Flower initiation and development of Protea cv. Carnival

Dissertation (PhD(Agric))--University of Stellenbosch, 2006.

ENGLISH ABSTRACT: Advancement of the flowering time of Protea cv. Carnival by approximately three months, without compromising the product quality, was achieved by the application of 6- benzyladenine-containing plant growth regulators to three-flush shoots in autumn. This earlier flowering time coincides favourably with the prime European marketing period (November-January). The percentage three-flush shoots initiating an inflorescence following the brush application of the 6-benzyladenine (BA)-containing regulators, ABG- 3062 (active ingredient: BA 2% w/w) and Accel® (active ingredients: BA 1.8% w/w; gibberellins A4A7 0.18% w/w) on dormant terminal buds, increased with later application dates and flowering percentages as high as 90% was achieved. No inflorescences were initiated on flushes induced by Promalin® (active ingredients: BA 1.8% w/w; gibberellins A4A7 1.8% w/w). Phenological phase progression of green point, flush expansion and inflorescence development of 'Carnival' shoots as induced by BA was calculated to have base temperatures of 8°C, 6°C and 1°C respectively. The days required from application of the BA-containing growth regulator until green point stage increased progressively over the six consecutive treatment dates in autumn (14 March - 22 May 2003). In contrast, the days required to complete inflorescence development decreased with each successive treatment date. The days required between the respective stages were mostly negatively correlated with temperature, except for the phase 'green point to flush expansion', where the relationship was unclear. For three-flush shoots of eight-year old plants, between 13-57, 39-65 and 121-177 days were required to reach green point, to achieve full flush expansion following green point and to complete inflorescence after flush expansion respectively. BA application enhanced budbreak in most dormant shoots, irrespective of plant age, BA concentration, decreasing temperature over time or shoot characteristics. However, twoflush shoots treated in late May had low budbreak and hence low flowering percentages. Shoots varied considerably in their responsiveness to BA treatments. BA application (500mg·L-1) as MaxCelTM (active ingredients: BA 1.9% w/w) to terminal buds alone of mature three-flush shoots from less vigorous growing plants resulted in the highest flowering percentages. Applications were most effective when applied to the terminal bud in the dormant state or up to the ‘green point’ stage. Shoot characteristics such as flush length, leaf area, shoot dry mass, number and proximity of the leaves to the terminal bud were all positively correlated with the propensity of shoots to initiate inflorescence under BA induction. Terminal flush intercalation shoot diameter (>7mm) was identified as the most important variable influencing the likeliness of flowering and can effectively serve as a nondestructive estimation of a shoot's propensity to flower. The presence of developing inflorescences or possible floral inhibiting factors derived from the previous flowering season is suggested to be inhibitory to inflorescence initiation following BA application. Synchronisation of shoot growth by pruning plants in late winter appears to be an essential step to ensure high percentages inflorescence initiation with BA treatment the following autumn. The use of BA as a management tool to control flowering times in Protea for better market opportunities is shown to hold considerable commercial potential.

AFRIKAANSE OPSOMMING: Protea cv. Carnival se blomtyd is met ongeveer drie maande vervroeg sonder om produkkwaliteit prys te gee. Hierdie vervroegde blomtyd wat gunstig saam val met die optimale Europese bemarkingstyd van November-Januarie is bewerkstelling deur die herfstoediening van 6-bensieladenien-bevattende plantgroei-reguleerders op lote bestaande uit drie groeistuwings. Die persentasie lote met drie groeistuwings wat 'n bloeiwyse geïniseer het na 'n kwas-aanwending met die 6-bensieladenien (BA)-bevattende groeireguleerders, ABG-3062 (aktiewe bestandeel: BA 2% w/w) en Accel® (aktiewe bestandele: BA 1.8% w/w; gibberellins A4A7 0.18% w/w), het toegeneem met latere behandelingsdatums en blompersentasies so hoog as 90% is behaal. Geen bloeiwyses is geïnisieer op groeistuwings wat deur Promalin® (aktiewe bestandeel: BA 1.8% w/w; gibberellins A4A7 1.8% w/w) teweeggebring is nie. Basis temperature van 8°C, 6°C en 1°C respektiewelik is bereken vir fenologiese fasevordering vanaf groeireguleerder toediening tot by groenpunt, groeistuwing-voltooing en bloeiwyse-ontwikkeling van 'Carnival' lote soos geïnduseer deur BA. Die dae wat benodig was vanaf toediening van die BA-toediening totdat groenpunt stadium bereik is, het progressief toegeneem oor die ses opeenvolgende herfsbehandelingsdatums (14 Maart-22 Mei 2003). In teenstelling met bostaande, het die vereiste aantal dae om bloeiwyseontwikkeling te voltooi afgeneem met elke opeenvolgende behandelingsdatum. Die aantal dae wat benodig was vir die onderskeie fases was meestal negatief gekorreleer met temperatuur, behalwe vir die fase 'groenpunt tot groeistuwing-voltooing', waar die verhouding onduidelik was. Vir lote van agt-jaar-oue plante met drie groeistuwings was tussen 13-57, 39-65 en 121-177 dae respektiewelik benodig om groenpunt te bereik, volledige groeistuwingverlenging te bewerkstellig en om bloeiwyse-ontwikkeling wat volg na groeistuwing verlenging, te voltooi. BA-toediening het knoprusbreking bevorder in die meeste dormante lote, ongeag plant ouderdom, BA konsentrasie, afname in temperatuur met tyd of loot eienskappe. Lote met twee groeistuwings wat laat in die herfs behandel is, het egter lae rusbreking en dus gevolglik ook lae blompersentasies getoon. Lote varieer aansienlik in hul reaksie op BA behandeling. BA toediening (500mg·L-1) as MaxCelTM (active ingredients: BA 1.9% w/w) op die terminale knop van afgeharde lote met drie groeistuwings en afkomstig van minder groeikragtige plante het tot die hoogste blompersentasies gelei. Die effektiwiteit van die behandeling was die hoogste met toedienings aan dormante terminale knoppe tot en met groenpuntstadium. Loot eienskappe soos groeistuwinglengte, blaaroppervlakte, loot droë massa, asook die aantal en nabyheid van die blare relatief tot die terminal knop was almal positief gekorreleerd met die vermoë van die loot om 'n blom te inisisieer in reaksie op BA induksie. Terminale groeiverstuwing interkalasie-lootdikte (>7mm) is geïdentifiseer as die belangrikste veranderlike wat die vermoë om te kan blom kan beïnvloed en kan gebruik word as 'n nie-destruktiewe voorspeller vir blom-inisiasie. Die teenwoordigheid van ontwikkelende bloeiwyses of potensiële blom-inhiberende faktore aanwesig in die loot na die vorige blomperiode, word moontlik beskou om inhiberend te wees vir BA-geïnduseerde blom-inisiasie. Sinchronisering van lootgroei deur die snoei van plante in laat-winter blyk krities te wees om 'n hoë blompersentasie met BA behandeling te verseker in die daaropvolgende herfs. Die aanwending van BA as 'n bestuurstegniek om die blomtyd van Protea te posisioneer vir beter bemarkingsgeleenthede toon aansienlike kommersiële potensiaal.

Doctoral