Much of the current literature on the mechanisms of plant resistance to pathogens has focused on the role of cellular sensors that initiate a "pathogen-associated molecular-pattern triggered immunity" or PTI response. Less attention has been given to the benefits that some common metabolites may provide to plant resistance. In this study, an untargeted metabolomic analysis identified 230 metabolites that were 3-fold higher in the trap crop Solanum sisymbriifolium than in two nematode-susceptible potato varieties. Several of these metabolites had nematicidal activity in vitro against the root-knot nematodes, Meloidogyne chitwoodi, M. incognita, and M. hapla, at concentrations measured in Solanum sisymbriifolium roots. The most effective of the chemicals tested were furoic, aconitic, and quinic acids. Further studies revealed first that the 3 acids were most effective at or below their acid dissociation constant (pKa) implying that the protonated forms were better able than the charged ones to cross cell membranes and/or bind to critical targets. Second, that the effects of these chemicals were due partially to their structures and not to the creation of an acidic environment. Third, that these chemicals acted additively indicating that S. sisymbriifolium resistance may be partially due to a combination of metabolites rather than to any single chemical.

Globodera pallida, a quarantine potato cyst nematode (PCN), has had a significant economic impact on the Idaho potato industry. Developing resistant commercial varieties has been challenging because the predominant russet potato market class lacks resistance to G. pallida, and no single major resistance gene has been identified. This study characterized the phenotypic resistance to the Idaho G. pallida pathotype Pa2/3 population in a tetraploid russet potato population derived from PCN-resistant ‘Eden’ and PCN-susceptible ‘Western Russet’. A total of 227 offspring were distributed over three years with a different subset of the population evaluated each year alongside four cultivar controls, and four PCN differential clones. Phenotypic evaluations were conducted under greenhouse conditions to evaluate traits related to cyst and egg development. Progeny showing resistance similar to ‘Eden’ constituted 13.7

Multigenerational stress exposure induces stress memory in plants, influencing resource allocation, defence mechanisms, and productivity. Weed competition imposes both resource-based (abiotic) and allelopathic (biotic) stress, engaging overlapping hormonal pathways. This study examined the hormonal and transcriptomic mechanisms underlying multigenerational stress memory in wheat subjected to inter-specific competition with kochia and Italian ryegrass and intra-specific competition with other wheat plants. Phytohormone analysis revealed increased salicylic acid levels, promoting systemic acquired resistance, whereas jasmonic acid levels declined, indicating suppressed jasmonate-mediated defence. Abscisic acid responses varied, reflecting shifts in water-use efficiency. Cytokinins and auxins exhibited generation- and treatment-specific trends, suggesting adaptive resource acquisition but potential hormonal imbalances. These hormonal shifts corresponded with phenotypic responses, where adaptive benefits peaked at Generation 3 before transitioning to maladaptive responses in later generations. Transcriptomic analysis identified dynamic changes in differentially expressed genes (DEGs) and key pathways. Wheat-only competition peaked in stress-responsive DEGs in Generation 3, while wheat-kochia and wheat-ryegrass exhibited early generation transcriptional reprogramming and long-term adaptations. Intra-specific wheat competition showed early generation transcriptomic surges but persistent growth repression in the current study. These findings provide mechanistic insights into multigenerational stress memory mechanisms and reveal how phytohormonal crosstalk and transcriptional reprogramming shape wheat responses to competition stress across generations.

Competitiveness is essential for plants to survive abiotic and biotic stressors. Studies reveal that plants can store and recall stress memories, influencing their future responses—known as the plant memory response. This study explored how multigenerational weed exposure affects the phenotypic plasticity of spring wheat. Wheat was grown in 3 L pots, surrounded by 8 kochia, 8 Italian ryegrass, 8 wheat, or no surrounding plants, with 15 replicates. Seeds harvested from generation 1 were used to plant generation 2, and this process was repeated through generation 5. Seed yields in generation 3 showed increases of 385% (wheat‐only), 123% (wheat‐kochia), 9% (wheat‐ryegrass), and 35% (wheat‐wheat) compared to generation 1. Conversely, generation 2 saw yield reductions of 59%, 64%, and 28% in the wheat‐kochia, wheat‐ryegrass, and wheat‐wheat treatments, respectively. The yield improvements observed in generation 3 were not sustained in generations 4 and 5, possibly due to the erasure of somatic stress memory. Wheat‐ryegrass and wheat‐wheat treatments caused the greatest reductions in yield and biomass relative to kochia competition. The wheat‐only treatment consistently produced the most spikes, biomass, and yield, peaking in generation 3 or 4, with seed numbers tripling compared to generation 1. These results indicate a possible positive effect of multigenerational stress memory on wheat in generation 3, followed by a maladaptive response to weed competition in later generations.

The potato (Solanum tuberosum) cyst nematode Globodera pallida induces a multinucleate feeding site (syncytium) in potato roots as its sole source of nutrition. Here, we demonstrate that the G. pallida effector RING-H2 finger A1b (RHA1B), which is a functional ubiquitin ligase, interferes with the carbon catabolite repression 4 (CCR4)-negative on TATA-less (NOT) deadenylase-based RNA metabolism machinery that regulates syncytium development in G. pallida-infected potato. Specifically, RHA1B targets the CCR4-associated factor 1 (CAF1) and StNOT10 subunits of the CCR4-NOT complex for proteasome-mediated degradation, leading to upregulation of the cyclin gene StCycA2 involved in syncytium formation. The StCAF1 subunit of CCR4-NOT recruits the RNA binding protein StPUM5 to deadenylate StCycA2 mRNA, resulting in shortened poly-A tails of StCycA2 mRNA and subsequently reduced transcript levels. Knockdown of either subunit (StCAF1 or StNOT10) of the CCR4-NOT complex or StPUM5 in transgenic potato plants resulted in enlarged syncytia and enhanced susceptibility to G. pallida infection, which resembles the phenotypes of StCycA2 overexpression transgenic potato plants. Genetic analyses indicate that transgenic potato plants overexpressing RHA1B exhibit similar phenotypes as transgenic potato plants with knockdown of StNOT10, StCAF1, or StPUM5. Thus, our data suggest that G. pallida utilizes the RHA1B effector to manipulate RNA metabolism in host plants, thereby promoting syncytium development for parasitic success. The potato cyst nematode effector RHA1B targets components of the RNA metabolic machinery of potato for proteasome-mediated degradation to promote syncytium development.

Root-knot nematodes (RKNs) are a major pest of Solanum and other economically important crops worldwide. Two species of RKNs ( Meloidogyne chitwoodi and Meloidogyne hapla ) are persistent threats to potato growers of the United States. These RKNs infect potato roots and tubers, causing tuber blemishes that decrease potato market value and significantly impact the profitability of the infected potato crop. Due to environmental, health, and economic concerns, the longstanding control methods of using soil fumigants and post-plant nematicides are not favored by producers and consumers. Therefore, deploying RKN resistant cultivars is an alternative method to control RKN damage. However, there is no genetic resistance to RKN in commercially-available, cultivated potatoes. Therefore, the critical first step to breed a RKN resistant plant is to identify a genetic source of RKN resistance. A wild Solanum species, Solanum sisymbriifolium, also known as litchi tomato, can effectively control several agronomically important species of plant parasitic nematodes. Solanum sisymbriifolium is completely resistant to RKNs; only a few nematodes enter the plant roots and those that do, cannot establish a feeding site. To understand its ability to prevent RKNs from forming feeding sites, we performed transcriptomic analysis of S. sisymbriifolium roots inoculated with the Northern root knot nematode, M. hapla . Combined with the annotation of the recently published S. sisymbriifolium genome assembly, we discovered 13 differentially expressed resistance-related genes upon nematode inoculation. By transforming potatoes with candidate resistance genes from S. sisymbriifolium , we aim to understand the strong genetic resistance in S. sisymbriifolium and whether those genes are necessary and sufficient to drive resistance to RKN in potatoes. This information will help us understand gene functions and help us generate RKN resistance in relevant Solanum crops. ### Competing Interest Statement The authors have declared no competing interest.

In this study, we show that the potato ( Solanum tuberosum ) pattern recognition receptor (PRR) NEMATODE-INDUCED LEUCINE-RICH REPEAT (LRR)-RLK1 (StNILR1) functions as a dual receptor, recognizing both nematode-associated molecular pattern ascaroside #18 (Ascr18) and plant hormone brassinosteroid (BR) to activate two different physiological outputs: pattern-triggered immunity (PTI) and BR response. Ascr18/BR-StNILR1 signaling requires the coreceptor potato BRASSINOSTEROID INSENSITIVE 1-ASSOCIATED RECEPTOR KINASE 1 (StBAK1) and perception of either ligand strengthens StNILR1 interaction with StBAK1 in plant cells. Significantly, the parasitically successful potato cyst nematode ( Globodera pallida ) utilizes the effector RHA1B, which is a functional ubiquitin ligase, to target StNILR1 for ubiquitination-mediated proteasome-dependent degradation, thereby countering Ascr18/BR-StNILR1-mediated PTI in potato and facilitating nematode parasitism. These findings broaden our understanding of PRR specificity and reveal a nematode parasitic mechanism that targets a PTI signaling pathway.

Litchi tomato (LT) (Solanum sisymbriifolium) is a solanaceous weed that is considered a biological control tool to manage potato cyst nematode (PCN) in Europe and is being explored for use in Idaho. Two Several LT lines were clonally maintained as stocks in the university greenhouse since 2013 and were also established in tissue culture at the same time. In 2018, tomato (Solanum lycopersicum cv. Alisa Craig) scions were grafted onto two LT rootstocks originating either from healthy-looking greenhouse stocks or from tissue culture-maintained plants. Unexpectedly, tomatoes grafted onto the greenhouse-maintained rootstocks of LT displayed severe symptoms of stunting, foliar deformation, and chlorosis, while grafts onto the same LT lines from tissue culture produced healthy-looking tomato plants. Tests for the presence of several viruses known to infect solanaceous plants were conducted on symptomatic tomato scion tissues using ImmunoStrips (Agdia, Elkhard, IN) and RT-PCR (Elwan et al. 2017) but yielded negative results. High throughput sequencing (HTS) was then used to identify possible pathogens that could have been responsible for the symptoms observed in tomato scions. Samples from two symptomatic tomato scions, two asymptomatic scions grafted onto the tissue culture-derived plants, and two greenhouse-maintained rootstocks were subjected to HTS. Total RNA from the four tomato and two LT samples was depleted of ribosomal RNA and subjected to HTS on an Illumina MiSeq platform producing 300-bp paired-end reads and raw reads were adapter and quality cleaned. For the tomato samples, the clean reads were mapped against the S. lycopersicum L. reference genome, and unmapped paired reads were assembled producing between 4,368 and 8,645 contigs. For the LT samples, all clean reads were directly assembled, producing 13,982 and 18,595 contigs. In the symptomatic tomato scions and the two LT rootstock samples, a 487-nt contig was found, comprising an ~1.35 tomato chlorotic dwarf viroid (TCDVd) genome and exhibiting 99.7% identity with it (GenBank accession AF162131; Singh et al. 1999). No other virus-related or viroid contigs were identified. RT-PCR analysis using a pospiviroid primer set Pospi1-FW/RE (Verhoeven et al. 2004), and a TCDVd-specific primer set TCDVd-Fw/TCDVd-Rev (Olmedo-Velarde et al. 2019) produced 198-nt and 218-nt bands, respectively, thus confirming the presence of TCDVd in tomato and LT samples. These PCR products were Sanger sequenced and confirmed to be TCDVd-specific; the complete sequence of the Idaho isolate of TCDVd was deposited in GenBank under the accession number OQ679776. Presence of TCDVd in LT plant tissue was confirmed by the APHIS PPQ Laboratory in Laurel, MD. Asymptomatic tomatoes and LT plants from tissue culture were found negative for TCDVd. Previously, TCDVd was reported to affect greenhouse tomatoes in Arizona and Hawaii (Ling et al. et al. 2009; Olmedo-Velarde et al. 2019), however, this is the first report of TCDVd infecting litchi tomato (S. sisymbriifolium). Five additional greenhouse-maintained LT lines were found TCDVd-positive using RT-PCR and Sanger sequencing. Given the very mild or asymptomatic infection of TCDVd in this host, molecular diagnostic methods should be used to screen LT lines for the presence of this viroid to avoid inadvertent spread of TCDVd. Another viroid, potato spindle tuber viroid, was reported to be transmitted through LT seed (Fowkes et al. 2021), and transmission of TCDVd through LT seed may also be responsible for this TCDVd outbreak in the university greenhouse, although no direct evidence was collected. To the best of our knowledge, this is the first report of TCDVd infection in S. sisymbriifolium and also the first report of the TCDVd occurrence in Idaho.

Plants use pattern recognition receptors (PRRs) to perceive conserved molecular patterns derived from pathogens and pests, thereby activating a sequential set of rapid cellular immune responses, including activation of mitogen-activated protein kinases (MAPKs) and Ca2+-dependent protein kinases (CDPKs), transcriptional reprogramming (particularly the induction of defense-related genes), ion fluxes, and production of reactive oxygen species.1 Plant PRRs belong to the multi-membered protein families of receptor-like kinases (RLKs) or receptor-like proteins (RLPs). RLKs consist of a ligand-binding ectodomain, a single-pass transmembrane domain, and an intracellular kinase domain, while RLPs possess the same functional domains, except for the intracellular kinase domain.2 The most abundant nematode ascaroside, Ascr18, is a nematode-associated molecular pattern (NAMP) that induces immune signaling and enhances resistance to pathogens and pests in various plant species.3 In this study, we found that the Arabidopsis NEMATODE-INDUCED LRR-RLK1 (NILR1) protein4 physically interacts with the Ascr18 elicitor, as indicated by a specific direct interaction between NILR1 and Ascr18, and NILR1 is genetically required for Ascr18-triggered immune signaling and resistance to both bacterium and nematode, as manifested by the abolishment of these immune responses in the nilr1 mutant. These results suggest that NILR1 is the immune receptor of the nematode NAMP Ascr18, mediating Ascr18-triggered immune signaling and resistance to pathogens and pests.

Understanding belowground chemical interactions between plant roots and plant-parasitic nematodes is immensely important for sustainable crop production and soilborne pest management. Due to metabolic diversity and ever-changing dynamics of root exudate composition, the impact of only certain molecules, such as nematode hatching factors, repellents, and attractants, has been examined in detail. Root exudates are a rich source of biologically active compounds, which plants use to shape their ecological interactions. However, the impact of these compounds on nematode parasitic behavior is poorly understood. In this study, we specifically address this knowledge gap in two cyst nematodes, Globodera pallida , a potato cyst nematode and the newly described species, Globodera ellingtonae . Globodera pallida is a devastating pest of potato ( Solanum tuberosum ) worldwide, whereas potato is a host for G. ellingtonae , but its pathogenicity remains to be determined. We compared the behavior of juveniles (J2s) hatched in response to root exudates from a susceptible potato cv. Desirée, a resistant potato cv. Innovator, and an immune trap crop Solanum sisymbriifolium (litchi tomato – a wild potato relative). Root secretions from S. sisymbriifolium greatly reduced the infection rate on a susceptible host for both Globodera spp. Juvenile motility was also significantly influenced in a host-dependent manner. However, reproduction on a susceptible host from juveniles hatched in S. sisymbriifolium root exudates was not affected, nor was the number of encysted eggs from progeny cysts. Transcriptome analysis by using RNA-sequencing (RNA-seq) revealed the molecular basis of root exudate-mediated modulation of nematode behavior. Differentially expressed genes are grouped into two major categories: genes showing characteristics of effectors and genes involved in stress responses and xenobiotic metabolism. To our knowledge, this is the first study that shows genome-wide root exudate-specific transcriptional changes in hatched preparasitic juveniles of plant-parasitic nematodes. This research provides a better understanding of the correlation between exudates from different plants and their impact on nematode behavior prior to the root invasion and supports the hypothesis that root exudates play an important role in plant-nematode interactions.

Cultivated potato is a clonally propagated autotetraploid species with a highly heterogeneous genome. Phased assemblies of six cultivars including two chromosome-scale phased genome assemblies revealed extensive allelic diversity, including altered coding and transcript sequences, preferential allele expression, and structural variation that collectively result in a highly complex transcriptome and predicted proteome, which are distributed across the homologous chromosomes. Wild species contribute to the extensive allelic diversity in tetraploid cultivars, demonstrating ancestral introgressions predating modern breeding efforts. As a clonally propagated autotetraploid that undergoes limited meiosis, dysfunctional and deleterious alleles are not purged in tetraploid potato. Nearly a quarter of the loci bore mutations are predicted to have a high negative impact on protein function, complicating breeder’s efforts to reduce genetic load. The StCDF1 locus controls maturity, and analysis of six tetraploid genomes revealed that 12 allelic variants of StCDF1 are correlated with maturity in a dosage-dependent manner. Knowledge of the complexity of the tetraploid potato genome with its rampant structural variation and embedded deleterious and dysfunctional alleles will be key not only to implementing precision breeding of tetraploid cultivars but also to the construction of homozygous, diploid potato germplasm containing favorable alleles to capitalize on heterosis in F1 hybrids.

Solanum glycoalkaloids are gaining increased scientific attention due to their bioactive potential in the defense of plants against pests and pathogens. The comprehensive glycoalkaloid profiling from the leaves, stems, and roots of seven underexploited Solanum species (S. caripense, S. melanocerasum, S. muricatum, S. nigrum, S. quitoense, S. retroflexum, and S. sisymbriifolium) was conducted using high-performance liquid chromatography–time-of-flight mass spectrometry. A total of 51 glycoalkaloids were shared among the studied Solanum species, with concentrations ranging from 7 to 5.63 × 105 ng g−1. Based on the glycoalkaloid composition, plants were separated into two clusters, Cluster 1 (S. melanocerasum, S. nigrum, and S. retroflexum) and Cluster 2 (S. caripense, S. muricatum, S. quitoense, and S. sisymbriifolium). The inhibition activity of glycoalkaloid extracts on acetylcholinesterase showed a half-maximal inhibitory concentration (IC50), ranging from 0.4 (S. nigrum stems) to 344.9 µg mL−1 (S. sisymbriifolium leaves), that was not directly correlated to the total glycoalkaloid contents. This suggests that the composition of glycoalkaloids in the plant extract, rather than the total concentration, is a driver of biological activity. The study provides a framework for the bioprospecting of underexploited Solanum species for exploring bioactive glycoalkaloids and other compounds with potential pesticidal activities for the development of green bioformulation. This is the first comprehensive report on the glycoalkaloid profiles of S. retroflexum.

Potato cyst nematodes (PCN; Globodera pallida and G. rostochiensis) are among the most significant pathogens limiting the production of potato globally. Since the first PCN detection, research has focused on a diversity of topics, including species identification, geographic distribution, and pathotype characterization. While many have focused on characterizing potato-nematode interactions, identification of resistance has been a challenge, particularly for G. pallida. This, in turn, makes it difficult to recommend nematode management strategies. South America is the center of diversity for PCN and includes numerous international institutes and universities conducting PCN resistance research at the regional level. For breeding programs and other users of this information and associated germplasm, a consolidated overview of this research would be beneficial. This review reports on South American research conducted to evaluate potato germplasm response to PCN in the Andean region of South America.

Potato cyst nematodes (PCN) are economically important pests with a worldwide distribution in all temperate regions where potatoes are grown. Because above ground symptoms are non-specific, and detection of cysts in the soil is determined by the intensity of sampling, infestations are frequently spread before they are recognised. PCN cysts are resilient and persistent; their cargo of eggs can remain viable for over two decades, and thus once introduced PCN are very difficult to eradicate. Various control methods have been proposed, with resistant varieties being a key environmentally friendly and effective component of an integrated management programme. Wild and landrace relatives of cultivated potato have provided a source of PCN resistance genes that have been used in breeding programmes with varying levels of success. Producing a PCN resistant variety requires concerted effort over many years before it reaches what can be the biggest hurdle—commercial acceptance. Recent advances in potato genomics have provided tools to rapidly map resistance genes and to develop molecular markers to aid selection during breeding. This review will focus on the translation of these opportunities into durably PCN resistant varieties.

Potato cyst nematodes (PCN) are economically important pests with a worldwide distribution in all temperate regions where potatoes are grown. Because above ground symptoms are non-specific, and detection of cysts in the soil is determined by the intensity of sampling, infestations are frequently spread before they are recognised. PCN cysts are resilient and persistent; their cargo of eggs can remain viable for over two decades, and thus once introduced PCN are very difficult to eradicate. Various control methods have been proposed, with resistant varieties being a key environmentally friendly and effective component of an integrated management programme. Wild and landrace relatives of cultivated potato have provided a source of PCN resistance genes that have been used in breeding programmes with varying levels of success. Producing a PCN resistant variety requires concerted effort over many years before it reaches what can be the biggest hurdle-commercial acceptance. Recent advances in potato genomics have provided tools to rapidly map resistance genes and to develop molecular markers to aid selection during breeding. This review will focus on the translation of these opportunities into durably PCN resistant varieties.

Potato cyst nematodes (PCNs), such as Globodera pallida and Globodera rostochiensis, are some of the most agriculturally and economically important pests of potato. Upon nematode infection, a principal component of plant defense is the generation of the reactive oxygen species (ROSs). ROSs are highly toxic molecules that cause damage to pathogens and host alike. To infect the plant, nematodes protect themselves from ROSs by activating their own antioxidant processes and ROS scavenging enzymes. One of these enzymes is a superoxide dismutase (SOD; EC 1.15.1.1), which prevents cellular damage by catalyzing conversion of the superoxide radical (O 2 −· ) to hydrogen peroxide (H 2 O 2 ) and molecular oxygen (O 2 ). We have isolated a putatively secreted isoform of a Cu–Zn SOD (SOD-3) from G. pallida and localized the expression of this gene in the posterior region of the nematode. Furthermore, we studied the expression of the SOD-3 gene during early parasitic stages of infection (24 to 72 h) in the susceptible potato cultivar Desiree, the resistant potato cultivar Innovator, and an immune host, Solanum sisymbriifolium. The SOD-3 gene was significantly upregulated, regardless of the host type; however, the expression pattern differed between the susceptible and the resistant or immune hosts. This finding suggests that SOD-3 gene is responding to infection in plant roots differently depending on whether the nematode is experiencing a compatible or an incompatible interaction.

Potato cyst nematodes (PCN; Globodera pallida and Globodera rostochiensis) are among the most significant pathogens limiting the production of potato globally. Potato cyst nematodes occur in cooler areas of subtropical and tropical regions and temperate regions throughout the world. Both species have the potential to significantly reduce potato yields. In the South American Andes highlands, potato is a major staple crop and is used mainly for local consumption. Most of the potatoes produced in South America are consumed unprocessed, a principal reason why potatoes remain a staple food for the majority of families. Plant-parasitic nematodes are among the most important phytosanitary pests limiting potato production in these Andean countries. In South America, research has focused on taxonomy and on frequency and severity of PCN, and in calculating damage or yield loss to potato due to PCN. This review reports the distribution of the PCN in the main potato-growing areas of the Andean region of South America, as well as the impact of PCN on regional potato production.

The plant-parasitic nematode Globodera pallida is an obligate biotroph that only reproduces on select species in the Solanum family. The establishment of the feeding site, the syncytium, involves secretion of effectors into the plant cell to combat the plant defense response and facilitate transformation of root cells into the syncytium. Despite the important predicted roles of effectors in the plant_ pathogen interactions, the functionality of G. pallida effectors is largely unknown. In this study, we identified and characterized a G. pallida effector protein disulfide isomerase (GpPDI1). GpPDI1 contains two thioredoxin domains that function together to reduce disulfide bonds, as manifested by the nullification of enzymatic activity when either domain is absent. The transcript of GpPDI1 is localized in the dorsal gland of the nematode during the J2 stage. In addition, GpPDI1 can trigger defense- related cell death in Nicotiana benthamiana and tomato (Solanum lycopersicum) leaf tissue and localizes in the plant host cell's cytoplasm and nucleus when transiently expressed in plant cells. Significantly, the ability of elicitation of cell death is not dependent on the enzymatic activity of GpPDI1 or correlated with the subcellular distribution of GpPDI1, suggesting that a nondisulfide reducing function or structural feature of GpPDI1 is responsible for the recognition by the host immune system to elicit cell death.