Optimization of bulblet production by leaf cuttings in Lachenalia

Abstract

Lachenalia is a genus endemic to South Africa and Namibia. It is propagated vegetatively by daughter bulbs, bulbi Is, tissue culture and leaf cuttings. In Europe, the demand for Lachenalia bulbs is estimated at 20 million per annum and thus the need for a rapid and cheap way of propagation. Of all the vegetative methods for propagating Lachenalia, the easiest and cheapest method is by leaf cuttings. Cook first reported this method of propagation in 1931. Nothing was done at that time, as the natural way of propagation sufficed for the demand. No efforts were, however, made to optimize the technique of leaf cuttings. In this study various aspects aimed at optimizing the production of bulblets by leaf cuttings of Lachenalia were studied. These included: stage of the donor (mother) plant, leaf section position, medium, disinfectants, and starch deposition in leaves and bulbs during the growing season. Other aspects studied included the ontogenetic origin of bulblets and roots on leaf cutting. The optimal physiological stage to take leaf cuttings was found to be when the inflorescence was visible between the sheath of the leaves and the worst stage was at full flowering. As the donor plant matures, there was a reduction in the number, size and mass of bulblets produced by leaf cuttings. The proximal sections performed better than their distal counterparts in all variables evaluated. Considering cost and time, applying disinfectants when planting the leaf cuttings seem not to be necessary. Decomposed bark was the best medium for Lachenalia leaf cuttings. Bulblets were mostly formed on the adaxial leaf surface on Lachenalia leaf cuttings and developed as a result of the division of the epidermal cells. Both the leaf cutting and the bulblet formed roots. On the leaf cuttings, roots originated from the parenchyma cells associated with the vascular system while on the bulblets they developed from the base of the meristematic mass of cells, which formed the bulblets, and were attached to the bulblet. In a TEM study of the leaf, no starch was observed in leaf sections. Starch was, however, observed in all sections from bulb parts. More starch grains were observed on the inflorescence stalk than in other bulb parts.