Search Results
Orchid cut flower industry has contributed substantially to the economy of Singapore, Thailand, Malaysia and other Asean countries. Singapore exports US$13 million dollar worth of orchid cut flower in 1990 and Thailand's export was at least 3 to 4 times higher. Germany and Japan are the major markets for tropical orchid cut flowers. Economically important orchid genera are Aranda, Dendrobium, Mokara, Oncidium and Vanda. This paper will review the agronomic practices in orchid cultivation, the current status and development of orchid industry and the research and development made towards the improvement of the orchid industry in Asean countries.
The growth and photosynthesis of Oncidium Goldiana, a popular tropical orchid for cut flower production, have been studied. Four main developmental stages of Oncidium Goldiana vert identified: bud stage, plantlet stage, unsheathing stage and pseudobulb stage. Pseudobulb formation occured during the unsheathing stage which was closely followed by the formation of inflorescence. The pseudobulb of Oncidium Goldiana is of heterblastic type and lacks stomata.
Oncidium Goldiana is a C3 shade plant based on Cb1 a/b ratio, CO2 compensation point, postillumination CO2 outburst and light saturation. The rate of photosynthesis increased with the development of the inflorescence and auxillary bud. Pseudobulbs contain chlorophyll but show no sign of gas exchange in light and dark. However it fixes CO2 in light with the partial removal of cuticle.
The kinetics and efficiency of uptake of minerals (ammonium, nitrate, phosphate, potassium, calcium and magnesium) by roots of three tropical orchid genera (Aranda, Dendrobium and Oncidium) were studied and compared. Mericloned plantlets of these three orchids were cultured in solid Vacin and Went medium. The pattern of mineral uptake by orchids of these three orchid genera was similar. There was a preferential uptake of ammonia over nitrate. Rapid nitrate uptake by roots began only after 3 weeks in culture. Initial uptake of potassium, calcium and magnesium were rapid but the residual levels of these minerals either remained constant (Mg, PO4) or increased (K, Ca) after the 4th week. The % of uptake for ammonium nitrate, phosphate, potassium, calcium and magnesium over 9 weeks of culture was 60-76%, 24-28%, 12.8-27%, 17–30%, 17-26% respectively for the three orchid genera. A good correlation between growth of plantlets and uptrake was observed.
The uptake of nitrate and ammonium by a terrestial (Bromheadia finlaysonia) and an epiphytic (Dendrobium hybrid) orchid in solution culture has been studied. The rates of nitrate and ammonium were relatively linear, with higher rate of uptake for ammonium. The rates of nitrate uptake in terrestial and epiphytic orchids were 0.4 and 0.9 μmole gm fw-1 hr-1 respectively and they were considerably lower than those of most major crops. SEM studies show that the velamen of Bromheadia was 2 cells thick whereas that of Dendrobium was 8-10 cells thick. It is unlikely that the velamen is the major factor in restricting influx of nitrate or ammonium. Nitrate reductase (NR) and glutamine synthetase (GS) were present in roots and leaves of both orchids. NR was high in roots but low in leaves. The reverse was for GS. The activities of NR and GS was low but high enough to account for the rate of nitrate or ammonium uptake. It appears that the movement of ions across the transfer junction at the exodermis plays a major regulatory role in ion uptake by orchid root.
A circadian rhythm in CO2 production was observed in three cultivars of Anthurium andraeanum Andre (`Jaya', `Fla-range', `Leonette') flowers. The rhythmicity was not affected by light, darkness, and detachment. However, the amplitude was dampened in darkness and after detachment. Spadix respiration accounted for 90% of the total flower respiration. Rhythmicity in CO2 production continued after spathe removal. Less pronounced rhythmicity was observed following spadix removal.
Abstract
Callus tissues of orchid Aranda Tay Swee Eng (Archnis Lily Chong × Vanda Piha Moon) were cultured in Vacin and Went's medium that contained between 0% and 2% fructose. The chlorophyll content of callus tissues measured after 31 days of incubation ranged from 59 to 133 µg·g–1 tissue and was inversely proportional to the C/N ratio of the initial culture medium. The number of protocorm developed on callus tissue was instead inversely proportional to the residual C/N ratio of the 31-day-old culture medium and ranged from 13 to 74. The interrelationship of the C/N ratio of the medium, chlorophyll content, and protocorm formation in Aranda callus tissues is discussed.