Flowering represents the most important process in the reproductive stage of fruit trees, including olive trees. Previous studies have demonstrated that the genotype–environment interaction (GEI) has a considerable influence on olive flowering time. This study investigated the GEI and genetic parameters influencing olive flowering phenology in Southwestern China (a non-Mediterranean region), using multi-trait-based stability selection methods. Sixteen olive cultivars from five countries were evaluated over two years in two distinct climatic regions of Southwestern China. Flowering phenology was assessed based on three parameters: full-bloom date (FBD), flowering-period length (FP), and full-bloom-period length (FBP). In the analyses, the best linear unbiased prediction (BLUP) to predict genetic value and genotype + genotype by environment interaction (GGE) biplot methods to visualize and assess stability and performance were employed across four environments. The results showed that genotype, environment, and GEI had highly significant effects on flowering traits, with GEI accounting for 54.12% to 89.62% of the variance. Heritability values were low (0.0589 to 0.262), indicating that genetic factors had limited control over flowering phenology compared to environmental factors. A stability analysis using a mean performance and stability (MPS) index identified genotypes with earlier flowering dates and longer flowering periods. Multi-trait selection using a multi-trait mean performance and stability (MTMPS) index further highlighted six superior genotypes with high performance and stability across environments. The findings emphasize the critical role of environmental factors on olive flowering phenology, highlighting the challenges in breeding for stable flowering traits. This study demonstrates the effectiveness of multi-trait selection methods in identifying genotypes with superior performance and stability under different environmental conditions. These results provide valuable insights for olive breeding programs, particularly in non-Mediterranean regions, suggesting that targeted selection and multi-trait evaluation could enhance the adaptability and productivity of olive cultivars under changing climatic conditions.

Corylus yunnanensis (Franch.) A. Camus is a deciduous shrub, native to the Hengduan Mountain of Qinghai–Tibetan Plateau, and is an economically and ecologically important woody crop species. In the present study, one hundred and fifty trees sampled from ten populations of C. yunnanensis in Sichuan Province were investigated to assess the population genetic variation using nine SSR markers. The results revealed that C. yunnanensis has an average value of 12.111 alleles, 3.376 effective alleles, an expected heterozygosity of 0.648, and an observed heterozygosity of 0.630, presenting a relatively high level of genetic diversity. The C. yunnanensis populations in Maoxian and Wenchuan of Aba Prefecture expressed the highest value of genetic diversity, whereas the Hanyuan and Muli populations showed the lowest. Moreover, the genetic differentiation of ten C. yunnanensis populations averaged to 0.106. Correspondingly, AMOVA revealed that 87% of the total variance was accounted for the variation within populations, and only 13% was among the populations. Both UPGMA and Bayesian STRUCTURE clustering suggested that the ten C. yunnanensis populations could fall into three clusters: the Aba Prefecture population, the Ya’an population, and the population of Ganzi and Liangshan Prefecture, indicating a significant geographic distribution, which was also confirmed by the Mantel test. Our study could provide a better understanding of population genetic diversity, and serve valuable information for the genetic improvement of C. yunnanensis.

Olive (Olea europaea L.) is one of the oldest woody oil crops. Previous studies, by integrating transcriptomics and metabolomics, have identified glycerol-3-phosphate acyltransferase 4 (GPAT4) as a key regulatory gene involved in oil biosynthesis in olive fruits. Although GPAT4 was identified as a key regulator, the overall function of the GPAT gene family in olive remains largely unknown. As a critical rate-limiting enzyme catalyzing triacylglycerol production, GPAT plays an important role in oil synthesis in oil crops. However, the function of the GPAT gene in olive remains unclear. A systematic analysis of the olive GPAT gene family showed that 12 OeGPAT proteins can be divided into four subclasses, all containing the conserved GPAT domain. These genes are distributed across chromosomes and scaffolds, with highly conserved motifs and variable gene structures. Functional studies revealed that overexpression of OeGPAT1.1, OeGPAT1.2, OeGPAT2, OeGPAT3, OeGPAT4, OeGPAT7, and OeGPAT8 significantly increased total oil content in transgenic Arabidopsis leaves and seeds. Further experiments in olive fruit at maturity stages II, III, and IV demonstrated that overexpression of the same set of OeGPAT genes elevated total oil content, while their silencing resulted in a decrease. In summary, this study reveals that OeGPATs can serve as ideal targets in metabolic engineering to regulate oil content in oil crops, providing a theoretical foundation for further research on oil biosynthesis in olive fruit.