Suppressive biomasses and antagonist bacteria for an eco-compatible control of Verticillium dahliae on nursery-grown olive plants

Abstract

Two organic amendments (OMW-M1 and OMW-M2), based on olive mill wastes (OMWs) subjected to advanced processes of aerobic static storage or composting, were tested for their suppressive activity against Verticillium dahliae, the causal agent of olive Verticillium wilt. OMW-M1 and OMW-M2 drastically inhibited the pathogen growth in vitro and then were further tested in suppressive pot experiments. The amendments, mixed at 15 % (v/v) with a nursery standard plant-growth matrix, were tested alone or in combination with two biocontrol bacteria (Bacillus amyloliquefaciens and Burkholderia cepacia) selected from suppressive soils. All mixtures were artificially contaminated with V. dahliae microsclerotia (MS), the density of which was periodically monitored by either a semi-selective medium or a specific real-time Polymerase Chain Reaction technique. In plant-less pot assays conducted in a growth chamber, OMW-M1 was the most effective amendment, reducing V. dahliae MS density by 100 % after 90 days with respect to the untreated control. In nursery experiments with pot-growing olive plants, OMW-M1, particularly when combined with the biocontrol bacteria, confirmed its strong suppressive activity reducing up to 100 % the density of V. dahliae MS in the rhizosphere behaving even better than a commercial biofungicide (Trichoderma asperellum TV1) used as a control. The best combined treatment also reduced plant mortality and increased root and shoot extension. It is concluded that organic amendments from stabilized olive mill by-products showed positive agronomic and phytosanitary properties on pot-growing olive plants and, particularly when enriched with biocontrol agents, they are potentially suitable for use in sustainable agriculture.

Evaluation of organic amendments from agro‐industry waste for the control of verticillium wilt of olive

“…These results are in agreement with those obtained by Vitullo et al . (), who also demonstrated that the volatile compounds produced by OAs were effective in controlling V. dahliae on nursery‐grown olive plants. These results are relevant because antagonistic effect of OAs on mycelial growth development could be useful to prevent pathogen establishment/development in nursery substrates as well as in natural soils.…”

“…However, the effect of OAs as a potential control tool against VW of olive was not studied again until recently, when Vitullo et al . () showed the effect of olive mill liquid wastes on nursery‐grown olive plants.…”

“…Vitullo et al . () demonstrated an effective control of MS and VW development in olive by applying olive mill wastes in combination with Bacillus amyloliquefaciens and Burkholderia cepacia . This study suggests that OAs can also be applied in combination with other control measures to refine an integrated disease management strategy (Melero‐Vara et al ., ).…”

“…These authors highlighted the importance of this olive disease and the need to look for effective control measures which could be focused on the use of OAs (Wilhelm et al, 1962). However, the effect of OAs as a potential control tool against VW of olive was not studied again until recently, when Vitullo et al (2013) showed the effect of olive mill liquid wastes on nursery-grown olive plants.…”

“…Introduction of BCAs into soils, either directly by application of microbial antagonist formulations or indirectly by combination with OAs, also has a potential impact on the indigenous soil microbial communities (Ruano-Rosa & Mercado-Blanco, 2015). Vitullo et al (2013) demonstrated an effective control of MS and VW development in olive by applying olive mill wastes in combination with Bacillus amyloliquefaciens and Burkholderia cepacia. This study suggests that OAs can also be applied in combination with other control measures to refine an integrated disease management strategy (Melero-Vara et al, 2011).…”