A study of greenhouse production techniques for evergreen disas
Thesis (MScAgric (Agronomy)--University of Stellenbosch, 2005.
The seven evergreen Disa species are indigenous to South Africa. These orchids grow on mountain ranges subject to winter rainfall and are found on stream banks, around waterfalls and in other damp areas. Although the Disa genus accommodates more than 130 species, by far the most commonly grown is Disa uniflora and hybrids stemming from this species. Disas have great potential as cut flowers and pot plants, but production techniques need to be further investigated since cultivation methods vary greatly between hobbyists. This study evaluated the effect of N-source, shading, root medium temperature, electrical conductivity (EC), irrigation method, foliar feeding at different plant growth stages and substrate on the growth of evergreen Disa hybrids in a controlled environment. Results showed that Disa plants can be classified as being ammonium tolerant. Disa unidiorosa performed best with 40% of the applied N in the NH4 form, while D.kewensis was more tolerant towards a higher level of NH4 and grew best at 60% NH4. Shading levels (56% and 69%) were compared and did not differ regarding the growth of plants. A cooled root medium was found to have a negative effect on root growth and a positive effect on leaf length. High EC levels produced heavier mother plants with a bigger root:shoot ratio and a bigger stem diameter. Biomass accumulation was the best in plants receiving ‘Drip’ irrigation, compared to ‘Ebb-and-Flood’ irrigation treatments. Plants in the vegetative reproducing stage were more susceptible to leaf abscission and new leaves formed at a low rate compared to small- and potential flowering plants. Where foliar feeding is concerned plants seemed to benefit more by the presence of NH4NO3 than urea. There were no significant differences in root development between substrates in the ‘hardening-off’ phase. ‘Hydroton’ (clay pebbles) was not suitable as substrate for the cultivation of Disa plants. The growth and flowering properties of plants were optimal with sphagnum moss and peat but were negatively affected when the pH of acid peat:sand mixtures were increased. More research is needed before Disas can be cultivated on a commercial scale, while the effect of the treatments on flowering properties has to be investigated.