Improving oil quality and increasing yield per hectare in oil palm is a major concern in the oil processing industry. Agrosavia’s palm breeding program has focused on interspecific crosses of OxG. According to Bastidas  the OxG hybrids of Agrosavia present heterosis in traits such as resistance to diseases, fruit number and weight, leaf length and trunk diameter. To our knowledge, this study represents the first geno-phenotypic and GWAS analysis of an OxG hybrid population. Our 378 OxG hybrid population was screened for a set of morphological and yield-related traits and genotyped with 3,776 high-quality SNPs uncovered by a GBS approach. Correlation analysis results among yield-related traits indicated that BN could be a potential and better selection criterion for production than BW in the hybrid population. It is known that the leaf emission rate determines the bunch number in a palm, being BN negative correlated with number of leaves . In our study, no significant correlations were found between yield and leaf-related traits (FA, LA, LDW, LXL, RL), however, a previous study in E. oleifera and OxG found that BN can be greater that number of leaves just when oil palms carry in their genotype a prolific trait . Increases in BN and BW are also expected to correlate with increased mesocarp and kernel oil yields as shown in other oil palm germplasm studies . Future studies specifically related to oil yields for the OxG hybrid population should be conducted considering their importance in oil palm breeding.
GBS and its combination with GWAS has allowed the genetic dissection of variation in complex traits in many plant species [35–37]. Specifically, in oil palm the GBS technique has been used for identifying candidate genes in intraspecific populations related to oil bunch , average bunch weight [21, 38] and stem height  with the enzyme ApeKI, meanwhile the enzymes PstI-MspI have been used for oil quality traits studies . We used GBS with the enzyme PstI in morphological and yield-related traits in an interspecific OxG hybrid population. The use of this enzyme allowed the discovery of new genetic variants, which according to Chung et al.  is one of the most important advantages of GBS.
In the present study, association mapping resulted in the identification of 12 SNPs related to 10 morphological and yield-related traits (Table 2). For morphological traits, a significant association was found for LDW on chromosome 3 explaining 10% of the phenotypic variation. This SNP was located in a mechanosensitive (MS) ion channel protein 10-like (MSL10) gene. In plants, MS ion channels have been proposed to play a wide array of roles, from the perception of touch and gravity to the osmotic homeostasis of intracellular organelles . Besides, mechanoperception genes are essential for normal cell and tissue growth and development as well as for the proper response to an array of biotic and abiotic stresses . A second gene associated with TD was identified on chromosome 15. This gene is involved in nucleic acid binding and has a C2H2-type Zinc finger domain. The C2H2-ZF gene family has been proposed to be involved in the formation of wood and shoot and cambium development in species such as Poplar, as well as playing a role in stress and phytohormone response .
For HT trait, different studies have reported associated QTLs in chromosomes 2, 6, 7 and 9 [22, 34]. In our study, we reported three candidate genes on chromosome 15, which is similar to the results reported by Pootakham et al. . However, our candidate genes were positioned in the vicinity of the ones reported by Pootakham et al. , which highlights the importance of this region (from 19.3 to 23.6 Mbp) in the phenotypic variance of HT (Table 2). The closest gene to the SNPs S15_22553489 and S15_22553493 SNPs, corresponds to a STYK gene, which is involved in the control of stomatal movement in response to CO2 . Recent studies also showed the role of STYK gene in stem diameter by increasing the number of xylary fibers in species such as Bambusa balcooa .
For RL and LXL traits QTLs have been reported on chromosomes 4, 2, 10 and 16 . In our study, four SNPs were associated with four different candidate genes for RL on chromosome 13. The SNP S13_20856724 is the closest to the AGC3 gene and encodes different G proteins. G proteins had been reported to be involved in a wide range of developmental and physiological processes, having a high potential for yield improvement in crops such as rice . The other significant association was found with the SNP S13_23674227, which is located in an extracellular ribonuclease gene (RNase gene). RNase genes have been studied for years in plants, playing an important role in plant defense mechanism  or plant development due to their ability to modify RNA levels, and thereby influence protein synthesis . Other candidate genes were also found for RL and LXL, but further studies are necessary to determine their role in regulating these traits.
For yield-related traits, previously studies reported associated SNPs in chromosomes 1, 3, 4 and 6 [21, 38, 49]. In our study, other major associations peaks were observed on chromosomes 5 and 10, explaining 11% of the phenotypic variance. A significant SNP related to Yield and BN was located in the gene p5.00_sc00003_p0367, coding for a cation/H(+) antiporter gene. Antiporter proteins function as regulators of monovalent ions, pH homeostasis, and developmental processes in plants . On chromosome 10, the gene p5.00_sc00004_p0097, associated with BW, encodes the zinc finger protein 8. The zinc finger proteins (ZFP) are a large protein family, involved in plant development, regulation of plant height, root development, flower development, seed germination, secondary wall thickening, anther development, and fruit ripening . Studies conducted by Wu et al.  demonstrated that silencing a gene related to ZFP hampered fruit development in Nicotiana benthamiana . This ZFP gene might play an important role on yield-related traits in oil palm, as shown in other plants, where overexpression of zinc finger proteins are related with higher yields in crops  although, further analysis are needed to determine its role in bunch weight and yield in oil palm.
In oil palm, harvesting of fruit bunches after certain age is a very difficult labor due to their tallness. For this reason, genotypes with less HT and TD are preferred among oil palm farmers. Likewise, larger foliar (RL and LDW) is related to a greater photosynthetic production which could be involve in higher productivity. But most importantly, increasing the number and weight of fruits means higher productivity per palm and therefore higher incomes for farmers. For this reason, leveraging QTLs or genes related to these traits could contribute to develop plant breeding strategies such as marker-assisted selection (MAS), that helps to select promising accessions in in earlier stages (greenhouse conditions), and therefore reduce the breeding cycle. Further work needs to be focus on the biological functions of the set of candidate genes found in our research, though the correlations identified in association studies cannot be dubbed as causations.