Aims

The aim of this study was to establish a method to collect root exudates from olive plants. The method was validated by determining the effect of root exudates on the viability of Verticillium dahliae conidia and microsclerotia.

Methods

Three collection media (deionized distilled water, 0.01 M CaSO₄ solution, Hoagland nutrient solution) and four collection periods (2, 4, 6, 12 h) were assessed to identify the most appropriate combination for root exudate collection in olive plants (‘Picual’). To validate the method, root exudates were collected from olive cultivars with different susceptibilities to V. dahliae [‘Frantoio’ (resistant); ‘Arbequina’ (moderately susceptible), and ‘Picual’ (highly susceptible)] and treated or not treated with two microorganisms (Bacillus amyloliquefaciens PAB-024; Aureobasidium pullulans AP08) or two phosphite salts (Naturfos®; Phoscuprico®). The effect of root exudates on the germination of V. dahliae conidia and microsclerotia was evaluated in vitro. The dissolved organic carbon in the root exudates was estimated.

Results

A 0.01 M CaSO₄ solution and 4 h were confirmed to be the preferred medium and timing combination to collect root exudates from olive. Root exudates from ‘Arbequina’ and ‘Picual’ significantly induced conidia and microsclerotia germination in comparison with the control without exudates. AP08 was the most effective treatment to enhance the effectiveness of root exudates in decreasing conidia and microsclerotia viability. Root exudates from ‘Picual’ or, ‘Frantoio’ treated with AP08 showed the highest levels of organic carbon.

Conclusions

The collection method for root exudates developed herein was useful to assess the effect of root exudates from olive plants and the olive-V. dahliae interaction.