Sources of Verticillium wilt resistance in wild olive germplasm from the Golestan province, Northern Iran

Nine wild olive accessions collected from the Golestan province, the North of Iran, were screened under greenhouse conditions for their resistance to Verticillium wilt. Plants of the highly susceptible cv. ‘Zard’, frequently used as a local cultivar, were also included in this test. Nine-month-old nursery olive plants were inoculated by root-dip method with defoliating (VCG1, D) and non-defoliating (VCG4B, ND) isolates of Verticillium dahliae, both obtained from diseased olives in Golestan province. Resistance was evaluated by assessing symptom severity using 0-4 rating scale and estimating the area under disease progress curves. The percentage of plants killed, final mean severity of symptoms, frequency of V. dahliae reisolation from olive xylem, dry weight of new green leaves and shoots and total phenol content in root tissues were used as additional parameters. The results showed that seven of the nine wild olive accessions were highly resistant to D and ND isolates of V. dahliae. A second group of wild olive accessions (P4 and P7) were classified as moderately resistant and resistant to D and ND isolates of V. dahliae, respectively. Phenol content was significantly higher in highly resistant plants and correlation coefficient analyses revealed a negative relation between disease severity and root total phenol contents. Dendrogram of wild olive accessions and ‘Zard’ cultivar based on all parameters represented two main clusters, major and minor. Minor cluster comprised only two wild olive accessions and ‘Zard’ cultivar. Major cluster could be divided into two groups, I and II, showed a highly resistance reaction to pathotypes of V. dahliae.