Suppression on plant-parasitic nematodes using a soil fumigation strategy based on ammonium bicarbonate and its effects on the nematode community

Combating Root-Knot Nematodes (Meloidogyne spp.): From Molecular Mechanisms to Resistant Crops

Root-knot nematodes (RKNs; Meloidogyne spp.) are significant plant-parasitic nematodes that cause major yield losses worldwide. With growing awareness of the harmful effects of chemical pesticides on human health and the environment, there is an urgent need to develop alternative strategies for controlling RKN in agricultural fields. In recent years, implementing multiple approaches based on transcriptomics, genomics, and genome engineering, including modern platforms like CRISPR/Cas9, along with traditional genetic mapping, has led to great advances in understanding the plant-RKN interactions and the underlying molecular mechanisms of plant RKN resistance. In this literature review, we synthesize the contributions of relevant studies in this field and discuss key findings. This includes, for instance, transcriptomics studies that helped expand our understanding of plant RKN-resistance mechanisms, the overexpression of plant hormone-related genes, and the silencing of susceptibility genes that lead to plant RKN resistance. This review was conducted by searching scientific sources, including PubMed and Google Scholar, for relevant publications and filtering them using keywords such as RKN-plant defense mechanisms, host-plant resistance against RKN, and genetic mapping for RKN. This knowledge can be leveraged to accelerate the development of RKN-resistant plants and substantially improve RKN management in economically important crops.

Suppression potential of selected vermicomposts against root-knot nematode (Meloidogyne incognita) under in vitro, pot, and field conditions

The root-knot nematode Meloidogyne incognita presents a serious threat to high-value crops in tropical and subtropical regions, particularly in Ethiopia, causing substantial yield and quality losses. Vermicompost, whether applied in solid form or as an extract, has shown promise in managing root-knot nematodes (RKNs). However, its effectiveness is influenced by factors such as the quality and type of vermicompost, the application rate, and the composition of parasitic nematode communities in the soil. This study utilized selected vermicomposts at varying rates in in vitro, pot, and field experiments to evaluate their potential for suppressing M. incognita and their effects on the growth and yield of tomato and hot pepper. The in vitro experiments demonstrated that all vermicompost extracts exhibited toxicity to J2. In particular, VC10 and VC11 showed higher efficacy, resulting in 55% and 78% mortality of J2 after 24 and 72 h of exposure, respectively, compared to the control and VC12. The interaction between vermicompost type, application rate, and nematode density significantly influenced tomato growth and nematode parameters in the pot experiment. The application of VC10 and VC11 at high doses (10 and 20 t ha-1) and low nematode density (50 J2) increased root fresh weight while reducing galls and nematode populations in tomato roots. Conversely, VC12 at a high application rate (20 t ha-1) and high nematode density (500 J2) led to an increase in root galls and nematode populations, suggesting a preference for RKNs rather than the expected nematicidal effect. The study indicates that the suppressive effect of vermicompost on nematodes varies with nematode density, depending on the type and amount of vermicompost used. Field experiments revealed that vermicompost amendments not only suppressed posttreatment nematode populations but also significantly improved hot pepper yield. Particularly, VC10 applied at high rates (10 and 20 t ha-1) resulted in lower nematode densities and higher marketable fruit yield compared to other vermicompost treatments and the conventional treatments (control, farmer practice, and recommended fertilizer). This highlights the long-term benefits of vermicompost application for nematode management and soil health. In addition, vermicompost amendments improved soil chemical properties. Overall, vermicompost offers greater benefits than farmers' practices and high-cost chemical fertilizers for soil improvement, while also enhancing tomato and hot pepper yields in nematode-infested smallholder farms.

Classical Batch Distillation of Anaerobic Digestate to Isolate Ammonium Bicarbonate: Membrane Not Necessary!

The excessive mineralization of organic molecules during anaerobic fermentation increases the availability of nitrogen and carbon. For this reason, the development of downstream processing technologies is required to better manage ammonia and carbon dioxide emissions during the storage and land application of the resulting soil organic amendment. The present work investigated classical distillation as a technology for valorizing ammoniacal nitrogen (NH4+-N) in anaerobic digestate. The results implied that the direct isolation of ammonium bicarbonate (NH4HCO3) was possible when applying the reactive distillation to the food waste digestate (FWD) with a high content of NH4+-N, while the addition of antifoam to the agrowaste digestate (AWD) was necessary to be able to produce an aqueous solution of NH4HCO3 as the distillate. The reason was that the extraction of NH4HCO3 from the AWD required a higher temperature (>95 °C) and duration (i.e., steady state in batch operation) than the recovery of the inorganic fertilizer from the FWD. The titration method, when applied to the depleted digestate, offered the quickest way of monitoring the reactive distillation because the buffer capacity of the distillate was much higher. The isolation of NH4HCO3 from the FWD was attained in a transient mode at a temperature below 90 °C (i.e., while heating up to reach the desired distillation temperature or cooling down once the batch distillation was finished). For the operating conditions to be regarded as techno-economically feasible, they should be attained in the anaerobic digestion plant by integrating the heat harvested from the engines, which convert the biogas into electricity.

Survival and infectivity of second-stage root-knot nematode Meloidogyne incognita juveniles depend on lysosome-mediated lipolysis

Adaptation to nutrient deprivation depends on the activation of metabolic programs to use reserves of energy. When outside a host plant, second-stage juveniles (J2) of the root-knot nematode (Meloidogyne spp.), an important group of pests responsible for severe losses in the production of crops (e.g., rice, wheat, and tomato), are unable to acquire food. Although lipid hydrolysis has been observed in J2 nematodes, its role in fitness and the underlying mechanisms remain unknown. Using RNA-seq analysis, here, we demonstrated that in the absence of host plants, the pathway for the biosynthesis of polyunsaturated fatty acids was upregulated, thereby increasing the production of arachidonic acid in middle-stage J2 Meloidogyne incognita worms. We also found that arachidonic acid upregulated the expression of the transcription factor hlh-30b, which in turn induced lysosomal biogenesis. Lysosomes promoted lipid hydrolysis via a lysosomal lipase, LIPL-1. Furthermore, our data demonstrated that blockage of lysosomal lipolysis reduced both lifespan and locomotion of J2 worms. Strikingly, disturbance of lysosomal lipolysis resulted in a decline in infectivity of these juveniles on tomato roots. Our findings not only reveal the molecular mechanism of lipolysis in J2 worms but also suggest potential novel strategies for the management of root-knot nematode pests.

Influences of nitrogen inputs on nematode populations under highbush blueberry

This study examined the effects of nitrogen fertilization on populations of Rotylenchus robustus, Pratylenchus crenatus, and Paratrichodorus renifer, and indices of free-living nematode community structure, in relation to highbush blueberry production in British Columbia, Canada. The field experiment was established in fall of 2008 with six replicate plots of each of four experimental N fertilization treatments: 0, 100, 150, and 200% of the annual application rate recommended for conventional blueberry production in the region. Nematode populations were quantified annually from 2009 through 2015, and then nematode populations and root biomass were quantified at seven sample dates from 2016 through 2019. Population densities of R. robustus were consistently greater in the 100% treatment than in the 0, 150, and 200% treatments which did not differ from each other. Population densities of P. crenatus were consistently greater in the 150% treatment than in the 0, 100%, and 200% treatments. The nematode structure index and two indices of diversity declined monotonically with N fertilizer rate, indicating broader changes in the soil food web that could have had indirect, feedback effects on population dynamics of the plant-parasitic nematodes.

This study examined the effects of nitrogen fertilization on populations of Rotylenchus robustus, Pratylenchus crenatus, and Paratrichodorus renifer, and indices of free-living nematode community structure, in relation to highbush blueberry production in British Columbia, Canada. The field experiment was established in fall of 2008 with six replicate plots of each of four experimental N fertilization treatments: 0, 100, 150, and 200% of the annual application rate recommended for conventional blueberry production in the region. Nematode populations were quantified annually from 2009 through 2015, and then nematode populations and root biomass were quantified at seven sample dates from 2016 through 2019. Population densities of R. robustus were consistently greater in the 100% treatment than in the 0, 150, and 200% treatments which did not differ from each other. Population densities of P. crenatus were consistently greater in the 150% treatment than in the 0, 100%, and 200% treatments. The nematode structure index and two indices of diversity declined monotonically with N fertilizer rate, indicating broader changes in the soil food web that could have had indirect, feedback effects on population dynamics of the plant-parasitic nematodes.

Effective approaches to study the plant-root knot nematode interaction

Plant-parasitic nematodes cause major agricultural losses worldwide. Examining the molecular mechanisms underlying plant-nematode interactions and how plants respond to different invading pathogens is attracting major attention to reduce the expanding gap between agricultural production and the needs of the growing world population. This review summarizes the most recent developments in plant-nematode interactions and the diverse approaches used to improve plant resistance against root knot nematode (RKN). We will emphasize the recent rapid advances in genome sequencing technologies, small interfering RNA techniques (RNAi) and targeted genome editing which are contributing to the significant progress in understanding the plant-nematode interaction mechanisms. Also, molecular approaches to improve plant resistance against nematodes are considered.

Balance design for robust foliar nutrient diagnosis of "Prata" banana (Musa spp.)

The "Cavendish" and "Prata" subgroups represent respectively 47% and 24% of the world banana production. Compared to world average progressing from 10.6 to 20.6 t ha-1 between 1961 and 2016, and despite sustained domestic demand and the introduction of new cultivars, banana yield in Brazil has stagnated around 14.5 t ha-1 mainly due to nutrient and water mismanagement. "Prata" is now the dominant subgroup in N-E Brazil and is fertigated at high costs. Nutrient balances computed as isometric log-ratios (ilr) provide a comprehensive understanding of nutrient relationships in the diagnostic leaf at high yield level by combining raw concentration data. Although the most appropriate method for multivariate analysis of compositional balances may be less efficient due to non-normal data distribution and limited nutrient mobility in the plant, robustness of the nutrient balance approach could be improved using Box-Cox exponents assigned to raw foliar concentrations. Our objective was to evaluate the accuracy of nutrient balances to diagnose fertigated "Prata" orchards. The dataset comprised 609 observations on fruit yields and leaf tissue compositions collected from 2010 to 2016 in Ceará state, N-E Brazil. Raw nutrient concentration ranges were ineffective as diagnostic tool due to considerable overlapping of concentration ranges for low- and high-yielding subpopulations at cutoff yield of 40 Mg ha-1. Nutrient concentrations were combined into isometric log-ratios (ilr) and normalized by Box-Cox corrections between 0 and 1 which may also account for restricted nutrient transfer from leaf to fruit. Despite reduced ilr skewness, Box-Cox coefficients did not improve model robustness measured as the accuracy of the Cate-Nelson partition between yield and the multivariate distance across ilr values. Sensitivity was 94%, indicating that low yields are attributable primarily to nutrient imbalance. There were 148 false-positive specimens (high yield despite nutrient imbalance) likely due to suboptimal nutrition, contamination, or luxury consumption. The profitability of "Prata" orchards could be enhanced by rebalancing nutrients using ilr standards with no need for Box-Cox correction.

Isolation of Antagonistic Endophytes from Banana Roots against Meloidogyne javanica and Their Effects on Soil Nematode Community

Banana production is seriously hindered by Meloidogyne spp. all over the world. Endophytes are ideal candidates compared to pesticides as an environmentally benign agent. In the present study, endophytes isolated from banana roots infected by Meloidogyne spp. with different disease levels were tested in vitro, and in sterile and nature banana monoculture soils against Meloidogyne javanica. The proportion of antagonistic endophytes were higher in the roots of middle and high disease levels. Among those, bacteria were dominant, and Pseudomonas spp., Bacillus spp. and Streptomyces spp. showed more abundant populations. One strain, named as SA, with definite root inner-colonization ability was isolated and identified as Streptomyces sp. This strain showed an inhibiting rate of >50% in vitro and biocontrol efficiency of 70.7% in sterile soil against Meloidogyne javanica, compared to the control. Greenhouse experiment results showed that the strain SA exhibits excellent biological control ability for plant-parasites both in roots and in root-knot nematode infested soil. SA treatment showed a higher number of bacterivores, especially Mesorhabditis and Cephalobus. The maturity index was significantly lower, while enrichment index (EI) was significantly higher in the SA treatment. In conclusion, this study presents an important potential application of the endophytic strain Streptomyces sp. for the control of plant-parasitic nematodes, especially Meloidogyne javanica, and presents the effects on the associated variation of the nematode community.