Evaluating the germination potential of Pterocarpus angolensis and Strychnos cocculoides with tissue culture techniques

Thesis (MScFor)--Stellenbosch University, 2018.

ENGLISH ABSTRACT: The importance of indigenous tree species to local livelihoods can never be overstated. The species provide wood materials and non-woody resources, such as fruits and traditional medicines. Pterocarpus angolensis and Strychnos cocculoides are two important tree species found in a Namibian and adjacent countries’ woodlands. Local people highly depend on the trees for wood (P. angolensis) and fruits (S. cocculoides). Due to over-exploitation of P. angolensis and S. cocculoides, the trees are on the verge of getting extinct. For instances; P. angolensis is mostly used for its ever-demanded wood products, thus become vulnerable to immense cutting down. Several attempts to propagate these two-tree species using traditional/conventional method i.e. nursery, are reported to have produced futile results. As such, there is need to explore other alternative germination methods for these trees. The current study evaluated germination potential of P. angolensis and S. cocculoides using the tissue culture germination method. The study objectives were: To compare the effect of tissue culture and nursery techniques on the germination success of P. angolensis and S. cocculoides; to develop a robust tissue culture protocol to optimise in vitro germination of P. angolensis and S. cocculoides and to evaluate the effect of different tissue culture aspects on the germination of these species. This was achieved by planting 60 seeds (30 each) of P. angolensis and S. cocculoides seed in the nursery and the performance of several in vitro tissue culture experiments under a controlled laboratory conditions. The influence of several aspects of tissue culture namely, the explant types (buds, seeds without seed coat, embryos, apical and axillary shoots); Agar media (Agar without hormone and Agar with hormones); pH (5.5 and 5.8); and surface sterilisation of explants on the germination success of P. angolensis and S. cocculoides were also investigated to identify optimal tissue culture protocol. Whereby, petri dishes with three treatments (sterilised, agar and explants) were placed randomly inside an SMC 1400 lowtemperature incubator at 25°C with a 12-hour day and night photoperiod. Every third day, growth parameters such as germinated seedlings, plantlets length (roots and shoots), contamination and germination date were recorded up to 10 weeks after inoculation. The results show that germination of P. angolensis and S. cocculoides can be promoted using tissue cultures as opposed to the nursery methods. For instance, up to seven plantlets (P. angolensis and S. cocculoides) can be produced in tissue culture methods within seven days. This however, cannot be reported from the nursery counterpart which only produces two and seven seedlings from P. angolensis and S. cocculoides after 30 days respectively. From the tissue culture aspects, the results have shown that only seed (explants) without the seed coat and embryos yielded sufficient results for both species. For instance, there was no significant difference (P = 0.12) for germination percentage between the two types of explants (seeds without seed coat and embryo) for P. angolensis as contrasting to S. cocculoides explants (dry and fresh embryo) were a significantly different (P = 0.0010) was obtained. There was a significant difference in germination of explants between agar medium without hormones (A) and with hormones (A+H) in both P. angolensis (P = 0.0049) and S. cocculoides (P = 0.0001), with A producing high germination in all the species. Pterocarpus angolensis seed explants yielded high germination percentage at pH 5.8 while there was no significant difference in germination success between pH of 5.5 and 5.8 in S. cocculoides explants (fresh and dry embryos). The study will be the first to demonstrate and develop a tissue culture protocol for P. angolensis and S. cocculoides of Namibia. It´s finding may contribute to the replanting of the two-tree species and eventually increase the tree stands reported depleting from the ecosystem. Therefore, the study recommends the use of tissue culture over the nursery germination method for P. angolensis and S. cocculoides. While suggesting for further investigation on aspects such as optimal temperature and light intensity required in tissue culture. Lastly, Improved germination of indigenous species has potential to contribute significantly to the conservation of these tree species which are under threat of extinction due to over-exploitation.

AFRIKAANSE OPSOMMING: Die belang wat inheemse plant spesies het vir gemeenskappe kan nie oorbeklemtoon word nie. Hierdie spesies voorsien hout en nie-hout produkte soos vuurmaakhout, vrugte en tradisionele medisyne. Pterocarpus angolensis en Strychnos cocculoides is twee belangrike boom spesies wat in Namibië en aangrensende lande gevind word. Gemeenskappe is afhanklik van hierdie bome vir hout (P. angolensis) en vrugte (S. cocculoides). Weens oorontginning van beide P. angolensis and S. cocculoides, is hierdie bome op die brink van uitsterwing, veral P. Angolensis as gevolg van onbeheerde afkapping vir die toename in aanvraag van houtprodukte. Verskeie vergeefse pogings is al aangewend om hierdie twee boomspesie met behulp van traditionele kwekery metodes te vermeerder. Daar is dus ‘n groot behoefte om ander metodes van vermeerdering te ondersoek wat moontlik die ontkieming van P. angolensis and S. cocculoides kan verbeter, asook herplanting van woude. Daarom het hierdie studie die moontlikheid ondersoek om die ontkiemings persentasie van P. angolensis en S. cocculoides nie net met weefselkultuur te verbeter nie, maar ook met tradisionele kwekery metodes vergelyk. Resultate het aangedui dat die ontkieming van P. angolensis en S. cocculoides verbeter kan word met weefselkultuur tegnieke in vergeleke met kwekery metodes. Byvoorbeeld, tot sewe plantjies (P. angolensis and S. cocculoides) kan binne sewed dae met weefselkultuur geproduseer word in vergelyking met twee (P. angolensis) en sewe saailinge (S. cocculoides) na 30 dae met die kwekery metode. Hierdie studie het verskeie aspekte ondersoek om die ontkieming te verbeter, byvoorbeeld: eksplante, agar media, pH en patogene beheer. Resultate het aangedui dat slegs saad (as eksplant), sonder die saadhuid, en embrios betekenisvol meer ontkieming tot gevolg gehad het vir beide spesies. Byvoorbeeld, daar was geen betekenisvolle verskil tussen die twee tipes eksplante (saad met saadhuid en embrio) vir P. angolensis in vergeleke met S. cocculoides eksplante (droog en vars embrios) wat wel betekenisvol verskil het. Verskillende agar media (A en A+H) het ook gelei tot betekenisvolle verskille in die ontkieming van eksplante in beide spesies, met agar medium A wat ‘n hoër ontkieming persentasie per spesies gehad het. Pterocarpus angolensis saad eksplante het ‘n hoër ontkiemings persentasie by beide pH’s gehad. Maar, geen betekenisvolle verskil was verkry by ‘n pH van 5.5 en 5.8 vir S. cocculoides vars en droë embrios. Die vlak van kontaminasie was aansienlik verminder met die gebruik van NaCIO en opwasmiddel. In die algemeen, het resultate aangedui dat die weefselkultuur tegnieke die ontkieming van P. angolensis en S. cocculoides bevorder het, alhoewel aspekte soos optimale temperatuur, ligintensiteit nie ondersoek was nie. Hierdie aspekte moet egter in verdure studies ondersoek word. Ten slotte bevel hierdie studie aan dat daar ‘n behoefte is om ander inheemse spesies van Namibië te ondersoek en vas te stel of weefselkultuur op ‘n kommersiële skaal ingespankan word om die bewaring van hierdie spesies te bewerkstellig.

Masters