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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. [ABSTRACT FROM AUTHOR]

Purpose: The aims of this work were (i) to find a soil indicator to predict durum wheat yield response to Zn fertilization, (ii) to compare the effect of various Zn fertilization strategies on wheat yield and Zn biofortification in calcareous Vertisols of southern Spain, and (iii) to assess the effect of these Zn fertilization strategies on crop P uptake (durum and bread wheat). Methods: Different Zn fertilization strategies, soil application (0.3–10 kg ha−1) and foliar spraying (two rates, different growth stages), were tested in wheat crops under field conditions in the period 2012–2019. Results: A simple soil indicator failed to predict durum wheat response to Zn fertilization. Only one of the combinations tested increased wheat yield in the 11 field experiments carried out. Zinc foliar spraying (1.28 kg ha−1) was effective for wheat biofortification when applied at early booting (durum wheat) or flowering, and also when splitting this application between stem elongation and flowering stages (bread wheat). The foliar treatments produced the highest zinc use efficiencies (6–19%) and soil applications the lowest (0.2–1.3%). Moreover, foliar treatments increased grain Zn concentrations by 12–51% while soil application increased such concentrations by only 4–13%. None of the Zn fertilization strategies altered P uptake. Conclusion: No yield increase in wheat is expected from Zn fertilization for the application methods and rates used here and the soils studied (calcareous Vertisols under Mediterranean climate). However, foliar applications at and after early booting stage are promising for durum and bread wheat biofortification. [ABSTRACT FROM AUTHOR]

Background and aims: The possible influence of phosphorus (P) on iron (Fe) deficiency chlorosis in susceptible plants needs elucidation. In this work, we tested the hypothesis that Fe chlorosis can be aggravated at high levels of P in the substrate. Methods: Chickpea, lupin and peanut (in a preliminary experiment), and lupin and sorghum (in a second, factorial experiment) were successively grown on artificial substrates consisting of mixtures of Fe oxide-coated sand (FOCS), calcium carbonate (calcite) sand (CCS) and quartz sand to which phosphate was added at different doses. Results: The proportion of FOCS in the substrate had a significant positive effect on leaf chlorophyll concentration (as estimated via SPAD) in all crops. In the factorial experiment, the SPAD value was negatively affected by the proportion of CCS in the dicot (lupin) but not in the monocot (sorghum). In the preliminary experiment, increasing the P dose generally had little effect on the SPAD of plants grown on the FOCS-rich substrate but a negative effect on those grown on the FOCS-poor substrate. In the factorial experiment, the P dose negatively affected SPAD in both lupin and sorghum. Conclusions: Iron acquisition by the plant is negatively influenced by P probably because the solubility of the Fe oxides decreases with increasing coverage of their surfaces by sorbed phosphate. [ABSTRACT FROM AUTHOR]