From the huge reservoir of potential new floricultural crops in the Cape Floral Region (CFR) of South Africa, its outstanding variety of geophytes, namely 16% of its total species (Van Wyk and Smith, 2001), forms a largely untouched plant group in horticulture. The Iridaceae, containing 27 genera and ≈700 species in the CFR (Manning et al., 2002)—among them the well-known genera Freesia and Gladiolus—are characterized by their diversity of flower colors (Niederwieser et al., 2002).
Freesia laxa (Thunberg) Goldblatt & Manning, Sparaxis ×tricolor, Tritonia deusta Ker Gawler, and Tritonia securigera Ker Gawler have a flower color range with mainly shades of orange, red, and pink. They were chosen for their potentially high ornamental value, but also for their commercial availability in sufficient numbers to conduct statistically adequate trials.
All four species/hybrids are winter-growing and spring-flowering in South Africa and 15 to 40 cm tall. They form corms that enable survival of the hot and dry summers during which they become dormant. The temperature drop and the onset of winter rains evoke their sprouting and vegetative growth, during which an inflorescence is formed by the shoot apical meristem (Manning et al., 2002). Hence, unlike species forming true bulbs, inflorescence formation is only initiated within the apical meristem once vegetative growth has started and not during dormancy (De Hertogh and Le Nard, 1993).
Exporting dormant corms from South Africa and keeping them in their South African growth rhythm to force them in the fall and winter months of the Northern Hemisphere offers two interesting prospects. First, the European and North American pot plant assortment during that season is limited and needs diversification. Second, originating from a Mediterranean climate, the chosen species and hybrids have low temperature requirements for forcing and their production is therefore energy cost-saving during winter months compared with crops originating in the tropics.
To be able to force the chosen species/hybrids as pot plants, detailed investigations on growth rhythms and growth requirements need to be undertaken to provide information on their physiology, especially the mechanisms of flower induction, and on how their cultivation can be regulated and optimized to eventually determine their potential as new pot plants (Dole, 2003; Rees, 1992). The findings of Ascough et al. (2006) for several species of Watsonia, also members of the Iridaceae and originating in South Africa, showed facultative or obligate vernalization requirements for successful flowering as well as an improved flowering percentage under long day conditions. Because of the limited information regarding the physiology and cultivation of the investigated species/hybrids, the chosen trial treatments were based on and compared with findings for the taxonomically related Freesia hybrids well known in cultivation. Results presented focus on the mechanisms of flower induction in the investigated species/hybrids and the influence of temperature and light intensity during that process.
Ascough, G.D., Mtshali, N.P., Thompson, D.I., Anderson, N.O., Erwin, J.E. & van Staden, J. 2006 Watsonia 599 605 Teixera da Silva J.A. Floriculture, ornamental and plant biotechnology Vol. IV Global Science Books Isleworth, UK
Berghoef, J. & Zevenbergen, A.P. 1990 The effect of precooling environmental factors and growth-regulating substances on plant height of Freesia as a pot plant Acta Hort. 266 251 257
Halevy, A.H. 1975 Light energy flux and distribution of assimilates as factors controlling the flowering of flower crops Proc. 19th International Horticultural Congress (1974) 4 125 134
Wulster, G.J., Cartwright, S. & Gianfagna, T.J. 1989 The effects of greenhouse temperature and ancymidol concentration on height and flowering time of Freesia hybrida grown as container plant Acta Hort. 252 97 103