MORPHOLOGICAL AND CHEMICAL CHARACTERIZATION OF HYPERFLOWERING IN MICROPROPAGATED STRAWBERRY PLANTS (CV. GORELLA)

Micropropagated strawberry plants (cv Gorella) tend to produce an increased number of flowers after many in vitro multiplication cycles. This abnormal reproductive behaviour results in the development of numerous small and malformed fruits, with reduced commercial value. The aim of this work, performed in controlled environmental conditions, is to further characterize these plants because an early detection would allow to take them away from propagation fields. We first observed that, in clones having undergone much multiplication cycles, there were always some plants which did not produce many flowers. However, runners issued from these apparently normal plants exhibited the hyperflowering trait indicating that it is an attribute of the whole clone which will be reffered to as ‘hyperflowering’ in contrast to the so-called ‘normal’ plants regenerated after a limited number of subcultures on the multiplication medium. Thus, the hyperflowering character is not necessarily expressed in all plants of a clone in the course of one culture, but we found that it is rather stable since it persisted at least up to the 5th progeny of runner-plants obtained from tissue cultured plants exhibiting the disorder.

Comparison of hyperflowering and normal clones indicated that the rhythms of leaf and runner production and, consequently, their number, as well as the area and petioles length of mature leaves were identical in both plant types. Similarly, cytokinin levels within xylem sap and phloem exudate collected from leaves during the vegetative phase of the plants were unaffected by the number of subcultures. Measurements of cytokinin levels during the reproductive phase are in progress. In conclusion, discrimination between normal and hyperflowering plants is feasible only after the examination of the reproductive structures. The increased number of flowers per inflorescnece, resulting partly from an enhanced ramification of the cyme, is the only valid criterion to detect hyperflowering plants.