Browsing by Author "Bezuidenhout, Eugenie-Lien"

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    High temperature effect on physiology, growth and flowering of Protea cv. Pink Ice.
    (Stellenbosch : Stellenbosch University, 2010-03) Bezuidenhout, Eugenie-Lien; Midgley, S. J. E.; Hoffman, L. (Lynn) (Horticulturalist); Stellenbosch University. Faculty of Agrisciences. Dept. of Horticulture.
    ENGLISH ABSTRACT: As production areas expand to new, warmer areas, little information is available on the effect of high temperatures on the growth, physiology and flowering of Protea. In addition, high temperature effects on crops are becoming increasingly important as global temperatures rise. In this study, the influence of high temperature on Protea ‘Pink’ Ice was investigated. The expectation was that optimal and supra-optimal temperature regimes could be identified with respect to parameters of importance to commercial protea production. Firstly, a greenhouse-based experiment with potted plants subjected to five levels of warming with a temperature gradient ranging from ambient to ambient+3.1°C, was established with infra-red lamps. A field verification experiment with two treatments, ambient and ambient+2.9°C, was established in a commercial orchard. Leaf net CO2 assimilation rate (Amax) and dark respiration rate (Rd) acclimated to the temperature gradient on a leaf area-basis. However, on a leaf mass-basis Amax and Rd decreased at higher temperatures. Stomatal conductance (gs) remained approximately constant over the temperature gradient, but increased at higher temperatures on a mild spring day and decreased on hot days. On a seasonal basis, maximum Amax and gs values were reached during spring, whilst maximum Rd rates were achieved during mid-summer. Topt tracked seasonal temperatures closely. At higher temperatures spring budbreak advanced by 1-2 weeks in both the greenhouse and field verification experiments. Flowering took place on the spring flush at ambient temperature, but this bearing habit shifted to summer flushes at the high temperature treatments. In the field verification experiment inflorescences on warmed plants were harvested earlier compared to those at ambient temperatures, as warming was possibly more optimal in the field than in the greenhouse (greenhouse “ambient” being warmer than field “ambient”). In the second experiment conducted on a commercial farm, shoots bearing inflorescences which initiated on the autumn flush (April-May) were compared with shoots bearing inflorescences on the spring flush (August-September). Inflorescences initiated on the autumn flush, three months prior to those on the spring flush, were harvested one month earlier with a significantly higher final dry mass. When comparing the gas exchange capacity of the two systems, seasonal climatic changes was found to have a stronger controlling influence than the phenological stage of the shoot. For the third part of the study, vegetative and reproductive growth, physiology, gas exchange and carbohydrate trends were observed for one year in a commercial Protea ‘Pink Ice’ orchard. A threshold concentration of starch in mature leaves of the terminal flush, together with an estimated minimum stem diameter of 7.6 mm of a four- or five-flush shoot was suggested as a partial requirement for inflorescence initiation in Protea ‘Pink Ice’. The results of this study show that Protea ‘Pink Ice’ is well able to photosynthesise, grow and reproduce at temperatures 1-2°C higher than ambient. However, shifts towards weaker reproductive growth in favour of stronger vegetative growth under strong warming could have negative implications for commercial producers.