Browsing by Author "Mzize, Nolubabalo"

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    Quantifying the role of vapour pressure deficit in the development of lenticel breakdown in ‘Braeburn’ apple
    (Stellenbosch : Stellenbosch University, 2021-12) Mzize, Nolubabalo; Lotze, Elmi; Crouch, E. M.; Stellenbosch University. Faculty of Agrisciences. Dept. of Horticulture.
    ENGLISH ABSTRACT: Lenticel breakdown (LB) is a physiological disorder that can develop in different apple cultivars including Braeburn during cold storage and shipping. Several researchers mentioned various pre and post-harvest factors influencing LB, however, the effect of vapour pressure deficit (VPD) has not been discussed. In trial 1, the anatomical and morphological development of lenticels on ‘Braeburn’ fruit was studied from 40 to 166 DAFB, and fruit harvested post-optimum to increase risk of LB incidence. Fruit from the East side had smaller epidermal and hypodermal cell sizes, a higher number of lenticels per fruit, open lenticel and developed more LB. Lenticel developmental stage was not influenced by canopy side and transitioning of stomata into lenticel was only observed from 82DAFB onwards, a bit later compared to other apple cultivars. In trial 2, LB incidence was related to: delayed cooling (24 h, 0 h) and the use of wet blankets in the orchard (+/- Blanket), in ‘Braeburn’ after harvest. The study showed that 24 h– Blanket increased cumulative VPD significantly and the 0 h (immediate cooling) and wet blanket reduced cumulative VPD significantly over time. Delayed cooling and wet blanket (24 h + Blanket) contributed to LB incidence, with the 24 h+Blanket treatment developing 7%, 0 h-Blanket 5% and other treatments, 3% (2019/2020). No significant effects were found in 2018/2019. Delayed cooling advances maturity whereas use of wet blanket and immediate cooling-maintained fruit quality. In trial 3, LB incidence was related to: two precooling types (Forced air (FAC) and passive cooling (PC)) and different times and temperatures (-1 °C and 3 °C) with reference to cooling speed before storage. Passive cooling is a non-mechanical cooling system that cools fruit inside the cool room, while forced air cooling is a technique that exposes fruit to forced cooled air at a higher pressure, either in situ, though a tunnel or in the cool room. The study revealed no significant effect between treatments in cooling speed, time and temperature (2018/2019), yet, the -1 °C temperature had a faster cooling speed and shorter cooling time (2019/2020). The PC -1 °C showed increase in cumulative VPD, whilst FAC -1 °C lowered cumulative VPD significantly. LB incidence, fruit weight loss and firmness were not significantly affected by the treatments. In trial 4, LB incidence was related to: the use of different fan speeds, liners and packaging on re-cooling rate during 6 weeks of simulated shipping. Fan speeds 2 and 3 had a rapid re- cooling rate, shorter re-cooling time and higher cumulative VPD compared to Fan speed 1. Fan speed 3 showed significantly increased fruit weight loss compared to Fan speeds 1 and 2. The study did not show any significant effect in LB incidence, although treatments had a significant effect on fruit quality. Punched and Micro-perforated liners showed a slower re-cooling rate, extended re-cooling time, lower cumulative VPD and reduced fruit weight loss. Both liners significantly and conversely developed more LB, whereas No liner maintained fruit quality at optimum levels. The application of a wet blanket shortly after harvest, immediate cooling (0 h), no application of wet blanket, 24 h delay cooling (24 h) thereafter and packing fruit without liners showed a reduction in LB incidence, but additional studies are required to obtain conclusive results. Thus, whilst fruit quality is maintained, none of the postharvest treatments consistently resulted in LB increases/decreases and therefore we postulated that LB incidence is initiated pre-harvest, as result of a self-defence mechanism of fruit exposed to stress conditions, and not primarily by storage regimes.