Browsing by Author "Ngindi, Buhle"

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    The stability of productivity and fruit quality traits of ‘Fuji’ apples on different Rootstocks
    (Stellenbosch : Stellenbosch University, 2024-03) Ngindi, Buhle; Siboza, Xolani ; Theron, Karen ; Stellenbosch University. Faculty of Agrisciences. Dept. of Horticulture.
    ENGLISH ABSTRACT: Rootstocks of apple trees are essential for productive and economical orchards. Rootstocks influence tree architecture, yield, and fruit quality. Most of the current rootstocks used in South African apple orchards lack precocity, are vigorous and not able to overcome some of the challenges faced in these orchards. Some of these challenges include poor soils, lack of winter chill as well as the prevalence of pests and diseases. Thus, productivity is negatively affected. The Geneva rootstocks are being bred to confer pest and disease resistance/tolerance, a range of tree vigour, but highly precocious. In this study, rootstock genotypes were planted in two separate but adjacent plantings, i.e., vigorous rootstocks and dwarfing rootstocks. The Fuji cultivar was evaluated on these genotypes in three different environments across South Africa – Oak Valley Estate and Breëvlei, both in Grabouw, Western Cape, and Helderwater, Eastern Cape. These environments differed in climatic conditions, soil conditions and management practices such as training systems used, irrigation and pruning strategies. The vigorous plantings consisted of MM.109, M.793, M.7 EMLA (control), G.778, G.228 and G.202. The dwarfing plantings comprised of M.9 EMLA, M.9 Nic29, M.7 EMLA (control), G.222, G.778/G.222, G.778/M.9 EMLA, MM.109/G.222, MM.109/M.9 EMLA, M.793/G.222 and M.793/M.9 EMLA. The influence of rootstocks on tree vigour, yield and yield efficiency, and fruit quality traits (mass, diameter, ground colour, red foreground colour, firmness, total soluble solids (TSS) and starch breakdown) was determined. The tendency of ‘Fuji’ apples planted on different rootstocks to bear alternately was investigated from the first year of harvest (2016/2017) to 2020. Rootstock productivity maybe influenced by the genotype (i.e., rootstock and scion), the environment and the interaction between the genotype and environment (GEI). The environment includes soil, climate and management factors. The influence of GEI on tree vigour and productivity was investigated. The presence of GEI complicates selection and requires that the stability and adaptability of genotypes be assessed to select for the most stable and adaptable rootstock genotypes. Stability refers to a genotypes’ ability to behave predictably against environmental fluctuations whilst adaptability refers a genotype’s ability to show high and constant yields in certain environments. For the vigorous rootstocks, GEI was significant (p < 0.001) for all yield traits and was non-significant for tree vigour. The most stable and high-yielding genotype was G.778 based on 2016/20 cumulative yield (149.00 kg/tree) and 2016/20 cumulative yield efficiency (2.39 kg/cm2 TCSA). For the dwarfing rootstocks, the GEI was significant for all yield traits and tree vigour. The most stable and high-yielding dwarfing genotype combinations based on 2016/20 cumulative yield and 2016/20 cumulative yield efficiency were G.778/G.222 and G.778/M.9 EMLA. ‘Fuji’ apples are prone to the development of internal browning during long-term storage. Since rootstocks may influence fruit maturity, the rootstock genotype may influence the occurrence and severity of internal browning. Thus, the influence of rootstocks on the occurrence of internal browning and postharvest fruit quality was investigated. Fruit were stored under controlled atmosphere conditions for 5 months at -0.5 °C, then subsequently moved to regular atmosphere conditions for 6 weeks, after which fruit were subjected to shelf-life conditions. A significant GEI (p < 0.001) on the occurrence of internal browning was obtained. As such, the environment also influenced the occurrence of internal browning. Fruit from trees on Geneva rootstocks (including those with interstems) had higher and more severe incidences of internal browning compared to the industry standards due to the more advanced maturity.