Spatial relationships between entomopathogenic nematodes and nematophagous fungi in Florida citrus orchards

Abstract

Relationships between entomopathogenic nematodes (EPNs), nematophagous fungi (NF) and soil physical and chemical properties were studied in a survey of 53 citrus orchards in central ridge and flatwoods ecoregions of Florida. Seven species of NF associated with nematodes were quantified directly using a real time qPCR assay. All nematophagous fungi studied except Arthrobotrys musiformis and Hirsutella rhossiliensis were frequently detected (24-56%) in both regions. Paecilomyces lilacinus and Gamsylella gephyropagumwere encountered more frequently in the flatwoods (P=0.03) and on the ridge (P=0.02), respectively. Redundancy analysis revealed seven abiotic and biotic factors as significantly related to the NF occurrence. Multiple regression of fungi on these variables explained 78%, 66%, 48%, 36%, 23% and 4% of the variation in Catenaria sp., A. musiformis, A. dactyloides, P. lilacinus, A. oligospora and G. gepharopagum, respectively. When the data from citrus were pooled with those reported previously from natural areas and subjected to principle component analysis, the first two principle components explained 43% of the variation in NF communities. The surveys (citrus vs natural areas) were discriminated by PC2 (P<0.001) and the ecoregion by PC1 (P<0.002), and all but one NF species were related (P<0.01) to one or both components. NF communities tended to have more species and greater diversity in the flatwoods, where EPN richness and diversity were the least. However, the strength of associations between individual EPN and NF species as measured by SADIE reflected the associations between each species and ground water depth, suggesting that ecoregion preferences affected the species associations. Within each ecoregion, significant relationships between the individual NF and EPN species measured by stepwise regression tended to be positive. The results did not support the hypothesis that NF modulate the spatial patterns of EPN species between or within these two ecoregions.

Managing nematodes in Egyptian citrus orchards

“…This is timely with the frequently reported incidence of naturally occurring communities of nematophagous fungi and parasitic bacteria such as Pasteuria species in citrus orchards (Shokoohi and Duncan 2018). Pathak et al (2017) demonstrated habitat variation in the predominance of two of seven species of biocontrol fungi found in the DNA recovered from samples of nematodes in citrus orchards. The predator-prey model parameters for a Pasteuria sp.…”

Impact of vineyard ground cover management on the occurrence and activity of entomopathogenic nematodes and associated soil organisms

“…It is likely that not only abundance but also the proportions of the identified NF species could be one of the keys to explaining these observations. We reported significantly higher presence of NF-IR on grassseeded covers, the treatment that recorded the highest content in organic matter and the lowest sand percentages, two of the key factors that favor NF occurrence on soils (Nordbring-Hertz et al, 2006;Pathak et al, 2017). Endoparasitic fungi (H. rhossilliensis and Catenaria sp.)…”

Fungi–Nematode Interactions: Diversity, Ecology, and Biocontrol Prospects in Agriculture

“…Recent greenhouse trials also showed that parasitism of H. rhossiliensis was strongly correlated with the density of the soybean cyst nematode [30]. At broader geographic scales, in a survey of 53 citrus orchards in central ridge and flatwood ecoregions of Florida, the spatial patterns of entomopathogenic nematode species were found to be modulated by variations in their susceptibilities to nematophagous fungal species (Catenaria sp., A. musiformis, Arthrobotrys dactyloides, Paecilomyces lilacinus, A. oligospora, and Gamsylella gephyropaga) across habitats [95]. However, strong and diverse top-down control effects on the nematode community in coastal sand dunes were found in a recent study, where three microbial enemies of nematodes (Catenaria spp., H. rhossiliensis, and Pasteuria penetrans) were correlated, either positively or negatively, with plant parasitic nematode population size [96].…”