Frost tolerance of 24 olive cultivars and subsequent vegetative re-sprouting as indication of recovery ability

- Defoliation and bark spilt were evaluated in olive trees after a freezing event.
- The recovery ability of the cultivars was assessed after the frost damages.
- 'Ascolana dura' and 'Orbetana' resulted the least frost sensitive cultivars.
- 'Arbequina' resulted very sensitive to frost and showed strong vegetative re-sprouting.

The objective of the present study was to assess the frost tolerance of 24 olive cultivars after a freezing event that occurred in February 2012 in Marche Region (Central Italy), and their recovery ability during the following growing seasons (2012 and 2013). The studied cultivars were locally, nationally and internationally spread. Trees were three-year-old and in the rest phase at the time of the freezing event. Frost tolerance was determined by two damage visual scoring: defoliation and bark split, both defined three months after the event. During the following growing seasons, the recovery ability of the cultivars was also assessed throughout a third visual index describing the vegetative re-sprouting. Results indicated differences in frost tolerance and recovery ability among the studied cultivars. In particular, 'Arbequina' recorded the highest canopy defoliation together with 'FS17', 'Raggia' and 'Sargano di San Benedetto', whereas 'FS17', showed the highest level of bark split on primary branches and trunk. This cultivar also registered a strong vegetative re-sprouting, mainly from the basal portion of the trunk. On the contrary, 'Ascolana dura' and 'Orbetana' resulted the most frost tolerant cultivars and showed the best recovery ability in 2012 and 2013, with a re-sprouting activity from the 1- and 2-year-old shoots. The results suggest low frost tolerance for the tested varieties and supply helpful information for the selection of the most suitable ones for the set of new olive orchards in cold climates.