Date of Award

2017

Degree Type

Thesis

Degree Name

Master Of Science (Biological Sciences)

School

School of Science

First Advisor

Dr Ian Bennett

Second Advisor

Dr Kristina Lemson

Third Advisor

Professor William Stock

Field of Research Code

0607

Abstract

The aim of this research was to examine whether the method of micropropagation and tissue source affects the early growth and development of Paulownia in the first six months following transfer from tissue culture and establishment in soil. This tree species was chosen as it is a fast growing, short-rotation timber tree and able to adapt successfully to new environments. It is easily established in vitro and has been micropropagated using a range of different techniques. Three methods of micropropagation were chosen: callus regeneration, somatic embryogenesis and the third method was inducing root suckers in vitro. The third method was developed during this study and has never been documented in other research. Newly established explants and stabilised explants that had been in culture for over 6 months were used to test the efficacy of these methods. Genotype was also another important aspect to examine, as clones of the same species have shown differing response to being micropropagated. Previous studies have not compared different methods of micropropagation and rarely past the initial stages of laboratory experiments to fully determine the influence they have on the explants development ex vitro.

Cultures were sourced from five clones (P1, P2, P3, P4, P5) of mature Paulownia elongata x fortunei stock plants. P1 was first established in vitro and had been micropropagated for five years to induce stabilisation. Newly established explants from clones P1, P2, P3, P4 and P5 had been established in culture for three months before being utilised for micropropagation analysis experiments. Examination of these methods in vitro showed that tissue sources from P1 were the easiest to manipulate and propagate in vitro. Callus regeneration was the most successful in its ability to produce explants and in large quantities. Initial callus experiments showed a significant response in shoot regeneration from stabilised cultures. Subsequent experiments showed a greater response from greenhouse material and newly established cultures, while stabilised cultures failed to produce shoots. Root sucker induction was also successful in stabilised and newly established clones of P1, however, it took a significant amount of time to induce root suckers and the quantity of material produced was limited. Somatic embryogenesis was unsuccessful in regenerating new shoots and the complexity of current methods made it difficult to develop a full protocol in this study.

Explants produced from callus regeneration and root sucker induction were transferred to the greenhouse, along with controls from stabilised and newly established cultures. All sources readily produced adventitious roots and there was a 100% survival rate upon transfer to the greenhouse. While initial comparisons showed slight variations in growth factors such as height and floral development, these were not statistically significant. Any slight variation became indistinguishable after two months of growth. Most importantly, after six months, plants from all sources readily produced flowers, indicating that the explants retained the mature phenology of the parent material while being maintained in culture. While callus regeneration and root sucker induction were successful in producing new explants in vitro, these methods had no effect on the overall growth and development under greenhouse conditions. All explants exhibited early flowering, which indicates that they maintained the mature characteristics of the parent material. This is not necessarily an undesirable outcome if the intention is to micropropagate mature tissue while still retaining their mature phenology. Ultimately, the method of micropropagation utilised is determined by what growth characteristic is desired and the purpose for which the plants are being propagated.

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