PRUNING AND HARVESTING EFFECTS ON LEAF YIELD OF CULTIVATED GREYIA RADLKOFERI TREES.
For product development, leaf production of G. radlkoferi must be available in quantities required and sustainable to the industry. Information on the agronomic management of G. radlkoferi trees especially those that would enhance leaf production is lacking. The purpose of this study was to determine the effect of pruning and harvesting frequencies on fresh and dry weights of G. radlkoferi leaves. Four pruning treatments (‘pruned but not tipped’, ‘tipped but not pruned’, ‘not pruned nor tipped’ as well as ‘pruned and tipped’) and three harvesting periods (monthly, bimonthly and once–off) were applied. Results revealed that harvesting bimonthly is the best harvesting practice which can be adopted for G. radlkoferi with fresh weight yields of 238 g per tree or 2.38 tons/hectare dry weight yield of 83 g per tree or 0.830 tons/hectare. Bimonthly harvests showed higher leaf fresh weights and therefore increased leaf production compared to trees that were harvested monthly and once-off. Furthermore, this study suggests that a suitable pruning practice for G. radlkoferi would be either to ‘prune only’ or ‘cut back’ the main stem rather than a combination of the two treatments.
There is a worldwide increase in interest in the production of herbal products derived from wild indigenous plants. This increase is incited by the large plant biodiversity available for exploitation as well as consumer needs for safer and cheaper alternative products. As a result scientific research in South Africa has increasingly progressed to exploring the possibility of developing and commercializing products obtained from indigenous plants (Van Wyk 2008). However, the attention given to the use of plant resources obtained from indigenous plants requires an increase in medicinal plant research that investigates production techniques of such plants having promising potential as cultivated crops. Greyia radlkoferi, an indigenous plant in South Africa has been identified for commercialization for the production of cosmeceutical products that can treat hyperpigmentation. Leaves are the outmost important part of this plant as its ethanolic extracts and its isolated compounds highly inhibited the enzyme tyrosinase and further reduced melanin in melanocyte studies.
Young G. radlkoferi trees have a tendency to grow straight and tall with leaves clustered towards the stem tips (Wentzel n.d.), possessing little to no branching (Figure 4.1). This type of development results in limited vegetative growth and thus limits availability of leaf material per plant. Sustainable production of active ingredients for commercialization requires a more reliable supply and volume of plant material. The herbal market requires standardized plant material not just qualitatively, but also in quantitative terms, meaning increased biomass production (Maggini et al. 2014). Success in maintaining abundance and adequate leaf material supply will require continuous focus on developing best production practices that will ensure sustainable levels of production. Therefore, the shoot development structure of G. radlkoferi requires that it should be in some way trimmed to promote branching, to increase yields, and to facilitate harvesting. Failure to cut the main trunk might result in trees with no branches and leaves will mainly be growing on the primary stems. This could be achieved through silvicultural practices such as pruning.
Pruning involves the selective removal of a part of a plant; either the shoot (branches, bud) or the root system (Preece & Read 2005). Plants are pruned for a number of reasons depending on the purpose for which they are grown or used. Pruning can be done to improve plant health, to correct structural defects, to achieve a desired shape, to save space, to improve appearance and function (Preece & Read 2005). According to these authors plants are often pruned to stimulate branching through disruption of apical dominance and thus resulting in a bushy plant. This can be achieved through application of shoot pruning which essentially is the artificial removing of leaf bearing branches of the plant. The operation is aimed at keeping the size and vegetative vigor of the plant in a condition most conducive for maximum vegetative growth and cropping (Tea Research Institute of Sri Lanka 1986).
In order to achieve the desired outcome in terms of growth and appearance, various basic types of pruning are used i.e. heading cuts and thinning cuts. In heading cuts the tip of the main branch is cut with the intension to encourage the growth of side stems and thus making denser, compact foliage trees. In thinning cuts, the branches are removed entirely, leaving no buds to grow. Their energy is diverted into remaining branches, which grow more vigorously.
According to our knowledge, information on how cultivated G. Radlkoferi trees could be managed is lacking. Traditional agricultural practices that could influence leaf yield production such as pruning and harvesting frequency on G. radlkoferi have never been documented. Understanding the fundamental response of this tree to pruning as well as harvesting periods may help to increase leaf biomass production and improve supply. Therefore, the objectives of the current study were to determine the effects of harvesting frequency and pruning on leaf fresh and dry matter yield of cultivated G. radlkoferi.
MATERIALS AND METHODS
Study Site and Climate
The study was conducted in Mothong African Heritage Trust garden site, in Mamelodi, Pretoria (Figure 4.2). Mamelodi township is at an elevation of 1307m above sea level (Climate-data.org n.d.). It experiences mild, generally warm temperate climates with the average annual temperature of 17.5⁰C. January is the hottest month of the year with average temperatures of 22.1⁰C while June is the coldest month with average temperatures of 10.8⁰C. The rainfall is significant in Mamelodi with precipitation even during the driest month. Precipitation is the lowest in July with an average of 6 mm and reaches its peak in January with an average of 134 mm. The rainfall averages 694mm per year.
Source of plant material
Greyia radlkoferi trees of around 1 m in height were purchased from Random harvest; a commercial supplier (nursery) based in Honeydew, Johannesburg and were kept in the shade-net at the Agricultural Research Council-Vegetable and Ornamental Plants (ARC-VOP) in Roodeplaat, Pretoria.
Planting and maintenance of trees
The plantation was established during the planting season in September 2013. The trees were transported from ARC-VOP to Mothong African Heritage Trust gardens where they were planted in an experimental area of 800m2 in pits of 50 cm deep with open diameters of 50 cm each. The pits were filled with composted bark and soil in 1:1 ratio. The trial was conducted with three replicates in a randomized complete block design with 12 treatments consisting of 4 trees each and a total of 48 trees in each block. Individual trees within a treatment were planted at 1 m apart and the treatments were spaced at 2 m apart from each other while the blocks or replicates were placed at 3 m spacing from each other. The trees were irrigated immediately after planting and further irrigation was done every two weeks. Spot weeding by hand-picking was only done directly around the trees and no pesticide or herbicides were applied. The trees were left for establishment until October 2013 before pruning was done. The main stem of the trees was cut back by 30 cm from the top and they were referred to as tipped treatments. The plantation consisted of 4 treatments consisting of trees that were ‘pruned but not tipped’, ‘tipped but not pruned’, ‘not pruned nor tipped’ and those that were ‘pruned and tipped’. Three harvesting periods which were selected for yield comparison were monthly, bimonthly and once-off. d bimonthly harvest was done on the 15th day of the month from January to May 2014 while once-off harvest was only done at the end of the harvesting period, that is, May 2014.
Determination of leaf yield and statistical analysis
Harvesting of leaf material began 3 months following the cutting back of the main stem. Harvesting was done using pruning shears and every second leaf was picked from each tree within the experimental plots at each harvesting period. This approach to harvesting was undertaken so that trees were not completely stripped of all their leaves. Harvested leaves were grouped according to treatments and immediately taken to the laboratory where they were weighed to determine fresh leaf yield using a weighing balance. After recording fresh leaf weight values, the leaves were allowed to dry for 2 weeks in a well-ventilated room away from the sun after which leaf dry weight values were determined using a weighing balance. Yield was expressed by the leaf biomass produced per plant.
The data obtained was subjected to analysis of variance. Tukey’s LSD multi comparison test at 5 level was used to test the significance between the treatment means using GenStat® (Payne, 2014) statistical package.
Pruning experiments (‘prune or no prune’ and ‘tip or no tip’) did not seem to have influenced fresh and dry weight yields of G. radlkoferi as there was no particular trend observed in the treatments (Figure 4.3). However, when data analysis excluded harvest frequencies, a clear difference in leaf yield was observed among treatments (Figure 4.4).
Plants that were ‘tipped but not pruned’ recorded higher fresh leaf weights of 180g per plant followed by those that were ‘not tipped but pruned’ with 173g per plant. The lowest fresh leaf weights of 151g per plant were observed in plants that were ‘tipped and pruned’. On the other hand, higher dry leaf weight yields of 68g per plant were recorded in plants that were neither tipped nor pruned. Similar to fresh weight yields, the second highest dry leaf yield was observed in plants that were ‘not tipped but pruned’ and the lowest leaf dry weights in plants that were ‘tipped and pruned’. The ‘no tip but pruned’ plants recorded 62g per plant dry leaf yield while ‘tipped and pruned’ treatment recorded 54g per plant dry leaf weight. However, the differences observed among pruning treatments were not significant.
LIST OF FIGURES
LIST OF TABLES
CHAPTER 1: GENERAL INTRODUCTION
1.2 AIM AND OBJECTIVES
1.3 STRUCTURE OF THE THESIS
CHAPTER 2: LITERATURE REVIEW
2.1 GREYIA RADLKOFERI
2.2 INTRODUCING MEDICINAL PLANTS INTO CULTIVATION
2.4 CULTIVATION OF MEDICINAL PLANTS: A POSSIBLE SOLUTION TO QUALITY PRODUCTS
2.5 BRIEF HISTORY INTO CULTIVATION OF SOUTH AFRICAN INDIGENOUS PLANTS FOR COMMERCIALIZATION
2.6 PLANT METABOLOMICS AS A QUALITY CONTROL TOOL FOR MEDICINAL PLANTS
CHAPTER 3 DEVELOPMENT OF VEGETATIVE AND SEED PROPAGATION PROTOCOLS FOR THE EFFICIENT CULTIVATION OF GREYIA RADLKOFERI
3.2 MATERIALS AND METHODS
CHAPTER 4 PRUNING AND HARVESTING EFFECTS ON LEAF YIELD OF CULTIVATED GREYIA RADLKOFERI TREES.
4.2 MATERIALS AND METHODS
CHAPTER 5 METABOLOMIC PROFILE AND ANTI-TYROSINASE ACTIVITY OF GREYIA RADLKOFERI LEAF EXTRACTS IN RESPONSE TO SEASONAL CHANGES
5.2 MATERIALS AND METHODS
CHAPTER 6 METABOLITE PROFILING AND ANTI-TYROSINASE ACTIVITY OF PHYTOCHEMICAL CONSTITUENTS OF GREYIA RADLKOFERI LEAF EXTRACTS SUBJECTED TO DIFFERENT DRYING METHODS .
6.2 MATERIALS AND METHODS
CHAPTER 7 GENERAL DISCUSSION, CONCLUSIONS AND RECOMMENDATIONS
CHAPTER 8 APPENDIX
GET THE COMPLETE PROJECT
PROPAGATION AND QUALITY ASSESSMENT FOR THE INTRODUCTION OF GREYIA RADLKOFERI INTO COMMERCIALIZATION