Flowering physiology of selected Disa hybrids in cultivation

Franken, Elri (2013-03)

Thesis (MScAgric)--Stellenbosch University, 2013.

Thesis

ENGLISH ABSTRACT: Disa is an unique South African orchid, currently cultivated on a limited scale. Knowledge on the timing of floral initiation is of key importance in understanding the floral biology of a new floricultural crop. Floral initiation of the Disa hybrids, ‘LM0739’ and ‘LM0721’, was determined by means of stereomicroscopy to be at the end of May and June, respectively and the duration of floral differentiation was 15-16 weeks. Floral differentiation was divided into ten stages and the vegetative phenology was studied in relation to the reproductive phenology. It was evident that the growth strategies of tuber-forming and non-tuber forming hybrids differed. Floral abnormalities were also observed and a first report on bud abortion prior to anthesis was made. The effect of plant size and factors affecting plant size, such as the cultural practice of plant separation (separating mother plants from offsets) and higher light intensities were also studied. Furthermore, the effects of photoperiod, smoke water, the plant growth regulators MaxCel™ (6-benzyladenine (6-BA) and Promalin® (6-BA + Gibberellin G4+7 (GA4+7) as well as potassium chlorate (KClO3) on flowering of Disa hybrid ‘LM0739’ were also investigated. Plant size influenced flowering, although the critical plant size required for flowering became less obligatory as the season progressed. The separation practice showed no advantages for vegetative growth or flowering and the commercial viability of this practice should be re-evaluated. None of the growth regulators or KClO3 positively affected flowering time and are not considered as viable options for future flower manipulation strategies. No short day photoperiodic effect was recorded when night break treatments, consisting of three different exposures time to night break regimes (58, 74 and 167 days), were applied. The effect of additional lighting on the four Disa hybrids ‘LM67’ ‘LM66’, ‘LM56’ and ‘LM48’ were studied. On the mature leaves of light-treated plants a red/brown colouration was observed. This colouration was presumed to be induced light stress, but when quantified by photosynthesis and fluorescence recordings, no significant differences were observed between treated and control plants. Transmission electron microscope (TEM) imaging was furthermore inconclusive. The observed symptoms were suggested to possibly be an ameliorating mechanism against high light intensities by accumulating anthocyanins as screening pigments. Photosynthesis measurements were recorded for Disa hybrid ‘LM0739’for part of a season in which recorded maximum photosynthesis values ranged between 2 and 5 μmol.m-1.s-2. Non-structural carbohydrate analysis conducted on Disa hybrids ‘LM0739’ and ‘LM0721’ indicated that sucrose and glucose were the main soluble sugars in the plant material and that starch levels were extremely low in all samples, except the underground components of the tuber forming hybrid where up to 4.5% starch were recorded. It was furthermore recorded that the root fraction of the tuber forming hybrid (‘LM0721’) showed much higher levels of hydrolyzed sugars than any of the other samples. Results indicated different carbon allocation strategies for hybrids with- and without root tubers and possibly indicated glucomannan as possible storage reserve compound. These studies provide a basis for future studies with the goal to establish the successful commercial production of Disa as a potted plant on the international floricultural market.

AFRIKAANSE OPSOMMING: Disa is ‘n unieke Suid-Afrikaanse orgidee wat tans slegs op ‘n beperkte skaal gekweek word. Inligting aangaande die tyd van blom inisiasie is nodig om die blom biologie van ‘n nuwe blomgewas te verstaan. Die tyd van blom inisiasie van twee Disa hibriede, ‘LM0739’ en ‘LM0721’ was met behulp van 'n stereomikroskoop bepaal om aan die einde van Mei en Junie respektiewelik plaas te vind, terwyl blom differensiasie tussen 15 en 16 weke geduur het. Blom differensiasie was onderskei in tien kenmerkende fases en die vegetatiewe fenologie van Disa was ook bestudeer met betrekking tot die reproduktiewe fenologie. Hieruit was dit duidelik dat groei strategieë tussen hibriede wat stoorwortels vorm, en dié wat nie vorm nie verskil. Blom abnormaliteite was waargeneem en hierdie studie verskaf ook die eerste verslaggewing van blomknop-aborsie in Disa. Die rol van plant grootte, asook faktore soos kommersiële plant-verdeling (skeiding van ouer- en dogterplante) en hoër ligintensiteite wat plant grootte beïnvloed is bestudeer. Verder was die effek van fotoperiode, rookwater, twee groei reguleerders naamlik MaxCel™ (6-benzieladenien (6-BA) en Promalin® (6-BA + Gibberellien G4+7 (GA4+7) asook kalium chloraat (KClO3) op die blomvorming van Disa ‘LM0739’ getoets. Dit is vasgestel dat plantgrootte blom inisiasie beïnvloed maar dat hierdie minimum plantgrootte vereiste meer fakultatief raak later in die seisoen. Kommersiële plant-verdeling blyk om geen positiewe effek op plantgroei of blomvorming te hê nie en behoort heroorweeg te word. Verder het geen van die toegediende groeireguleerders of KClO3 plantgroei of blomvorming bevoordeel nie. Geen kortdag-fotoperiodiese effek was gedokumenteer toe nagbreekbehandelings van drie verskillende tydsperiodes (58, 74 en 167 dae) toegedien was nie. Verder is die effektiwiteit van addisionele lig, om moontlik plantgrootte van vier Disa hibriede ‘LM67’, ‘LM66’, ‘LM56’ en ‘LM48’ te verbeter, ook getoets. Volwasse blare van plante wat aan die addisionele ligbehandeling blootgestel was, het ‘n rooi-bruin verkleuring getoon. Hierdie verkleuring was toegeskryf aan ligskade, maar met die kwantifisering van ligskade deur fotosintese en fluorosensie metings is geen verskille tussen die kontrole en lig-behandelde plante waargeneem nie. Die verkleuring word toegeskryf aan die akkumulasie van antosianiene as ‘n verdedigingssmeganisme teenoor hoë ligintensiteite. Die fotosintetiese kapasiteit van Disa ‘LM0739’ was vir ‘n gedeelte van die seisoen gemonitor waartydens maksimum fotosintetiese waardes van tussen 2 en 5 μmol.m-1.s-2 waargeneem is. In die ontleding van nie-strukturele koolhidrate van beide bo-en ondergrondse plant materiaal van Disa hibriede ‘LM0721’ en ‘LM0739’ is glukose en sukrose geïdentifiseer as die twee hoof oplosbare suiker fraksies. Styselvlakke in die bogrondse materiaal van beide hibriede, asook in die ondergrondse materiaal van ‘LM0739’ was besonder laag (<2%). Die styselinhoud in die ondergrondse materiaal van hibried ‘LM0721’ was egter hoër en het tot 4.5% van die totale droë gewig bygedra. Die wortelfraksie van die stoorwortel-vormende hibried (‘LM0721’) het veral ook hoë vlakke van gehidroliseerde suikers getoon. Resultate het getoon dat hibriede met en sonder stoorwortels moontlik van verskillende koolhidraat allokasiestrategieë gebruik maak en dui ook aan dat glukomanaan moontlik gebruik word as stoorvorm . Hierdie studies verskaf ʼn basis vir toekomstige studies met die doel om die suksesvolle, kommersiële produksie van Disa as potplant op die internasionale ornamentele blommark te verseker.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/79857
This item appears in the following collections: