Assessment of the internal quality of stored flower bulbs using magnetic resonance imaging

Abstract

Many flower bulbs have a life cycle of a year or more, flowering either in spring or in summer. Nevertheless, year-round production of cut flowers has become common practice in horticulture. To control flowering, which is necessary for the year-round production of flowers, bulbs are exposed to specific temperature regimes to affect their growth and development. When storage or planting conditions are not properly chosen, physiological disorders in bulb development may occur. Flower bud abortion and aberrant leaves are examples of such physiological disorders. Disorders in the bulbs are usually not visible externally. They become apparent after planting even though they are often induced during storage. The aim of this study was to gain a better insight in the processes underlying physiological disorders in flower bulbs, induced by improper storage conditions. Changes in the water status are expected to be often involved in the development of the induced aberrations. The water status of stored flower bulbs was therefore assessed using both magnetic resonance imaging (MRI, known from the medical applications) as well as classical water status measurements. It was assessed whether the obtained parameters might serve as ‘early indicators’ of an impaired flower bulb quality and thus as indicators for the internal quality of stored bulbs. This might lead to a tool to detect the presence of disorders at an early stage of development. Such an application could avoid further cost of storage and planting of impaired bulbs and potentially increases the chances to minimize the damage. Furthermore, it would enable optimization of storage conditions of new flower bulb genera more easily. In addition, flower quality can be better guaranteed. The possibilities of MRI to assess non-invasively the internal quality of flower bulbs appear extensive. T2-weighted imaging appeared to be a suitable application to visualize morphological changes like the growth of the shoot and the development of daughter bulbs. Aberrant developments of the floral parts in tulip bulbs after storage at high temperatures and the presence of aborted buds in Hippeastrum (amaryllis) bulbs could well be observed. Water concentration and T1 and T2 relaxation times were successfully used to assess the water status in the bulbs and to monitor water status related disorders like bud abortion in tulips after long-term cold and dry storage and freezing injury and water-soaking in lily bulbs. Thus, MRI has a great potential for the evaluation of the internal quality of flower bulbs and horticultural products in general. However, currently the technique is still too expensive for routine, high-throughput applications, but on-line applications will become more feasible in the future.