School of Agricultural, Earth and Environmental Sciences

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Efficacy of enhanced freshness formulation as a novel postharvest treatment for gold kiwifruit (actinidia chinensis) = Ukusebenza kahle kwendlela entsha ethuthukisiwe yokugcina i-Gold Kiwifruit (Actinidia chinensis) ifreshi emva kokuvunwa.
(2023) Mthembu, Sisanda Sibusiso Luyanda.; Mditshwa, Asanda.; Magwaza, Lembe Samukelo.; Tesfay, Samson Zeray .
When exporting kiwifruit, the main limiting factors are excessive fruit softening and fungal decay. Furthermore, exposing kiwifruits to low temperatures induces the mechanisms involved in the softening process. In addition, kiwifruit become much more susceptible to fungal decay as they soften, which exacerbates deterioration of kiwifruit during transit. Fruit firmness is an important criterion for the market value of kiwifruit and storage life for the wholesale and retail trade. Therefore, loss in firmness is a serious problem resulting in postharvest and economic losses. Given that cold storage alone is not enough to optimise firmness retention of kiwifruit, the current study aimed to investigate the capacity of enhanced freshness formulation (EFF) to reduce kiwifruit softening. Kiwifruits were subjected to eight weeks of storage at 0 °C and 90 % relative humidity, followed by one week at ambient storage. The efficacy of EFF to regulate the mechanisms behind the softening process such as cell wall degradation, membrane deterioration and fungal infection was evaluated. Furthermore, the efficacy of EFF to preserve bioactive compounds was also evaluated to assess the effect of this treatment on these highly appreciated quality attributes. The first study evaluated the efficacy of EFF to delay softening of kiwifruit harvested at both the mid and late maturity stage. The influence of EFF on cell wall polysaccharides (CWPs) and cell wall degrading enzymes (CWDEs) was assessed. The findings showed that EFF optimised firmness retention of kiwifruit by preserving CWPs through the suppression of CWDEs which are responsible for initiating fruit softening. Furthermore, EFF maintained fruit quality and marketability, characterised by significantly lower mass loss, total soluble solids and higher titratable acidity. The second study examined the capacity of EFF to inhibit the excessive production of reactive oxygen species (ROS) which induce membrane damage, resulting in softening and senescence. EFF treatment effectively delayed the progression of kiwifruit senescence by reducing membrane deterioration and the accumulation of ROS. The mechanism by which EFF reduced membrane damage caused by ROS was attributed to its capacity to enhance the activities of antioxidant enzymes involved in neutralising ROS and suppressing Phospholipase D which destroys membrane integrity, resulting in improved storability of treated fruit. The third study assessed the efficacy of EFF to inhibit the fungal growth of Botrytis cinerea, which one of the major postharvest pathogens of kiwifruit that contribute to excessive softening. The findings show that EFF effectively suppressed the fungal growth of Botrytis cinerea in a dose -dependent manner. The results demonstrate that EFF can serve as a potential disease control strategy for kiwifruit at the postharvest stage. The mechanism by which EFF suppressed fungal decay can be attributed to the treatment’s capacity to induce disease resistance against Botrytis cinerea, by enhancing the synthesis of secondary metabolites and the action of defence-related enzymes, thus conferring greater protection against pathogen attack. The fourth study investigated the ability of EFF to retain the antioxidant quality of kiwifruit during prolonged storage. The bioactive compounds of EFF-treated kiwifruits were effectively maintained throughout the storage period. The findings of the present study further revealed that the mechanism by which EFF optimises antioxidant retention is due to its ability to regulate enzymes involved in the synthesis and oxidation of bioactive compounds. Despite the positive results, further research on transcriptome analysis is needed to elucidate how EFF regulates softening and antioxidant enzymes. Iqoqa. Izimo eziyizihibe eziphambili uma kuthunyelwa emazweni angaphandle i-kiwifruit ukuthamba okwedlulele kwezithelo kanye nokonakala ngokukhunta okubhebhethekiswa amazinga aphansi okushiwa ngesikhathi izithelo zisendleleni, Ukuthamba akwandisi nje kuphela ukudaleka kokonakala kepha kuholela nasekulahlekelweni ngokwezomnotho. Ukugcina izithelo ziqinile kubaluleke kakhulu ngokwamanani ezimakethe kanye nokuhlala zifreshi lapho zigcinwe khona. Kodwa-ke, izindlela ezijwayelekile zokugcina impahla endaweni enamakhaza azanele ekubhekaneni nalezi zinselelo. Ngakho-ke, lolu cwaningo luhlola ukusebenza kahle kwendlela eyaziwa nge-Enhanced Freshness Formulation (EFF) ekunciphiseni ukuthamba kwe-kiwifruit. Ama-kiwifruit agcinwa amasonto ayisishiyagalombili endaweni eyisibandisi emazingeni okushisa awu-0°C kanye nama-90% okuswakama okuhambisanayo. Kwalandeliswa ngesonto elilodwa ngaphansi kwesimo sokushisa esikahle. Lolu cwaningo luhlola ukuthi i-EFF inamthelela muni ekuthambisekeni kwezithelo, okuhlanganisa nokulimala kwezindonga zamaseli/kongwengwezi lwamaseli, ukuqina kongwengwezi, kanye nokutheleleka ngokukhunta. Okunye futhi, ucwaningo luhlola amandla e-EFF ekulondolozeni izinhlanganisela okuyizona ezinomthelela kokuphilayo, okuyikhona okubalulekile ekugcineni ikhwalithi yezithelo ingaguquki. Uhlangothi olulodwa locwaningo luhlola ukusebenza ngendlela efanele kwe-EFF ekudambiseni ukushesha kokuthamba kwe-kiwifruit evunwe maphakathi nesigaba sokuvuthwa kanye nevunwe uma sekuseduze kakhulu ukuthi avuthwe. Imiphumela iveza ukuthi i-EFF iyakwazi ukulondoloza ama-polysaccharide ongwengwezi lwamaseli ngokucindezela ama-enzyme alimaza ungwengwezi lwamaseli, ngaleyo ndlela kuthuthukiseke ukuqina kwezithelo kanye nekhwalithi yazo. Okunye futhi ukuthi izithelo okwasetshenziswa kuzo i-EFF zakhombisa ukunganciphi ubungako bazo kanye nomthamo odlekayo, kanti futhi nobumuncwana bazo banda okwathuthukisa ukudayiseka kwazo. Kwagxilwa futhi nasemandleni e-EFF ukunciphisa ukukhiqizeka kwe-reactive oxygen species (ROS) eyaziwa kakhulu ngokusheshisa ukuzwela kanye nokuthamba. Ukukwazi kwe-EFF ukuthiya i- Phospholipase D ibe ithuthukisa ukusebenza kwe-antioxidant enzyme kwanciphisa ukwakheka nokudaleka kwe-ROS kanye nokulimala kongwengwezi. Ngaleyo ndlela kwandiseka isikhathi okungagcinwa ngaso lezi zithelo. Okunye, ucwaningo luhlola ukusebenza kwe-EFF ekulwisaneni ne-Botrytis cinerea, okuyigciwane elivame ukuhlasela emva kokuvuna. I-EFF ikucindezela kakhulu ukukhula nokwanda kokukhunta ngenxa yokuthi ikwazi ukuthuthukisa ukulwisana nezifo ngokuhlanganisa okwaziwa nge-secondary metabolite kanye nokusebenza kwama-enzyme ahambisana nokuvikela. Okunye futhi, lolu cwaningo lwahlola umthelela we-EFF ekugcinekeni kwama-antioxidant ngesikhathi izithelo zisagcinwe isikhathi eside. Imiphumela iveza ukuthi i-EFF yakuthuthukisa kakhulu ukugcineka kwama-antioxidant ezithelweni ama-kiwifruit esetshenziswe kuzo ngokulawula ama-enzyme atholakala ekuhlanganisweni kwezinhlanganisela ezinomthelela kokuphilayo kanye nesimo esaziwa nge-oxidation lapho kwakheka khona i-oksijini eningi noma kulahleke i-hydrogen. Ekuphetheni, i-EFF ikhombisa ukuthi likhona ithemba lokuthi kungabhekwana nezinselelo eziphathelene nokuhanjiswa kwe-kiwifruit emazweni angaphandle ngokunciphisa ukuthamba kanye nokonakala kokukhunta, lokho okungathuthukisa ikhwalithi yezithelo kanye nokudayiseka kwazo. Lusadingeka olunye ucwaningo ukuze kuqondakale kahle ukusebenza kwamamolekhuli ekulawuleni ukuthamba kanye nama-antioxidant enzyme, kanye nokuthuthukisa ukusetshenziswa kwayo kulo mkhakha womkhiqizo.
Ethephon-induced changes in macadamia nuts: implications for dietary indicators, nutritional quality, and postharvest shelf life = Okulawula ukukhula kokwenziwa kwesihlahla okunomthelela emantongomaneni iMacademia: Isiphakamiso esimayelana nezinkombaluhlelo zokudla, izingabunjalo lomsoco nobude besikhathi sokuyigcina emva kwesivuno.
(2024) Aruwajoye, Noluthando Noxolo.; Tesfay, Samson Zeray.; Mditshwa, Asanda.; Magwaza, Lembe Samukelo.
The thriving macadamia nut industry, prized for its nutritional value, grapples with the challenge of inconsistent abscission seasons, leading to variable harvest times and increased operational costs. To address this, the traditional application of ethephon induces uniform nut abscission and streamlines harvesting. However, it is crucial to investigate how ethephon impacts the nutritional quality and postharvest shelf life of macadamia nuts. This study focuses on the effect of ethephon on the postharvest quality of the ‘788’ and ‘Beaumont’ cultivars, comparing various categories: nuts that successfully abscised due to ethephon (ED), those manually picked from ethephon-treated trees (ET), nuts naturally dropped from control trees (CD), and those manually picked from control trees (CT). Guided by industryrecommended doses, Ethephon 480 SL® was administered using a Cima mist blower to facilitate nut abscission, specifically targeting physiologically mature nuts. The research explores the influence on fatty acids, dietary indicators, biochemical components, and polyphenol oxidase (PPO) activity. Various parameters, including total phenolics, flavonoids, antioxidant activities, sucrose, and total protein, were assessed across treatments using standardized procedures. samples were collected over a 72-day accelerated storage period. The study further assessed the effect of Ethephon on the physical attributes of macadamia during a 56-day accelerated storage, analyzing mass, diameter, colour (L*, a*, b*, and hue angle), and texture. Kernels were roasted at 125 °C for 15 minutes using a hot air oven dryer post drying and dehusking. Models were then developed to predict the firmness and colour parameters of macadamia nuts harvested with ethephon from the ‘788’ and ‘Beaumont’ cultivars based on drying days and storage conditions. The aim was to determine the minimal processing requirements for achieving satisfactory postharvest nut appearance. Input parameters considered included storage temperature, drying temperature, and storage days, vi while the resulting outputs were firmness and colour parameters (L*, a*, b*, and hue angle). The range of the input parameters spanned from -22℃ to 25℃ for storage temperature, 35 to 57℃ for drying temperature, and 0 to 70 days for storage duration. Significant changes were observed in the fatty acid profiles of macadamia nuts exposed to ethephon treatment. Notably, ethephon led to a substantial increase in stearic acid content, reaching 24,622 µg/g in (ED) after 72 days, compared to 16,764 µg/g in (CD), thereby impacting their nutritional quality. Conversely, ED nuts exhibited a reduction in unsaturated fatty acids (USFAs). Hierarchical clustering analysis identified strong correlations between ED and saturated fatty acids (SFAs) in both ‘Beaumont’ and ‘788’ cultivars, with coefficients of 0.78 and 0.80, respectively. This was accompanied by an increase in atherogenic indices, thrombogenic index, and saturation index, along with a decrease in the hypocholesterolemic/hypercholesterolemic ratio. Concurrently, a robust correlation (0.97) between sucrose and Polyphenol Oxidase (PPO) was observed in ‘Beaumont’, underscoring the influence of ethylene treatment. Notably, ED ‘Beaumont’ nuts exhibited the highest sucrose content at 18.63 mg/g, coupled with elevated PPO activity at 1.06 U g-L. For the physical attributes, ED exhibited a notable influence on the ‘Beaumont’ cultivar, particularly affecting parameters such as a*, b*, mass, and diameter. Conversely, in the ‘788’ cultivar, Principal Component Analysis (PCA) revealed that CD treatment held prominence, showing elevated values for firmness, a*, and b*. Furthermore, model development demonstrated significance, with high coefficients of determination ranging between 0.83 and 0.97. Notably, under reduced drying days and optimal storage temperature, the models predicted maximum L* values of 76.253 and 79.748 for the ‘788’ cultivar. This study provides a theoretical framework for identifying optimum set points crucial for the effective preservation of both the ‘788’ and ‘Beaumont’ varieties of macadamia nuts, particularly in preventing external discolouration. The proposed set points aim to enhance the quality and overall market value of these macadamia nut varieties. The overall findings offer a comprehensive perspective on the effects of ethephon application on macadamia nuts. Stakeholders, producers, and processors in the macadamia nut industry can leverage this research to make informed decisions that enhance overall efficiency and quality while ensuring optimal nutritional value and extended shelf life for macadamia nuts. Iqoqa. Imboni yokukhiqiza amantongomane abizwa ngemacadamia ibhekene nezinkinga ngenxa yezikhathi ezingenayo inhlalanjalo zokuwohloka kwamahlamvu ezihlahla eyenzeka noma yinini, okwenza isivuno singazinzi kahle futhi kunyuke nezindleko. Ukusetshenziswa komuthi i-ethephon kusiza ekutheni ukuwohloka kwamahlamvu ezihlahla kwenzeke ngesikhathi sonyaka esifanele, nokho umphumela walo muthi ezingeni lokudla nesikhathi sokugcinwa kwakho awaziwa. Lolu cwaningo lucubungula imiphumela ye-ethephon mayelana nezinga lokudla osekuvuniwe i-788 nezitshalo ezahlukene zeBeaumont. Izinhlobo ezahlukene zamantongomane, okufaka nalawo awiswe yi-ethephon, nathathwa ezihlahleni ezilashiwe, naziwele ngokwawo, kwahlolwa futhi kwaqhathaniswa. I-ethephon yasetshenziswa kulandelwa imigomo ebekiwe yezimboni, kubhekwa amantongomane asevuthiwe. Lolu cwaningo lwaluhlola isimuncwane esinafutha, izinkomba zokudla, amakhemikhali nepolyphenol oxidase (PPO). Amasampula ocwaningo aqoqwa esikhathini esiyizinsuku ezingama-72 sokugcinwa kwawo, ukucubungula izinto ezibonakalayo njengesisindo, umnqamulankaba, umbala kanye nobunjalobotho. Imifanekisomumo iqagule ukuzinza nemibala emihle ngezikhathi ezinzima namazinga okugcineka kokudla, ukuhlonza nokugcina isikalo esibekiwe. Inguquko ekwakhekeni kwamfutha yabonakala yenzeka, amantongomane afakwe i-ethephon akhombisa ukwenyuka kwesimuncwane esigcwele amafutha nokuncipha kwesimuncwane esinamafutha angagcwele. Kwatholakala ubudlelwane obuqinile phakathi kokusetshenziswa kwe-ethephon kanye nesimuncwane samafutha aphelele. Kwatholakala kunokwenyuka kwesakhi sikashukela kamoba noma webhithrudi kanye noksebenza kwe-PPO emantongomaneni eBeaumont alashwe kusetshenziswa i-ethephon. Ukuhlaziya okukhulu kocwaningo kwaveza imiphumela ehlukile ngokwakheka kwesitshalo ngasinye esasicwaningwa. Indlela ecwaninga ukukhula yaveza ukwenyuka kwesibalo, esasifinyelela phezulu emibaleni ngendlela eyayilindekile. Indlela yokubheka ukuzinza yayibaluleke kakhulu ezitshalweni ze-788. Lolu cwaningo luza nomhlahlandela mayelana nokugcinwa kwamantongomane emacadamia, ukuthuthukiswa kwezinga kanye namanani okudayisa. Abathintekayo bangasebenzisa le miphumela yocwaningo ukuthuthukisa indlela yokusebenza kahle, izinga, kanye nokukwazi ukugcina ukudla isikhathi eside futhi kuqinisekiswe nokuthi ukudla kunomsoco odingekayo.
The evaluation and quantification of the drought propagation process using satellite earth observation products.
(2022) Sukhdeo, Trisha.; Chetty, Kershani Tinisha.; Gokool, Shaeden.
Droughts can be categorized in four types namely, meteorological, agricultural, hydrological and socio-economic drought. Droughts have the potential to occur either as an isolated event, mutually exclusive event or through the progression from one form to another. The use of drought indices were recognized as an approach capable evaluating and monitoring the characteristics of the different drought types. The aim of this study is to evaluate and quantify drought characteristics as it evolves and propagates form meteorological to agricultural drought, within two climatically different regions within South Africa, namely the uMngeni Catchment and the Breede-Overberg Catchment. These areas generally have insufficient networks of ground-based observations to provide continuous and long-term data. Therefore, Satellite Earth Observation (SEO) data and Google Earth Engine (GEE) were utilized. The Standardized Precipitation Index (SPI) was selected to quantify meteorological drought, whilst the Standardized Precipitation Evapotranspiration Index (SPEI) and Vegetation Health Index (VHI) was chosen to assess agricultural drought at both of the selected sites. The methodology undertaken firstly involved validating the SEO data against in-situ data. Thereafter, historical droughts were calculated by the SPI and SPEI indices at various timescales. Assessments were then conducted to determine the applicability of satellite based drought index VHI on quantifying agricultural drought conditions. The final assessment involved conducting propagation analysis between the drought indices. The findings of this study indicated that SEO have the potential to be utilized in the collection and monitoring of drought conditions. VHI was recognized to be scale dependent index, especially when considering averaging values. The findings of this study further suggested that the uMngeni region was more susceptible to the impacts associated with meteorological droughts characteristics whilst the Breede-Overberg region was more susceptible to the impacts associated with agricultural drought characteristics. Understanding the impacts and characteristics associated with the drought propagation process may further provide theoretical knowledge that can be used to facilitate more informed disaster, water and agricultural management and mitigation strategies to be implemented. If decision makers were to only consider drought using meteorological assessments for management decisions, the resulting strategies produced may be misleading as the impacts of an agricultural drought event may still be persistent.
The evaluation of the effect of biological control agents and melatonin against fusarium oxysporum infecting potatoes.
(2023) Mbatha, Londeka Akhona.; Mbili, Nokwazi Carol.
Potatoes (Solanum tuberosum L.) are essential to the South African agricultural industry. Postharvest diseases, including Fusarium dry rot (FDR) caused by Fusarium oxysporum (S.), are detrimental to the potato industry, resulting in yield and economic losses. Currently, fungicides are the primary means of controlling the disease commercially. However, the use of synthetic chemicals has reduced their efficacy against some Fusarium strains. Therefore, there is a need for safer, more sustainable, and environmentally friendly control methods for the management of postharvest fungal diseases such as FDR. Biological control agents (BCAs) and generally regarded as safe (GRAS) products have inhibitory effects against various pathogensand can be used as alternatives to synthetic chemicals. The aim of the study was to evaluate the efficacy of biological control agents (yeast and bacteria) and melatonin, individually and in combination, against F. oxysporum in vitro and in vivo. To evaluate the efficacy of the potential BCAs, 30 isolates were obtained from the exocarps and leaves of various crops, namely, potatoes(Solanum tuberosum), sweet potatoes (Ipomoea batatas), erect prickly pear (Opuntia stricta), Ganoderma mushrooms (Ganoderma resinaceum, Ganoderma austroafricanum,) and tomatoes (Solanum lycopersicum). The isolates were screened against F. oxysporum using the streaking method. Isolates NG1, NG2, NG3, NG4, and KG1 inhibited the growth of F. oxysporum on potato dextrose agar by more than 50% and were selected for secondary screening. In the secondary screening, isolates NGI (60%) and NG2 (62%) significantly inhibited mycelial growth of F. oxysporum on PDA compared to the control. In vivo, isolates NG1 and NG2 significantly reduced the severity of FDR on inoculated ‘Sifra’ potato tubers and had disease severity percentages of 47,2% and 46,1%, respectively, compared to the untreated control. BLAST prediction identified isolate NG1 as the bacterial species Burkholderia cenocepacia (strain LMG 16656) and isolate NG2 as Bacillus amyloliquefaciens (strain MPA 1034). The efficacy of melatoninwas determined by screening six concentrations (0 M; 1 M; 10 M; 15 M; 50 M and 100M) of the phytohormone against F. oxysporum using the disc fusion method. The best- performing melatonin concentrations were selected for secondary screening and progressed to in vivo screening. Melatonin concentration of 100 M had the highest inhibition percentage (40,83%) of F. oxysporum in vitro compared to the untreated control. The second and third best concentrations were 15 M and 50 M with inhibition percentages of 35,83% and 34,17%, respectively. The efficacy of melatonin as an antifungal agent, was significantly lower in vitro compared to the in vivo results. In vivo, the ‘Sifra’ potato tubers treated with 100 M showed the lowest FDR severity of 58,57%, followed by 50 M and 15 M with disease severity percentages of 59,54% and 60,31%, respectively. Subsequently, the effects of the integration of best-performing BCAs and melatonin were evaluated. BCAs, (Burkholderia cenocepacia and Bacillus amyloliquefaciens) were integrated with six melatonin concentrations and screened against F. oxysporum in vitro and in vivo. In vitro, treatment Bamy + MEL100 had the highest mycelial growth inhibition percentage (59,92%), followed by Bamy + MEL15 and Bamy + MEL50 with mycelial growth inhibition percentages of 56,12% and 55,27%, respectively. ‘Sifra’ potato tubers treated with treatment Bamy + 100 M melatonin had the lowest disease severity of FDR of 50,61% compared to control treatment after 9 days at 25℃. Bcen + 100 M melatonin and Bamy + 50 M melatonin exhibited the disease severity percentages of 52,63% and 59,72%, respectively. Overall, tubers treated with a combination of melatonin and B. amyloliquefaciens showed less severe symptoms of FDR across all concentrations. Furthermore, the effects of the exogenous application of B. amyloliquefaciens and melatonin on the quality parameters of the potato tubers were evaluated. The treatments were administered to tubers using the dipping method and stored at ambient temperature for 14 days. The treated tubers were sampled and prepared for phenolic, protein, and ascorbic acid determination assays. The exogenous application of 100 M melatonin combined with B. amyloliquefaciens was the most effective treatment with the highest phenolic content (144,1 mg GAE/g DW), and protein content (68 mg/g DM). Tubers treated with melatonin had the highest ascorbic acid content (5,48 mg AAE/100g DM). Findings indicated that the exogenous application of melatonin and B. amyloliquefaciens do not have adverse effects on the quality parameters of potato tubers. This study demonstrated for the first time, the efficacy of melatonin as an antifungal agent against F. oxysporum causing FDR on potatoes and the effectiveness of the combination of melatonin and the antagonistic microorganism, B. amyloliquefaciens against F. oxysporum.

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