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Quantifying the orchard transpiration and fruit vascular flows in two high performing pear orchards grown under Mediterranean climatic conditions
Thesis (MScAgric)--Stellenbosch University, 2026.
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| Format: | Thesis |
| Language: | English |
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Stellenbosch : Stellenbosch University
2026
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| _version_ | 1867613956091150336 |
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| access_status_str | Open Access |
| author | Pienaar, Johan Cornelissen |
| author2 | Dzikiti, Sebinasi |
| author_browse | Dzikiti, Sebinasi Pienaar, Johan Cornelissen |
| author_facet | Dzikiti, Sebinasi Pienaar, Johan Cornelissen |
| author_sort | Pienaar, Johan Cornelissen |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Thesis (MScAgric)--Stellenbosch University, 2026. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/135938 |
| institution | Stellenbosch University (South Africa) |
| language | English |
| last_indexed | 2026-06-10T12:44:22.712Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2026 |
| publishDateRange | 2026 |
| publishDateSort | 2026 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/135938 Quantifying the orchard transpiration and fruit vascular flows in two high performing pear orchards grown under Mediterranean climatic conditions Pienaar, Johan Cornelissen Dzikiti, Sebinasi Stellenbosch University. Faculty of AgriSciences. Dept. of Horticultural Science. Thesis (MScAgric)--Stellenbosch University, 2026. Pienaar, J. C. 2026. Quantifying the orchard transpiration and fruit vascular flows in two high performing pear orchards grown under Mediterranean climatic conditions. Unpublished masters thesis. Stellenbosch: Stellenbosch University [online]. Available: https://scholar.sun.ac.za/items/8f6cc99a-3c1d-4903-9997-e81a1c6bd977 To ensure the long-term resilience and sustainability of South Africa’s pear industry amid climate change, on-farm water management must be optimized. Accurate quantitative data on water requirements are currently lacking for widely planted pear cultivars (Pyrus communis L.) such as ‘Packham’s Triumph’ and ‘Forelle’. Little is known about how their water use relates to yield under local warmer, drier conditions compared to milder temperate climates of prior studies. This knowledge gap leads to inaccurate irrigation scheduling, poor water allocation, and wastage of scarce resources. Key physiological processes like photosynthesis and transpiration depend on plant tissue water status. Consequently, precise irrigation is shifting toward plant-based stress detection. Since fruits are the primary economic output in orchards, they are ideal for sensing water stress, enabling timely interventions to meet tree needs, optimize yields, and boost income. Electronic dendrometers are commonly used for plant-based scheduling, typically on stems or branches. A recent South African study on pears placed them on fruits to indicate stress. Maximum daily shrinkage (MDS) and daily growth rate (DG) from fruit data proved reliable indicators of irrigation need early in the season, but later showed poor correlation with soil water deficit, revealing limitations for pear irrigation scheduling. The reasons for this late-season unreliability were previously unknown. This study had two main objectives: (1) quantify maximum unstressed water use in two high-performing Western Cape pear orchards, providing critical baseline data for water resource management; (2) examine detailed vascular flow dynamics (xylem, phloem, transpiration) in fruit of ‘Forelle’ and ‘Packham’s Triumph’ to explain changes in daily/seasonal growth patterns and why fruit dendrometers become unreliable for precise irrigation later in the season. Research was conducted in productive orchards in two key regions with contrasting climates: Ceres (Koue Bokkeveld, ‘Forelle’) and Wolseley (Warm Bokkeveld, ‘Packham’s Triumph’). Tree sap flow was monitored over two seasons using the heat ratio method and scaled to orchard-level seasonal transpiration. Fruit growth was tracked during sequential treatments which allowed for the calculation of vascular inflow rates and their seasonal shifts. Complementary hourly measurements included stem, fruit, and leaf water potential, leaf gas exchange, and microclimate variables to link them to plant and fruit water relations. Key findings (under non-severe stress): Seasonal transpiration reached 814 mm (8,140 m³/ha) for ‘Forelle’ and 635 mm (6,350 m³/ha) for ‘Packham’s Triumph’. Leaf area index peaked higher in ‘Forelle’ (3.8) than ‘Packham’s Triumph’ (3.3). Water use rates resembled those of some apple cultivars in comparable regions. Physical water productivity was 8.7 kg/m³ (‘Forelle’) and 9.3 kg/m³ (‘Packham’s Triumph’), lower than typical apple values due to pears’ lower yields. Atmospheric evaporative demand drove most transpiration in both orchards. In early November 2023, average daily fruit flow rates (phloem / xylem / transpiration) were 0.03/0.11/0.10 g/g/day for ‘Forelle’ and 0.05/0.11/0.10 g/g/day for ‘Packham’s Triumph’. Near harvest, all rates dropped sharply, but phloem least so. Progressive isolation of fruits from tree xylem and atmosphere appears to reduce early-season growth drivers (organ water potential gradients and air VPD) and weaken fruit sensitivity to plant water stress. This study provides initial estimates of maximum water requirements for high-yielding Western Cape pear orchards and clarifies fruit vascular flow magnitudes, diurnal/seasonal patterns, and their influence on fruit growth under the semi-arid, conditions of the Western Cape. Masters 2026-04-15T12:58:02Z 2026-04-15T12:58:02Z 2026-03 Thesis https://scholar.sun.ac.za/handle/10019.1/135938 en Stellenbosch University 233 pages application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Pienaar, Johan Cornelissen Quantifying the orchard transpiration and fruit vascular flows in two high performing pear orchards grown under Mediterranean climatic conditions |
| title | Quantifying the orchard transpiration and fruit vascular flows in two high performing pear orchards grown under Mediterranean climatic conditions |
| title_full | Quantifying the orchard transpiration and fruit vascular flows in two high performing pear orchards grown under Mediterranean climatic conditions |
| title_fullStr | Quantifying the orchard transpiration and fruit vascular flows in two high performing pear orchards grown under Mediterranean climatic conditions |
| title_full_unstemmed | Quantifying the orchard transpiration and fruit vascular flows in two high performing pear orchards grown under Mediterranean climatic conditions |
| title_short | Quantifying the orchard transpiration and fruit vascular flows in two high performing pear orchards grown under Mediterranean climatic conditions |
| title_sort | quantifying the orchard transpiration and fruit vascular flows in two high performing pear orchards grown under mediterranean climatic conditions |
| url | https://scholar.sun.ac.za/handle/10019.1/135938 |
| work_keys_str_mv | AT pienaarjohancornelissen quantifyingtheorchardtranspirationandfruitvascularflowsintwohighperformingpearorchardsgrownundermediterraneanclimaticconditions |