Wong, Yick Ching
(2025)
Phenotyping oil palm for drought adaptation using photosynthetic and root traits as indicators.
PhD thesis, University of Nottingham.
Abstract
Oil palm is the highest oil producing crop of all other oil crops at present. It contributes the largest (37%) share to the global edible oil consumption. Malaysia and Indonesia are the two largest palm oil producing countries, which account for major (84%) palm oil in total world production. However, unpredictable and extreme weather conditions caused by external factors such as El Niño could make the production of oil palm in the future a challenge. The exposure of oil palm to various environmental stresses such as drought throughout its life cycle could cause yield loss up to 25%. Selection of oil palm materials that could withstand drought without compromising the yield production is crucial. The hypothesis is that it is possible to select drought tolerant oil palm genotypes at seedlings stage through combination of various phenotyping methods.
In the present study, the drought responses of three-month old oil palm seedlings was first investigated under controlled-environment. This was followed by the nursery trial to identify the suitable phenotyping methods for potential drought tolerant oil palm genotypes selection at nursery stage. To understand the molecular responses in oil palm seedlings under drought stress, gene expression and biochemical analysis was performed. Under controlled-environment study, three commercial oil palm genotypes (BC21, GS1 and GS2) were tested. Various measurements were taken including soil volumetric water content (VWC), photosynthesis parameters such as stomatal conductance (gs), net photosynthesis rate (A), maximum quantum yield efficiency of photosystem II (Fv/Fm), effective quantum yield efficiency of photosystem II (QY) and non-photochemical quenching (NPQ), and vegetative measurements such as plant height and girth diameter. Reduction in VWC significantly (P<0.05) impacted gs and A, causing a significant reduction (gs, 30 % reduction and A, 18 % reduction) at day-7 of drought treatment (S-7). Similarly, the maximum quantum yield efficiency of photosystem II (Fv/Fm) and effective quantum yield efficiency of photosystem II (QY) showed significant reduction (Fv/Fm, 7 % reduction and QY, 29 % reduction) at S-14 when the soil VWC reduced to 15-20 %. Genotype GS2 showed slower in reduction of gs (at S-11) and A (at S-14) as compared to other genotypes. Similar observation in Fv/Fm (S-21), QY (S-17) and NPQ (S-21). Furthermore, the significant reduction in girth diameter was only observed at S-21 compared to other genotypes.
Similar to controlled environment study, the gs, A, Fv/Fm and QY of four commercially breed oil palm genotypes (DT02, DT06, DT10 and DT22) were significantly impacted during 32 days of drought treatment followed by 32 days of water recovery. The results showed significant reduction (P<0.05) of gs (19.9% reduction) and A (7.6% reduction) at S-7 for all genotypes. QY and Fv/Fm measurements showed significant (P<0.05) reduction at S-18 and S-22, respectively during drought treatment. Comparisons between genotypes revealed that DT10 has significantly higher (P<0.05) gs and A compared to other genotypes at S-15 until S-25 of drought treatment. DT10 also showed significantly higher (P<0.05) of QY among treated plants when compared to DT02 and DT22 at S-18 until S-25 during drought treatment.
Vegetative traits such as plant height, canopy size, stomatal density, biomass (shoot and roots) were found significantly (P<0.05) reduced during drought stress. The variations of impact were observed between genotypes. Significant reduction (P<0.05) of plant height was observed in DT02, DT06 and DT22 but no significant difference (P>0.05) was observed in DT10 throughout the trial. In canopy development, DT10 showed a slower reduction (P<0.05) of canopy area (6 %) at day-4 of recovery phase (R-4) as compared to other genotypes. In addition, DT10 showed significantly (P<0.05) higher root-to-shoot (R/S) ratio as compared to DT06 and DT22 at S-32. In root analysis, drought stress caused significant reduction in all root parameters including root length (RL), root surface area (SA), average root diameter (RD) and root volume (RV). DT10 and DT02 showed significantly (P<0.05) higher RL (2816 cm for DT02 and 2098 cm for DT10) and SA (702 cm2 for DT02 and 590 cm2 for DT10) in treated plants compared to DT06 and DT22 at the end of drought treatment, S-32.
To further understand the impact of drought stress on different oil palm genotypes at the molecular level, gene expression quantification and biochemical assay were carried out. The expression analysis revealed that majority of the photosynthesis-related genes were significantly (P<0.05) down-regulated during drought stress, including genes that encode for complex protein of photosystem I (PSI) and photosystem II (PSII). The antioxidant genes, WRKY transcription factors (TFs) and DREB1 were found significantly (P<0.05) up-regulated in their expression during drought stress, indicating that these genes, including TFs were drought-induced. From the gene expression results, DT10 had significantly (P<0.05) higher expression in photosynthesis-related genes compared to all the other genotypes.
From the biochemical analysis, proline, chlorophyll content, reducing sugar and total phenolic compounds significantly (P<0.05) increased in both leaves and roots as a result of drought stress. DT22 showed significantly (P<0.05) higher proline, chlorophyll content, reducing sugar and total phenolic content compared to DT10 at S-32.
Physiological and morphological data from nursery trial showed DT10 could be potentially drought tolerant compared to the other genotypes with its significantly (P<0.05) higher gs, A, Fv/Fm and QY during drought stress. DT10 was also found to be significantly (P<0.05) shorter and had a smaller canopy and higher in R/S ratio during drought stress, indicating that it could be better at both water uptake and conservation. The significant higher of expression data in photosynthesis related genes further supported the physiological findings. The significant lower in proline, could further indicated that DT10 was less sensitive towards drought stress as compared to other genotypes.
Overall, this work provides new knowledge on the impact of drought stress in oil palm seedlings at physiological, morphological and molecular level. The integration of data from the present study provides methods and approaches that could be explored for the selection of drought tolerant phenotypes in oil palm. Combining all the data from physiology, morphology gene expression and biochemical compounds, it appears that DT10 is potentially drought tolerant oil palm and could be a suitable material to be planted in low rainfall areas. Field validation is necessary to translate growth chamber and nursery results into real field conditions where phenotypes experience multiple confounding factors. Ultimately, if confirmed under field conditions drought selection indicators presented in this study could be developed for early selection of drought tolerant oil palm materials at nursery stage.
| Item Type: |
Thesis (University of Nottingham only)
(PhD)
|
| Supervisors: |
Massawe, Festo
Murchie, Erik
Singh, Ajit
Neoh, Bee Keat |
| Keywords: |
oil palm (Elaeis guineensis Jacq.); photosynthesis; drought tolerant; phenotyping; root traits |
| Subjects: |
S Agriculture > SB Plant culture |
| Faculties/Schools: |
University of Nottingham, Malaysia > Faculty of Science and Engineering — Science > School of Biosciences |
| Item ID: |
80814 |
| Depositing User: |
Wong, Yick
|
| Date Deposited: |
26 Jul 2025 04:40 |
| Last Modified: |
26 Jul 2025 04:40 |
| URI: |
https://eprints.nottingham.ac.uk/id/eprint/80814 |
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