Document Type : Full Paper

Authors

• Ali Tanhaei ¹
• Ahmad Reza Dadras ²
• Hossein Sabouri ¹
• Ebrahim Gholamalipour Alamdari ³
• Sayed Javad Sajadi ⁴
• Hossein Hosseini Moghaddam ⁴

¹ Department of Plant Production, College of Agriculture Science and Natural Resources, Gonbad Kavous University, Gonbad Kavous, Golestan, Iran

² Olive Research Station of Tarom, Crop and Horticultural Science Research Department, Zanjan, Agricultural and Natural Resources Research and Education Center, AREEO, Tarom, Zanjan, Iran

³ Department of Plant Production, College of Agriculture and Natural Resources of Gonbad Kavous University, Gonbad Kavous, Golestan, Iran

⁴ Department of Department of Plant Production, College of Agriculture Science and Natural Resources, Gonbad Kavous University, Gonbad Kavous, Golestan, Iran

Abstract

Keywords

• Association analysis
• Phenotypic diversity
• Regression
• DNA markers

Main Subjects

• Fruit Science

Extended Abstract

Introduction

The Olive tree (Olea europaea L.) is among the oldest cultivated plants found in the Mediterranean region. Owing to scientific progress and heightened awareness, the consumption of olives has grown significantly. Olive oil, which is rich in oleic acid, is esteemed for its therapeutic and medicinal properties. In Iran, olives are particularly important due to their high oil content. Understanding different genotypes and their relationships are crucial for genetic studies, and this require examining both morphological and employing molecular markers. Morphological traits, such as fruit characteristics, are crucial as they reflect the genetic makeup of the plant and its interaction with the environment. Molecular markers, which can be easily measured, are also powerful tools for identifying genotypes and assessing genetic diversity. This study explored the extent of genetic diversity in a large collection of olive germplasm utilizing morphological characteristics of fruit and molecular markers. The findings of this study could be valuable for olive breeding programs, helping to select parent plants with desirable traits for improved yield, quality, and disease resistance.

Materials and Methods

A total of 89 olive genotypes cultivated in Tarem Olive Research Station of Zanjan Province, Iran were analyzed in this study during 2019-2021. To evaluate the characteristics of fruit length, fruit diameter, fruit symmetry, fruit shape, position of maximum diameter, fruit apex, nipple, presence of lenticels, size of lenticels, site of color change initiation, flesh thickness, flesh-to-stone ratio, stone length, stone shape, number of grooves, stone apex, fruit weight, fruit flesh weight, and stone weight, the sum of 150 fruits from each genotype were selected. For the purpose of molecular analysis, fresh and young leaves of olive trees were collected for DNA extraction. The leaves were powdered with the aid of liquid nitrogen and extracted using the CTAB method. The quality of DNA was assessed through horizontal electrophoresis with 0.8% agarose gel. PCR reactions were performed using CAAT, ScoT, ITS, and IJS markers. SPSS software version 24 was used to analyze the relationship between morphological traits and the analysis between morphological and molecular traits.

Results and Discussion

All the investigated traits showed significant differences among olive genotypes at the 1% probability level, indicating very high genetic diversity among the genotypes. The results of mean comparisons showed that “Caridolia” and “D1” genotypes demonstrated the greatest fruit length and diameter, while 'D1' also excelled in fruit weight, fruit flesh weight, and stone weight. The 'Amygdalolia' genotype had the longest stone length. The highest significant positive correlations were observed between fruit length and diameter (0.909*), as well as between fruit flesh weight and fruit weight (0.994*). Additionally, there was a positive and significant correlation between fruit weight and stone weight (0.842) at the 1% probability level. The finding of regression analysis, considering fruit weight as the dependent variable and other traits as independent variables, showed that fruit flesh weight and stone weight had the highest correlation with fruit weight at the 1% probability level. Furthermore, fruit weight, flesh-to-stone ratio, fruit diameter, and flesh thickness were most related to fruit weight. Cluster analysis divided the genotypes into four groups based on fruit traits, with the third group being superior in traits such as fruit length, stone length, fruit weight, fruit flesh weight, stone weight, fruit diameter, flesh thickness, flesh-to-stone ratio, size of lenticels, and number of grooves. Association analysis between molecular markers and various traits revealed that fruit length, fruit symmetry, nipple, stone shape, number of grooves, and stone weight were controlled by multiple alleles. Among these traits, fruit symmetry, nipple, and number of grooves had the highest cumulative coefficient of determination. The strongest association of the alleles to traits was obtained from allele SCoT21-B and IJS9-A with nine five traits, respectively.

Conclusion

This study revealed significant genetic diversity among olive genotypes, with 'Caridolia' and D1 genotypes showing superior fruit traits. Strong correlations were found between key traits, and regression analysis highlighted fruit flesh weight and stone weight as major factors influencing fruit weight. Molecular marker analysis identified important alleles, with SCoT21-B showing the strongest association with multiple traits. These findings are valuable for breeding programs aimed at improving olive cultivars.

Author contributions

A.R. Dadars and H. Sabouri carried out the planning and design of the experiment. Experimental sample collection was carried out by A.R. Dadars. A. Tanhaei conducted the experiments. A.R. Dadars, H. Saboor, and S.J. Sajadi analyzed the data. A. Tanhaei, H. Sabouri, and A.R. Dadars wrote the initial draft of the manuscript. A.R. Dadars, H. Sabouri, and S.J. Sajadi contributed to the interpretation of the results. All authors provided critical feedback and made significant contributions throughout all stages of the research, data analysis, and manuscript completion.

Data availability statement

Data available on request from the authors

Acknowledgements

The authors would like to express their gratitude and appreciation to the Olive Research Station of Tarom County and the Agricultural Research Center of Zanjan Province for their collaboration in providing the plant materials for the present research.

Ethical considerations

The authors avoided data fabrication, falsification, plagiarism, and misconduct.

Conflict of interest

     The authors declare no conflict of interest.