Interspecific OxG hybrids of African palm Elaeis guineensis Jacq. and the American palm Elaeis oleifera Cortes produce high-oleic palm oil (HOPO) with low saturated fatty acid content. OxG hybrids are highly productive, grow slowly, and are resistant to bud rot disease. However, OxG hybrid pollen presents low viability and germinability, so assisted pollination is a must. Hybrids can produce parthenocarpic or seedless fruits, with the exogenous application of plant growth regulators. Thus, naphthalene acetic acid (NAA) effects on parthenocarpic fruits induction, bunch formation, and oil quality were evaluated. The OxG hybrid Coari x La Mé was used. NAA doses, frequency, number of applications, and the phenological stages for the treatments were defined. A total dose of 1200 mg L⁻¹ NAA applied three or four times produced bunches with better fruit set, similar average bunch weight, and oil to dry mesocarp than those obtained with assisted pollination. At a semi-commercial scale, 1200 mg L⁻¹ NAA induced bunches that consisted of 93% or more of seedless fruits. Bunch number (2208 ± 84 versus 1690 ± 129) and oil to bunch (32.2 ± 0.7 versus 25.3 ± 0.8) were higher in the NAA induced bunches than in the assisted pollination. However, the average bunch weight was lower (12.2 ± 0.4 versus 14.9 ± 0.6). NAA increased oil to bunch in 36% (8.7 ± 0.1 versus 6.4 ± 0.3). Thus, with this technology, it is plausible to reach more than 10 tons per hectare per year of HOPO. Potentially, without increasing the planted oil palm area, OxG hybrids and NAA applications could alone meet the world’s fats and oil demands.

Oil palm is the most important oil crop globally, accounting for almost 40% of fats and oil consumption worldwide. The OxG interspecific hybrid results from the crossing of African oil palm Elaeis guineensis Jacq. and the American oil palm Elaeis oleifera Cortes. It is a promising genotype for its high productivity, oil quality, and partial resistance to some diseases. These hybrids require assisted pollination, an activity that is time-consuming and expensive. Oil production in the OxG hybrids depends on the formation of normal (fertile) fruits and seedless (parthenocarpic) fruits. Thus, it is appealing to stimulate parthenocarpic fruits without assisted pollination. This research evaluated artificial methods of inducing parthenocarpy by applying plant hormones, and the effect on bunch formation and oil quality and its potential implementation at an industrial scale. The study was carried out in a 6-year-old hybrid (OxG) Coari x La Mé. The effects of the plant hormones indoleacetic acid (IAA), 2,4-dichlorophenoxyacetic acid (2,4-D), naphthalene acetic acid (NAA), and an ethylene precursor (ethephon) were evaluated. IAA and ethephon did not result in consistent bunch production of parthenocarpic fruits. The plants presented abnormal fruit growth, low-weight bunches, and high abortion rates. 2,4-D and NAA promoted proper parthenocarpic fruit development with oil-to-bunch (O/B) values similar to those obtained with assisted pollination. Thus, NAA and 2,4-D are an excellent alternative for oil production in the OxG hybrids that can be implemented in the African oil palm, with particular relevance that pollinators are endangered, and highly female genotypes are widely used. GRAPHICAL ABSTRACT

Oil palm (Elaeis guineensis Jacq.) is a highly productive crop economically significant for food, cosmetics, and biofuels. Abiotic stresses such as low water availability, salt accumulation, and high temperatures severely impact oil palm growth, physiology, and yield by restricting water flux among soil, plants, and the environment. While drought stress’s physiological and biochemical effects on oil palm have been extensively studied, the molecular mechanisms underlying drought stress tolerance remain unclear. Under water deficit conditions, this study investigates two commercial E. guineensis cultivars, IRHO 7001 and IRHO 2501. Water deficit adversely affected the physiology of both cultivars, with IRHO 2501 being more severely impacted. After several days of water deficit, there was a 40% reduction in photosynthetic rate (A) for IRHO 7001 and a 58% decrease in IRHO 2501. Further into the drought conditions, there was a 75% reduction in A for IRHO 7001 and a 91% drop in IRHO 2501. Both cultivars reacted to the drought stress conditions by closing stomata and reducing the transpiration rate. Despite these differences, no significant variations were observed between the cultivars in stomatal conductance, transpiration, or instantaneous leaf-level water use efficiency. This indicates that IRHO 7001 is more tolerant to drought stress than IRHO 2501. A differential gene expression and network analysis was conducted to elucidate the differential responses of the cultivars. The DESeq2 algorithm identified 502 differentially expressed genes (DEGs). The gene coexpression network for IRHO 7001 comprised 274 DEGs and 46 predicted HUB genes, whereas IRHO 2501’s network included 249 DEGs and 3 HUB genes. RT-qPCR validation of 15 DEGs confirmed the RNA-Seq data. The transcriptomic profiles and gene coexpression network analysis revealed a set of DEGs and HUB genes associated with regulatory and transcriptional functions. Notably, the zinc finger protein ZAT11 and linoleate 13S-lipoxygenase 2-1 (LOX2.1) were overexpressed in IRHO 2501 but under-expressed in IRHO 7001. Additionally, phytohormone crosstalk was identified as a central component in the response and adaptation of oil palm to drought stress.