Research Article

Evaluation of Some Promising Varieties of Olive (Olea europaea L.) for Growth and Yield under Pothwar Regions of Punjab, Pakistan

Muhammad Ashraf Sumrah1*, Muhamad Jan1, Azhar Hussain2, Shoaib Akhtar1, Hussain Nawaz1, Muhammad Afzal3 and Humara Umar1

1Centre of Excellence for Olive Research and Training (CEFORT), Pakistan; 2Barani Agricultural Research Institute, Chakwal, Pakistan; 3Hill Fruit Research Station (HFRS), Murree, Pakistan.

Received | February 18, 2021; Accepted | May 18, 2021; Published | June 18, 2021

*Correspondence | Muhammad Ashraf Sumrah, Centre of Excellence for Olive Research and Training (CEFORT), Pakistan; Email: [email protected]

Citation | Sumrah, M.A., M. Jan, A. Hussain, S. Akhtar, H. Nawaz, M. Afzal and H. Umar. 2021. Evaluation of some promising varieties of olive (Olea europaea L.) for growth and yield under Pothwar Regions of Punjab, Pakistan. Pakistan Journal of Agricultural Research, 34(3): 446-453.

DOI | https://dx.doi.org/10.17582/journal.pjar/2021/34.3.446.453

Keywords | Olive, Varieties, Growth, Oil recovery, Pothwar

Introduction

Olive is getting popularity among all spheres of society due to its medicinal and dietary value. Previously, Olive was considered as a crop of the Mediterranean countries. The Mediterranean region is the main olive producing area including Syria, Turkey and Israel (Trujillo et al., 2014). Presently many other regions of the world are adapting olive cultivation in their cropping system due to its economic value, comparatively easy production technology and wider adaptability. During last couple of decades, consumption and cultivation of olive also started in many countries other than Mediterranean basin like Australia, India, China, Pakistan and the American southern part (Awan et al., 2011). Olive plant have an adaptive mechanism to grow well and produce fruit under rain fed conditions (Ahmed et al., 2009; Giuffre, 2017; Lorite et al., 2018).

According to International Olive Council (IOC), global virgin olive oil was 3207,000 tons in which maximum oil was produced by Spain (1125, 300 tons), Italy (366,000 tons), Tunisia (350, 000 tons), Greece (275, 000 tons), Turkey (225, 000 tons), Morocco (145, 000 tons) and Portugal (140,500 tons). The total Olive Oil production of the IOC member countries in 2020/21 was 2,999,500 tons comprising of 93.8% of the world total production, a decrease of 0.3% compared to the last year. Olive fruit production for 2019-20 amounted to 3,057,500 tons, an increase of 5.5% compared to the last year. Among the IOC member countries, Spain stands out for its weight in world production (15%), despite a 22.5% drop. Egypt’s production has increased by 25% compared to the 2018-19 campaign, contributing 24.5% of the world total. According to estimates for the 2020-21 campaign, production could increase by 2.5% compared to 2019-20, reaching 3,134,000 tons, and consumption would increase by 0.4% (Anonymous, 2020-21).

Awareness of olive cultivation among farming community of Pakistan shows economical survival of olive in Pakistan. The increasing demand of Olive oil and its value-added products like Olive pickles, jam, squash, murabah, candies and other sweet products encouraging farmers to produce more and more fruit. Total plantation in Pakistan is now 29,48,780 by Pakistan Agricultural Research Council (PARC) source (Khaliq et al., 2020). Olive is being cultivated in Pothwar region of Punjab, Pakistan but Chakwal district’s contribution is highest. In Chakwal 3285 acre area is under olive cultivation. Overall Area under olives in Pothwar is 8615 acres there is an increasing trend in the area of olive groves in Pakistan. In BARI, according to the development programs i.e. Developing Pothwar into Olive Valley and Public Sector Development Program (PSDP) projects olive plantation in Punjab Pakistan was 1,77,4019 and 75,250 respectively. Olive can play its essential role in our country’s economy. It is evaluated that Pakistan’s aggregate household edible oil use is around 2.9 million tons. Approximately, 67% of this consumption is met through import (Azmat et al., 2020).

It is crucial to known olive varietal performance under sub mountainous agro climatic conditions for successful olive cultivation and development of economical olive industry in the area. Vegetative and reproductive growth characters in olive tree strongly respond to light availability, canopy differences, and architecture of different cultivars (Schneider et al., 2012; Cherbiy-Hoffmann et al., 2013; Rousseaux et al. 2020). Olive varieties to compare the leaf area distribution, canopy architecture, leaf anatomical characteristics and production efficiency of Arbequina, Coratina and Frantoio are currently considered as best varieties for olive production under Mediterranean climate (Tous, 2010; Neri et al., 2020).

Olive varieties like Nevadillo, Manzanilla and Lechín, showed a less percentage changes in adequate area, as for Verdial and Picual. Different researchers suggested that the difference in stem girth of olive varieties might be due to inhabitant suitability occur both inside and outside the species´ distribution range (Rosati et al., 2017). In areas of Tunisia, Methamem et al. (2015) reported highest oil contents in Picholine and Fougi as compared to Dahbia and Lucques. In case of Pakistan climatic conditions, Gemlik variety is one of the dominant varieties regarding oil recovery %. Among few olive varieties like Dolce agogia, Moraiolo, Coratina, Leccino, Uslu and Gemlik. Arbequina and Frantoio contained the significant amount of olive oil (Khaliq et al., 2020).

Olive cultivation history of the Punjab province is not very long. Throughout the last one-decade, olive gained much popularity as a result of its great socio-economic importance. During the past ten years, Olive was cultivated on area of more than 4494.36 hectares in the Pothwar region (Anonymous, 2020; Anonymous, 2018). Pakistani agro-climatic conditions are not exactly like the Mediterranean countries. Various olive varieties are being cultivated in Pothwar region and the provinces of Baluchistan and Khyber Pakhtunkhwa (Awan et al., 2014; Pulido-Fernández et al., 2019).

Olive varieties do not perform uniformly in all climatic conditions in olive producing countries. Every climatic zone has to select suitable varieties of olive for adaptability and profitability through local research system. A lot of research was done at BARI Chakwal for performance evaluation of different table varieties of olive to ensure the maximum profitability from olive cultivation. Eight varieties having promising results were compared to find the most suitable variety for economical production in particular conditions of olive growers. The present study was conducted to select the most suitable olive varieties for cultivation in sub mountainous area of the Punjab Province. Olive variety having maximum fruit yield and good oil recovery along with uniform, thin distribution of leaves and balanced tree canopy is required for cultivation in extreme cold and hot temperatures during summer and winter season. The main objective of the this study was to compare and evaluate the performance of some promising olive varieties for growth and production potential under local agro climatic conditions for general cultivation in sub mountainous area of the Punjab.

Materials and Methods

The current experiment was conducted at the research area of Barani Agricultural Research Institute (BARI), Chakwal, Pakistan. BARI is located on 72o longitude, 32olatitude and 575m altitude. The Climate of BARI Chakwal area is arid to semi-arid, having annual rainfall of 772 mm annually. The area having lowest temperature during January is -4.00°C and maximum 36.00 – 38.00 °C during summer. Maximum rainfall (408 mm) is received during the months of July to September.

Experimental plants of olive varieties i.e. Ascolana, BARI Zaitoon-1, Earlik, Gemlik, Hamdi, Hojiblanca, Manzanilla and Picual selected with uniform canopy having age of 9 to 10 years. Soil texture was sandy loam which was measured by hydrometer method, organic matter (OM) 0.89 % which was calculated through wet oxidation method, EC= 1.5 d Sm-1, which was calculated by using EC meter (DDS-307A), pH of 8.1 which was calculated by using pH meter (Mettler Toledo Delta 320), CaCO3= 4.23% calculated through titration method. Planting geometry of 6.00×6.00 meter was established for experimental layout. The cultural practices like weeding, hoeing, fertilization and irrigation were kept same to get maximum precision and accuracy. The aforementioned olive varieties were selected for their better performance regarding vegetative growth and production behavior in local agro climatic conditions. Plant height was measured with the help of measuring tape from ground level to apex of the plant (cm). Stem girth was measured by calculating average annual growth rate of the stem girth (cm) and inter nodal distance was measured with meter rod (cm). Average fruit weight (g) was calculated from fifty fruits randomly selected from all canopy of the tree from all directions. Fruit sample was randomly selected regarding fruit size and maturity stage. Fruit yield (kg) was calculated by weighing the whole harvested fruit from each experimental unit (24 plants). Oil recovery (%) was calculated after 1st press of fruit harvested from each experimental unit. Olive oil was extracted by commercial extraction unit having centrifugal technology with fruit crushing capacity of 600 Kg/hour (Model Pieralisi, Italy).

Statistical analysis

The mean data regarding vegetative, productive and oil recovery were analyzed statistically. Least significance difference (LSD) calculated at the P< 0.05 (Steel et al., 1997).

Results and Discussion

Morphological characteristics of olive

Plant height: Plant height is not a permanent trait that should be same among the all varieties, but it varies according to genetic makeup, climatic conditions and cultural practices. Olive cultivars were evaluated for plant height. Maximum plant height (258.30 cm) was recorded in Earlik variety while minimum plant height (192.50 cm) was observed in Manzanilla olive variety (Figure 1).

 

Numerous distinguishing techniques used in olive trees to evaluate its diversity. There are various techniques for evaluation of olive tree diversity. Among those, morphological characteristics are most important. There are different quantitative and qualitative characteristics that can be studied through physical observations like plant height. Plant height actually determine the growth and development of a tree according to its existing climate (Kareem et al., 2018; Sharief et al., 2019; Nafees et al., 2020). A variation in plant height among the olive varieties actually results due to the effect of environmental conditions and genetic makeup of the variety which perform differently in specific climatic conditions (Hammami et al., 2011). The current results are also in line with the findings of Mnasri et al. (2017) and Bartoli et al. (2020) who reported that plant height is an important tool for evaluating the olive varieties.

Stem girth: Maximum plant girth (5.26 cm) of olive tree was recorded in Hamdi variety while minimum girth (4.55 cm) of olive tree was observed in BARI Zaitoon-1 olive variety (Figure 2).

 

Genetic varietal make up and environmental conditions results into growth rate of stem girth which ultimately strengthen the plant existence (Naqvi et al., 2015; Akram et al., 2019). Olive trees having better stem girth are stronger and more resistant against wind storms and helpful in better management of tree canopy. These results are in conformity with the results obtained by some other researchers (Moriondo et al., 2013; Viola et al., 2013; Olesen and Wirthensohn, 2020; Ponti et al., 2014; Fraga et al., 2019; Arenas-Castro et al., 2020).

Internodal distance: Inter nodal distance of olive varieties determines the canopy shape and porosity of the branches favoring for light and air permeability. Maximum intermodal distance (5.26 cm) of olive tree was recorded in Earlik variety while minimum intermodal distance (4.55 cm) of olive tree was observed in Hamdi olive variety (Figure 3).

 

Olive branches internodal distance variation actually resulted due to its higher number of primary branches, conical canopy and a reproductive ability equivalent to cuttings. Some other researchers also reported the same findings in case of internodal distance (Neri et al., 2020). Internodal distance variation was also in consistent to other investigators (Hannachi et al., 2008; Poljuha et al., 2008). These findings were like those of Fayek et al. (2014) who reported similar results while comparing Egyptian olive clones with the international genotypes.

Fruit weight: Fruit weight is the main trait that should be consider for yield estimate of Olive tree. In the current study, Olive varieties like Ascolana, Earlik and Gemlik having a fruit with more pulp which ultimately impact the fruit size. Maximum fruit weight (4.12 g) of olive tree was recorded in Earlik variety while minimum fruit weight (1.52 g) of olive tree was observed in Manzanilla olive variety (Figure 4).

 

Average fruit weight of a variety indicates the productivity potential of the specific variety. Fruit weight of a variety reflects its yield and multiple use of fruit for developments of olive products. Similar results in case of fruit weight also reported by other researchers (Shahzad et al., 2013; Mahmood et al., 2014; Marino et al., 2019; Rosati et al., 2018; Proietti et al., 2015).

Fruit yield: Fruit yield per plant indicates economic potential of the variety along with its adaptability with olive growers. Maximum fruit yield (22.66 Kg plant-1) of olive tree was recorded in Earlik while minimum fruit yield (15.71 Kg plant-1) of olive tree was observed in Manzanilla olive variety (Figure 5).

Olive varieties have a varietal variation keeping in view oil and fruit production some have dual purpose. In the current experiment mostly table varieties were studies. Earlik was the prominent one as compared to other varieties. In the previous studies of Pothwar region of Pakistan, “Nocellara” was the only genotype which was used for table purpose while another genotype “Sorani” was used for both table and oil (dual) purpose (Qureshi et al., 2020). The table varieties have a bold fruit size as compared to oil varieties which ultimately increased the fruit yield Trentacoste and Puertas (2011).

 

Oil recovery (%): Oil recovery from an olive variety is main tool for its acceptability among olive growers and processors. Maximum oil recovery (24.66 %) from olive fruit was recorded in Earlik variety while minimum oil recovery (14.36 %) was observed in BARI-Zaitoon-1 (Figure 6). In a previous study, it was found that every cultivar have a variation in oil contents which is actually due to its genetic trait besides of this some management factors like soil, temperature and climate have a significant impact but the temperature is the dominant factor which effect the oil contents (Oteros et al., 2014). Oil contents variation of fruit also correlate with fruit size that affected from exogenous and endogenous factor (Hammami et al., 2011).

 

Highest fruit weight, pit weight and concentration of fatty acid directly correlate with oil recovery percentage. (Mehri and Mehri, 2007; Hannachi and Marzouk, 2012). Qureshi et al. (2020) also observed similar observation in their study of olive adaptation in Pothwar climate of Pakistan, they reported maximum oil recovery from olive verity “Mariania”.

Conclusions and Recommendations

Olive varieties respond differently regarding the growth and yield parameters. All the varieties showed a different response according to Pothwar climate. The table varieties like Ascolana, Earlik, Gemlik and Hamdi performed well under the climatic condition of Pothwar area. The findings of present study led us to conclude that various olive varieties performed differently for growth, yield and quality parameters under sub-mountainous climate condition. The olive varieties like Ascolana, Earlik, Gemlik, and ‘Hamdi’ found as most suitable varieties of olive with potential growth and high yield potential. The proposed selected olive varieties can be recommended for commercial cultivation in Pothwar region and the adjoining areas of Punjab for better yield and oil recovery.

Acknowledgments

The authors wish to thank Director, CEFORT Barani Agricultural Research Institute, Chakwal, Pakistan for the research support.

Novelty Statement

The current experiment is the first one which highlighted the adaptation of Olive varieties in the Pothwar climate because being a tree it require huge time for its adaptation especially to study its yield and growth parameters. BARI Chakwal is the one designated institute who working in the Olive sector in Pakistan.

Author’s Contribution

Muhammad Ashraf Sumrah conducted this experiment and data were collected and analyzed by Muhamad Jan and Azhar Hussain who designed this experiment. The first draft of the article was prepared by Muhammad Ashraf Sumrah and Muhammad Jan. Final draft was also prepared by Shoaib Akhtar and Humara Umar after a proof reading of Hussain Nawaz and Muhammad Afzal.

References

Ahmed, C.B., B.B. Rouina, S. Sensoy, M. Boukhris and F.B. Abdallah. 2009. Changes in gas exchange, proline accumulation and antioxidative enzyme activities in three olive cultivars under contrasting water availability regimes. Environ. Exp. Bot. 67(2): 345-352. https://doi.org/10.1016/j.envexpbot.2009.07.006

Akram, M.T., R.W.K. Qadri, M.J. Jaskani and F.S. Awan. 2019. Ampelographic and genetic characterization of grapes genotypes collected from potohar region of Pakistan. Pak. J. Agric. Sci., 56: 595-605.

Anonymous, 2020-21. International Olive Council (IOC), Spain. https://www.internationaloliveoil.org/

Anonymous, 2020. Barani Agricultural Research Institute (BARI) Chakwal, Pakistan. https://barichakwal.punjab.gov.pk/

Anonymous, 2018. Pakistan Agricultural Research Council (PARC). Islamabad, Pakistan. http://www.parc.gov.pk/index.php/en/

Arenas-Castro, S., J.F. Gonçalves, M. Moreno and R. Villar. 2020. Projected climate changes are expected to decrease the suitability and production of olive varieties in southern Spain. Sci. Total Environ., 709: 136161. https://doi.org/10.1016/j.scitotenv.2019.136161

Awan, A.A., M. Zubair, A. Iqbal, S.J. Abbas and N. Ali. 2011. Molecular analysis of genetic diversity in olive cultivars. Afr. J. Agric. Res. 6(21): 4937-4940.

Awan, AA., 2014. Influence of agro-climatic conditions on fruit yield and oil content of olive cultivars. Pak. J. Agric. Sci., 51(3).

Azmat, M. A., Khan, A. A., Khan, I. A., Buerkert, A and M. Wiehle. 2020. Morphology, biochemistry, and management of Russian olive (Elaeagnus angustifolia L.) accessions in Gilgit-Baltistan, northern Pakistan. J. Agri. Rural Develop. Trop. Subtrop. Vol. 121 No. 2 151–160.

Bartoli, M., M.A. Nasir, P. Jagdale, E. Passaglia, R. Spiniello, C. Rosso and A. Tagliaferro. 2020. Influence of pyrolytic thermal history on olive pruning biochar and related epoxy composites mechanical properties. J. Comp. Mat., 54(14): 1863-1873. https://doi.org/10.1177/0021998319888734

Cherbiy-Hoffmann, S.U., A.J. Hall and M.C. Rousseaux. 2013. Fruit, yield, and vegetative growth responses to photosynthetically active radiation during oil synthesis in olive trees. Sci. Hortic., 150: 110-116. https://doi.org/10.1016/j.scienta.2012.10.027

Fayek, M.A., M.A. Abdel-Mohsen, S.I. Laz and S.M. El-Sayed. 2014. Morphological, agronomical and genetic characterization of Egyptian olive clones compared with the international cultivars. Egypt. J. Hortic., 41: 59-82. https://doi.org/10.21608/ejoh.2014.1354

Fraga, H., J.G. Pinto and J.A. Santos. 2019. Climate change projections for chilling and heat forcing conditions in European vineyards and olive orchards: a multi-model assessment. Clim. Change, 152(1): 179-193. https://doi.org/10.1007/s10584-018-2337-5

Giuffre, A.M., 2017. Biometric evaluation of twelve olive cultivars under rainfed conditions in the region of Calabria, South Italy. Emir. J. Food Agric., pp. 696-709. https://doi.org/10.9755/ejfa.2017.v29.i9.110

Hammami, S.B., T. Manrique and H.F. Rapoport. 2011. Cultivar-based fruit size in olive depends on different tissue and cellular processes throughout growth. Sci. Hortic. 130(2): 445-451. https://doi.org/10.1016/j.scienta.2011.07.018

Hannachi, H. and S. Marzouk. 2012. Flowering in the wild olive (Olea europaea L.) tree (oleaster): Phenology, flower abnormalities and fruit set traits for breeding the olive. Afr. J. Biotechnol., 11: 8142-8148. https://doi.org/10.5897/AJB11.3477

Hannachi, H., C. Breton., M. Msallem. S.B. Elhadj., M. El-Gazzah and A. Berville. 2008. Differences between native and introduced olive cultivars as revealed by morphology of drupes; oil composition and SSR polymorphisms: A case study in Tunisia. Sci. Hortic., 116: 280-290. https://doi.org/10.1016/j.scienta.2008.01.004

Kareem, A., M.J. Jaskani, A. Mehmood, I.A. Khan, F.S. Awan and M.W. Sajid. 2018. Morpho-genetic profiling and phylogenetic relationship of guava (Psidium guajava L.) as genetic resources in Pakistan. Rev. Bras. Frutic. 40: e-069. https://doi.org/10.1590/0100-29452018069

Khaliq, A., S.M. Ali Shah, M. Akram, M., N. Munir, M. Daniyal, M. Irshad, and S. Ahmad. 2020. Determination of oil contents from eight varieties of Olea Europaea (Olive) grown in Pakistan. Natural Product Res. 34(13), 1951-1955.

Lorite, I.J., C. Gabaldón-Leal, M. Ruiz-Ramos, A. Belaj, R. De la Rosa, L. Leon and C. Santos. 2018. Evaluation of olive response and adaptation strategies to climate change under semi-arid conditions. Agric. Water Manage. 204: 247-261. https://doi.org/10.1016/j.agwat.2018.04.008

Marino, G., L. Macaluso, F. Grilo, F.P. Marra and T. Caruso. 2019. Toward the valorization of olive (Olea europaea var. europaea L.) biodiversity: Horticultural performance of seven Sicilian cultivars in a hedgerow planting system. Sci. Hortic., 256: 108583. https://doi.org/10.1016/j.scienta.2019.108583

Mehmood, A., M.J. Jaskani, I.A. Khan, S. Ahmad, R. Ahmad, S. Luo and N.M. Ahmad. 2014. Genetic diversity of Pakistani guava (Psidium guajava L.) germplasm and its implications for conservation and breeding. Sci. Hortic., 172: 221-232. https://doi.org/10.1016/j.scienta.2014.04.005

Mehri, H. and K.R. Mehri. 2007. The bioagronomic characteristics of a local olive cultivar Gerboui. J. Plant Physiol., 2: 1-16. https://doi.org/10.3923/ajpp.2007.1.16

Methamem, S., H. Gouta, A. Mougou, M. Mansour and D. Boujnah. 2015. Yield, fruit and oil content of some olive (Olea europaea L.) cultivars field-grown in Tunisia. Ann. Biol. Res., 6: 64-71.

Mnasri, S.R., O.D. Saddoud, S. Rouz, M.B. Saleh and A. Ferchichi. 2017. Fingerprinting of the main olive cultivars in Tunisia by morphological and AFLP markers. J. New Sci., 37: 220-228.

Moriondo, M., G. Trombi, R. Ferrise, G. Brandani, C. Dibari, C.M. Amman and M. Bindi. 2013. Olive trees as bio-indicators of climate evolution in the Mediterranean Basin. Glob. Ecol. Biogeo., 22(7): 818-833. https://doi.org/10.1111/geb.12061

Nafees, M., M.J. Jaskani, I. Ahmad, Maryam, I. Ashraf, A. Maqsood, S. Ahmar, M. Azam, S. Hussain, A. Hanif and J.-T. Chen. 2020. Biochemical analysis of organic acids and soluble sugars in wild and cultivated pomegranate germplasm based in Pakistan. Plants, 9: 493. https://doi.org/10.3390/plants9040493

Naqvi, S.A., I.A. Khan, J.C. Pintaud, M.J. Jaskani and A. Ali. 2015. Morphological characterization of Pakistani date palm (Phoenix dactylifera L.) genotypes. Pak. J. Agric. Sci., 52: 645-650.

Neri, D., T. Cioccolanti, G. Zuccherelli, O. Navacchi, V. Giorgi and E.M. Lodolini. 2020. Micropropagation effects on juvenile traits, flower differentiation, and tree architecture in young olive trees. Agron., 10(11): 1742. https://doi.org/10.3390/agronomy10111742

Olesen, T. and M. Wirthensohn. 2020. The flush development of evergreen recurrent flushing perennials: an experimental overview with insights into the flowering of olive. Aust. J. Bot., https://doi.org/10.1071/BT19159

Oteros, J., F. Orlandi, H. García-Mozo, F. Aguilera, A.B. Dhiab, T. Bonofiglio and C. Galán. 2014. Better prediction of Mediterranean olive production using pollen-based models. Agron. Sustain. Dev., 34(3): 685-694. https://doi.org/10.1007/s13593-013-0198-x

Poljuha, D., S. Barbara, B.B. Karolina, R. Marina, B. Kristina, K. Marin and M. Aldo. 2008. Istrian olive varieties characterization. Food Technol. Biotechnol., 46: 347-354.

Ponti, L., A.P. Gutierrez, P.M. Ruti and A. Dell’Aquila. 2014. Fine-scale ecological and economic assessment of climate change on olive in the Mediterranean Basin reveals winners and losers. Proc. Natl. Acad. Sci., 111(15): 5598-5603. https://doi.org/10.1073/pnas.1314437111

Proietti, P., L. Nasini, L. Reale, T. Caruso and F. Ferranti. 2015. Productive and vegetative behavior of olive cultivars in super high-density olive grove. Sci. Agric. 72(1), 20-27.

Pulido-Fernandez, J.I., J. Casado-Montilla and I. Carrillo-Hidalgo. 2019. Introducing olive-oil tourism as a special interest tourism. Heliyon, 5(12): e02975. https://doi.org/10.1016/j.heliyon.2019.e02975

Qureshi, M.S., R.W.K. Qadri, M.J. Jaskani and R. Ahmad. 2020. Morphological and biochemical assessment of eight olive genotypes growing in potohar region of Pakistan. Pak. J. Agric. Sci., 57(4): 1036-1043.

Rosati, A., A. Paoletti, G. Pannelli and F. Famiani. 2017. Growth is inversely correlated with yield efficiency across cultivars in young olive (Olea europaea L.) trees. Hortic. Sci., 52: 1525–1529. https://doi.org/10.21273/HORTSCI12321-17

Rosati, A., A. Paoletti, R. Al-Hariri, A. Morelli and F. Famiani. 2018. Partitioning of dry matter into fruit explains cultivar differences in vigor in young olive (Olea europaea L.) trees. Hortic. Sci., 53(4): 491-495. https://doi.org/10.21273/HORTSCI12739-17

Rousseaux, M.C., S.U. Cherbiy-Hoffmann, A.J. Hall and P.S. Searles. 2020. Fatty acid composition of olive oil in response to fruit canopy position and artificial shading. Sci. Hortic. 271: 109477. https://doi.org/10.1016/j.scienta.2020.109477

Schneider, D., M. Goldway, R. Birger, and R.A. Stern. 2012. Does alteration of ‘Koroneiki’olive tree architecture by uniconazole affect productivity? Sci. Hortic. 139: 79-85. https://doi.org/10.1016/j.scienta.2012.03.006

Shahzad, U., M.A. Khan, M.J. Jaskani, I.A. Khan and S.S. Korban. 2013. Genetic diversity and population structure of Moringa oleifera. Conserv. Genet., 14: 1161-1172. https://doi.org/10.1007/s10592-013-0503-x

Sharief, N., M.J. Jaskani, S.A. Naqvi and F.S. Awan. 2019. Exploitation of diversity in domesticated and wild ber (Ziziphus mauritiana Lam.) germplasm for conservation and breeding in Pakistan. Sci. Hortic., 249: 228-239. https://doi.org/10.1016/j.scienta.2019.01.041

Steel, R.G.D., J.H. Torrie and G.H. Dickey. 1997. Principles and Procedures of Statistics. A Bio-Matrical Approach, 3rd edition. McGraw Hill Book Co., Inc. New York. pp. 400-428.

Tous, J., 2010. Olive production systems and mechanization. In XXVIII International Horticultural Congress on Science and Horticulture for People (IHC2010): Olive Trends Symposium-From the 924. pp. 169-184.

Trentacoste, E.R. and C.M. Puertas. 2011. Preliminary characterization and morpho-agronomic evaluation of the olive germplasm collection of the Mendoza province (Argentina). Euphytica, 177: 99-109. https://doi.org/10.1007/s10681-010-0270-4

Trujillo, I, M.A. Ojeda, N.M. Urdiroz, D. Potter, Barranco, D.L. Rallo and C.M. Diez. 2014. Identification of the worldwide olive germplasm bank of Cordoba (Spain) using SSR and morphological markers. Tree Gen. Genom., 10(1): 141-155. https://doi.org/10.1007/s11295-013-0671-3

Viola, F., D. Caracciolo, D. Pumo and L.V. Noto. 2013. Olive yield and future climate forcings. Proc. Environ. Sci., 19: 132-138. https://doi.org/10.1016/j.proenv.2013.06.015