Euphorbia ×lomi Rauh, an interspecific hybrid of Euphorbia milii Des Moulins (or Crown-of-thorns) and E. lophogona Lamarck, both endemic to Madagascar (Graf, 1985), was recently introduced to the Mediterranean countries as a new floral crop according to the increased demand for new low-maintenance ornamental plants. Euphorbia ×lomi is a succulent shrub characterized by an erect, thick, fleshy, branched spiny stems up to 1 to 1.5 m long with long, lanceolate leaves and brightly colored bracts (Rauh, 1979). These hybrids can be year-round grown in dry, high temperature and high solar radiation areas as potted, bedding, or garden plants (Jankalski, 2000).
Crown-of-thorns and the hybrids are generally propagated by tip cuttings (Smoley, 2000), which is the most economic way to produce these plants, but information on the vegetative propagation is still limited. Mother plants are normally cultivated in soil, so disease problems such as root rot are frequent if drainage is not adequate and there is no possibility to monitor plant uptake with dispersion of water and nutrient excesses. V-cleft grafting could reduce the risk of rot associated with direct rooted cuttings but limit large-scale propagation (McLaughlin and Garofalo, 2002). Seeds should not be used to propagate these genotypes because of producing extremely variable seedlings. Recently, Euphorbia milii species was also introduced and cultured in vitro (Airò et al., 2007), also by using a bioreactor system (Dewir et al., 2005). However, tissue culture is very expensive and often requires a high amount of labor (Saranga and Cameron, 2007).
Therefore, in 2004, a research program was initiated at the Research Unit for Mediterranean Flower Species of Palermo, Italy, to develop a comprehensive vegetative propagation system. The objective of this study involved the following steps: 1) growing mother plants of two Euphorbia ×lomi Thai hybrids year-round in soilless media; 2) rooting cuttings harvested from 1-year-old mother plants in different media with or without auxin application; and 3) planting rooted cuttings to produce potted plants. Three experiments were conducted on two cultivars: 1) to evaluate the effect of soilless media on plant growth and cuttings production; 2) to determine the influence of substrates and auxin application on rooting; and 3) to study the effect of growing media on growth of rooted cuttings and pot plant production.
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