Canopy re-establishment after severe winter cold damage of mature olive (Olea europaea L.) trees cultivars 'Blaidy' and 'Mission' grown under Tehran environment condition

The severe cold winter usually damages the olive (Olea europaea L.) tree canopy of the currently established orchards in some regions of Iran. The present research aimed to explore the amount of tree canopy growth and analysis of mature olive trees damaged after a harsh winter cold in 2007 in Tehran, Iran. The own-rooted olive tree cultivars ‘Mission’ and ‘Blaidy’ were planted in March 2004 in 1 m distance within the row in the research orchard of the Department of Horticultural Science, Tarbiat Modares University (TMU), in Tehran. Mature olive trees had been tested for severe winter cold in 2008, so the top growth was completely damaged with the root system remaining alive. Trees allowed re-establishing their canopy after cold, so the top growth was recovered. To evaluate and analyze top growth, some mature trees were randomly selected and destructively harvested for top growth analysis in the 2017 early growing season. The canopy was divided into the leaves, shoots, and trunk and scaffold branches. Results indicated the difference between total top dry mass among the studied cultivars, so ‘Mission’ showed higher total dry mass than ‘Blaidy’. Also, the highest dry matter increments belonged to the trunk and main scaffold branches and then to the leaves and shoots. Research is continued to explore the effect of soil volume and the possible existence of harmful nematodes in the soil. Besides, the effect of top to root ratio and the impact of root volume, as well as the possible existence of harmful nematodes in the soil on dry matter partitioning of the mature own-rooted olive trees was investigated. The obtained result showed no harmful nematode species in root system regions of the studied olive trees. In conclusion, and to reduce the cost of the damaged olive orchards re-establishment from the un-damaged root system, we do not suggest olive grafting in the olive-growing regions of Iran that are faced with severe winter cold. The damaged canopy system after harsh winter cold in such a region might be re-covered with a proper and suitable orchard management system.