The study, led by Sara Rodriguez-Mena of the Institute for Sustainable Agriculture in Córdoba, Spain, together with Mario González, Diego Rubiales and collaborators in Portugal and Iran, set out with a simple but urgent question. Grass pea cultivation declined for decades in many regions where Aphanomyces is endemic, which may explain why the pathogen was never reported as a problem in this crop. But renewed interest in grass pea as a model crop for sustainable agriculture, driven by its resilience and its ability to fix atmospheric nitrogen, means that expanded cultivation could bring the crop back into contact with infested soils. As legume acreage grows across Europe and beyond, so too does the risk that Aphanomyces spreads with it. Understanding whether grass pea can withstand this pathogen before farmers commit to the crop is therefore a matter of practical urgency.

To answer it, the researchers assembled a globally diverse panel of 169 grass pea accessions, drawn from the Mediterranean basin, South Asia, Eastern Europe, Sub-Saharan Africa, North Asia and the Americas. The collection spanned differences in seed colour and seed size that would later prove biologically meaningful. Each accession was inoculated under controlled conditions with the RB84 isolate of A. euteiches, a pea-derived strain known for its ability to cross host boundaries and infect multiple legume species. Ten-day-old seedlings received a zoospore suspension adjusted to 1,000 zoospores per millilitre, applied directly at the base of each stem. Twenty days later, the team scored both foliar symptoms on a scale of 0 to 5 and root rot symptoms on a scale of 0 to 9, with the highly susceptible pea cultivar Messire serving as a positive control to confirm that the inoculation had worked.

The results revealed an extraordinary spectrum of responses. Average foliar symptom scores ranged from 0.08 to 4.50, and root rot scores from 1.64 to 8.73, meaning the collection captured everything from near-complete susceptibility to something approaching immunity. Twelve accessions qualified as resistant, with low scores on both scales, and two of them, PI283570_A and PI283580, displayed complete resistance to the tested isolate, a level of protection that has never been documented in pea, where breeders have managed only to identify partial resistance. Ten further accessions showed partial resistance, including STUDENICA, a commercial variety with strong agronomic credentials that could be recommended for cultivation in infested soils right away. Notably, several of the resistant accessions, including PI283580, BGE17185 and PTLS1006, had previously shown low symptom levels against another soil-borne pathogen, Fusarium oxysporum f. sp. pisi, making them doubly valuable given how frequently Aphanomyces and Fusarium co-infect legume fields.

Genotype was the dominant driver of symptom variation, with high broad-sense heritability for both foliar and root scores, exactly the property breeders need for genetic improvement. But seed characteristics left a visible fingerprint too. Accessions with large, light-coloured seeds, which are typical of Mediterranean origins, showed significantly lower disease symptoms than small, dark-seeded accessions of South Asian provenance. This echoes earlier findings in the same collection for Fusarium resistance, hinting that shared defence mechanisms may underpin grass pea tolerance to both soil-borne pathogens. The correlation between foliar and root symptoms was moderate but significant, confirming that what happens underground reliably manifests above ground, as it does in pea.

The real breakthrough came from combining these phenotypes with an upgraded genomic data set. Building on a previously published grass pea reference genome, the team re-called variants from genotyping-by-sequencing data and mapped DArTseq markers onto the seven chromosomes of the L. sativus assembly. The original data set of 26,876 SNPs, of which only 5,651 passed earlier quality filters, was transformed into a far denser resource: 44,383 SNPs detected in total, with 12,974 high-quality markers passing rigorous filtering for minor allele frequency and missing data. This nearly tripled the usable marker count and provided comprehensive genome-wide coverage, giving the association study the resolution it needed.

Using four different genome-wide association models, the team identified 20 SNPs significantly associated with resistance, distributed across five of the seven grass pea chromosomes, with chromosomes 2 and 3 entirely free of associations. Thirteen markers tracked foliar symptoms, eight tracked root rot, and one, SNP007517 on chromosome 6, was associated with both. Two markers, SNP032149 and SNP007517, were independently detected by two different statistical models, reinforcing confidence in their relevance. The proportion of phenotypic variance explained by individual markers ranged from a modest 0.13 percent to 11.62 percent, a pattern that screams polygenic inheritance: no single locus dominates, and resistance emerges from the combined action of many genes scattered across the genome. Clusters of closely linked markers on chromosomes 5 and 6 point to candidate quantitative trait loci that future studies can target with finer mapping.

In silico annotation of the genomic regions surrounding the significant SNPs identified seven putative candidate genes with plausible roles in defence. A wax ester synthase gene on chromosome 1 and a fatty-acid metabolism gene on chromosome 5 connect to evidence that fatty-acid accumulation mediates reactive oxygen species production during Aphanomyces infection in pea. A component of the exocyst complex on chromosome 4, involved in vesicle trafficking, has been implicated in plant immunity, though its specific role against this oomycete remains poorly understood. Chromosome 6 contributed two protein kinase genes and an ethylene receptor gene, and here the parallels with other legumes are striking: serine/threonine protein kinases and ethylene signalling have both been repeatedly linked to Aphanomyces defence in pea and barrel medic, with the ethylene pathway promoting lignin deposition that forms a protective ring around the root’s central cylinder, physically blocking pathogen entry. A callose synthase gene on chromosome 7 rounds out the list, suggesting reinforcement of cell walls at infection sites to limit hyphal spread.

What makes these findings particularly interesting from an evolutionary and agronomic standpoint is that the genomic distribution of resistance markers in grass pea does not overlap with the conserved syntenic QTL regions identified in pea, lentil, faba bean and barrel medic. Grass pea appears to have evolved its own, independently assembled resistance toolkit. This lack of a conserved pattern could complicate cross-species marker transfer, but it also opens exciting possibilities: if breeders can overcome crossability barriers between grass pea and its close relatives, these novel resistance loci could diversify the genetic defences available across legume agriculture, reducing the selective pressure that intensively cultivated, genetically similar crops place on pathogen populations. Because Aphanomyces populations are genetically diverse and reproduce both sexually and asexually, quantitative, polygenic resistance stacked across multiple loci is widely regarded as the most durable long-term strategy, far more robust than reliance on any single resistance gene.

The authors are careful to note the caveats. The RB84 isolate is a pea pathogen, so the response characterised here is a non-host-specific infection; grass pea-specific isolates, if they exist, could be more aggressive and might overcome even the complete resistance observed in PI283570_A and PI283580. Field validation is essential, as is testing against a broader panel of isolates to determine whether the identified regions confer broad-spectrum or pathotype-specific resistance, and whether the two fully resistant accessions owe their protection to monogenic or polygenic mechanisms. Functional validation of the seven candidate genes in planta will clarify their actual roles and guide precision breeding. Still, the significance of this work is hard to overstate. For the first time, breeders have identified sources of resistance to Aphanomyces root rot in grass pea, together with associated loci and candidate genes, transforming an uncharted vulnerability into a well-mapped opportunity. As climate change pushes agriculture toward resilient crops, grass pea may be entering hostile territory, but it is arriving armed with a genetic arsenal that science is only beginning to decode.

Subject of Research: Genetic resistance of grass pea (Lathyrus sativus) to the oomycete root rot pathogen Aphanomyces euteiches

Article Title: Aphanomyces euteiches causes disease in Lathyrus sativus with a globally diverse, polygenic resistance landscape

Article References: Aphanomyces euteiches causes disease in Lathyrus sativus with a globally diverse, polygenic resistance landscape. (n.d.). https://doi.org/10.1007/s00122-026-05372-w

Image Credits: AI Generated

DOI: 10.1007/s00122-026-05372-w

Keywords: grass pea, Lathyrus sativus, Aphanomyces euteiches, root rot, genome-wide association study, polygenic resistance, candidate genes, legume breeding, plant pathology, SNP markers, quantitative resistance, sustainable agriculture

The experimental design was elegant in its simplicity. Detached composite leaves from greenhouse-grown plants of each variety were either left untreated as healthy controls, mock inoculated with water, or inoculated with droplets containing one million zoospores per millilitre of a fluorescently labelled P. infestans strain. Samples were collected at 48 hours post inoculation both inside the inoculated area and in surrounding tissue, allowing the team to distinguish local responses from more systemic ones. In total, 36 samples were sequenced using Illumina paired-end technology, with reads mapped to the reference potato genome at rates of 85 to 92 percent. Visual symptoms told the first part of the story: Sarpo Shona developed dark necrotic spots by 24 hours after inoculation, while Duke of York did not react until 48 hours, and by nine days the susceptible variety’s leaves were extensively yellowed and colonised. Callose staining revealed that Duke of York deposited substantially less of this defensive wall material at 24 hours than either resistant variety, with Sarpo Mira showing the strongest accumulation.

Principal component analysis of the thousand most variable genes showed that the first principal component, explaining 51 percent of the variation, cleanly separated healthy leaves from all inoculated conditions, while the second component, explaining 26 percent, separated the two resistant Sarpo varieties from Duke of York across every condition. This was a striking finding: even in completely healthy, uninfected leaves, resistant and susceptible potatoes occupied distinct transcriptional states. The largest number of differentially expressed genes appeared when comparing healthy controls with mock-inoculated leaves after 48 hours of incubation, but the infection response itself revealed an asymmetry that would prove central to the study’s conclusions. Sarpo Mira showed the smallest transcriptional response to infection, Sarpo Shona an intermediate one, and Duke of York the largest, with more than twice as many genes downregulated in the susceptible variety as in either resistant one.

Gene ontology enrichment analysis sharpened this picture considerably. In Duke of York, genes downregulated inside the infected area were enriched for 16 biological process terms, including abscisic acid biosynthesis and signalling, jasmonic acid signalling, and several defence-related categories, none of which were enriched in the resistant varieties. This pattern suggests that P. infestans actively suppresses hormone signalling and defence pathways in the susceptible host, effectively disarming the plant’s response machinery. Downregulation of specific WRKY transcription factors was observed only in Duke of York, consistent with pathogen-mediated suppression of transcriptional regulation. Meanwhile, all three varieties upregulated lignin biosynthesis genes inside the infected area, but the response was markedly stronger in the Sarpo varieties, which activated 19 and 20 lignin-related genes respectively compared with 15 in Duke of York. Crucially, seven of these upregulated lignin genes were also induced outside the infected area in each Sarpo variety, compared with only two in the susceptible potato, hinting at a broader systemic reinforcement of cell walls.

The most provocative finding emerged when the researchers compared gene expression across all conditions between resistant and susceptible varieties. A total of 685 genes had consistently higher expression and 431 genes consistently lower expression in both Sarpo varieties than in Duke of York, regardless of whether the plants were healthy, mock treated, or infected. Among the top upregulated genes were a glycosyl hydrolase, a beta-1,3-glucanase capable of degrading pathogen cell walls, an R gene encoding a leucine-rich repeat and NB-ARC domain resistance protein, a protein kinase, and a raffinose synthase. The single most highly upregulated gene across all conditions, with a log2 fold change exceeding 15, was a basic chitinase. These are not emergency responses; they are standing garrisons. The resistant varieties maintain elevated expression of a broad arsenal of defence genes even in the absence of any threat, a state the authors describe as stressed-like expression patterns existing before the onset of stress.

Wall-associated kinase receptors emerged as a particularly compelling component of this pre-armed state. WAKs are cell surface receptors that recognise pectin fragments released from the plant cell wall during the early stages of pathogen attack, functioning as damage-sensing sentinels that trigger pattern-triggered immunity. Ten WAK genes were consistently differentially expressed in one or both Sarpo varieties compared with Duke of York, with seven upregulated in Sarpo Mira and six in Sarpo Shona. Most of these were not themselves induced by infection, meaning the resistant varieties simply carry more of these receptors at all times. Combined with the upregulation of specific pectin lyase-like genes that generate oligogalacturonide fragments acting as damage-associated molecular patterns, the resistant potatoes appear to operate both a louder alarm and more sensitive detectors, enabling faster activation of pattern-triggered immunity when the pathogen breaches the wall.

Resistance genes told a similar story of abundance rather than activation. Ninety-one R genes showed consistent differential expression in one or both Sarpo varieties relative to Duke of York, and almost none of these were further induced during infection. Several, including a cluster on potato chromosome 4 containing multiple known resistance genes, were expressed at consistently higher levels in the resistant varieties. Notably, the three major qualitative resistance genes of Sarpo Mira, R3A, R3B and R8, were not differentially expressed at a log2 fold change of one or greater during infection in any variety, suggesting that the variety’s celebrated resistance cannot be explained by these five genes alone. High basal expression of many R proteins likely provides more intracellular receptors poised to detect P. infestans effectors, allowing a faster hypersensitive response without the growth penalties associated with constitutive R protein activation.

Cell wall composition itself appears to differ between the varieties before infection. Lignin-related genes were expressed at higher levels in healthy Sarpo leaves, implying a physically tougher wall, a pattern previously observed in Camelina sativa resistant to Sclerotinia sclerotiorum. Cutin transport genes were also more highly expressed in healthy resistant leaves, suggesting a thicker cuticular barrier against pathogen penetration. In contrast, Duke of York upregulated numerous xyloglucan endotransglucosylase/hydrolase genes during infection, enzymes that remodel hemicellulose and alter wall extensibility, while the resistant varieties tended to downregulate them. The susceptible variety also downregulated seven lignin-related genes, including five phenylalanine ammonia lyases, the gateway enzymes of the phenylpropanoid pathway that feeds monolignol biosynthesis. Perhaps most tellingly, both Sarpo varieties strongly and consistently downregulated three target of rapamycin genes, the master growth-promoting kinase that suppresses defence, indicating that these varieties actively prioritise immunity over growth, accepting a metabolic trade-off in exchange for protection.

The study’s authors acknowledge limitations, including the absence of pathogen load quantification, the use of a single 48-hour time point, and the need to validate cell wall composition biochemically and candidate genes functionally, potentially through genome editing. Nevertheless, the findings provide a transcriptome-wide blueprint for quantitative late blight resistance that could transform breeding strategies. Rather than pyramiding single R genes that P. infestans has repeatedly overcome in its evolutionary arms race, breeders may be able to select for the basal expression states that make varieties like Sarpo Mira and Sarpo Shona permanently vigilant: higher standing levels of wall-associated kinases, R proteins, beta-1,3-glucanases, lignin and cutin machinery, and phosphorylation components, coupled with suppressed growth signalling. As climate change threatens to expand the disease burden of this devastating oomycete, the insight that durable resistance begins before infection may prove one of the most valuable lessons the humble potato has to offer.

Subject of Research: Basal expression of defence mechanisms underlying quantitative resistance to potato late blight

Article Title: Keep up your guard: basal expression of defence mechanisms distinguishes blight resistant from blight susceptible potato varieties

Article References: Ponce, O. P., Dunne, N., Cremona, L., Edbali, O., Woellwarth, T., Bosanquet, J., Luna, E., Prashar, A., & Compton, L. (2026). Keep up your guard: basal expression of defence mechanisms distinguishes blight resistant from blight susceptible potato varieties. BMC Agriculture, 2(1), Article 21. https://doi.org/10.1186/s44399-026-00041-1

Image Credits: AI Generated

DOI: 10.1186/s44399-026-00041-1

Keywords: potato, late blight, Phytophthora infestans, transcriptomics, quantitative resistance, Sarpo Mira, Sarpo Shona, Duke of York, wall-associated kinase, R genes, cell wall, plant immunity