Determination of the Optimal Time for Topworking of Olive (Olea europaea L.) Trees in Different Regions of Iran

In some olive trees despite suitable vegetative growth and reproductive to maturity stage, fruits do not set and development do not occur, due mainly to lack of the adaptability. This research was conducted to determine the optimal time for topworking in olive trees using scions from two common cultivars in each of the six provinces including Fars, Khuzestan, Kermanshah, Lorestan, Ilam and Qazvin in Iran during 2021-2022. Results showed that optimal time for topworking in olive trees in Khuzestan was in the mid-October with cv. Conservolia scion, in Ilam in the second half of October with cv. Conservolia and cv. Diereh scions, in Lorestan in the first half of October with cv. Amygdalia scion, in Fars in the first half of October with cv. Consevolia scion, in Kermanshah in September with cv. Conservolia scion, in Qazvin on May 20^th with cv. Conservolia scion.
 
Keywords: Olive, scion, grafting succes rate, scion vegetative growth, growth rate.
 
Introduction
In some olive trees despite suitable vegetative growth and reaching to maturity stage, fruits does not set and development do not occur, due mainly to lack of the adaptability (Hartman et al., 2017). Topworking has been practiced, for long-time, in some fruit trees such as pecan (Yates and Sparks, 1992) and walnut (Rezaee and Vahdati, 2008). Sometime in a region, a fruit tree variety is planted without assessment of its adaptability and quality properties. Therefore, its performance is not satisfactory and economically profitable. Therefore, changing the variety is necessary. In such a case, topworking-using scions from adapted and high yielding with desirable fruit and oil quality is a strategy to save farmer’s investments.
 It has been demonstrated that topworking in different olive varieties resulted in better vegetative growth and fruit yield. However, it differed with rootstock variety (Lion et al., 2020). In recent decades olive orchards in Khuzestan and Fras provinces in Iran has been established using olive varieties that are not well adapted and produce low yield with low quality (Ajamgard and Zeinanloo, 2013; Taslimpour, et al., 2016). To change the variety of olive orchard, olive producers should bear high costs. Therefore, topworking can help to graft scions from adapted high yield varieties on the rootstock of existing orchards. 
The main objective of this research was to determine the optimal time for topworking in olive trees in different regions of Iran, and to recommend the optimal time and suitable scion cultivars for each region.
 
Materials and Methods
The experiments were carried out, during 2021 and 2022, as split-plot arrangements in completely randomized design with three replications. Grafting dates at five levels from Auguest 29^th to November 28^th (in Qazvin from May) were assigned to main plots, and olive cultivar at two levels (cv. Conservolia was common + one adapted cultivar in each location) were randomized in sub-plots. The grafting success rate and the scion growth were evaluated and recorded. Analysis of variance for data was performed using SAS 9.4 software. Duncan’s Multiple Range Test was employed for means comparsion at the 5% and 1% probability levels.
 
Results and Discussion
The results showed that in Khuzestan province the mid-October was the optimal date for topworking of olive trees. Also cv. Conservolia’s scions had significantly (P ≤ 0.01) greater growth than cv. Avan scions. In Ilam province, the results showed that the maximum grafting success rate achieved in the second half of October with cv. Conservolia nd cv. Diereh scions. In Lorestan province, the grafting success rate, using scions of cv. Conservolia and cv. Amygdalolia were 88% and 80%, respectively, in the first half of October. In Fars province, the success of topworking in the first half of October was 80%, while the vegetative growth of cv. Conservolia’s scion was greater than cv. Amygdalolia. In Kermanshah province, the results showed that the grafting success rate of olive trees was significantly (P≤ 0.05) higher in September with cv. Consevolia scion. In Qazvin province, the results showed that the optimal date for topworking of olive trees was May 20^th with grafting success rate of 75% and 94% for cv. Conservolia and cv. Zard, respectively. Hussain et al. (2021) reported that topworking in olive trees in Pakistan was more successful in June-July. Yates and Sparks (1992) and Rezaee and Vahdati (2008) also reported that topworking improved yield and quality of pecan and walnut, respectively.
The highlight of the results of this research was determination of optimal time (optimal window) and suitable cultivars (scions) for topworking in olive trees in the six target regions in Iran.
 
References
Ajamgard, F., and Zeinanloo, A.A., 2013. Comparison of quantitative and qualitative yield of olive cultivars in north of Khuzestan province. Seed and Plant Improvement Journal, 29 (3), pp.567-579 (In Persian).
Hartman, H., Kester, D., Davies, F.T., Geneve, R.L. and Wilson, S.B., 2017. Hartman and Kester’s plant propagation: principles and practices (what’s new in trade and technology). 9^th edition. Pearson 1024 pp.
Rezaee, R. and Vahdati, K., 2008. Introducing a simple and efficient procedure for topworking Persian walnut trees. Journal of American Pomological Society, 62(1), pp.21-26.
Yates, I.E. and Sparks, D., 1992. Pecan cultivar conversion by grafting onto roots of 70-year-old trees. HortScience, 27(7), 803-807.