The potential impact of increasing temperatures driven by climate change on cultivated Protea cut flower production systems is not known. This study used a biennial pruning system in Protea ‘Pink Ice’ to track the physiological and reproductive responses in comparable phenological stages, but exposed to different seasonally determined temperature conditions. Protea ‘Pink Ice’ generally initiates inflorescences terminally on the spring flush. A limited number of shoots can initiate inflorescences on the preceding autumn flush, leading to an advanced harvesting time compared with that of the spring-initiated inflorescences. In a commercial Protea orchard in Hopefield, South Africa, gas exchange, carbohydrate availability, and vegetative and reproductive growth were compared between the two shoot types in the context of seasonal temperature differences. Leaves of shoots, which initiated inflorescences on the autumn flush, generally had higher light-saturated net carbon dioxide (CO2) assimilation capacities in autumn (April–May) and spring (October–November). There is evidence of a requirement of minimum shoot diameter of 7.6 mm (four- or five-flush shoot), as measured directly above the intercalation between the terminal (uppermost mature flush) and subterminal flush, when the subsequent flush was at budbreak stage during April (autumn) and at least five flushes to be required for floral initiation in Protea ‘Pink Ice’. Spring-initiated inflorescences had a shorter developmental period (4 months) than that of autumn-initiated inflorescences (7 months) and developed into significantly smaller (width) inflorescences with a lower width and dry weight at harvest. These inflorescences were harvested on average a month later compared with autumn-initiated inflorescences. The ambient temperature during inflorescence development played a significant role in the inflorescence growth rate, affecting the time required from visible inflorescence detection to harvest. At the calculated optimum base temperature of 9 °C, autumn-initiated inflorescences required 41,010 growing degree hours (GDH), whereas spring-initiated inflorescences required 35,872 GDH from initiation to anthesis. Under future warmer growing conditions, anticipated decreased size and dry weight of inflorescences may reduce marketability and income for Protea producers.
This research was financially supported by Cape Flora SA (CFSA), the National Research Foundation (NRF), and Stellenbosch University.
CaustonD.R.DaleM.P.1990The monomolecular and rectangular hyperbola as empirical models of the response of photosynthetic rate to photon flux density, with applications to three Veronica speciesAnn. Bot.380389394
Causton,D.R.Dale,M.P.1990The monomolecular and rectangular hyperbola as empirical models of the response of photosynthetic rate to photon flux density, with applications to three Veronica species380389394)| false
MidgleyS.J.E.NewM.MethnerN.ColeM.CullisJ.DrimieS.DzamaK.GuillotB.HarperJ.JackC.JohnstonP.KnowlesT.LouwD.MapiyeC.OosthuizenH.SmitJ.van den BroeckD.2016A status quo review of climate change and the agriculture sector of the Western Cape Province. Report submitted to the Western Cape Department of Agriculture and the Western Cape Department of Environmental Affairs & Development Planning. African Climate & Development Initiative University of Cape Town Cape Town South Africa
NieuwoudtG.JacobsG.2010Time of pruning affects yield, flowering time and flower quality of Protea ‘Pink Ice’Acta Hort.8696370
Nieuwoudt,G.Jacobs,G.2010Time of pruning affects yield, flowering time and flower quality of Protea ‘Pink Ice’8696370)| false