Identification and characterization of Javanese root-knot nematode (Meloidogyne javanica) suppressive soils in Florida

Abstract

In Florida, Javanese root-knot nematode (Meloidogyne javanica) is widely distributed and causes extensive damage to a number of economically important crops. Soil fumigants are commonly used to manage this soilborne pest; however, increasing societal concerns regarding the negative effects of these products on environmental and human health are driving a shift towards more sustainable management options. Of particular interest are naturally occurring nematode suppressive soils. Identifying farming practices and ecological factors that enable suppressive organisms to function and persist in soil will support the implementation of natural biological control. In this study, we evaluated suppressiveness to M. javanica in 12 soils from Florida. Using next-generation sequencing technology, we characterized the bacterial and fungal communities in these soils to further understand how those communities may contribute to nematode suppressive soils. In spring 2018, soil was collected from multiple geographic regions, production systems, and management practices within the state of Florida. In a soil-based suppressiveness assay, soil collected from 7 out of 12 of the sites reduced the recovery of inoculated J2-stage M. javanica relative to that of soil that had been steam-pasteurized. In a plant-based suppressiveness assay, all soils reduced root galling on cucumber by M. javanica relative to that of their steam-pasteurized counterparts. Contrary to other studies on pathogen suppressive soils, enhanced soil bacterial and fungal diversity was not associated with suppressiveness to M. javanica. Differences in soil fungal community composition was a stronger driver of suppressiveness than bacterial community composition, with the fungal orders Xylariales, Mortierellales, and Agaricales showing positive correlation with nematode suppressiveness across 64 % of the sites surveyed. Overall, Florida soils hold considerable potential to naturally regulate M. javanica populations. The use of soil management practices that promote the abundance and activity of suppressive microorganisms may reduce horticultural reliance on soil fumigants.