A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of requirements for the degree of Master of Science. School of Animal, Plant and Environmental Sciences, University of the Witwatersrand, Johannesburg, South Africa. 3 June 2016. / Currently Eucalyptus plantations in the warm and cool temperate parts of South Africa are being
exposed to damaging temperature extremes and unseasonal frost events that, in particular, have
detrimental effects on juvenile plantations. To accommodate these conditions, E. grandis and
E. nitens have been selected for hybridization in efforts to identify and select clones suitable for
successful plantation establishment in affected areas. Biochemical and physiological responses of
plants to cold shock and simulated frost conditions offers a means for this type of selection. In this
study, the responses of E. grandis, E. nitens and 8 characterized E. grandis x E. nitens (GN) hybrid
clones to cold shock and simulated frost conditions were evaluated. The responses elicited were used
as an indication of the eucalypts low temperature and frost tolerance potential, based on levels of:
reactive oxygen species (ROS), phenolic acids (PA), starch, total soluble sugars (TSS), chlorophyll
fluorescence (CF) and relative electrolyte conductance (REC). Plants were subjected to standard
growth conditions of 25°C day/14°C night temperature and a 12h photoperiod for 7 days and
subsequently cold shocked at 5°C for 24h. Frost conditions were simulated by freezing excised leaf
discs from 2°C to -6°C at a rate of -4°C/h with a one hour hold at -6°C. The results showed an upregulation
of ROS in E. grandis, GN 1, GN 4 and GN 6, 30-90 minutes into the cold shock; and levels
were highest in E. nitens, GN 3 and GN 7 only 24h after the cold shock exposure. PA levels changed
marginally under cold shock conditions, with levels of GN 4 increasing the most by 58%. Starch
levels of GN 6 were the most affected by the cold shock, where a 33% increase in levels was
recorded. TSS levels of E. grandis and GN 6 increased by 201% and 409% respectively, while TSS
levels of GN 2 and GN 3 decreased by 41% and 76% respectively. CF levels of E. nitens and two
GNs were most affected by the cold shock, however, all the eucalypts tested, except GN 2, GN 3 and
GN 6, displayed a high recovery potential to the cold shock. REC levels fluctuated slightly between
unfrozen and frozen samples under standard and cold shock conditions and it was found that
E. grandis, GN 1 and GN 3 were the least frost tolerant; and GN 4, GN 7 and GN 8 were the most
frost tolerant according to REC levels under cold shock and simulated frost conditions. The results
indicate that of all the tested eucalypts, only three GNs were not tolerant to the cold shock and
E. grandis and two GNs were not tolerant to the simulated frost. Therefore, it was concluded that all
of the eucalypts investigated, apart from E. grandis, GN 1 and GN 3, may be suitable for plantation
establishment in areas prone to frost in South Africa. / GR2016
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/21248 |
| Date | January 2016 |
| Creators | Bahadur, Yakira |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
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