Screening Olive Progenies for Resistance to Verticillium dahliae

Verticillium wilt of olive (Olea europaea), caused by the fungus Verticillium dahliae, is the most serious disease in the Mediterranean countries. The use of resistant cultivars or rootstocks is one of the most efficient measures for the control of this disease. Olive shows a wide range of genetic variability useful for finding resistance to the disease. The first step to achieve this objective is the identification of resistance-transmitting genitors, in order to screen many genotypes for resistance to V. dahliae. More than 100 olive seedlings from one crossing and open pollination of different genitors were evaluated for resistance to V. dahliae under controlled conditions. Two-month-old seedlings were inoculated by dipping their root system in a conidial suspension of the highly virulent isolate V117. Disease symptoms (defoliation, wilt, chlorosis and necrosis) were assessed by using a 0-4 scale. Results demonstrated that young olive seedlings can be successfully infected by V. dahliae, showing consistent Verticillium wilt symptoms. Results have provided preliminary information about inheritance of resistance, and they have highlighted 'Frantoio' as a suitable genitor to breed for Verticillium wilt resistance in olive. Several olive genotypes were selected for resistance to Verticillium wilt and they will be tested in field conditions.