South Africa is the second largest exporter of citrus fruit in the world. There has
recently emerged a strong demand for lemons in the world market due to their nutritional
value, culinary and non-culinary uses. During exportation, fruit are subjected to low
temperature (-0.5°C) for varying periods of time as an obligatory quarantine treatment.
However, lemons are sensitive to low temperatures and easily develop chilling injury during
this obligatory quarantine treatment. This has become a major limitation to the expansion of
South Africa’s lemon industry. Postharvest treatments with methyl jasmonate (MJ) and / or
salicylic acid (SA) have been successfully used in horticultural crops to reduce chilling injury.
A similar treatment was applied to ‘Eureka’ lemons. During the 2008 harvest season,
postharvest fruit were either dipped in 10 or 50 μM MJ or 2 or 2.5 mM SA solutions. A
control or no dip treatment was also applied. Three replicates of 15 fruits per treatment were
used. During the 2009 harvest season the following postharvest treatments were applied as
dips: 10 μM MJ, 2 mM SA, 10 μM MJ & 2 mM SA, 1 μM MJ & 0.2 mM SA, or 0.1 μM MJ
& 0.02 mM SA solutions. A control or no dip treatment was also applied. Three replicates of
15 fruits per treatment were used.
Subsequently fruit were stored at -0.5ºC for 0, 7, 14, 21, 28, 35, and 42 days, before
being transferred to room temperature (25°C) for 7 days where after chilling injury was rated.
Treatments with 10 μM MJ and / or 2 mM SA reduced chilling injury symptoms in lemons
harvested during the 2009 season. Although no visual symptoms of chilling injury were
observed during the 2008 harvest season, treatments with 10 μM MJ and / or 2 mM SA
reduced fruit mass loss, delayed the occurrence of stress symptoms such as lipid peroxidation
and suppressed accumulation of ROS in the rind. Treatments with 10 μM MJ and / or 2 mM
SA were more effective in inducing antioxidant capacity and other defence compounds such
as phenolics, ascorbic acid, carbohydrates and chilling injury responses such as accumulation
of proline in the rind. This may have increased the chilling tolerance of fruit during the cold
storage. Therefore, this study revealed that MJ and SA have the potential to reduce and delay
symptoms of chilling injury in lemons. This lead to the suggestion that both, MJ and SA dips
should be further tested as treatments to mitigate chilling injury in lemons. Future studies
should focus more on preventing the injury itself or preventing the primary event of chilling
injury. This could probably reduce the chances of secondary events to take place. / Thesis (M.Sc.Agric.)-University of KwaZulu-Natal, Pietermaritzburg, 2010.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ukzn/oai:http://researchspace.ukzn.ac.za:10413/7887 |
| Date | January 2010 |
| Creators | Siboza, Xolani Irvin. |
| Contributors | Bower, John P., Bertling, Isa. |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
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