Complex relationships between lettuce (Lactuca sativa), arbuscular mycorrhizal fungi, and a leafminer pest in a context of ecological soil management

Conventional agriculture has negative impacts on the ecosystems while ecological intensification can ameliorate these effects by enhancing ecological processes. Arbuscular mycorrhizal fungi (AMF) are plant root symbionts that improve access to soil nutrients affecting plant growth and biotic interactions. Agricultural managements differentially affect AMF communities, but how these changes feedback on aboveground plant interactions remains poorly studied. Lettuce (Lactuca sativa) is a common crop severely attacked by Liriomyza huidobrensis (Diptera: Agromizydae), a polyphagous leafminer that has developed resistance to various pesticides, for which managing plant defenses and tolerance represents a feasible option to regulate populations. The aim of this study was to investigate if AMF communities from ecological and conventional management produce differential effects on mycorrhizal interaction, tissue phosphorus content and growth of lettuce plants and on L. huidobrensis oviposition preference. In greenhouse, we compared the effects of soils from farms with conventional and ecological managements from central Argentina on lettuce plants, and exposed them to L. huidobrensis mated females. Mycorrhizal colonization was higher with AMF from ecological than conventional treatments, although plant biomass was lower in treatments with AMF than with sterile soils (Strl), or with soil microorganisms without AMF (MO), in both managements. Phosphorus content was significantly higher in plants with MO and AMF in comparison to Strl, with no difference between managements. Plants grown with AMF from ecological management soils were less attacked by leafminers. Also, the insect preferred to oviposit on plants with higher aerial biomass, and this preference increased in plants with lower P content.