Growth and nutrition of Bruniaceae

[摘要] ENGLISH SUMMARY: Bruniaceae are increasingly being harvested commercially as cut flowers in South Africa for theEuropean cut flower markets. The need to cultivate certain species requires research to developeconomically viable cultivation methods and the selection of productive cultivars. This study dealswith horticultural and nutritional aspects of Bruniaceae, particularly Brunia albiflora (Pillans). Flowerinitiation and development of two species of Bruniaceae, Brunia albit/ora and Berzelia galpinii(Pillans) were investigated to determine when floral initiation occurred and to qualify progression offlower differentiation and development. It was observeq that development was six months apartwith Brunia albiflora initiating florets in October and Berzelia galpinii in May. Carbohydrate studieswere also carried out over a one year period, to determine seasonal changes of carbohydrateswhich would enable manipulation of cultural practices for increased yield. It was observed that newshoots had lower carbohydrate contents compared to flowering shoots. Side shoots of floweringshoots had higher starch and sugar content than main shoots after winter. The starch contentdecreased in side shoots following flower initiation in October, with the total sugar content of sideshoots showing the same pattern. It appeared that side shoots were net carbohydrate sources andexported assimilates to the developing inflorescence. The increase in carbohydrates of theinflorescence was higher than the loss in the side shoots and it seems that Brunia albiflora is mainlyreliant on current photosynthates for their growth.Soil and plant nutrient requirements of Brunia albiflora were investigated by selecting threelocalities in the Western Cape. Variation in terms of growth performance was large at each locality,presumably because of different soil types. Calcium in topsoils showed a significant negativecorrelation with plant performance, whereas higher exchangeable Na correlated with good plantperformance. Soils with high clay-content seem to be unsuitable for Brunia albiflora possibly due topoor aeration. Positive correlations with plant performance were also found for organic carbon, N,P and K, as well as exchangeable acidity and exchange capacity of the B horizon. Leaf and stemswere sampled at two dates to determine which component and time of sampling best reflected thenutrient status of the plant. Leaves were decided on as index tissues and sampling at anthesis(February) was appropriate. Leaf nutrient concentrations of Brunia albiflora were found to be low inN, P, K, Mg and Zn compared to other woody plant, whereas Ca, Cu and Mn appeared to havesimilar concentrations. The removal of macro-elements by cropping a plantation in full productionwas calculated as 38 kg N, 1.5 kg P, 35 kg K, 40 kg Ca and 5 kg Mg per hectare based on 25flowering stems per plant and 5 000 plants per hectare. These results can be used as a basis forfertiliser recommendations, pending the results of fertiliser trials. As the demand for these flowersincreases, there will be a greater demand for better quality. Improved production and flower qualityshould compensate for the extra costs of fertilisers.

[发布机构] Stellenbosch University