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Aims: 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. Methods: 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. Results: 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). Conclusions: 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. [ABSTRACT FROM AUTHOR]

The article presents author's comments on Verticillium (V.) wilt which is one of the threatening biotic constraint in the production of olive. It presents information on the decline of young olive trees, in Sicily due to the infections of V. dahliae and Phytophthora palmivora. It mentions that phytotoxin (VdT) developed from an olive-infecting isolate can be purified from cultures.

Aims: The potential of grafting susceptible cultivars onto resistant rootstocks was evaluated for the control of Verticillium wilt in olive. Methods: Clones of the cultivars 'Frantoio' (highly resistant), 'Coratina' (susceptible) and 'Leccino' (highly susceptible) were used as scions and rootstocks in all combinations, inoculated by root-dipping with a defoliating (D) pathotype of Verticillium dahliae, and incubated in the greenhouse for 3 months. Results: Ninety days after inoculation, non-grafted plants of 'Frantoio' and all cultivars grafted onto 'Frantoio' were devoid of wilt symptoms, while non-grafted plants of 'Coratina' (AUDPC = 203.3) and 'Leccino' (AUDPC = 167.3) were characterized as susceptible. In contrast, when 'Frantoio' was grafted onto susceptible rootstocks, plants became susceptible (AUDPC of 139.8 and 108.9 on 'Frantoio' grafted onto 'Coratina' and Leccino', respectively). No significant difference occurred for vascular browning severity and frequency of V. dahliae reisolation from trunk tissues, though the pathogen was less abundant in the xylem of 'Frantoio'. Microscopic observations on plugging of xylem vessels are presented. Conclusions: Grafting of susceptible olive cultivars 'Leccino' and 'Coratina' onto resistant rootstock 'Frantoio' provided an excellent control of Verticillium wilt. It is postulated that the resistance of 'Frantoio' occurs mainly in the roots and involves biochemical mechanisms rather than plant structural characteristics. [ABSTRACT FROM AUTHOR]

Olive ( Olea europaea L.) is one of the first domesticated and cultivated tree species and has historical, social and economical relevance. However, its future as a strategic commodity in Mediterranean agriculture is threatened by diverse biotic (traditional and new/emerging pests and diseases) and abiotic (erosion, climate change) menaces. These problems could also be of relevance for new geographical areas where olive cultivation is not traditional but is increasingly spreading (i.e., South America, Australia, etc). One of the major constraints for olive cultivation is Verticillium wilt, a vascular disease caused by the soil-borne fungus Verticillium dahliae Kleb. In this review we describe how Verticillium wilt of olive (VWO) has become a major problem for olive cultivation during the last two decades. Similar to other vascular diseases, VWO is difficult to manage and single control measure are mostly ineffective. Therefore, an integrated disease management strategy that fits modern sustainable agriculture criteria must be implemented. Multidisciplinary research efforts and advances to understand this pathosystem and to develop appropriate control measures are summarized. The main conclusion is that a holistic approach is the best strategy to effectively control VWO, integrating biological, chemical, physical, and cultural approaches. [ABSTRACT FROM AUTHOR]

Zoosporic root-infecting pathogens are the most destructive organisms in enclosed environment agricultural systems which recycle irrigation water. Numerous strategies have been proposed for reducing or eliminating these pathogens from recycled irrigation water. These strategies include the following: filtration, sedimentation, chlorination, ozonation, heat, ultraviolet light, application of antimicrobial chemicals, suppressive potting substrates, and biological control agents. The latter strategy has been the focus of numerous investigations but consistency in performance in disease abatement following their application has not been realized. This has been attributed, in part, to the inability of these potential biocontrol bacteria to maintain a critical threshold population necessary for sustained biocontrol activity. That threshold population has been estimated at not less than 106 CFU g−1 of soil or root. Recently, we demonstrated that amending recycled irrigation water with specific carbon substrates (i.e., N-Serve® or Truban®) resulted in the selective enhancement of the indigenous fluorescent pseudomonad populations to levels at or above the presumed threshold levels necessary for disease control. In our current study, we verified the ubiquity of that response in different cultural systems involving two different host plants (i.e., cucumber and pepper) and, most significantly, we document, for the first time, significant and sustained disease abatement. Additionally, we demonstrated that nitrapyrin, the active ingredients in N-Serve® and Truban®, exerted direct antifungal activity whereas the inert ingredients had an indirect role in disease suppression. Specifically, the inert ingredients were responsible for the increase in the fluorescent pseudomonad population. Amending the recirculating nutrient solution with a representative fluorescent pseudomonad isolate verified and substantiated their role in disease control. Cumulatively, our results support the hypothesis that it is possible to modify the environment to make it more conducive to the multiplication and survival of indigenous biocontrol bacteria. The resident microflora in many, if not most, habitats already contain prospective biological control members who, if enhanced, could function as antagonists to other microorganisms in the same habitat. [ABSTRACT FROM AUTHOR]