Thermal resilience of olive accessions evaluated through pomological traits, lipid profile, and gene expression responses

Background: Ongoing global warming makes the selection and deployment of tolerant olive cultivars a strategic priority for sustainable agriculture and for mitigating the negative impacts of heat stress. Warm summers markedly reduce the performance and quality of olive plants. In this context, the present study evaluated 41 olive cultivars, including 17 genotypes from Kermanshah (Ds1, Ds2, Ds3, Ds4, Ds5, Ds7, Ds8, Ds10, Ds11, Ds12, Ds13, Ds14, Ds16, Bn1, Bn2, Bn5, D1), 13 genotypes from Ilam (Ske7, Ske8, Pg1, Pg3, Bsch1, Bsch2, Bsch3, Sbm5, Kf8, Dz1, Dz4, Ns3, Ns4), 3 genotypes from Tarom (T2, T3, T7), and 5 genotypes from Gorgan (B1, B3, G4, M6, E2), along with 3 control cultivars (Zard, Amygdalolia and Amphysis), by examining their pomological traits, olive oil, fatty acids profile and molecular analysis under rising summer temperature at the Dallaho Olive Research Station (Sarpole-Zahab in Kermanshah) province in 2023. Results: After assessing pomological traits, oil content, and yield, the results indicated that Dz4 excelled due to its superior pomological traits and oil yield (1817.1 kg·ha-1), Ds13 and T3 for their higher fruit yield (11667 and 11444 kg·ha- 1), Bn2 for its greater oil content in dry matter (45.33%), and B3 for its superior pomological traits, fruit pulp percent (93.29%) and B1 for its higher oil content in dry matter (45.5%) under warm conditions during the fruit growth period. In the next stage, these five elite genotypes, along with three control cultivars (Zard, Amphysis, and Amygdalolia), were evaluated and compared for their fatty acid profiles and molecular responses in warm summer conditions. The assessment of fatty acids in these eight olive genotypes and cultivars revealed that Ds13, B1, T3 and Bn2 produced higher levels of palmitic, palmitoleic and linolenic, vaccenic, and linoleic acids, respectively. Molecular analysis showed that FAD2-2 was significantly upregulated in fruit tissue compared to leaf tissue, with a mean fold change of 1.75. In conclusion, superior pomological traits were found in T2, B1, and B3, while Dz4 and Bn2 excelled in oil productivity. Under heat stress, Ds13, B1, T3, and Bn2 maintained oil quality by producing higher levels of essential fatty acids. Gene expression showed strong FAD2-2 induction in fruit tissues and marked repression of SAD2 and PDCT. Conclusion: These findings support breeding for heat tolerance, highlighting Ds13, Bn2, Amphysis, Amygdalolia, and Zard as promising choices for warm regions.