Date palms (Phoenix dactylifera L.) and papayas (carica papaya L.) are two
commercially important plantation crops. Their economic potential in South Africa
and worldwide is increasing. However, due to disease, pests and socio-economic
reasons, planting material is in short supply. Micropropagation provides a method for
rapidly propagating selected superior cultivars for commercial and environmental interests.
A satisfactory process for the regeneration of elite cultivars should result in
individuals phenotypically and genetically identical to the explant from which they
were derived. However, due to somaclonal variation generated during in vitro
culture, the true-to-typeness is questionable. For this reason a southern African
survey for off-types on date palms produced using somatic embryogenesis was
conducted. Plant growth variations such as leaf variegation, seedless fruit, broad
leaves, compact growth habit and parthenocarpic fruit were recorded and possible explanations for each phenomenon given.
Factors influencing the date palm initiation process such as decontaminating agents,
plant growth regulators, explant type and nurse cultures were investigated. A double
decontamination process with 2.6% and 1.3% sodium hypochlorite was most
effective at reducing contamination. Alternative plant growth regulators, TIBA and
NAA were ineffective as a substitute to 2,4-D for somatic embryogenesis. The size of
the explant and "nurse cultures" played an important role in explant growth and
initiating callogenesis. A "nurse culture" reduced the time in culture significantly. The
problem areas in the three commercial tissue culture techniques used for date palms were outlined.
In the second part of the study, factors influencing initiation, multiplication and
rooting of papaya were determined. Presoaking with antibiotic, Rifampicin, and
various fungicides had a positive effect on decontaminating papaya explants, while
Bronocide™ had little effect. Various methods and materials were used to optimize
papaya multiplication and rooting in vitro. The growth and multiplication of papaya
was optimal at 50 g l ¯¹ sucrose. Gelling agent, Gelrite, increased multiplication rates significantly but had a negative effect on overall growth causing plants to become
vitrified. The addition of activated charcoal reduced vitrification but also reduced
multiplication rate. Activated charcoal greatly improved overall growth of papaya and
reduced leaf senescence. No vitrification was observed in multiplying papaya cultures
where agar and Gelrite combinations were used, but multiplication rate was reduced
compared to cultures grown on Gelrite alone. callus removal from the bases of
papaya at subculturing reduced multiplication rate and influenced elongation, growth and leaf senescence.
Lower concentrations magar and Gelrite improved rooting percentages, but did not
provide good support. Damaged roots and lower rooting percentages were observed
on plantlets treated with IBA for four weeks compared to those exposed for only two
days. A one hour pulse with a higher concentration (5 mg l ¯¹)
of IBA greatly
improved rooting percentage and further eliminated a second subculture onto an
IBA-free medium after two days. Good, strong roots with root hairs were produced
on vermiculite medium containing equal volumes of DS salts and vitamins. Modified lids with cotton-wool plugs also reduced leaf abscission.
In vitro grafting using stericrepe proved impractical, while grafting in vitro unrooted
papaya plants onto ex vitro seedlings was more successful, using wedge and slant
grafts. Grafts sealed with pegs and Parafilm™ were less effective. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 2000.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ukzn/oai:http://researchspace.ukzn.ac.za:10413/10266 |
| Date | 19 December 2013 |
| Creators | McCubbin, Michelle Jacqueline. |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
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