Synchrony of Inflorescence Initiation and Shoot Growth in Selected Protea Cultivars

Abstract

<jats:p><jats:italic>Protea</jats:italic> 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.</jats:p>

Exogenous Cytokinin Induces “Out of Season” Flowering in Protea cv. Carnival

“…Shoot growth of 'Carnival' occurs in distinct flushes with flowers initiating almost exclusively on a spring flush that develops terminally on overwintering shoots (Gerber, 2000). Flower initiation occurs during early elongation of the spring flush following budbreak (Gerber et al, 2001b), a time that coincides with the peak values of cytokinin determined (Fig. 2).…”

“…It is possible that in crops exhibiting ephemeral flush growth with periodic shoot dormancy, floral induction may occur before shoot initiation, but that floral initiation only occurs after bud sprouting. Flower initiation in 'Carnival' occurs shortly after bud sprouting in spring (Gerber et al, 2001b). The cytokinin peak in 'Carnival' that coincides with the onset of bud sprouting in spring (Fig.…”

“…The developmental stage of the terminal bud of the upper flush also appears to be an important criterion in determining the efficacy of BA to induce inflorescence initiation (Table 4). Based on studies of the apical meristem during the transition from vegetative to reproductive growth, Gerber et al (2001b) established that inflorescence initiation takes place in the early stages of the elongation of the flush that will subtend the inflorescence. Results from this study (Table 4) restrict the window in which the decision regarding the reproductive or vegetative nature of the succeeding flush is made to the stage where elongation of the new flush has advanced to developmental stage 3 (green point stage).…”

“…Inflorescence initiation on flushes of 'Carnival' induced by treatment with BA in April or May (autumn) advanced flowering from the ''normal'' time of March to May the following year to such an extent that flowers were ready for the Christmas market. It is possible that application of cytokinin to control flowering time in 'Carnival' may also be effective in related cultivars because flower initiation during the early elongation phase of flush development appears to be a common strategy in proteas (Gerber et al, 2001b). The effective use of cytokinin to initiate inflorescences in 'Carnival', without the exposure of the shoot to inductive winter conditions, is a first report for Proteaceace and has significant commercial potential for Protea as a cut flower crop.…”

“…and 'Carnival' (Nieuwoudt, 2006). Gerber et al (2001b) showed that flower initiation in 'Carnival' coincided with the early phases of spring flush elongation. In a number of perennial woody plants, spring budbreak is correlated with an increased concentration of cytokinins in the xylem sap just before budbreak (Tromp and Ovaa, 1990;Van Staden and Davey, 1979).…”