In vitro propagation of four Watsonia species

The genus Watsonia has a number of species with potential to be developed as new ornamental crop plants, but to date there are no reports on in vitro propagation of any member of this genus. Seeds from four Watsonia species, Watsonia gladioloides, Watsonia lepida, Watsonia laccata, and Watsonia vanderspuyiae were decontaminated and germinated on one-tenth strength MS media without hormones or sucrose. Shoots were induced from seedling hypocotyl segments when both an auxin [α-naphthaleneacetic acid (NAA)] and cytokinin [N⁶-benzylaminopurine (BA)] were present in the medium, while root and leaf explants failed to produce shoots. Multiplication of axillary shoots was greatest when only BA (0.5 mg l^-1) was added to the medium. Shoot explants propagated in a 'liquid-shake' culture exhibited greater growth rates than those on agar-solidified medium, but shoot production varied between species. Meristemoids were induced in all species, but no significant trend was found between growth index (GI) and meristemoid formation, suggesting that reduction in GI may not necessarily be a prerequisite for producing meristemoids. Corm formation was inconsistent and storage organs could only be induced in one of the four species, W. vanderspuyiae. This occurred best at 25°C with 3% sucrose and an agar level of 15%. Indole-3-acetic acid (IAA) and NAA at 1 mg l^-1 significantly increased mean number of roots per shoot explant on all four species, while indole-3-butyric acid (IBA) was more effective when applied at 0.1 mg l^-1. Plantlet survival ex vitro was negatively affected when NAA and 2,4-dichlorophenoxyacetic acid (2,4-D) were used to root shoot explants for all species. In W. laccata, all auxin treatments [IAA, IBA, NAA, phenylacetic acid (PAA), and 2,4-D] at a concentration of 1 mg l^-1 significantly reduced ex vitro survival of plantlets. Successful micropropagation of Watsonia is an important step in the further development of this genus as a horticultural crop.