Natural recovery from Verticillium wilt in olive: can it be exploited in a control strategy?

Abstract

Our objective was to evaluate if natural recovery may be exploited in disease control of Verticillium wilt in olive. Therefore, we evaluated the following: the incidence of natural recovery; the Verticillium dahliae viability within olive tissues over time and the effectiveness of soil solarization, calcium cyanamide and pollarding of trees at soil level in promoting natural recovery. Three different experiments (A, B and C) were performed in commercial olive orchards planted with the highly susceptible cv. ‘Bella di Cerignola’ and infested with the non-defoliating V. dahliae pathotype. In experiment A, in the period 2010–2012, natural recovery occurred on 35 of 138 diseased trees (25 %); however, this recovery was transient and lasted between 3 months for 11 trees (8 %) and 21 months for one tree (0.7 %). V. dahliae tended to be inactivated in twigs within 1 or 2 years after symptom onset (experiment A). However, it was evident that V. dahliae was more abundant in larger (trunk and first- or second-order branches) versus thinner woody parts of olive trees (roots; experiment B). In the attempt to explore whether natural recovery could be further stimulated artificially, it was observed that soil solarization and soil application of calcium cyanamide were ineffective in promoting its occurrence. Tree pollarding at soil level induced a transient recovery, which lasted only 1 year (experiment C). Based on our observations, natural recovery of susceptible olive from Verticillium wilt has a low impact on the disease epidemiology in the short-term only and cannot be effectively stimulated in practice by soil solarization, calcium cyanamide or tree pollarding.