Understanding the dynamic interactions of root-knot nematodes and their host: role of plant growth promoting bacteria and abiotic factors.

Root-knot nematodes (Meloidogyne spp., RKN) are among the most destructive endoparasitic nematodes worldwide, often leading to a reduction of crop growth and yield. Insights into the dynamics of host-RKN interactions, especially in varied biotic and abiotic environments, could be pivotal in devising novel RKN mitigation measures. Plant growth-promoting bacteria (PGPB) involves different plant growth-enhancing activities such as biofertilization, pathogen suppression, and induction of systemic resistance. We summarized the up-to-date knowledge on the role of PGPB and abiotic factors such as soil pH, texture, structure, moisture, etc. in modulating RKN-host interactions. RKN are directly or indirectly affected by different PGPB, abiotic factors interplay in the interactions, and host responses to RKN infection. We highlighted the tripartite (host-RKN-PGPB) phenomenon with respect to (i) PGPB direct and indirect effect on RKN-host interactions; (ii) host influence in the selection and enrichment of PGPB in the rhizosphere; (iii) how soil microbes enhance RKN parasitism; (iv) influence of host in RKN-PGPB interactions, and (v) the role of abiotic factors in modulating the tripartite interactions. Furthermore, we discussed how different agricultural practices alter the interactions. Finally, we emphasized the importance of incorporating the knowledge of tripartite interactions in the integrated RKN management strategies.

First Report of Belonolaimus Longicaudatus Infecting Soybean in Indiana.

Soybeans (Glycine max) are an important crop for Indiana, playing a major role in the state's economy. In June 2021, symptomatic soybean plants were submitted to Purdue University's Plant and Pest Diagnostic Laboratory for diagnosis. Sting nematodes were observed on the surface of the washed roots using stereo- and brightfield compound microscopy. A total of 76 sting nematodes per 100 cm3 soil were recovered from a composite soil sample. Morphological features and measurements of adult females and males of the sting nematode population were similar to those described for Belonolaimus longicaudatus. Molecular analysis confirmed the morphological identification using D2-D3 expansion segment of the 28S large subunit ribosomal DNA and internal transcribed spacer (ITS) regions. The consensus sequences were submitted to the National Center for Biotechnology Information (NCBI) database with accession numbers OM632679 and OM632681 for the D2-D3 and ITS regions, respectively. Parasitism of the sting nematode population to soybean plants was confirmed as its average population increased from 27 to 40 nematodes per pot 4 wk after inoculation under greenhouse conditions. To the best of our knowledge, this represents the first report of the sting nematode B. longicaudatus in Indiana.

First Report of Meloidogyne Incognita Infecting Mitragyna Speciosa in the United States.

Kratom (Mitragyna speciosa) belongs to the coffee family of Rubiaceae. The tree is native to Southeast Asia and primarily grown in Malaysia, Thailand, and Indonesia. Recently, it has been introduced and cultivated in other countries including the United States. The leaves and extracts of the leaves are used for medicinal and recreational purposes. In February 2022, kratom root and soil samples were submitted to the University of Florida Nematode Assay Laboratory for diagnosis by a commercial grower in Florida. Root galls were observed on the roots. On examination of soil and root samples, it is revealed that high numbers of root-knot nematodes (Meloidogyne sp.) are present. Molecular species identification was performed by a combination of the mitochondria haplotyping and species-specific primer techniques using TRNAH/MHR106 and MORF/MTHIS primer sets and Meloidogyne incognita-specific primers (MIF/MIR). The root-knot nematode infecting kratom is identified as M. incognita by molecular analysis. To our knowledge, this paper is the first report of M. incognita infecting kratom in the United States.

Nematicide efficacy at managing Meloidogyne arenaria and non-target effects on free-living nematodes in peanut production.

Meloidogyne arenaria (peanut root-knot nematode (PRKN)) is a major pest of peanut. Nematicide application is an important tool for the management of PRKN. Nematicides with minimal effects on free-living nematodes are desired. Fluopyram nematicide is recently introduced in peanut production and needs to be assessed. The objective of this research is to evaluate fluopyram and the established nematicides 1,3-Dichloropropene (1,3-D) and aldicarb for efficacy at managing PRKN and impacts on free-living nematodes. Nematicides were evaluated in field studies in 2017 and 2018 conducted in commercial peanut fields. All nematicides increased peanut yield in 2017 compared with untreated control, but did not affect soil PRKN abundances or root galling. In 2018, PRKN infestation was too low to accurately assess PRKN management by nematicides. Aldicarb and fluopyram did not affect any free-living nematode trophic group or individual genera. In contrast, 1,3-D decreased total fungivore and fungivore genera Filenchus and Aphelenchus soil abundances, but did not affect bacterivores, omnivore-predators, total herbivores, or any other nematode genera. In summary, 1,3-D, but not aldicarb or fluopyram, had non-target effects on free-living nematodes, particularly fungivores.Meloidogyne arenaria (peanut root-knot nematode (PRKN)) is a major pest of peanut. Nematicide application is an important tool for the management of PRKN. Nematicides with minimal effects on free-living nematodes are desired. Fluopyram nematicide is recently introduced in peanut production and needs to be assessed. The objective of this research is to evaluate fluopyram and the established nematicides 1,3-Dichloropropene (1,3-D) and aldicarb for efficacy at managing PRKN and impacts on free-living nematodes. Nematicides were evaluated in field studies in 2017 and 2018 conducted in commercial peanut fields. All nematicides increased peanut yield in 2017 compared with untreated control, but did not affect soil PRKN abundances or root galling. In 2018, PRKN infestation was too low to accurately assess PRKN management by nematicides. Aldicarb and fluopyram did not affect any free-living nematode trophic group or individual genera. In contrast, 1,3-D decreased total fungivore and fungivore genera Filenchus and Aphelenchus soil abundances, but did not affect bacterivores, omnivore-predators, total herbivores, or any other nematode genera. In summary, 1,3-D, but not aldicarb or fluopyram, had non-target effects on free-living nematodes, particularly fungivores.

Mist chamber extraction for improved diagnosis of Meloidogyne spp. from golf course bermudagrass.

Meloidogyne spp. are among the most damaging plant-parasitic nematodes to golf course bermudagrass in the southern United States. Diagnostic samples processed by centrifugal flotation often recovered only low numbers of vermiform Meloidogyne spp. life stages (J2 and males) from soil, while roots were found to be heavily infested by sedentary life stages. Therefore, the University of Florida Nematode Assay Lab (NAL) evaluated mist extraction from turf plugs as a method for diagnosis of Meloidogyne spp. from golf course bermudagrass. Soil and turf plugs were obtained from 596 golf course bermudagrass small plots from multiple locations and cultivars over several years, and vermiform Meloidogyne spp. extracted from 100 cm3 of soil by centrifugal flotation and by mist chamber extraction from four 3.8-cm-diam. turf plugs were compared. Additionally, both extraction methods were performed on 431 golf course bermudagrass diagnostic samples received by the NAL from Florida, 36 golf course bermudagrass diagnostic samples from Texas, and 34 golf course bentgrass/bluegrass samples from California. In the small plots, and the bermudagrass samples from Florida and Texas, mist extraction had higher detection and recovery rates of vermiform Meloidogyne spp. than did centrifugal flotation. However, centrifugal flotation had higher detection and recovery rates than mist extraction from bentgrass/bluegrass samples from California. Mist extraction from turf plugs is superior to centrifugal flotation from soil for diagnosis of Meloidogyne spp. on golf course bermudagrass, but not on golf course bentgrass and bluegrass.