defoliation before elongation of the spring growth flush was complete prevented flowering, and shoots either remained vegetative or produced inflorescences that aborted. Levels of carbohydrates in the stem and leaves of overwintering shoots were low, and early growth and development of both the spring flush and inflorescence were, therefore, supported by current photosynthates from the mature leaves on the overwintering shoot. Likewise, reserve carbohydrates available in the flowering shoot were insufficient to account for the rapid increase in dry weight during the major portion of growth of the spring flush and inflorescence. This increase occurred after elongation of the spring flush was complete and was supported by current photosynthates from the leaves of the spring flush. Defoliation treatments that did not prevent inflorescence initiation had no effect on inflorescence development or on flowering time.

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Audrey I. Gerber, Karen I. Theron and Gerard Jacobs

The date of pruning affected flowering time of Protea cv. Sylvia (P. eximia × P. susannae) by influencing the flush on which inflorescence initiation occurred, and the harvest could be manipulated to fall within the optimum marketing period for export to Europe. Flowers initiated on the spring flush reached anthesis in January-February, those on the first and second summer flushes in April-May and July-August, respectively, and those on the autumn flush in November-December. Thus, flowering shoots harvested within the optimum marketing period (September to February) initiated inflorescences on the autumn and spring flushes. Because shoots on the spring flush initiated inflorescences readily, many flowering shoots harvested in January and February (following initiation the previous spring) were short and therefore unmarketable. For commercial production, pruning in July is recommended to allow harvest in October-December of the following year. Since the vegetative and reproductive cycles necessary to produce inflorescences on long stems span more than a year, a biennial cropping system is recommended.

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Audrey I. Gerber, Karen I. Theron and Gerard Jacobs

Protea L. sp. can be assigned to groups according to similar times of flower initiation and harvest. The stages occurring during flower initiation and their synchrony relative to shoot growth were investigated for three cultivars when flower initiation occurred on the spring growth flush. For all three cultivars, the spring flush was preformed and enclosed in the apical bud before spring budbreak. During elongation of the spring flush, the apical meristem produced floral primordia which differentiated into involucral bracts. After completion of the spring flush, meristematic activity continued and produced floral bracts with florets in their axils. The different cultivars were characterized by differences or similarities in the time of budbreak, and the rates of shoot growth, appendage formation, and flower development. Insight into the time of flower initiation relative to vegetative growth could be useful in making management decisions, as well as forming a basis for manipulation of the flowering process.

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Caroline J. Poole, Audrey I. Gerber and Gerard Jacobs

Brunia albiflora (Pillans) is harvested commercially in South Africa as a cut flower for export to European markets. To compete with European cut flowers high quality and continuity of product during the marketing period are essential. Optimizing the cut-flower potential of B. albiflora requires an understanding of the flowering process and selection of clonal material. We present a series of scanning electron micrographs which show three-dimensional images of the developmental stages of the shoot apex during the transition from the vegetative to the reproductive state. In B. albiflora the inflorescence consists of more than 15 individual rotund inflorescences arising from lateral positions on the terminal portion of the shoot. Development of the apical meristem of axillary shoots was studied to determine the time and sequence of inflorescence initiation and development. These observations identified that flower initiation occurs in October, followed by flower development through summer, with anthesis being reached from February to March.