Investigation of Involucral bract browning in Protea spp.

Abstract

Thesis (MScAgric)--Stellenbosch University, 2025.Smith, A. 2025. Investigation of Involucral Bract Browning in Protea spp. Unpublished masters thesis. Stellenbosch: Stellenbosch University [online]. Available: https://scholar.sun.ac.za/items/e51d8073-0b0f-4d0e-9517-f3f660fa4577ENGLISH ABSTRACT: Involucral bract browning (BB) is a pre-harvest disorder that significantly diminishes the aesthetic appeal and market value of Protea stems, a niche export product for the indigenous South African cut flower industry. Characterized by brown-black involucral bract blemishes, with the severity is increased with post-harvest storage and extended vase life, but not the incidence. Despite the disorder’s severe impact on the economic viability of protea exports, it is largely under-characterized as previous South African export standards only address general blemishes. A six-point classification system for more consistent scoring of incidence and severity for BB was thus proposed. This study explored possible factors influencing BB, including production area, cultivar, and harvest timing. Warmer and drier regions were found to be more prone to BB, particularly for inflorescences maturing in late summer. Cultivars with larger, darker coloured inflorescences visibly exhibited reduced BB severity compared to those with smaller, lighter-coloured inflorescences. Investigating possible physiological and environmental contributors to BB, a split-plot experiment was conducted, using potted Protea ‘Pink Ice’ plants, with temperature as the main effect and irrigation as the secondary factor. Warmed blocks (Ambient +1.6°C) were created using overhead infra-red lights, whilst water deficit irrigation of half optimal (½x), optimal (x), and double optimal (2x) was implemented. Results revealed that elevated temperatures and sub-optimal irrigation (½x) significantly increased BB occurrence while reducing inflorescence size, whereas optimal (x) and supra-optimal (2x) irrigation mitigated BB without negatively affecting plant water status. In a study considering amelioration treatments for BB, waxed paper bags (WPB), non-woven polyethylene (Innoseal) bags, shade netting bags (SNB), along with evaporative cooling (EC), and reflective Raynox Plus™ applications were compared. The WPB and Innoseal treatments showed potential for decreasing BB, whereas the SNB and Raynox Plus™ negatively affected the aesthetic appeal of the inflorescences, whilst the EC treatment was discontinued due to poor irrigation water quality. Covering inflorescences early or throughout their full floral development significantly reduced BB incidence by up to 60% compared to unprotected control stems, whereas limited benefit was derived from covering inflorescence later during development. When comparing the efficacy of overhead fixed 20% white shade netting (SN) to reduce BB compared to that of waxed paper bags (WPB), both treatments effectively reduced BB severity, but SN treatments were less effective in reducing BB than the WPB treatment which delivered larger, market-preferred inflorescences within a more stable temperature environment, without affecting the relative humidity. In a successive season, SN treatments caused minor delays in spring bud break but resulted in an advanced harvest time. While the use of WPB is considered more labour intensive a study comparing it with the cost-effectiveness and long-term sustainability of erecting shade netting is warranted. BB remains a critical concern for Protea production, particularly under predicted increasing harsh and unpredictable climatic conditions. While methods like WPB and SN show promise in mitigating BB, refining these strategies and exploring alternative solutions should be a priority for the South African protea industry.AFRIKAANSE OPSOMMING: Omhullende skutblaarverbruining (BB) is 'n voor-oes-afwyking wat die aantreklikheid en markwaarde van Protea snyblomme, 'n nis-uitvoerproduk vir die inheemse Suid-Afrikaanse snyblombedryf, aansienlik verminder. Hierdie afwyking word gekenmerk deur bruin-swart letsels op die omhullende skutblare waarvan die erns word verhoog met na-oes berging en verlengde vaas lewe, maar nie die voorkoms nie. Ten spyte van die afwyking se ernstige impak op die ekonomiese lewensvatbaarheid van die protea-uitvoerbedyrf, is dit grootliks ondergekenmerk aangesien vorige Suid-Afrikaanse uitvoerstandaarde net enkele letsels aanspreek. 'n Sespunt-klassifikasiestelsel vir meer konsekwente gradering van voorkoms en erns vir BB is dus voorgestel. Hierdie studie het moontlike faktore ondersoek wat BB beïnvloed, insluitend produksie area, kultivar en oes periode. Daar is gevind dat warmer en droër streke meer geneig is tot BB, veral vir bloeiwyses wat in die laat somer volwasse raak. Kultivars wat groter bloeiwyses met ‘n donkerder kleur het sigbaar verminderde BB-erns getoon in vergelyking met dié met kleiner, ligterkleurige bloeiwyses. Om moontlike fisiologiese en omgewingsbydraers tot BB te ondersoek, is 'n split-plot eksperiment uitgevoer, met gebruik van gepotte Protea 'Pink Ice' plante, met temperatuur as die hoof effek en besproeing as die sekondêre faktor. Verwarmde blokke (Omgewing +1.6°C) is geskep deur oorhoofse infrarooi ligte te gebruik, terwyl watertekortbesproeiing van halfoptimaal (½x), optimaal (x) en dubbeloptimaal (2x) geïmplementeer is. Resultate het aan die lig gebring dat verhoogde temperature en sub-optimale besproeiing (½x) die voorkom van BB aansienlik verhoog, wat gelei het tot kleiner terwyl bloeiwyses, terwyl optimale (x) en supra-optimale (2x) besproeiing BB verminder het sonder om plantwaterstatus negatief te beïnvloed. In 'n studie wat beheer metodes vir BB oorweeg, is waspapiersakke (WPB), nie-geweefde poliëtileen (Innoseal) sakke, skadunetsakke (SNB), asook verdampingsverkoeling (EC), en Raynox Plus™-toedienings vergelyk. Die WPB- en Innoseal-behandelings het potensiaal getoon om BB te verlaag, waar die SNB en Raynox Plus™ die aantreklikheid van die bloeiwyses negatief beïnvloed het, terwyl die EC-behandeling gestaak is as gevolg van swak kwaliteit van die water wat gebruik was. Deur bloeiwyses vroeg of regdeur hul volle blomontwikkeling te bedek, het BB-insidensie aansienlik verminder met tot 60% in vergelyking met onbeskermde kontrole bloeiwyses, terwyl beperkte voordeel verkry is uit die bedekking van bloeiwyses later tydens ontwikkeling. Wanneer die doeltreffendheid van oorhoofse vaste 20% wit skadu-net (SN) vergelyk word met dié van waspapiersakke (WPB) om BB te verminder, het beide behandelings die ernstigheid van BB effektief verminder, maar SN-behandelings was minder effektief in die vermindering van BB as die WPB- behandeling wat bo en behalwe groter bloeiwyses, wat dit mark voorkeur gee, gelewer het binne 'n meer stabiele temperatuur omgewing, sonder om die relatiewe humiditeit te beïnvloed. In 'n opeenvolgende seisoen het SN-behandelings geringe vertragings in die lentebot veroorsaak, maar het gelei tot 'n vroeër oestyd. Alhoewel die gebruik van WPB meer arbeidsintensief is, is 'n studie wat dit vergelyk met die koste doeltreffendheid en langtermyn volhoubaarheid van die oprigting van skadunet geregverdig. BB bly 'n kritieke bekommernis vir Protea-produksie, veral onder voorspelde toenemende moeilike en onvoorspelbare klimaatstoestande. Terwyl metodes soos WPB en SN belofte toon om BB te verminder, behoort die verfyning van hierdie strategieë en die ondersoek van alternatiewe oplossings 'n prioriteit vir die Suid-Afrikaanse proteabedryf te wees.Master