1. Discipline of Horticultural Science, School of Agricultural, Earth and Environmental Sciences, University of KwaZulu-Natal, Private Bag X01, Pietermaritzburg 3209, South Africa
2. Plant Science Laboratory, Cranfield University, Cranfield MK43 AL, UK
3. Department of Food Systems and Development, Faculty of Natural and Agricultural Sciences, University of Free State, Bloemfontein 9300, South Africa