Thesis (MScAgric)--University of Stellenbosch, 2007. / Bibliography. Also available via the Internet

Thesis (Ph.D.)--University of Adelaide, Dept. of Horticulture, Viticulture and Oenology, 2002. / Includes bibliographical references (leaves 152-164).

Thesis (Ph.D.) - University of Glasgow, 2008. / Ph.D. thesis submitted to the Division of Biochemistry and Molecular Biology, Institute of Biomedical and Life Sciences, University of Glasgow, 2008. Includes bibliographical references. Print version also available.

Thesis(M.S.)--Auburn University, 2005. / Abstract. Vita. Includes bibliographic references (p.41-45).

The regulation of citrus fruit color by various concentrations of sugars, sugar metabolites, and nitrogen compounds was investigated in peel segments of Citrus paradisi Macf. (cv. Marsh) cultured on modified media of Murashige and Tucker. Green and yellow peel segments were cultured for degreening and regreening studies, respectively, and chlorophyll level in the individual peel segments was measured with a reflectometer. Degreening was significantly promoted by 150 mM sucrose, 300 mM glucose and fructose, or 50 mM citrate but not by 300 mM of the hexoses galactose and mannose, 300 mM of the pentoses xylose and ribose, or 25, 50, and 100 mM succinate. Regreening was significantly inhibited by 150 mM sucrose, 300 mM glucose and fructose, or 50 mM citrate and malate. Succinate and α-ketoglutarate at concentrations of 50 mM did not inhibit regreening. The inhibition of regreening by 300 mM sucrose was reduced by 33 percent with the glycolytic inhibitor iodoacetic acid at 1 mM but not by DL-glyceraldehyde at 50 mM. Neither ethanol nor potassium bicarbonate inhibited regreening, suggesting that the regulation of citrus fruit color is specific to sugars or sugar metabolites. However, pyruvate did not promote degreening or inhibit regreening because it was probably not absorbed from the media by the flavedo of the peel. These results suggest that sucrose, glucose, fructose, and citrate maintain carotenoid synthesis and accumulation in both cultured green and yellow peel segments but cause the loss of chlorophyll from green peel segments. Treatment of either the green or yellow segments with sucrose or citrate may increase the partitioning of these compounds into the mevalonic acid pathway to provide carbon for synthesis or carotenoids, resulting in degreening of the green peels and maintaining the yellow color in the yellow peels. Malonate inhibited regreening when incorporated in media at concentrations of 4 mM. This inhibition was reversed by 60 mM glutamine but not by 5 mM glutamine or KNO₃. The action of malonate on regreening may be a specific effect of malonate on plastid development rather than by modifying the partitioning of sugar metabolites into the carotenoid synthetic pathway.

M.Com. (Business Economics) / Please refer to full text to view abstract

Reproduction de : Thèse d'exercice : Pharmacie : Nantes : 2009. / Bibliogr.

Thesis accepted for the Degree of Doctor of Science in Forestry at the University of Stellenbosch. / Research project sponsored by the South African Lumber Millers' and Shook Manufacturers' Association, and the South African Council for Scientific and Industrial Research.

Abstract Introduction. Green mould, Penicillium digitatum (Pers.: Fr.) Sacc., causes economically important postharvest disease in citrus. Materials and methods. Ethiopian plant extracts of Acacia seyal (Del. Var. Seyal) and Withania somnifera (L.) Dual were used to test the control of green mould in wound-inoculated fruit, stored for 21 d at 7 °C and at > 85% RH. The chemical compositions of the two extracts were determined using high-performance chromatography. Thereafter, freshly harvested (naturally infected) fruit were subjected to different postharvest treatments and stored for 50 d to investigate the effects of the two plant extracts on fruit quality parameters. Treatments included (pre-wax + leaf extracts), (wax + leaf extracts incorporated into wax, Citrosol A®), (leaf extract alone), (fruit washed in chlorinated water at 5.25%), (untreated fruit) and (commercially treated fruit). Results. Extracts of A. seyal and W. somnifera reduced the incidence of green mould by 56.1% and 50%, respectively, in wound-inoculated fruit. A. seyal extract contained a high concentration of gallic acid (60.3 mg·mL–1) whilst W. somnifera contained low concentrations of caffeic acid (8.7 mg·mL–1), salicylic acid (6.3 mg·mL–1) and 3,4 dihydroxy benzoic acid (3.8 mg·mL–1). Green mould was absent in naturally infected fruit subjected to (pre-wax + leaf extracts), (wax mixed with leaf extracts) and (leaf extracts) treatments. (Pre-wax + leaf extracts) and (wax mixed with leaf extract) treatments significantly reduced weight loss; retained firmness and colour; and they maintained eating qualities and a maturity index (SSC/TA) similar to commercial treatment. Conclusion. Both extracts of A. seyal and W. somnifera showed potential to be used as an alternative in combined applications with wax application under low temperature storage to replace synthetic fungicides, to ultimately control green mould and retain overall fruit quality.

Throughout history, harvesting of fruit from the wild has played a role in the livelihoods of people in South Africa. For the San, who lived in South Africa for thousands of years, wild fruits were a staple food during parts of the year (Fox & Norwood Young 1983). Among the Bantu people, who entered South Africa about two thousand years ago (Hammond-Tooke 1993), agriculture was the main way in which food was acquired, but they also collected food from the wild. Especially during times of hardship, when cattle herds were decimated or crops were destroyed, they relied on hunting and gathering of fruits and edible plants from the wild for survival (Shapera & Goodwin 1959; Stuart & Malcolm 1986; Bundy 1988). European people settling in South Africa learnt to use and appreciate wild fruits (van Dyk 1988). In the rural areas of the Southern African region, the utilization of wild fruits as a source of food has persisted, especially among black people (Walker 1989; Shackleton 1996; Rossiter, Pellegrin et al. 1997). There is increasing interest in the domestication and improvement of selected fruits, and their utilization as orchard crops, marula (Sclerocarya birrea subsp. caffra) being the prime example (Nerd et al.1990; Holtzhausen, Swart & van Rensburg 1990; Nerd & Mizrahi 1993; Geldenhuys 2001; Taylor 2001; Barton 2001). Research into the wild fruits of South Africa has been mainly botanical or anthropological.