ARC Infruitec-Nietvoorbij, Plant Protection
Objectives and Rationale
Ring nematodes are one of the most common and abundant nematode species in vineyards. Understanding the crop management practices that modulate the suppressive activity of the soil microbiome towards PPN will lead to long-lasting and cost-effective crop production. The aim of this study was to detect, identify and characterise soils that maintain specific suppressiveness to ring nematodes.
Absolute and relative suppressiveness were determined by means of lab assays. Greenhouse pot trials were used to assess nematode replication in different soils. Samples were also analysed for soil physicochemical properties. Different ecological indicators (nematode taxa abundance and microbially secreted enzymes) were used to correlate ring nematode suppression and abundance with properties of the soil food web by means of PCA analysis.
Sites that showed suppression as determined by the labassays and pot trials, also had high to very high numbers of ring nematodes, which seems to be the result of a density-dependant biological component present in these soils. Ring nematode numbers and relative suppression are also associated with higher levels of P and Ca, although these correlations were weak and not statistically significant. Ring nematode numbers were negatively correlated with soil enzyme activity, indicating lower numbers of nematodes at higher levels of these soil enzymes. It seems that increased microbial activity in the soil, associated with higher levels of these soil enzymes could inhibit the reproduction of ring nematodes in these soils. High ring nematodes numbers were positively correlated with the nematode-based index, EI, which parallels the intensity of nutrient enrichment in the soil. High values of EI indicate equivalent levels of food availability, which leads to an increase of the ring nematode population.
Key Conclusion and Discussion
Management practices should be targeted towards the inducement of nematode suppression in orchards. There are many factors that contribute to stimulating or even creating suppressive conditions against PPN, such as microbiota activities, organic matter amount, chemical composition and physical constitution.The presence of a nematophagous fungi in soils with high ring nematode numbers was not able to suppress the ring nematode population in those soils, but healthy soils have increased microbial activity which have a suppressive effect on ring nematodes. Therefore, practices aimed at enhancing these microbes in the soil, could lead to lower levels of ring nematodes. However, certain practices, like the overuse of inorganic fertiliser and the indiscriminate use of organic amendments could have the adverse effect, increasing the numbers of ring nematodes in the soil.
Take Home Message for Industry
Practices aimed at enhancing beneficial microbes and the soil food web could lead to the suppression of ring nematodes, whilst other practices such as the indiscriminate use of inorganic fertilizers could have the adverse effect.