Rhg1 has been the most effective QTL deployed in soybeans (Glycine max) to control soybean cyst nematode (Heterodera glycines; SCN). However, the resistance mechanisms and specificity of Rhg1 towards SCN as opposed to other plant parasitic nematodes are not well known. In this study we report that Rhg1 can hinder the parasitism of the root lesion nematode Pratylenchus penetrans (Pp), which is commonly found along with SCN in northern U.S. soybean fields. Two elite public soybean varieties, carrying either rhg1-a + Rhg4 or rhg1-b, negatively impacted Pp populations measured at 30 dpi. This contribution of Rhg1 was more rigorously demonstrated using near isogenic lines for rhg1-b. Additionally, in three of the four soybean genetic backgrounds tested we observed significantly more Pp at 30 dpi when Pp were co-inoculated with SCN, consistent with a previous study. No significant changes in SCN cyst numbers upon co-inoculation with Pp were observed for any of the SCN-resistant rhg1 lines. No nematode-induced changes in Rhg1 transcript abundances were observed when sampling infected root sections in any of the plant genotypes, and no changes in a jasmonate response indicator were observed. However, the 3 dpi salicylate-mediated response to SCN or Pp became more robust during SCN + Pp co-infection. Multiple hypotheses for further dissection and manipulation of soybean resistance to Pratylenchus root lesion nematodes are suggested based on the present findings.

The rhg1-a and rhg1-b haplotypes of the soybean Rhg1 locus are economically effective tools for the control of soybean cyst nematode (SCN; Heterodera glycines), but ongoing SCN evolution requires improved sources of resistance. Both Rhg1 haplotypes carry multiple tandem repeat copies of a four-gene block encoding four disparate proteins, and resistance efficacy scales with copy number. The haplotypes encode different variants of an unusual α-SNAP protein whose abundance increases in the nematode-reprogrammed plant cells that form the syncytium (nematode feeding site), which subsequently collapses. The present study explored the simultaneous presence of two α-SNAPRhg1 protein types and elevation of α-SNAPRhg1 abundance, which were hypothesized to improve SCN resistance but are not achievable by conventional soybean breeding. We accomplished both via transgenic additions to an rhg1-a Rhg4 soybean line. Existing resistance to the HG type 0 and HG type 2.5.7 SCN was strengthened, measured as cyst production and final SCN egg counts, but resistance was not improved against an HG type 1.3.6.7 SCN population that was already highly virulent on the parent line. Greenhouse and field studies with a subset of lines showed no significant yield penalties. We conclude that cisgenic combination or elevated expression of the different α-SNAP genes may extend the efficacy and/or durability of Rhg1-mediated resistance. We also observed differential protein abundances for some α-SNAPRhg1 isoforms after inoculation with different HG type populations of SCN. The studies provide a foundation for further refinement of Rhg1-based SCN control. [Formula: see text] Copyright © 2025 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

The soybean cyst nematode (SCN; Heterodera glycines) is the most economically consequential pathogen of soybeans worldwide. Although biological control of SCN was proposed decades ago, only a few products are available on the market. Mining for new fungal biological control organisms and evaluating their potential to enhance integrated management of SCN is crucial. In this study, we evaluated 20 candidate biological control organisms in vivo that were selected out of a culturable mycobiome of over 5000 isolates based on their performance in in vitro assays. Of these isolates, labelled A through T, we identified three isolates, one Ilyonectria sp. (D), and two Purpureocillium sp. isolates (E and T), that significantly reduced SCN reproduction on a susceptible soybean variety (Sturdy) inoculated with both high and low levels of SCN eggs, compared to an untreated control, in a growth chamber cone-tainer assay. In a greenhouse pot assay, Purpureocillium isolates E and T also controlled nematode reproduction better than an untreated control and performed on par with the commercial fungal biological control agent, MeloCon (R) WG, which was applied at 41-fold higher concentration. In a second greenhouse assay, with higher nematode numbers, only isolate E performed as well as MeloCon (R) WG. This research identified promising candidate biological control agents of SCN that are as or more effective than existing products at much lower spore inoculation levels.

The soybean cyst nematode (SCN) is the most important pest on soybean, a major crop worldwide. The SCN is considered both parasitic and pathogenic as it derives nutrition from the host and manipulates host physiology to do so. Currently, there are no commercially available chemicals that are specific, environmentally safe and cost effective to control SCN levels. Crop rotation, use of host resistance and other cultural practices remain the main management strategies. The need for bioprospecting other methods of controlling SCN is paramount, and fungi show promise in that respect. Several studies have evaluated fungi and fungal products as biocontrol options against plant-parasitic nematodes. This review discusses fungal genera isolated from the SCN with potential for use as biocontrol agents and the effects of their secondary metabolites on various stages of SCN development. The review also summarizes efforts to control SCN using soil amendments that could potentially impact fungal communities in the soil.

Robert Emerson’s original observation (1957) that “oxygenesis occurs even with far-red light excitation of Photosystem I” is incompatible with the extant Kok-Joliot cycle’s foundation that “photolysis occurs only at red-light stimulated Photosystem II harboring MnComplex”. Further, the Z-scheme of electron transfer cannot account for Emerson’s observations of enhanced oxygenesis by simultaneous excitation of the two photosystems with both red and far-red light because serially connected components would surely increase systemic resistance to flow of charges, impeding the overall electron transfer process from water to NADP+. To address such discrepancies, we propose that the photo-excitation of various pigments leads to the formation of aquated electrons (eaq) and diffusible reactive oxygen species (DROS) in milieu, which are stabilized by a pool of redox-active elements within chloroplasts. Subsequently, the ‘eaq+DROS’ pool is utilized and routed via disordered and parallel reactions by the ‘photosystem switches’ for NADP reduction, O2 liberation and ADP phosphorylation. The stochastic ‘murburn’ model is thermodynamically and kinetically favorable and evidenced by the identification of multiple ADP-binding sites on PS II/Cytochrome b6f, and structure/distribution of the concerned proteins, complexes and pigments. The new model also explains the observed synergy in functioning of photosystems and plants’ photosynthetic spectral range of 400-700 nm.

Biological control is a promising approach to reduce plant diseases caused by nematodes to ensure high productivity in agricultural production. Large‐scale analyses of genetic variation in fungal species used for biocontrol can generate knowledge regarding interaction mechanisms that can improve efficacy of biocontrol applications. In this study, we performed a genome‐wide association study (GWAS) for in vitro antagonism against the root lesion nematode Pratylenchus penetrans in 53 previously genome re‐sequenced strains of the biocontrol fungus Clonostachys rosea. Nematode mortality in C. rosea potato dextrose broth (PDB) culture filtrates was highly variable and showed continuous variation (p < .001) between strains, indicating a polygenic inheritance. Twenty‐one strains produced culture filtrates with higher (p ≤ .05) nematode mortality compared with the PDB control treatment, while ten strains lowered (p ≤ .05) the mortality. The difference in in vitro antagonism against P. penetrans correlated with antagonism against the soybean cyst nematode Heterodera glycines, indicating lack of host specificity in C. rosea. An empirical Bayesian multiple hypothesis testing approach identified 279 single nucleotide polymorphism markers significantly (local false sign rate < 10–10) associated with the trait. Genes present in the genomic regions associated with nematicidal activity included several membrane transporters, a chitinase and genes encoding proteins predicted to biosynthesize secondary metabolites. Gene deletion strains of the predicted nonribosomal peptide synthetase genes nps4 and nps5 were generated and showed increased (p ≤ .001) fungal growth and conidiation rates compared to the wild type. Deletion strains also exhibited reduced (p < .001) nematicidal activity and reduced (p ≤ .05) biocontrol efficacy against nematode root disease and against fusarium foot rot on wheat. In summary, we show that the GWAS approach can be used to identify biocontrol factors in C. rosea, specifically the putative nonribosomal peptide synthetases NPS4 and NPS5.

Although fungal endophytes are commonly investigated for their ability to deter microbial plant pathogens, few studies have examined the activity of fungal root endophytes against nematodes. The soybean cyst nematode (SCN; Heterodera glycines), the most severe yield-limiting pathogen of soybean (Glycine max), is commonly managed through rotation of soybean with corn (Zea mays), a nonhost of the SCN. A total of 626 fungal endophytes were isolated from surface-sterilized corn and soybean roots from experimental plots in which soybean and corn had been grown under annual rotation and under 1, 3, 5, and 35 years of continuous monoculture. Fungal isolates were grouped into 401 morphotypes, which were clustered into 108 operational taxonomic units (OTUs) based on 99% sequence similarity of the full internal transcribed spacer region. Morphotype representatives within each OTU were grown in malt extract broth and in a secondary metabolite-inducing medium buffered with ammonium tartrate, and their culture filtrates were tested for nematicidal activity against SCN juveniles. A majority of OTUs containing isolates with nematicidal culture filtrates were in the order Hypocreales, with the genus Fusarium being the most commonly isolated nematicidal genus from corn and soybean roots. Less commonly isolated taxa from soybean roots included the nematophagous fungi Hirsutella rhossiliensis, Metacordyceps chlamydosporia, and Arthrobotrys iridis. Root endophytic fungal diversity in soybean was positively correlated with SCN density, suggesting that the SCN plays a role in shaping the soybean root endophytic community.

Murburn concept is a new redox metabolic paradigm which advocates that several redox enzymes generate/stabilize diffusible reactive (oxygen) species (DRS or DROS) to carry out useful electron/moiety transfer reactions at biological membrane interfaces (Manoj 2020a). Herein, we show that the components and principles of redox reactions within chloroplasts/cyanobacteria share several similarities with soluble and simple extracellular or peroxisomal heme-enzymes that carry out electron/group transfer. We explore the comparison in detail with membrane-embedded and complex systems that catalyze: (i) microsomal xenobiotic metabolism and (ii) mitochondrial oxidative phosphorylation. We point out that the murburn interpretations of catalytic phenomena are consistent through the various reaction systems cited above. Further, we argue that evolutionary constraints and the physiological restrictions of neutral pH ranges discount proton-gradient based explanations for bioenergetic phosphorylations in chloroplasts. Therefore, we propose that the highly packed thylakoid membranes with minute aqueous volumes serve to enhance the lifetimes of oxygen-centered radicals and intermediates. The murburn perspective could also potentially explain protein supercomplexes in chloroplasts, and generation of ATP in mitochondria by photo-activation. Our proposal also highlights the evolutionary significance of lipid membranes and utility of oxygen in diverse life processes.

Fungal biological control of soybean cyst nematodes (SCN) is an important component of integrated pest management for soybean. However, very few fungal biological control agents are available in the market. In this study, we have screened fungi previously isolated from SCN cysts over 3 years from a long-term crop rotation field experiment for their ability to antagonize SCN using (i) parasitism, (ii) egg hatch inhibition, and (iii) J2 mortality. We evaluated egg parasitism using an in-vitro egg parasitism bioassays and scored parasitism using the egg parasitic index (EPI) and fluorescent microscopy. The ability of these fungi to produce metabolites causing egg hatch inhibition and J2 mortality was assessed in bioassays using filter-sterilized culture filtrates. We identified 10 high-performing isolates each for egg parasitism and toxicity toward SCN eggs and J2s and repeated the tests after storage for 1 year of cryopreservation at −80°C to validate the durability of biocontrol potential of the chosen 20 isolates. Although the parasitic ability changed slightly for the majority of strains after cryopreservation, they still scored 5/10 on EPI scales. There were no differences in the ability of fungi to produce antinemic metabolites after cryopreservation. [Formula: see text] Copyright © 2020 The Author(s). This is an open access article distributed under the CC BY 4.0 International license .

Corn (Zea mays) and soybean (Glycine max) production forms an integral part of economies worldwide, but yields are limited by biotic and abiotic factors associated with short rotations and long-term monocultures. The objectives of this study were (i) to investigate the role of corn-soybean crop rotations and continuous monocultures in shaping bulk soil fungal communities, ii) to identify fungal taxa or functional guilds correlated with SCN density, and (iii) to characterize relationships between biotic and abiotic factors and their effects on corn and soybean yields. The study utilized a long-term rotation site with corn and soybean planted in annual rotation, five-year rotation, and long-term monoculture. High throughput sequencing of the ITS1 region of fungal rDNA revealed that soil fungal community structure varied significantly by crop sequence, with fungal communities under five consecutive years of monoculture becoming progressively similar to corresponding communities in long-term monoculture plots. Total fungal alpha diversity was greater under corn, but patterns of diversity and relative abundance of specific fungal functional guilds differed by crop, with more nematophagous fungi proliferating under soybean and more arbuscular mycorrhizal fungi (AMF) proliferating under corn. The relative abundance of nematode-trapping fungi and several putative nematode egg parasites was positively correlated with SCN density at several time points, suggesting that these fungi may proliferate as a result of the availability of the SCN as a nutrition source. Soil properties also varied by crop sequence, with higher pH and P under continuous soybean and higher Fe, Mn, and Cu under continuous corn. Lower levels of P corresponded with the relative abundance of several orders of fungi with roles in P uptake and transfer to plants (Glomerales, Paraglomerales, and Sebacinales), while higher P levels corresponded with the relative abundance of Mortierellales, a fungal order containing phosphate-solubilizing fungi. Structural equation modeling identified the SCN and soil nitrogen as the most important variables explaining soybean yield and fungal pathogens of corn and soil nitrogen as the most important variables explaining corn yield.

The cyst of the soya bean cyst nematode (SCN; Heterodera glycines), an economically important pathogen of soya beans worldwide, represents a unique microhabitat in soil. The fungi inhabiting cysts may include natural antagonists of the SCN as well as saprotrophs and other opportunists. This study aimed to characterise the entire culturable mycobiome of SCN cysts obtained from a long-term soya bean-corn rotation experiment using ITS fungal barcoding. Fusarium was consistently the most frequently isolated taxon across all sampling time points and crop sequences, followed by Ilyonectria. Among fourteen genera frequently isolated from SCN cysts, five fell within the single family Nectriaceae (Sordariomycetes) and five within the order Pleosporales (Dothideomycetes), suggesting independent evolutionary origins and shared adaptations in these groups towards colonisation of SCN cysts. Six genera (Pochonia, Clonostachys, Fusarium, Neonectria, Alternaria, and Leptosphaeria) varied significantly by crop sequence in at least one year.

Soybean cyst nematode (SCN), Heterodera glycines Ichinohe, is the number 1 pathogen of the important economic crop soybean. Bacteria represent potential biocontrol agents of the SCN, but few studies have characterized the dynamics of bacterial communities associated with cysts under different crop rotation sequences. The bacterial communities in SCN cysts in a long-term soybean-corn crop rotation experiment were investigated over 2 years. The crop sequences included long-term soybean monoculture (Ss), years 1-5 of soybean following 5 years corn (S1-S5), years 1 and 2 of corn following 5 years soybean (C1 and C2), and soybean-corn annual rotation (Sa and Ca). The bacterial 16S rRNA V4 region was amplified from DNA isolated from SCN cysts collected in spring at planting, midseason (2 months later), and fall at harvest and sequenced on the Illumina MiSeq platform. The SCN cyst microbiome was dominated by Proteobacteria followed by Actinobacteria, Bacteroidetes, and Verrucomicrobia. The bacterial community composition was influenced by both crop sequence and season. Although differences by crop sequence were not significant in the spring of each year, bacterial communities in cysts from annual rotation (Sa and Ca) or crop sequences of early years of monoculture following a 5-year rotation of the alternate crop (S1 and C1) became rapidly differentiated by crop over a single growing season. In the fall, genera of cyst bacteria associated with soybean crop sequences included Rhizobacter, Leptothrix, Cytophaga, Chitinophaga, Niastella, Streptomyces, and Halangium. The discovery of diverse bacterial taxa in SCN cysts and their dynamics across crop rotation sequences provides invaluable information for future development of biological control of the SCN.