Control of flowering time in Protea cv. Pink Ice

Vivier, Marlie (2013-03)

Thesis (MScAgric)--Stellenbosch University, 2013.

Thesis

ENGLISH ABSTRACT: Protea cv. Pink Ice is harvested during a low profitability window, from February to May, where less than half the income is realized compared to the high demand and optimal marketing period of December and January. The manipulation of flowering time in ‘Pink Ice’ would be of great importance not only to increase profits, but also to avoid the high temperature summer months when losses due to sunburn on involucral bracts of the inflorescence are experienced. In a study which aimed to evaluate the efficacy of an autumn-application of benzyladenine (BA) to Protea ‘Pink Ice’ shoots to advance harvest time, four-flush shoots of mature plants were treated terminally at 500 mg.L-1, at both the dormant and greenpoint phenological stages, over ten and eight treatment dates respectively, in the autumn of 2008. Higher percentages of budbreak were achieved with the use of BA compared to that of untreated control shoots, but inflorescence initiation following the completion of a natural or BA-induced autumn-initiated flush, however, did not differ significantly from each other. In dormant shoots, BA promoted the initiation of an additional vegetative flush before winter, although no budbreak could be achieved for the late treatment dates of 22 May and 2 June. The harvest dates of five-flush autumn-initiated inflorescences from January to mid-February were comparable to harvest times observed for six-flush spring-initiated inflorescences. The synchronisation of shoot growth through the use of BA on ‘Pink Ice’ is therefore recommended to maximise the potential shoots that will budbreak in autumn. Harvests of BA-treated shoots can be advanced compared to that of spring-initiated inflorescences borne on five-flush shoots either by assisting in floral initiation in autumn or by providing an additional flush in spring. In a second trial the use of pruning and thinning regimes to advance flowering time was explored for ‘Pink Ice’, where plants were pruned to different numbers of bearers per plant and then thinned to various shoots per bearer. Evaluation of a total number of seven different combinations of bearers:shoots (40:1; 20:2; 13:3; 10:4; 16:2; 12:2 and 24:2) showed that harvests, irrespective of treatment combination, remained spread over a period of 12 months, with average harvest dates contained between 20 March and 14 April in the year following pruning. The percentage of stems harvested before Valentine’s Day did not differ significantly between treatments, nor did the percentage of autumn-initiated inflorescences. None of the bearer to shoot treatment combinations could produce shoots where shoot quality contributed to the significant advancement of flowering time. Lastly, CPPU (N-phenyl-N’-[2-chloro-4-pyridinyl] urea) as an alternative cytokinin source to BA was investigated for its efficacy to induce inflorescence initiation in Protea ‘Carnival’ and ‘Pink Ice’ during autumn. SitofexTM, in a concentration gradient of 1-10 mg.L-1, was applied to both ‘Pink Ice’ and ‘Carnival’ shoots on 1 April and 16 May 2008, respectively, whilst BA as MaxCelTM at 500 mg.L-1 was applied in April on both cultivars along with a MaxCelTM concentration gradient of 125-750 mg.L-1 included in the May treatment date for ‘Pink Ice’ only. In ‘Pink Ice’, MaxCelTM applied at 500 mg.L-1 together with CPPU at 1 mgL.-1 was found to be the most successful treatment in inducing high budbreak percentages of between 70-80% when applied in April. Shoots treated with 1 and 5 mg.L-1 CPPU in April induced a significant number of autumn-initiated inflorescences so that 72- 81% of shoots were harvested before Valentine’s Day. CPPU was, however, ineffective to induce budbreak and thus autumn initiation in both cultivars in May, whilst high budbreak percentages with the April application in ‘Carnival’ resulted in low or zero percentages of autumn inflorescence initiation in this cultivar. CPPU application both in April or May was unsuccessful to advance flowering time for ‘Pink Ice’ into the pre-Christmas period. The manipulation of flowering time in ‘Pink Ice’ is possible by means of cytokinin application. Further research is warranted into the application of cytokinin in combination with a pruning and thinning regime which can effectively improve plant complexity together with shoot quality in order to achieve harvests for ‘Pink Ice’ within the pre-Christmas period.

AFRIKAANSE OPSOMMING: Die natuurlike blomtyd van Protea kultivar Pink Ice val saam met ‘n niewinsgewende bemarkingsvenster, vanaf Februarie tot Mei, wanneer slegs die helfte van die inkomste bekom word, in vergelyking met ‘n meer optimale bemarkingstyd van Desember en Januarie. Die manipulasie van blomtyd in ‘Pink Ice’ is van groot belang, nie net om inkomste te verhoog nie, maar ook om die hoë temperature van die somer maande te vermy waartydens groot verliese gely word as gevolg van sonbrand op die omwindselblare van bloeiwyses. In hierdie studie wat die effektiwiteit van herfsaanwending van bensieladenien (BA) aan Protea ‘Pink Ice’ om blomtyd te vervroeg evalueer, is vierstuwingslote van volwasse plante terminaal behandel met 500 mgL-1, beide in die dormante en groenpunt fenologiese stadiums, oor tien en agt behandelingsdatums, respektiewelik, in die herfs van 2008. Hoë persentasie knopbreek was verkry met BA-behandelde lote teenoor onbehandelde, kontrole lote, maar bloeiwyse inisiasie wat gevolg het op die voltooiing van natuurlike of BA-geïnduseerde groeistuwing het nie betekenisvol van mekaar verskil nie. In dormante lote was BA in staat om die inisiasie van addisionele groeistuwing voor winter te bevorder, alhoewel geen knopbreek in dormante lote geïnduseer kon word in die laat behandelingsdatums van 22 Mei en 2 Junie nie. Die oesdatums van bloeiwyses soos geïnisieer op vyfgroeistuwingslote in Januarie tot middel Februarie was vergelykbaar met die oestye van lente-geïniseerde bloeiwyses soos gedra op ses-groeistuwingslote. Dus word die sinchronisasie van lootgroei deur die gebruik van BA op ‘Pink Ice’ aanbeveel om die aantal potensiële lote wat kan knopbreek te optimiseer. Blomtyd kan dus vervroeg word teenoor lente-geïnisieerde bloeiwyses soos gedra op vyf-groeistuwingslote deur blominisiasie in die herfs te induseer of deur addisionele groeistuwing in die lente te besorg. In ‘n tweede studie is die gebruik van snoei- en uitdunningspraktyke om blomtyd te vervoeg vir ‘Pink Ice’ verken waar plante gesnoei was tot verskillende aantal draers per plant en dan vervolgens uitgedun was tot verskeie aantal lote per draer. Evaluasie van totaal van sewe verskillende kombinasies van draers:lote (40:1; 20:2; 13:3; 10:4; 16:2; 12:2 en 24:2) het getoon dat oeste, ongeag die behandelingskombinasie, steeds versprei was oor ‘n periode van 12 maande, met gemiddelde oesdatums beperk tussen 20 Maart en 14 April, in die jaar daaropvolgende waarin snoei toegepas is. Die persentasie lote geoes voor Valentyns dag het nie betekenisvol van mekaar verskil nie, so ook nie die persentasie lote wat bloeiwyses in die herfs kon inisieer nie. Geen van die draer tot loot behandelingskombinasies kon lote produseer waarvan die loot kwaliteite kon bydra om blomtyd betekenisvol te vervroeg nie. Laastens, was die effektiwiteit van CPPU (N-feniel-N’-[2-chloro-4-pyridiniel] urea) as alternatiewe sitokinien bron tot BA om blom inisiasie in beide ‘Carnival’ en ‘Pink Ice’ gedurende herfs te induseer, bestudeer. SitofexTM aanwendings was gemaak as konsentrasie reekse van 1-10 mg.L-1 aan beide ‘Pink Ice’ en ‘Carnival’ lote op 1 April en 16 Mei 2008 onderskeidelik, terwyl BA as MaxCelTM teen 500 mg.L-1 aangewend was in April vir beide kultivars, tesame met MaxCelTM konsentrasie reeks van 125-750 mg.L-1 in die Mei aanwendingsdatum wat slegs toegedien was op ‘Pink Ice’. In ‘Pink Ice’ is bevind dat MaxCelTM aangewend teen 500 mg.L-1 tesame met CPPU teen 1 mg.L-1 die mees suksesvolle behandelings was om hoë rusbreek van tussen 70-80% te induseer met die April aanwendingsdatum. Lote behandel met 1 en 5 mg.L-1 CPPU in April kon betekenisvolle aantal herfsgeïnduseerde bloeiwyses inisieer sodat 72-81% van die lote voor Valentynsdag geoes kon word. CPPU was oneffektief om knopbreek te induseer en herf-inisiasie te vermag in beide kultivars in Mei, terwyl knopbreking persentasies met die April aanwending in ‘Carnival’ tot lae of geen inisiasie van herfsgeïnduseerde bloeiwyses gelei het nie. CPPU aanwendings, beide in April en Mei, was onsuksesvol om blomtyd van ‘Pink Ice’ in die periode direk voor Kersfees te skuif. Die manipulasie van blomtyd in ‘Pink Ice’ is moontlik met behulp van die aanwending van sitokiniene. Verdere navorsing is geregverdig, spesifiek met betrekking tot die aanwending van sitokinien in kombinasie met snoei- en uitdunningspraktyke wat effektief plant kompleksiteit tesame met lootkwaliteit kan verbeter om sodoende oestye vir ‘Pink Ice’ tot in die gesogte periode voor Kersfees te verskuif.

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