Detection of Resistance, Susceptibility, Tolerance, and Virulence in Plant-Nematode Interactions: Part I-Sedentary Endoparasitic Nematodes.

The use of nonhost, tolerant, or resistant plants, to manage plant parasitic nematodes (PPNs), is an appealing, economic, and environmentally friendly agronomic practice, which is effective when precise information on the identification of PPN species and their virulence to target host crops is available. This chapter describes suggested protocols to evaluate the reaction of the most important crops and fruit trees to infestation by the most damaging PPN with sedentary endoparasitic habits, with the aim of assessing resistance and tolerance traits, sources of resistance in progenies from breeding programs, the reaction to nematodes of newly released cultivars, and the virulence of the most noxious PPNs. These protocols consist of classical screening techniques not involving biochemical and molecular analyses. PPN species and genera considered in this chapter include (i) the most important species of root-knot nematodes Meloidogyne spp., including also M. chitwoodi, M. enterolobii, and M. graminicola, and (ii) the cyst-forming nematodes of the genera Globodera and Heterodera, such as the potato cyst nematodes (PCNs) Globodera rostochiensis and G. pallida, and also Heterodera avenae group, H. ciceri, H. glycines, and H. schachtii. Schemes are given to identify virulence groups for most of these nematodes.

Host status and susceptibility of Cannabis sativa cultivars to root-knot nematodes.

Root-knot nematode host status of hemp cultivars of different uses (fiber, dual, CBD/CBG) and from different regions (Europe, China, US) were evaluated in five different greenhouse trials. None of the tested cultivars showed resistance to any of the tested root-knot nematode species, and all tested hemp cultivars were good hosts for root-knot nematodes, especially to mixed populations of M. javanica and M. incognita. Root gall symptoms on hemp were less severe than on cucumber (and tomato), but reproduction rates were similar. Lower infection and reproduction rates were noted for M. hapla and M. enterolobii, which were probably due to the colder temperatures at the time of the trial, as the same effect was noted for the cucumber control plants. While no negative impact on hemp shoot growth was seen in trials where nematodes were added to pasteurized soil, a significant and visible negative effect on hemp growth was noted when two CBG hemp cultivars were planted in heavily naturally root-knot infested soil. This result indicates that hemp is not only a good host to root-knot nematodes, but also that root-knot can be a limiting factor for hemp production in Florida and other places with high abundance and pressure of root-knot nematodes.

Depth distribution of plant-parasitic nematodes on bentgrass golf greens in Missouri and Indiana.

Control of plant-parasitic nematodes (PPNs) on golf putting greens with nematicides is dependent on the seasonal occurrence and depth distribution of target PPN populations. This study aimed to determine if plant-parasitic nematode populations on golf course putting greens in Missouri and Indiana peaked at a targetable depth at a specific time in the year, focusing primarily on lance (Hoplolaimus spp.) and root-knot (Meloidogyne spp.) nematodes. To elucidate species diversity in the region, rDNA from a subset of lance and root-knot nematodes was sequenced and analyzed, with additional micromorphology of a lance nematode assessed in scanning electron micrographs (SEM). Soil samples were taken to a depth of 25 cm and stratified into 5 cm increments during April, June, August and October at seven sites across Missouri, three in the Kansas City metro of Kansas in 2021 and in ten sites across Indiana in 2022. Samples were stratified in five-centimeter increments and aggregated for a total of 100 cm3 of soil at each depth for each sampling. Samples were processed using a semi-automatic elutriator followed by the sucrose-flotation method, and populations were counted using a hemocytometer and recorded. For molecular characterization, rDNA was extracted and analyzed from 31 individual lance nematodes from one site in Missouri and eight sites in Indiana, and 13 root-knot nematodes from nine sites across Indiana. A significant interaction occurred between sampling month and depth for lance and ring nematodes Missouri/KS, with both PPN populations peaking at the 0-5 cm depth during October, which is well after most targeted nematicide applications are applied. Ring nematodes in Indiana did not follow this trend and were most abundant in August at a depth of 0-5 cm. No significant interaction between depth and month occurred for lance or root-knot nematodes in Indiana, or root-knot nematodes in Missouri/KS. Hoplolaimus stephanus and H. magnistylus were the lance species identified on golf greens, and Meloidogyne naasi, M. graminicola and M. marylandi were the root-knot species identified. Scanning-electron micrographs confirmed morphological characteristics unique to H. stephanus.

Microbiome-Mediated Strategies to Manage Major Soil-Borne Diseases of Tomato.

The tomato (Solanum lycopersicum L.) is consumed globally as a fresh vegetable due to its high nutritional value and antioxidant properties. However, soil-borne diseases can severely limit tomato production. These diseases, such as bacterial wilt (BW), Fusarium wilt (FW), Verticillium wilt (VW), and root-knot nematodes (RKN), can significantly reduce the yield and quality of tomatoes. Using agrochemicals to combat these diseases can lead to chemical residues, pesticide resistance, and environmental pollution. Unfortunately, resistant varieties are not yet available. Therefore, we must find alternative strategies to protect tomatoes from these soil-borne diseases. One of the most promising solutions is harnessing microbial communities that can suppress disease and promote plant growth and immunity. Recent omics technologies and next-generation sequencing advances can help us develop microbiome-based strategies to mitigate tomato soil-borne diseases. This review emphasizes the importance of interdisciplinary approaches to understanding the utilization of beneficial microbiomes to mitigate soil-borne diseases and improve crop productivity.

Marker assisted early generation identification of root knot disease resistant orange tomato segregants with multiple desirable alleles.

Enhanced bioavailability of cis-isomers of lycopene, accumulated in orange-fruited tangerine mutant has broadened the scope of nutritional enrichment in tomato. At the same time, advancements in the field of marker assisted selection (MAS) have made the stacking of multiple desirable alleles through molecular breeding to develop superior tomato genotypes possible. Here we report seedling stage MAS from 146 F2 plants, to identify 3 superior performing, root knot disease resistant orange-fruited segregants. In the selected segregants, fruit weight ranged from 39.2 to 54.6 g, pericarp thickness ranged from 4.56 to 6.05 mm and total soluble solid content ranged from 3.65 to 4.87° Brix. Presence of parental diversity allowed identification of the other desirable alleles of the genes governing late blight and mosaic disease resistance, growth habit (determinate and indeterminate) as well as fruit elongation and firmness. Resistance to root knot disease of the selected 3 segregants was also validated through a unique method employing in vitro rooted stem cuttings subjected to artificial inoculation, where the resistant parent and the selected segregants developed no galls in comparison to ~ 24 galls developed in the susceptible parent. The selected segregants form the base for development of multiple disease resistant, nutritionally enriched orange-fruited determinate/indeterminate tomato lines with superior fruit quality. The study also highlights the utility of early generation MAS for detailed characterization of segregants, through which multiple desirable alleles can be precisely targeted and fixed to develop superior tomato genotypes. Supplementary Information: The online version contains supplementary material available at 10.1007/s12298-023-01361-1.

First Report of Meloidogyne javanica Infecting Strawberry (Fragaria × ananassa) in the United States.

Strawberry (Fragaria × ananassa) is native to temperate regions. However, it has been produced in tropical areas, as a seasonal crop including in Florida, USA during the winter months. In March 2022, root galls resembling those induced by root-knot nematodes (Meloidogyne spp.) were observed in declining strawberry plants 'WinterstarTM FL 05-107' growing in an organic-certified research site in Hillsborough County, Florida, USA. To our knowledge, M. hapla is the only root-knot species reported to infect strawberry in Florida. Preliminary molecular analyses, including newly synthesized DNA sequences (TW81/AB28 = OQ469833 - OQ469836; D2A/D3B= OQ473043 - OQ473047) using extracted nematode females from the strawberry roots, initially identified the RKN as M. javanica. Nematode species confirmation was further performed using the morphology of the female perineal patterns and isozyme analysis, mainly esterase (EST) and malate dehydrogenase (MDH), DNA sequencing, (NAD5-F/NAD5-R) and the SCAR primer set (Fjav/Rjav), species-specific for M. javanica. Isozyme analyses, EST= J3, which is specific for M. javanica and MDH=N1, as well as the morphology of female perineal patterns, agreed with data previously reported for M. javanica. A pathogenicity test on strawberry 'WinterstarTM FL 05-107' transplants was performed using 10,000 eggs of the original M. javanica population, which induced galls on strawberry plants (Gall index, GI = 4.1) with egg masses clearly visible outside of the roots, producing an average of 1,344 eggs/gram of fresh root and 9,201 ± 4,206 eggs/root system. No galls or egg masses were observed on non-inoculated plants. Tomato 'HM 1823' was used as a control for the viability of the inoculum and showed numerous galls and egg masses (GI=5.0;). The newly obtained DNA sequences using NAD5-F/NAD5-R (OQ474970 - OQ474972) were compared with other sequences available in the GenBank and were shown to be 100% identical to five M. javanica populations from Polk County, Florida, USA (OM418745 - OM418749) and the complete mitochondrion genome of M. javanica (NC026556). To our knowledge, this is the first report of M. javanica infecting strawberry in the United States.

Activity of root-knot nematodes associated with composition of a nematode-attached microbiome and the surrounding soil microbiota.

We investigated if activity of the pre-infective juveniles (J2s) of root-knot nematodes is linked to the recruitment of a specific microbiome on the nematode surface and/or to the composition of the surrounding microbiota. For this, we determined the J2 activity (active vs. non-motile, which referred to dead and immobile J2s) upon a 3-day incubation in soil suspensions and studied the composition of bacteria, protists, and fungi present on the nematode surface and in the suspensions using amplicon sequencing of the 16S/18S rRNA genes, and ITS region. We also amended suspensions with Pseudomonas protegens strain CHA0 to study its effects on J2 activity and microbial composition. The J2 activity was suppressed in soil suspensions, but increased when suspensions were amended with P. protegens CHA0. The active and non-motile J2s differed in the composition of surface-attached bacteria, which was altered by the presence of P. protegens CHA0 in the soil suspensions. The bacterial genera Algoriphagus, Pedobacter, and Bdellovibrio were enriched on active J2s and may have protected the J2s against antagonists. The incubation time appeared short for attachment of fungi and protists. Altogether, our study is a step forward in disentangling the complex nematode-microbe interactions in soil for more successful nematode control.

Distribution, Diversity, and Soil Associations of Wine Grape Plant-Parasitic Nematodes in Georgia, U.S.A., Vineyards.

Wine grape (Vitis vinifera and V. vinifera hybrids) production in Georgia occurs in three distinct regions (North, West, and South) which can be characterized by sandy, sandy-loam, or sandy clay-loam soils. We studied plant-parasitic nematode (PPN) communities in 15 wine grape vineyards from the three primary growing regions to understand which nematodes are a concern and what soil characteristics are associated with their occurrence and relative abundance. Twelve genera of PPNs were detected throughout the state: Belonolaimus, Helicotylenchus, Hemicycliophora, Heterodera, Hoplolaimus, Meloidogyne, Mesocriconema, Paratrichodorus, Paratylenchus, Pratylenchus, Tylenchorhynchus, and Xiphinema. Nonmetric multidimensional scaling ordination and multirank permutation procedure identified PPN community differences and soil characteristics that were associated by region. Indicator species analysis identified Helicotylenchus, Mesocriconema, Tylenchorhynchus, and Xiphinema as statistically associated with the West while Meloidogyne and Paratrichodorus were associated with the South. Our analyses further suggested that soil texture (percent sand, percent clay, and percent silt) and the lime buffer capacity at equilibrium (LBCEQ) were associated with PPN community structure while pH was not. When focused on a single vineyard in the North, multiple logistic regression analysis suggested a statistically significant association between Meloidogyne spp. and soil characteristics, including percentages of sand, pH, and LBCEQ. Our study supports the association between soil characteristics and specific nematode genera, as well as the emergence of LBCEQ, the soil measurement with the strongest statistical association with nematode community structure and Meloidogyne presence.

Application Potential of Bacterial Volatile Organic Compounds in the Control of Root-Knot Nematodes.

Plant-parasitic nematodes (PPNs) constitute the most damaging group of plant pathogens. Plant infections by root-knot nematodes (RKNs) alone could cause approximately 5% of global crop loss. Conventionally, chemical-based methods are used to control PPNs at the expense of the environment and human health. Accordingly, the development of eco-friendly and safer methods has been urged to supplement or replace chemical-based methods for the control of RKNs. Using microorganisms or their metabolites as biological control agents (BCAs) is a promising approach to controlling RKNs. Among the metabolites, volatile organic compounds (VOCs) have gained increasing attention because of their potential in the control of not only RKNs but also other plant pathogens, such as insects, fungi, and bacteria. This review discusses the biology of RKNs as well as the status of various control strategies. The discovery of VOCs emitted by bacteria from various environmental sources and their application potential as BCAs in controlling RKNs are specifically addressed.

Root-knot nematode damage to a cucurbit double crop is increased by chloropicrin fumigation on the previous tomato crop.

BACKGROUND: Double-cropping is a common practice in vegetable plasticulture whereby a second crop is planted on the same plastic bed as the first crop. Root-knot nematodes (Meloidogyne spp.) are one of the major soilborne constraints in double-cropped vegetables due to nematode population build-up on the first crop. We evaluated the effect of fumigant and non-fumigant nematicides applied on the first crop, on nematode infection and yield of the second crop in 10 field trials between 2017 and 2020. Fumigants were chloropicrin (Pic100), chloropicrin +1,3-D (PicClor60), and non-fumigant nematicides were oxamyl (Vydate), fluensulfone (Nimitz), fluopyram (Velum) and fluazaindolizine (Salibro). The first crop was tomato and double crops were cucumber, squash, zucchini, and cantaloupe. RESULTS: Fumigation with chloropicrin on the first crop increased root-knot nematode damage on the double-crop at the end of the season in seven trials, while the opposite was noted in one trial, and no difference was noted in two trials. Fumigation with chloropicrin+1,3-D resulted in root-knot nematode damage less than chloropicrin but more than non-fumigated plots. Cucurbit yield was greater in non-fumigated beds in four trials, and in chloropicrin-treated beds in two trials. Fluensulfone reduced root-knot nematode damage on the second crop in five out of 10 trials. CONCLUSION: Our results indicate that chloropicrin applied on the tomato crop may lead to increased root-knot nematode damage on the double crop. More research is needed to understand the processes behind this, but it is possibly related to a reduction in natural nematode soil suppressiveness due to the broad-spectrum fungicidal activity of chloropicrin. © 2022 Society of Chemical Industry.

Microplate bioassay to examine the effects of grapevine-isolated stilbenoids on survival of root knot nematodes.

OBJECTIVES: Root knot nematodes can be major pests in vineyards and cause significant yield losses over time. Control involves the use of different resistant grapevine rootstocks, but it remains unclear the mechanisms that such rootstocks possess to limit root knot nematode infections. Defense-associated compounds called stilbenoids, a type of phenolic compound, are present in relatively substantial amounts in grapevine root tissues. Therefore, experiments were performed to assess how different stilbenoid compounds impact nematode survival in microplate assays. Data generated were part of a larger effort to understand potential mechanisms that resistant grapevine rootstocks have to limit root knot infections. DATA DESCRIPTION: The percentage of surviving root knot nematodes was assessed 1, 3, and 5 days after J2 juveniles were placed into microplate wells amended with 0, 1.25, 2.5, 5, or 10 ppm of piceid, ε-viniferin, a resveratrol trimer putatively identified as miyabenol C, or a putative mixture of resveratrol tetramers putatively identified as vitisin B and hopeaphenol. Both ε-viniferin and the resveratrol tetramers significantly reduced root knot survival at the higher concentrations. These data provide insight about one potential mechanism that grapevine rootstocks might possess to combat nematodes.

Eco-friendly dual-edged management of fly ash and its antagonistic interplay with Meloidogyne incognita on beetroot (Beta vulgaris L.).

Fly ash (FA) management is a key concern of ecologists around the world, so its potential as a nutritional supplement for agro-ecosystems needs to be explored. Therefore, alternate techniques that are eco-friendly to manage this emerging dual-edged waste are preferable in this field. The current study sought to determine the soil-modifying, crop yield improvement, and nematicidal properties of FA. In this study, beetroot seeds were sown in pots comprising field soil amended with differing proportions of FA (w/w) revealed the bio-fold properties of FA. Biomineralization and mapping of elements revealed that increased nutritional elements in soil supplemented with 15% FA induced growth-performance and yield of beetroot. Molecularly and morphologically characterized Meloidogyne incognita was used as nematode in this study for optimization of nematicidal properties FA. Plant growth performance, photosynthetic pigments, and yield of beetroot were significantly reduced owing to M. incognita as compared to control (un-treated and un-inoculated), and 15% FA reversed the negative effect of M. incognita significantly (P < 0.05) as compared to control plants. Confocal laser microscopy confirmed that 15% FA augmented in soil reduced nematode-juvenile invasion in beetroot as compared with control. The PCA (principal component analysis) accounted for 98.63% and 98.8% for the total-data variability in plants without nematodes and total data variability in treated plants (M. incognita + FA) respectively, which showed fit for a significant correlation between the various studied parameters in present study.

Supplemental Fumigant Placement Improves Root Knot and Fusarium Wilt Management for Tomatoes Produced on a Raised-Bed Plasticulture System in Florida's Myakka Fine Sand.

Fresh-market tomatoes are produced on a raised-bed plasticulture system that relies heavily on soil-applied preplant fumigants for the management of soilborne pathogens, nematodes, and weeds. Since the transition from methyl bromide to alternative fumigants, growers have experienced a resurgence of several soilborne pests and pathogens, including root-knot nematode caused by Meloidogyne spp. and Fusarium wilt caused by Fusarium oxysporum f. sp. lycopersici race 3. This resurgence is attributed to the inability of the alternative fumigants to effectively disperse through the soil in the same manner as methyl bromide. Two supplemental fumigation strategies, the application of chloropicrin (PIC) below bed edges (herein "supplemental PIC") and broadcast deep-shank applications of 1,3-dichloropropene (1,3-D), were evaluated in conjunction with standard raised-bed applications of Pic-Clor 60, Pic-Clor 80, and Pic 100 covered with a virtually impermeable film or a totally impermeable film. Large-plot replicated studies were conducted in two separate commercial tomato fields with a history of production losses caused by root-knot nematode and Fusarium wilt. Deep-shank 1,3-D applications significantly reduced the recovery of root-knot and total parasitic nematodes across field sites before the preparation of raised beds. Both supplemental PIC and deep-shank 1,3-D reduced root-knot galling and Fusarium wilt incidence, but the latter supplemental treatment statistically had the greatest impact. Fumigant applied within raised beds or plastic film had no significant effect on root-knot galling or Fusarium wilt. Although both supplemental fumigation strategies had a significant effect on pest and disease pressure, neither statistically improved tomato yields based on small subplot harvests. Controlled laboratory experiments confirmed the fungicidal activity of 1,3-D against F. oxysporum f. sp. lycopersici, with 75, 90, 95, and 99% lethal doses corresponding to estimated field application rates of 56.1, 93.5, 121.6, and 184.7 liters/ha, respectively. The results demonstrate how fumigant placement can improve pest and disease control activity with current fumigant alternatives to methyl bromide and further support the broader pesticidal activity of some chemical fumigants.

Prevalence and Molecular Diversity of Plant-Parasitic Nematodes of Yam (Dioscorea spp.) in China, with Focus on Merlinius spp.

There is little information about nematode pests associated with yam in China. Between 2020 and 2021, surveys of yam fields were conducted to investigate the abundance and prevalence of plant-parasitic nematodes in major yam growing areas. A total of 110 bulk soil samples from the yam rhizosphere and 48 yam tubers were collected from seven counties in Jiangxi and Shandong provinces. Standard protocols were used to extract nematodes from soil and tubers and identified at the genus level. In this study, 16 species and 13 nematode genera were recorded. The five most prominent species on the yam rhizosphere according to mean population densities were Pratylenchus coffeae (291/individuals), Meloidogyne (262/individuals), Rotylenchulus reniformis (225/individuals), Merlinius (224/individuals), and Helicotylenchus dihystera (171/individuals). In the tubers, the three most prominent species were Pratylenchus coffeae (415/individuals), Meloidogyne (331/individuals), and Rotylenchulus reniformis (115/individuals). These species were verified with appropriate molecular analysis. The high prevalence of the ectoparasite (Merlinius spp.) on the rhizosphere of yam also revealed that Merlinius spp. May be more important to yam than previously thought. Morphological and molecular analyses further confirmed the identity of the species as Merlinius brevidens and were characterized for the first time on yam in China. Minor morphometrical differences (slightly longer body and stylet) were observed in Chinese populations of M. brevidens compared to the original description. Additionally, this study reveals that M. brevidens isolated from China showed a higher nucleotide sequence in the ITS region compared to M. brevidens populations from India. This finding provides baseline information on the nematode pest occurrence on yam in China and calls for effective management.

Announcement of WormAtlas partnership with the Journal of Nematology.

A detailed understanding of nematode anatomy can be leveraged for the development of new parasitic nematode control strategies and for fundamental biological insights through nematode model organisms. The Center for C. elegans Anatomy, with its websites WormAtlas and WormImage, is the central anatomical resource for researchers studying the model organism Caenorhabditis elegans. Here, we announce our expansion of the WormAtlas and WormImage resources beyond C. elegans to include additional nematode species. Towards this goal, we will partner with the Journal of Nematology to write and solicit anatomically focused review chapters for publication in the Journal and corresponding inclusion on the WormAtlas website.

Effects of fluopyram and azadirachtin integration with sunn hemp on nematode communities in zucchini, tomato and sweet potato in Hawaii.

Fluopyram (Velum® One) is a synthetic nematicide and azadirachtin (Molt-X®) is a biological nematicide. Both have shown promise against plant-parasitic nematodes on several agriculturally important crops. There is a lack of information on integration of pre-plant sunn hemp (Crotalaria juncea) cover crop with these post-plant nematicides, aiming to improve plant-parasitic nematodes management and mitigate any detrimental effects on free-living nematodes. Three field trials were conducted to investigate the effects of fluopyram alone or in combination with pre-plant sunn hemp cover crop, and azadirachtin combined with pre-plant sunn hemp on Rotylenchulus reniformis and Meloidogyne spp., and free-living nematodes. Zucchini (Cucurbita pepo) and tomato (Solanum lycopersicum) were grown in Trials I and II, and sweet potato (Ipomoea batatas) only was grown in Trial III. In all three trials, early applications of fluopyram at crop planting were effective in suppressing the abundance of Meloidogyne spp. (M. incognita and M. javanica) but it was not effective in reducing R. reniformis in the soil. Combining sunn hemp with fluopyram was suppressive to R. reniformis on short-term zucchini crop, but not on longer term tomato and sweet potato crops. In addition, application of fluopyram at transplanting was the key to successful suppression of Meloidogyne spp. as later fluopyram chemigation (at 2 weeks after planting in Trial II or 1 month after planting in Trial III) had no effect against Meloidogyne spp. On the other hand, planting of sunn hemp followed by monthly post-plant azadirachtin application consistently suppressed R. reniformis, but this treatment did not suppress Meloidogyne spp. Integrating sunn hemp with fluopyram increased zucchini yield by >2.3 folds and that with azadirachtin increased the zucchini yield by >1.7 folds. Although no yield improvement was observed on tomato in Trial II, integrating sunn hemp with azadirachtin and fluopyram increased tomato yield by 0.23 and 1.12 folds, respectively, in Trial I. Marketable yield of sweet potato was increased by 4.5-6.4 folds in all the fluopyram treatments but was only increased 61.5% by sunn hemp plus azadirachtin treatment. While fluopyram alone often reduced the abundance of free-living nematodes, integrating with sunn hemp mitigated the negative impacts of fluopyram on soil health.

Influence of the Environment and Vegetable Cropping Systems on Plant-Parasitic Nematode Communities in Southern Georgia.

Plant-parasitic nematodes (PPN) limit yields of vegetable production in the United States. During the spring and fall cropping seasons of 2018, 436 fields in bare ground and plastic bed cropping systems were randomly sampled from 29 counties in southern Georgia. The incidence (%), mean relative abundance, and maximum relative abundance (nematodes per 100 cm3 of soil) of the 10 different PPN genera detected in 32 vegetable crops in bare ground and plastic bed cropping systems include Meloidogyne spp. (67.3%; mean, 292; maximum, 14,144), Nanidorus spp. (49.4%; mean, 6; maximum, 136), Mesocriconema spp. (39.6%; mean, 17; maximum, 340), Helicotylenchus spp. (31.6%; mean, 20; maximum, 1152), Pratylenchus spp. (20.1%; mean, 2; maximum, 398), Rotylenchulus spp. (5.9%; mean, 1; maximum, 116), Hoplolaimus spp. (12.6%; mean, 1; maximum, 78), Heterodera spp. (2.3%; mean, <1; maximum, 60), Tylenchorhynchus spp. (0.9%; mean, <1; maximum, 12), and Xiphinema spp. (0.2%; mean, <1; maximum, 2). A nonmetric multidimensional scaling analysis indicated that most environmental and geological factors (i.e., longitude, precipitation, soil moisture, sand and silt content, and soil electrical conductivity) had no apparent relationship with nematode counts, except for latitude, soil pH, and temperature. The multirank permutation procedure followed by indicator species analysis and nonparametric Kruskal-Wallis analysis of variance indicated that Meloidogyne spp. are the predominant PPN associated with plastic beds in the south region sampled. The south region consisted mainly of commercial fields that rotated multiple vegetables crops through the same plastic beds. All other PPNs were associated with bare ground beds in the north region that are commonly rotated with row crops. This study validates that Meloidogyne spp. are the most important PPN in vegetable fields of southern Georgia and suggests that cropping systems have a greater effect on PPN population dynamics than the environment.

Cucurbitaceae COld Peeling Extracts (CCOPEs) Protect Plants From Root-Knot Nematode Infections Through Induced Resistance and Nematicidal Effects.

With nematicides progressively being banned due to their environmental impact, an urgent need for novel and sustainable control strategies has arisen. Stimulation of plant immunity, a phenomenon referred to as "induced resistance" (IR), is a promising option. In this study, Cucurbitaceae COld Peeling Extracts (CCOPEs) were shown to protect rice (Oryza sativa) and tomato (Solanum lycopersicum) against the root-knot nematodes Meloidogyne graminicola and Meloidogyne incognita, respectively. Focusing on CCOPE derived from peels of melon (Cucumis melo var. cantalupensis; mCOPE), we unveiled that this extract combines an IR-triggering capacity with direct nematicidal effects. Under lab conditions, the observed resistance was comparable to the protection obtained by commercially available IR stimuli or nematicides. Via mRNA sequencing and confirmatory biochemical assays, it was proven that mCOPE-IR in rice is associated with systemic effects on ethylene accumulation, reactive oxygen species (ROS) metabolism and cell wall-related modifications. While no negative trade-offs were detected with respect to plant growth or plant susceptibility to necrotrophic pests or pathogens, additional infection experiments indicated that mCOPE may have a predominant activity toward biotrophs. In summary, the presented data illustrate a propitious potential for these extracts, which can be derived from agro-industrial waste streams.

Nematode RALF-Like 1 Targets Soybean Malectin-Like Receptor Kinase to Facilitate Parasitism.

Soybean [Glycine max (L.) Merr. ] is one of the most strategical oilseed crops that provides sustainable source of protein and oil worldwide. Cultivation of soybean is severely affected by root-knot nematode (RKN). However, the mechanism of RKN parasitism to soybeans is largely unknown. In this study, we identify GmLMM1, which encodes a homolog of FERONIA-like receptor kinase in soybean, as a susceptible gene toward nematode. Mutations of GmLMM1 exhibit enhanced resistance against the RKN Meloidogyne incognita. RNA-sequencing (RNA-seq) analysis reveals a similar differential expression pattern for genes regulated by GmLMM1 (Gmlmm1 vs. wild-type) and M. incognita (M. incognita vs. mock), supporting the role of GmLMM1 in M. incognita infection. Unlike FERONIA in Arabidopsis, GmLMM1 specifically binds to MiRALF1 and AtRALF23 that suppress plant immunity, but not MiRALF3 and AtRALF1. Moreover, we found that the single-nucleotide polymorphism (SNP) in GmLMM1 leads to the natural resistance against RKNs in soybeans. Collectively, these findings uncover GmLMM1 as a susceptible target of nematode RALF-like 1 and provide new genetic resource for nematode resistant breeding.