A Real-Time PCR Assay to Detect and Quantify Root-Knot Nematodes from Soil Extracts.

Root-knot nematodes cause forking and stubbing of the growing carrot root tip, decreasing market value and reducing yield by up to 45%. Since crop damage by these nematodes depends on their initial population densities at planting, preplant detection of potentially low nematode numbers is critical for predicting future yield loss. The aim of this study was to overcome some of the drawbacks of the labor- and time-intensive process of root-knot nematode identification and quantification by developing and field testing a real-time PCR (qPCR) assay. Primers were designed targeting the root-knot nematode Meloidogyne incognita species complex, which includes M. incognita as well as the closely related Meloidogyne javanica and Meloidogyne arenaria. The qPCR assay successfully detected each species and showed little amplification for nontarget nematode groups except for the sister group Meloidogyne enterolobii, which is not known to occur in California. Predicted nematode densities related well with microscopic counts of nematodes from prepared solutions, as well as from solutions extracted from field soil. In a greenhouse experiment, the qPCR assay distinguished between low, medium, and high levels of M. incognita infection and qPCR predicted densities at planting were negatively related in linear models with final carrot fresh weight, length, and diameter. These results suggest that qPCR assays could be a valuable diagnostic tool to predict nematode infections and prevent crop losses.[Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Almond processing residues as a source of organic acid biopesticides during biosolarization.

Biosolarization utilizes organic amendments to produce biopesticide compounds in soil that can work in tandem with other stresses to inactivate agricultural pests. The prospect of using by-products from industrial almond processing as amendments for biosolarization was assessed. Soil mesocosms were used to simulate biosolarization using various almond by-products, application rates, and incubation times. Several potentially biopesticidal organic acids were identified and quantified in the soil, and the toxicity of soil extracts was evaluated for the root lesion nematode (Pratylenchus vulnus). It was determined that both almond hulls and a mixture of hulls and shells harbored several acids, the concentration of which was enhanced 1-7 fold via fermentation by native soil microbes. Organic acid concentration in the soil showed a significant linear relationship with the quantity of waste biomass amended. Extracts from soils containing at least 2.5% incorporated biomass by dry weight showed a 84-100% mortality of nematodes, which corresponded to acid concentrations 0.75 mg/g (2.0 g/L) or greater. This study showed that almond processing by-products - hulls and a hull and shell mixture - were suitable amendments for control of P. vulnus and potentially other soil agricultural pests in the context of biosolarization.

Characterization of New Entomopathogenic Nematodes from Thailand: Foraging Behavior and Virulence to the Greater Wax Moth, Galleria mellonella L. (Lepidoptera: Pyralidae).

Entomopathogenic nematodes (EPNs) in the genera Steinernema and Heterorhabditis and their associated bacteria (Xenorhabdus spp. and Photorhabdus spp., respectively) are lethal parasites of soil dwelling insects. We collected 168 soil samples from five provinces, all located in southern Thailand. Eight strains of EPNs were isolated and identified to species using restriction profiles and sequence analysis. Five of the isolates were identified as Heterorhabditis indica, and one as Heterorhabditis baujardi. Two undescribed Steinernema spp. were also discovered which matched no published sequences and grouped separately from the other DNA restriction profiles. Behavioral tests showed that all Heterorhabditis spp. were cruise foragers, based on their attraction to volatile cues and lack of body-waving and standing behaviors, while the Steinernema isolates were more intermediate in foraging behavior. The infectivity of Thai EPN strains against Galleria mellonella larvae was investigated using sand column bioassays and the LC(50) was calculated based on exposures to nematodes in 24-well plates. The LC(50) results ranged from 1.99-6.95 IJs/insect. Nine centimeter columns of either sandy loam or sandy clay loam were used to determine the nematodes' ability to locate and infect subterranean insects in different soil types. The undescribed Steinernema sp. had the greatest infection rate in both soil types compared to the other Thai isolates and three commercial EPNs (Heterorhabditis bacteriophora, Steinernema glaseri and Steinernema riobrave).