Carbohydrate partitioning and developmental physiology of Nerine bowdenii Will. Watson

Nerine spp. are a bulbous genus that is grown commercially in Australia on a limited scale. However, environmental conditions in the south-eastern region of the continent, including the island state of Tasmania, are ideal for production of cut-flowers. However, large scale cultivation of the genus has been precluded to some extent not only by unpredictable flowering under field conditions but also unsatisfactory inflorescence scape lengths for export markets. The objective of these studies was to begin to elucidate some of the factors involved in the control of flowering in Nerine bowdenii Will. Watson, and to investigate the process of scape elongation. The Nerine bulb consists of a number of recently initiated and previously emerged annual units. The concentric leaf bases are retained and serve as a source of carbohydrates for the development of the units. Dry weight analysis of the bulb components over time showed that all outer units were utilised for current season leaf and inflorescence growth. Photoassimilates and carbon from senescing leaves appeared to predominantly accumulate in these organs but were not critical to flowering under glasshouse conditions. The major carbohydrates detected in bulbs were starch, sucrose, fructose, glucose, and fructans. Sucrose was found to be the major form of carbon transport in the vascular tissue of mature leaves. Fructan was present in very high concentrations in all organs, and the presence of this polymer has not been previously reported in this genus. To investigate the role of the reserve carbohydrate supply in inflorescence abortion C-sucrose was applied to the outer scales of bulbs. Bulbs containing an aborting inflorescence showed increased sink activity by leaf/floral primordia. C data indicated that outer-scale derived sucrose rapidly became dispersed throughout the bulb, with accumulation of radio-actively soluble sugars in the roots and basal plate. Expansion of leaves and scape was shown to be initially dependant on cell divisions within a plate meristem located at the base of the organs. This was followed by expansion of the cells. Control of flower height was able to be manipulated by the imposition of shading on plants, which resulted in longer scape lengths as a consequence of increased cell divisions. The data also suggested a potential role of shading in the regulation of leaf number.