Effect of temperature, light intensity and growth regulators on propagation of Ansellia Africana from cuttings

Ansellia africana (Orchidaceae) is an important endangered medicinal plant species of South Africa which has been heavily exploited in recent years. Experiments were conducted in growth rooms at different temperatures (16, 26, 36°C) and in a nursery at different light intensities induced by shade cloth densities (200, 400, 600, 800 mol m-2 s-1 light) at the University of Zululand, South Africa. Mature A. africana plants were cut into two lengths, the top leafy shoot and the bottom part with roots (10 – 15 cm in length, 3 - 8 mm diameter). The top leafy or leafless cuttings were used in all the experiments. Bud formation and rooting competence of cuttings were compared by growing cuttings treated with solutions of varying naphthaleneacetic acid (NAA) and kinetin concentrations in river sand. Three types of cuttings were used: a) mature cuttings with both green leaves and an inflorescence, b) mature cuttings with yellow leaves (or leafless) and an inflorescence, and c) young cuttings with green leaves but no inflorescence. The lowest percentage death was recorded in cuttings with both green leaves and an inflorescence in the growth room (10%) and nursery (5%), respectively. The same type of cuttings gave significantly higher (P < 0.05) percentage bud formation in the incubator (18%) and nursery (37%), respectively. NAA was effective in root initiation when applied after bud break. The best results for root number, root length and root dry weight were achieved at NAA concentration of 1 or 2 mg l-1. Optimum conditions for bud formation were temperature of 36°C, light intensity of 200 - 400 mol m-2 s-1 and kinetin concentration of 1 or 2 mg l-1. A maximum value of 57% was recorded for bud formation in this study.Keywords: Ansellia Africana, cuttings, kinetin, naphthaleneacetic acid, propagationAfrican Journal of Biotechnology Vol. 9(34), pp. 5566-5574, 23 August, 201

Monocarpic senescence in Bidens pilosa L.

Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 2000.Senescence was examined in the economic weed Bidens pilosa, with the objectives to a) determine the effects of deflowering and defruiting on growth, chlorophyll content, photosynthesis and transpiration; b) to identify the stage of development of the head at which the flowers, seeds/fruit produce senescence signals; and c) to test for senescence activity in plant extracts made from the receptacles and leaves of Bidens pilosa. Total chlorophyll content in the controls, in association with the development of fruit, was lower in the final harvests when compared with earlier harvests in both pot and field-grown plant experiments. Deflowered Bidens pilosa plants had a higher chlorophyll concentration than both defruited and control plants in both pot and field-grown plants. Stem death of the control plants was higher than that of deflowered plants in both field and pot experiments. The present results suggest that deflowering is essential if the leaves are to be harvested commercially because it retards senescence and maintains growth. Fruit and flower heads were responsible for the reduction in leaf and stem growth after flowering in Bidens pilosa. Removing these organs slowed plant decline, suggesting that the flower head and especially the fruit are responsible for senescence. In contrast, the fruit were the main organs responsible for the decline in leaf chlorophyll concentration. In pot-grown plants in full sunlight, photosynthesis and transpiration were low in deflowered plants compared with the control and defruited plants 45 days after treatment, and it coincided with a low stomatal conductance. These results suggest that stomatal conductance played a role in lowering photosynthesis in deflowered plants. In contrast, the control plants had a higher stomatal conductance than deflowered plants 75 days after treatment, yet photosynthesis and transpiration rates were the same in both treatments. Thus stomatal conductance alone does not successfully explain differences in photosynthesis in these treatments. The dry weight of head with mature dry fruit was higher in plants grown at high light intensities than at medium or low light intensities. It coincided with a greater decline in chlorophyll concentration in the leaf nearest to the head and fruit. In contrast, photosynthesis was the same at all light intensities in the leaf nearest to the head and fruit. This suggests that high light accelerated the process of fruit maturation of the fruit which then influenced senescence in the leaf nearest to the flower head. Ethanolic and water extracts of senescent receptacles purified using paper chromatography, induced senescence of leaves in light but not in the dark. In ethanolic extracts, activity was detected in R[f]s 0.1, 0.2 and 0.3. In water extracts, activity was detected in R[f] 0.1. Senescent leaf extracts purified using column chromatography also induced senescence in light under greenhouse conditions. At high concentrations, activity was detected in fraction 10 eluted with ethyl acetate: methanol (55:45); fraction 11 eluted with ethyl acetate: methanol (50:50); fraction 12 eluted with methanol (100%) and in fraction 13 eluted with ethylacetate : isopropanol: water: acetic acid (52:28:28:4). Under growth room conditions, activity was detected in fractions 12, eluted with methanol (100%) and 13, eluted with ethyl acetate: isopropanol: water: acetic acid (52:28:28:4) in the presence of light. Fraction 1 (R[f] 0.00-0.10) from senescent receptacles, non-senescent and senescent leaves, obtained following thin layer chromatography of ethanolic extracts induced senescence under light. Fraction 1 was eluted with methanol. This fraction lacked activity when eluted with ethyl acetate. Fraction 4 (R[f] 0.25 - 0.35) from non-senescent leaf extracts, which co-chromatographed with 4-chloroindole acetic acid, gave activity in bean cuttings kept under continuous low light. Senescent leaf extracts showed no activity. Fraction 7 (R[f] 0.9 - 1.0) from non-senescent leaf extracts, also induced senescence in bean cuttings under light. The same Fraction from senescent leaf extracts lacked activity