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Investigating the role of mycorrhizal fungi and associated bacteria in promoting growth of citrus seedlingsSitole, Phumeza January 2014 (has links)
South Africa is the world's second largest exporter of fresh citrus and is ranked 14th in citrus production. Fungal pathogens such as Phytophthora and Pythium cause economic losses as a result of root rot and brown rot. Mycorrhizal fungi are specialized members of the fungal community forming a mutualistic relationship with plant roots. Mycorrhizal fungal structures are known to associate with other soil microorganisms and these may contribute to improved plant growth. A diverse group of bacteria that interact with the mycorrhizal fungi are known as Mycorrhizal Helper Bacteria (MHB). The aim of this study was to investigate the role of arbuscular mycorrhiza and associated bacteria isolated from spores and determine whether they had any plant growth promoting potential. A total of 19 bacteria were isolated from arbuscular mycorrhizal spores and were molecularly identified as belonging to several Bacillus, Micrococcus, Onchrobactrum and Staphylococcus sp. All bacterial isolates were tested for plant growth promotion abilities. One Bacillus isolate was able to solubilise phosphate. Four isolates Micrococcus sp, Micrococcus leteus, Ochrobacterum sp and Ochrobacterum antropi were able to produce Indole Acetic Acid and three isolates showed potential to reduce growth of Phytophthora nicotianae, P. citrocola and P. citrophthora in in vitro plate cultures. Further tests using culture supernatants of the Bacillus sp, Micrococcus sp and Bacillus cereus confirmed their ability to inhibit or reduce growth of the three Phytophthora species in a 96 well bioassay. Bacillus sp and Bacillus cereus were able to inhibit Phytophthora spp by 95 to 100 % and Micrococcus spp was able to decrease pathogen growth by 60 to 94 %. These bacterial isolates were further evaluated for plant growth promoting abilities on citrus rough lemon seedlings alone or in combination with arbuscular mycorrhizal inoculum. Bacterial and mycorrhizal inoculants influence the increase in shoot and root biomass. Bacillus cereus in combination with mycorrhizal inoculum significantly increased seedling shoot to root ratio while root biomass was significantly increased with mycorrhizal inoculation. Due to the short duration of the trial mycorrhizal colonisation could not be assessed. It is evident that selected combinations of bacteria and mycorrhizal fungi could promote citrus seedling growth and potentially improve seedling health. Further studies under nursery conditions are recommended.
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Citrus, labour and gender in the Eastern Cape: the case of the Kat River areaMzitshi, Zoleka Alice Florence January 2010 (has links)
Agriculture plays a significant role in South Africa’s export earning and in providing employment opportunities. Amongst the major agricultural crops is citrus. Within the context of postmodern and feminist geographies and utilizing the intensive research design, this thesis discusses citrus production with a focus on growers and black women workers in the Kat River Valley area in Fort Beaufort, Eastern Cape. The thesis also explores the challenges and implications of restructuring within agriculture for growers, cooperatives and labour within the citrus industry. It is argued that whilst legislation related to labour and tenure within agriculture has changed since the mid-1990s, power relations in the citrus industry have remained firmly entrenched. Consequently, the flexible labour strategies that the citrus farmers adopted have had serious consequences for women worker
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Mathematical modelling of fungal contamination of citrus produce along the pre-harvest supply chainMuleya, Nqobile 05 1900 (has links)
MSc (Applied Mathematics) / Department of Applied Mathematcs / See the attached abstract below
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Effects of maturity and processing on quality properties of the watermelon (Citrullus lanatus) fruit juiceMaoto, Makaepea Mossa 17 May 2019 (has links)
MSCFST / Department of Food Science and Technology / Watermelon (Citrullus lanatus) juice is rich in phytochemicals that possess antioxidant
properties which are known to have a positive contribution to human health. Colour, pH, total
soluble solids, lycopene, β-carotene, ascorbic acid, total polyphenolic content and
antioxidants activity are quality properties that characterise watermelon juice. However,
these quality properties undergo some chemical changes throughout the stages of maturity
of the fruit as well as during thermal processing. The aim of this study was to investigate the
effects of maturity and filtration on the physicochemical properties (colour, pH, total soluble
solids) and the phytochemicals (lycopene, β-carotene, ascorbic acid, total polyphenolic
content and antioxidants activity) of fresh watermelon juice. It further investigated
thermosonication effects on these quality properties using response surface methodology
(RSM). RSM considering temperature (25 – 52ºC), time (2 – 10 min) and amplitude level
(24.1 – 60 μm) at a constant frequency of 20 kHz were the independent variables while
colour variables (L*, a* and b*, C* and h*), pH, total soluble solids, lycopene, β-carotene,
ascorbic acid, total polyphenolic content and antioxidants activity were the dependent
variables. Results showed that colour, pH, total soluble solids, lycopene, β-carotene,
ascorbic acid, total polyphenolic content and antioxidants activity of watermelon fruit juice
are maturity dependent. All the physicochemical and phytochemical properties increased
with maturity. The combination of the CIELAB parameters (L*, a*, b*) was clearly explained
by the Chroma (C*) and hue (hº). The (C*) and hº values of the watermelon fruit juice were
significantly (p < 0.05) affected by the stages of maturity. The red colour was observed to be
more saturated in the fully - ripe sample as indicated by the highest Chroma (7.35) values.
The half - ripe sample which was observed to be pink - red had a C* of 5.88 while the lowest
(4.32) value was observed from the unripe sample. The highest hº value was obtained from
unripe sample (83.89), while lower value was observed from the fully - ripe (76.03) sample
because of the saturation of the red colour in the fully - ripe sample. The total soluble solids
also increased with stages of maturity 6.66 to 6.60 at half - ripe while at fully - ripe redness
changed from 9.3 to 8.99 and TSS 8.37 to 8.02. Filtration has shown a significant (p < 0.05)
on the C* and hº values. There was a higher retention of all dependent variables at lower
thermosonication treatment (25ºC; 24.4 μm), especially the lycopene which increased by
127%. Model predictions for the colour properties and phytochemicals were closely
correlated to the experimental results obtained. Prediction models were found to be
significant (p < 0.05) with low standard errors and high coefficients of determination (R2). / NRF
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