Browsing by Author "Joubert, Jeanine"

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    Influence of rind water content on mandarin citrus fruit quality
    (Stellenbosch : Stellenbosch University, 2016-03) Joubert, Jeanine; Cronje, P. J. R.; Hoffman, L. (Lynn) (Horticulturalist); Zacarias, L.; Stellenbosch University. Faculty of Agrisciences. Dept. of Horticulture.
    ENGLISH ABSTRACT: ‘Nules Clementine’ and ‘Nadorcott’ mandarin are commercially important Citrus cultivars in South Africa. Both cultivars are prone to develop rind breakdown and pitting which are considered non-chilling related postharvest physiological rind disorders. The progressive and erratic nature of these rind disorders result in high financial losses. The incidence of a rind disorder is thought to be associated firstly with an increased susceptibility, as influenced by pre-harvest aspects; and secondly with a trigger in the postharvest environment. A study was conducted over two seasons a study to determine the effect of late nitrogen (stage II and after summer flush) application, pre-harvest water stress and postharvest handling were conducted. The rind quality of ‘Nules Clementine’ and ‘Nadorcott’ mandarin fruit harvested from Citrusdal and Riebeeck Kasteel was evaluated. Soil applications of nitrogen at 20 kg·ha-1 and 40 kg·ha-1 were done on 21 January and 26 March 2014/2015, respectively. This was in addition to the standard 300 kg·ha-1 nitrogen provided by the producer. During 2015 a 1% urea foliar application was sprayed on 26 March. During the post-harvest period all fruit were dehydrated at 25 °C and 60 to 80% RH (0.7 to 1.1 kPa vapour pressure deficit) for two days, followed by rehydration at 100% RH for one day. Subsequently fruit were stored at either -0.6 °C or 4 °C for a 30-day period. There were no significant differences in fruit colour or size between the different nitrogen treatments. No increase in rind disorders and no negative impacts on internal fruit quality were noted. To determine the impact of pre-harvest water stress, the soil below the tree was covered with plastic sheets three weeks prior to harvest to exclude rainfall or irrigation. The effect of postharvest stress was established by dehydrating and rehydrating fruit at 0.7-1.1 kPa vapour pressure deficit for different periods after harvest. Wax was applied on day 5 and thereafter fruit was stored at 4 °C for 30 days. The results indicated that pre-harvest water stress did not have a detrimental effect on fruit susceptibility to disorders. By early wax application, however, a decrease in moisture loss was recorded, coinciding with lower incidences of rind disorders. The final part of the study was aimed at determining if postharvest handling lending to water loss, as induced by high vapour pressure, could increase disorders. From the results of the trials it can be concluded that exposing fruit to dehydration increased rind disorder susceptibility. Dehydration prior to wax application on day 5 also increased pitting and rind breakdown, whereas an early wax application, 2 to 3 days after harvest, reduced incidence. This study serves as a step to resolve the impact of factors predisposing the citrus fruit rind to progressive postharvest disorders.