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ThePericoniafungal genus belongs to the phylum Ascomycota, order Pleosporales, family Periconiaceae.Periconiaare found in many habitats but little is known about their ecology. Several species from this genus produce bioactive molecules.Periconia digitataextracts were shown to be deadly active against the pine wilt nematode. Furthermore,P. digitatawas shown to inhibit plant pathogenic oomycetePhytophthora parasitica. BecauseP. digitatahas great potential as a biocontrol agent and high quality genomic resources are still lacking in the Periconiaceae family, we generated long-read genomic data forP. digitata. Using the PacBio Hifi sequencing technology, we obtained a highly-contiguous genome assembled in 13 chromosomes and totalling ca. 39 Mb. In addition, we produced a reference transcriptome, based on 12 different culture conditions, and proteomic data to support the genome annotation. Besides representing a new reference genome within the Periconiaceae, this work will contribute to our better understanding of the Eukaryotic tree of life and opens new possibilities in terms of biotechnological applications.

Background Muscadine (Muscadinia rotundifolia) is known as a resistance source to many pests and diseases in grapevine. The genetics of its resistance to two major grapevine pests, the phylloxera D. vitifoliae and the dagger nematode X. index, vector of the Grapevine fanleaf virus (GFLV), was investigated in a backcross progeny between the F1 resistant hybrid material VRH8771 (Vitis-Muscadinia) derived from the muscadine R source ‘NC184–4’ and V. vinifera cv. ‘Cabernet-Sauvignon’ (CS). Results In this pseudo-testcross, parental maps were constructed using simple-sequence repeats markers and single nucleotide polymorphism markers from a GBS approach. For the VRH8771 map, 2271 SNP and 135 SSR markers were assembled, resulting in 19 linkage groups (LG) and an average distance between markers of 0.98 cM. Phylloxera resistance was assessed by monitoring root nodosity number in an in planta experiment and larval development in a root in vitro assay. Nematode resistance was studied using 10–12 month long tests for the selection of durable resistance and rating criteria based on nematode reproduction factor and gall index. A major QTL for phylloxera larval development, explaining more than 70% of the total variance and co-localizing with a QTL for nodosity number, was identified on LG 7 and designated RDV6. Additional QTLs were detected on LG 3 (RDV7) and LG 10 (RDV8), depending on the in planta or in vitro experiments, suggesting that various loci may influence or modulate nodosity formation and larval development. Using a Bulked Segregant Analysis approach and a proportion test, markers clustered in three regions on LG 9, LG 10 and LG 18 were shown to be associated to the nematode resistant phenotype. QTL analysis confirmed the results and QTLs were thus designated respectively XiR2, XiR3 and XiR4, although a LOD-score below the significant threshold value was obtained for the QTL on LG 18. Conclusions Based on a high-resolution linkage map and a segregating grapevine backcross progeny, the first QTLs for resistance to D. vitifoliae and to X. index were identified from a muscadine source. All together these results open the way to the development of marker-assisted selection in grapevine rootstock breeding programs based on muscadine derived resistance to phylloxera and to X. index in order to delay GFLV transmission.

International audience; The dagger nematode Xiphinema index has a major economic impact because of its transmission of Grapevine fanleaf virus to grapevines. This vector nematode, which was introduced into Western countries from the Middle East together with the domesticated grapevine, mostly reproduces by meiotic parthenogenesis, but microsatellite multilocus genotype (MLG) analysis has revealed the occurrence of rare sexual reproduction events in field conditions. In a previous 6-year study under controlled conditions, we evaluated the durability of resistance to X. index in accessions derived from a muscadine resistance source and reference accessions. In this previous study, we used an equal-proportion mixture of four lines (from Spain, Italy, Greece, and Iran) representative of X. index diversity as the inoculum, and we collected random samples in 3-, 4-, 5-, and 6-year-old vines. Here, we genotyped the individuals from these samples using the MLG technique, and we analyzed the changes in line frequency and the occurrence of sexual reproduction events between lines over time. The nematode lines differed in aggressiveness and hybrids between lines were detected at a low, but apparently increasing rate. Hybridization events were recovered in all accessions, regardless of resistance status and propagation type. Finally, our data provide the first evidence of sexual reproduction in the nematode X. index under controlled conditions.

The dagger nematode

Breeding for varieties carrying natural resistance (R) against plant-parasitic nematodes is a promising alternative to nematicide ban. In perennial crops, the long plant-nematode interaction increases the risk for R breaking and R durability is a real challenge. In grapevine, the nematode

Breeding for varieties carrying natural resistance (R) against plant-parasitic nematodes is a promising alternative to nematicide ban. In perennial crops, the long plant−nematode interaction increases the risk for R breaking and R durability is a real challenge. In grapevine, the nematode Xiphinema index has a high economic impact by transmitting Grapevine fanleaf virus (GFLV) and, to delay GFLV transmission, rootstocks resistant to this vector are being selected, using Muscadinia rotundifolia in particular as an R source. To optimize in fine this strategy, the durability has been studied under controlled conditions in F1 and BC1 muscadine-derived resistant accessions previously obtained from either hardwood-cutting or in vitro propagation. After inoculation with a mix, in equal proportions, of four lines representative of the X. index diversity, multiplication on plants has been monitored 3 to 6 years. The nematode reproduction factor remained lower than 1 in resistant plants obtained from hardwood cuttings while it increased at values far beyond 1 in resistant plants of in vitro origin. Data for nematode numbers per gram of roots mostly paralleled those obtained for the reproduction factor. The effect of the propagation type on resistance over years was also evaluated for the ratio female/juvenile and the frequency of males. Altogether our results illustrate that the muscadine-derived resistance based on hardwood cuttings is durable. By contrast, in resistant and reference accessions obtained from in vitro, our data suggest that the increased nematode multiplication might be mainly due to the modification of root architecture consecutive to this propagation method.

International audience; Root-knot nematodes (RKN) (Meloidogyne spp.) are worldwide pests that affect a considerable number of plants, among which stone fruit (Prunus spp.) are severely attacked. Prevalent RKN species are Meloidogyne arenaria, M. incognita, and M. javanica in stone fruit but the emergent M. ethiopica and M. enterolobii are also reported to challenge perennial crops. In Prunus spp., the complete-spectrum resistance (R) gene Ma from plum and the more restricted-spectrum R genes RMia from peach and RMja from almond completely inhibit nematode multiplication and gall formation of the RKN species that they control. This study aimed to update the resistance spectra of these three major genes by evaluating their activity toward one isolate of the yet-untested RKN species mentioned above. To state whether a given gene controls a particular species, the principle of our experiment was to genotype with appropriate markers a number of individuals segregating for this gene and then to phenotype these individuals. A perfect matching of the genotype and the phenotype of individuals indicates that the gene of interest is active against and, thus, controls the corresponding isolate of this RKN species. Segregating materials used were an Ma F1 plum progeny, an RMia F2 peach progeny, and an RMja F2 almond progeny. In addition to previous data, our results establish a clear spectrum for each of the three genes toward isolates from both the three prevalent species and the two emerging species. Ultimately, our results reveal that (i) Ma controls all of them, (ii) RMja controls all species except M. incognita and M. floridensis, and (iii) RMia controls M. arenaria, M. incognita, and M. ethiopica but not M. javanica or M. enterolobii. Our data should have wide implications for RKN resistance management and breeding and for deciphering the molecular mechanisms of the spectrum of RKN R genes.

The NLRs or NBS-LRRs (nucleotide-binding, leucine-rich-repeat) form the largest resistance gene family in plants, with lineage-specific contingents of TNL, CNL and RNL subfamilies and a central role in resilience to stress. The origin, evolution and distribution of NLR sequences has been unclear owing in part to the variable size and diversity of the RNL subfamily and a lack of data in Gymnosperms. We developed, searched and annotated transcriptomes assemblies of seven conifers and identified a resource of 3816 expressed NLR sequences. Our analyses encompassed sequences data spanning the major groups of land plants and determinations of NLR transcripts levels in response to drought in white spruce. We showed that conifers have among the most diverse and numerous RNLs in tested land plants. We report an evolutionary swap in the formation of RNLs, which emerged from the fusion of an RPW8 domain to a NB-ARC domain of CNL. We uncovered a quantitative relationship between RNLs and TNLs across all land plants investigated, with an average ratio of 1:10. The conifer RNL repertoire harbours four distinct groups, with two that differ from Angiosperms, one of which contained several upregulated sequences in response to drought while the majority of responsive NLRs are downregulated.

International audience; Root-knot nematodes (RKNs) are considerable polyphagous pests that severely challenge plants worldwide and especially perennials. The specific genetic resistance of plants mainly relies on the NBS-LRR genes that are pivotal factors for pathogens control. In Prunus spp., the Ma plum and RMja almond genes possess different spectra for resistance to RKNs. While previous works based on the Ma gene allowed to clone it and to decipher its peculiar TIR-NBS-LRR (TNL) structure, we only knew that the RMja gene mapped on the same chromosome as Ma. We carried out a high-resolution mapping using an almond segregating F2 progeny of 1448 seedlings from resistant (R) and susceptible (S) parental accessions, to locate precisely RMja on the peach genome, the reference sequence for Prunus species. We showed that the RMja gene maps in the Ma resistance cluster and that the Ma ortholog is the best candidate for RMja. This co-localization is a crucial step that opens the way to unravel the molecular determinants involved in the resistance to RKNs. Then we sequenced both almond parental NGS genomes and aligned them onto the RKN susceptible reference peach genome. We produced a BAC library of the R parental accession and, from two overlapping BAC clones, we obtained a 336-kb sequence encompassing the RMja candidate region. Thus, we could benefit from three Ma orthologous regions to investigate their sequence polymorphism, respectively, within plum (complete R spectrum), almond (incomplete R spectrum) and peach (null R spectrum). We showed that the Ma TNL cluster has evolved orthologs with a unique conserved structure comprised of five repeated postLRR (PL) domains, which contain most polymorphism. In addition to support the Ma and RMja orthologous relationship, our results suggest that the polymorphism contained in the PL sequences might underlie differential resistance interactions with RKNs and an original immune mechanism in woody perennials. Besides, our study illustrates how PL exon duplications and losses shape TNL structure and give rise to atypical PL domain repeats of yet unknown role.

Advances in pyramiding resistance genes to root-knot nematodes in Prunus rootstocks. 9. International Peach symposiumHS

Background Plants develop sustainable defence responses to pathogen attacks through resistance (R) genes contributing to effector-triggered immunity (ETI). TIR-NB-LRR genes (TNL genes) constitute a major family of ETI R genes in dicots. The putative functions or roles of the TIR, NB and LRR domains of the proteins they encode (TNLs) are well documented, but TNLs also have a poorly characterised C-terminal region, the function of which is unknown in most cases. We characterised this prevalent stress-response protein family in a perennial plant, using the genome of peach (Prunus persica), the model Prunus species. The first TNL gene from this genus to be cloned, the Ma gene, confers complete-spectrum resistance to root-knot nematodes (RKNs) and encodes a protein with a huge C-terminal region with five duplicated post-LRR (PL) domains. This gene was the cornerstone of this study. Results We investigated the role of this C-terminal region, by first describing the frequency, distribution and structural characteristics of i) TNL genes and ii) their PL domains in the peach genome, using the v1.0 Sanger sequence together with the v2.0 sequence, which has better genome annotation due to the incorporation of transcriptomic data. We detected 195 predicted TNL genes from the eight peach chromosomes: 85 % of these genes mapped to chromosomes 1, 2, 7 and 8. We reconstructed the putative structure of the predicted exons of all the TNL genes identified, and it was possible to retrieve the PL domains among two thirds of the TNL genes. We used our predicted TNL gene sequences to develop an annotation file for use with the Gbrowse tool in the v2.0 genome. The use of these annotation data made it possible to detect transcribed PL sequences in two Prunus species. We then used consensus sequences defined on the basis of 124 PL domains to design specific motifs, and we found that the use of these motifs significantly increased the numbers of PL domains and correlative TNL genes detected in diverse dicot genomes. Based on PL signatures, we showed that TNL genes with multiple PL domains were rare in peach and the other plants screened. The five-PL domain pattern is probably unique to Ma and its orthologues within Prunus and closely related genera from the Rosaceae and was probably inherited from the common ancestor of these plants in the subfamily Spiraeoideae. Conclusions The first physical TNL gene map for Prunus species can be used for the further investigation of R genes in this genus. The PL signature motifs are a complementary tool for the detection of TNL R genes in dicots. The low degree of similarity between PL domains and the neighbouring LRR exons and the specificity of PL signature motifs suggest that PL and LRR domains have different origins, with PL domains being specific to TNL genes, and possibly essential to the functioning of these genes in some cases. Investigations of the role of the oversized Ma PL region, in ligand binding or intramolecular interactions for example, may help to enrich our understanding of NB-LRR-mediated plant immunity to RKNs. Electronic supplementary material The online version of this article (doi:10.1186/s12864-016-2635-0) contains supplementary material, which is available to authorized users.

Khallouk, S., Voisin, R., Van Ghelder, C., Engler, G., Amiri, S., and Esmenjaud, D. 2011. Histological mechanisms of the resistance conferred by the Ma gene against Meloidogyne incognita in Prunus spp. Phytopathology 101:945-951. The Ma gene from Myrobalan plum is a TNL gene that confers a highlevel resistance to all root-knot nematodes of major economic importance, including Meloidogyne incognita, M. javanica, M. arenaria, and M. enterolobii. The nematode behavior in the roots and the corresponding histological mechanisms of the Ma resistance to M. incognita in the resistant (R) accessions of the plum ‘P.2175’ and the interspecific hybrid P.2175 × almond-peach ‘35’, carrying the Ma1 allele (Ma1/ma), were characterized in comparison with the susceptible (S) accessions in the plum ‘P.2032’ and the interspecific hybrid P.2175 × almond-peach ‘253’ (ma/ma). Second-stage juveniles (J2s) were inoculated in micropropagated plantlets grown in soil substrate under controlled conditions at 25°C. Nematodes penetrated both R and S plants preferentially along the apical zone or close to the young lateral buds and moved via similar routes. Then they migrated into the cortex downward in the direction of the apex and turned up in the meristematic apical region to colonize the differentiating stele. In R accessions, motile J2s neither swelled nor developed into J3s, and initiation of feeding sites was never observed. This complete absence of gall symptoms is associated with cell necroses and corresponding hypersensitive-like reaction (HLR) phenotypes occurring either in the stele or in the meristematic apical region or in the cortex. Nematode attacks often disorganized the meristematic apical tissues of R accessions, which induced the development of subterminal lateral roots replacing primary terminal apices and, thus, provided an active resistance reaction to HLR damage.

L'article original est publié par The American Society of Plant Biologists Publication Inra prise en compte dans l'analyse bibliométrique des publications scientifiques mondiales sur les Fruits, les Légumes et la Pomme de terre. Période 2000-2012. http://prodinra.inra.fr/record/256699; International audience; Root-knot nematode (RKN) Meloidogyne species are major polyphagous pests of most crops worldwide, and cultivars with durable resistance are urgently needed because of nematicide bans. The Ma gene from the Myrobalan plum (Prunus cerasifera) confers complete-spectrum, heat-stable, and high-level resistance to RKN, which is remarkable in comparison with the Mi-1 gene from tomato (Solanum lycopersicum), the sole RKN resistance gene cloned. We report here the positional cloning and the functional validation of the Ma locus present at the heterozygous state in the P.2175 accession. High-resolution mapping totaling over 3,000 segregants reduced the Ma locus interval to a 32-kb cluster of three Toll/Interleukin1 Receptor-Nucleotide Binding Site-Leucine-Rich Repeat (LRR) genes (TNL1–TNL3), including a pseudogene (TNL2) and a truncated gene (TNL3). The sole complete gene in this interval (TNL1) was validated as Ma, as it conferred the same complete-spectrum and high-level resistance (as in P.2175) using its genomic sequence and native promoter region in Agrobacterium rhizogenes-transformed hairy roots and composite plants. The full-length cDNA (2,048 amino acids) of Ma is the longest of all Resistance genes cloned to date. Its TNL structure is completed by a huge post-LRR (PL) sequence (1,088 amino acids) comprising five repeated carboxyl-terminal PL exons with two conserved motifs. The amino-terminal region (213 amino acids) of the LRR exon is conserved between alleles and contrasts with the high interallelic polymorphisms of its distal region (111 amino acids) and of PL domains. The Ma gene highlights the importance of these uncharacterized PL domains, which may be involved in pathogen recognition through the decoy hypothesis or in nuclear signaling.

Publication Inra prise en compte dans l'analyse bibliométrique des publications scientifiques mondiales sur les Fruits, les Légumes et la Pomme de terre. Période 2000-2012. http://prodinra.inra.fr/record/256699; International audience; Resistant rootstocks offer an alternative to pesticides for the control of soil pests. In Prunus spp., resistance loci to root-knot nematodes (RKN) have been mapped and a transformation method is needed to validate candidate genes. Our efforts have focused on the generation of transformed hairy-roots and composite plants appropriate for nematode infection assays. An efficient and reliable method using the A4R strain of Agrobacterium rhizogenes for the transformation of Prunus roots with an Egfp reporter gene is given. The rooting efficiency, depending on the genotypes, was maximal for the interspecific hybrid 253 (Myrobalan plum x almond-peach), susceptible to RKN, that was retained for subsequent studies. From the agro-inoculated cuttings, 72% produced roots, mainly at the basal section of the stem. Transformed roots were screened by microscope detection of Egfp fluorescence and molecular analyses of the integration of the transgene. The absence of residual agrobacteria in the plants was checked by the non-amplification of the chromosomal gene chvH. Egfp was expressed visually in 76% of the rooted plants. Isolated hairy roots in Petri dishes and composite plants (transformed roots and non-transformed aerial part) in soil containers were inoculated with the RKN Meloidogyne incognita. In both cases, root transformation did not affect the ability of the nematodes to develop in the root tissues. Our results showed that isolated hairy-roots can be used to validate candidate genes and the conditions in which composite plants offer a complementary system for studying the function of root genes in physiological conditions of whole plants are discussed.

Grapevine fanleaf virus (GFLV) is vectored specifically from grapevine to grapevine by the ectoparasitic nematode Xiphinema index. Limited information is available on the vector competency of X. index populations from diverse geographical origins. We determined the transmissibility of two GFLV strains showing 4.6% amino acid divergence within their coat protein (e.g., strains F13 and GHu) by seven clonal lines of X. index developed from seven distinct populations from the Mediterranean basin (Cyprus, southern France, Israel, Italy, and Spain), northern France, and California. X. index lines derived from single adult females were produced on fig (Ficus carica) plants to obtain genetically homogenous aviruliferous clones. A comparative reproductive rate analysis on Vitis rupestris du Lot and V. vinifera cv. Cabernet Sauvignon showed significant differences among clones, with the single-female Cyprus line showing the highest rate (30-fold the initial population) and the Spain and California lines showing the lowest rate (10-fold increase), regardless of the grapevine genotype. However, there was no differential vector competency among the seven X. index lines for GFLV strains F13 and GHu. The implications of our findings for the dynamic of GFLV transmission in vineyards and screening of Vitis spp. for resistance to GFLV are discussed.

Plant-parasitic nematodes are major agricultural pests worldwide and novel approaches to control them are sorely needed. We report the draft genome sequence of the root-knot nematode Meloidogyne incognita, a biotrophic parasite of many crops, including tomato, cotton and coffee. Most of the assembled sequence of this asexually reproducing nematode, totaling 86 Mb, exists in pairs of homologous but divergent segments. This suggests that ancient allelic regions in M. incognita are evolving toward effective haploidy, permitting new mechanisms of adaptation. The number and diversity of plant cell wall-degrading enzymes in M. incognita is unprecedented in any animal for which a genome sequence is available, and may derive from multiple horizontal gene transfers from bacterial sources. Our results provide insights into the adaptations required by metazoans to successfully parasitize immunocompetent plants, and open the way for discovering new antiparasitic strategies

International audience; The RMia gene, which confers resistance (R) to the root-knot nematodes (RKN) Meloidogyne incognita and Meloidogyne arenaria, has been shown to segregate in the peach rootstocks Nemared, Shalil, and Juseitou on LG2 of the Prunus map. Here, we report the high-resolution mapping of RMia in Nemared, using the peach genome sequence and 790 individuals from two segregating peach populations, the F2 crossMontclar x Nemared and the four-way cross [(Pamirskij × Rubira) × (Montclar × Nemared)], in which Montclar, Pamirskij, and Rubira are susceptible (S) to RKN. Among the simple sequence repeat (SSR) markers designed for an initial flanking region of more than 1 Mb, five SSR markers specific for Nemared were characterized. The genotyping and phenotyping of recombinant individuals in this interval narrowed the gene’s location to a 300 kb physical distance between the SSR markers AMPP117 and AMPP116. In this interval, SNP polymorphisms were recovered from 1-kb-sequenced DNA fragments that were selected at 20 kb intervals. Two SNP markers (A20SNP and SNP_APP91) were shown to flank the gene in a final 92-kb region, containing four candidate genes from the TIR–NBS– LRR family. Finally, we studied the polymorphism of three closely linked markers, SNP_APP92, SNP_APP91, and AMPP117, on 28 R or S accessions fromdiverse Prunus species or hybrids. These markers discriminated between most R and S accessions, suggesting that at least the R sources of Nemared, Nemaguard, and Shalil share a common resistant ancestor

International audience; Root-knot nematodes (RKNs) (Meloidogyne spp.) are highly polyphagous pests that parasitize Prunus crops in Mediterranean climates. Breeding for RKN-resistant Prunus cultivars, as an alternative to the now-banned use of nematicides, is a real challenge, because the perennial nature of these trees increases the risk of resistance breakdown. The Ma plum resistance (R) gene, with a complete spectrum, and the RMia peach R gene, with a more restricted spectrum, both provide total control of Meloidogyne incognita, the model parthenogenetic species of the genus and the most important RKN in terms of economic losses. We investigated the durability of the resistance to this nematode conferred by these genes, comparing the results obtained with those for the tomato Mi-1 reference gene. In multiyear experiments, we applied a high and continuous nematode inoculum pressure by cultivating nematode-infested susceptible tomato plants with either Prunus accessions carrying Ma or RMia R genes, or with resistant tomato plants carrying the Mi-1 gene. Suitable conditions for Prunus development were achieved by carrying out the studies in a glasshouse, in controlled conditions allowing a short winter leaf fall and dormancy. We first assessed the plum accession 'P.2175', which is heterozygous for the Ma gene, in two successive 2-year evaluations, for resistance to two M. incognita isolates. Whatever the isolate used, no nematodes reproducing on P.2175 were detected, whereas galls and nematodes reproducing on tomato plants carrying Mi-1 were observed. In a second experiment with the most aggressive isolate, interspecific full-sib material (P.2175 x ['Garfi' almond x 'Nemared' peach]), carrying either Ma or RMia (from Nemared) or both (in the heterozygous state) or neither of these genes, was evaluated for 4 years. No virulent nematodes developed on Prunus spp. carrying R genes, whereas galling and virulent individuals were observed on Mi-1-resistant tomato plants. Thus, the resistance to M. incognita conferred by Ma in Prunus material in both a pure-plum and an interspecific genetic background, or by RMia in an interspecific background, appears to be durable, highlighting the value of these two genes for the creation of Prunus rootstock material.

National audience; Stone fruit crops Prunus spp. grown under Mediterranean climates are severely damaged by root-knot nematodes (RKN) Me/oidogyne spp. and breeding for RKN-resistant rootstocks is a promising control alternative to nematicide ban. Resistance (R) genes that confer different spectra have been identified and mapped in plums (Ma and Rjap), peach (RMia) and almond (RMja). Thus sustainable resistance in Prunus is based on pyramiding of R genes in interspecific rootstock mate rial to take into account the risk of resistance breaking in the durable plant-nematode interaction for perennials. The Ma gene from Myrabalan plum has been shown to confer a complete-spectrum, high-Ievel and heat-stable resistance to both mitotic (M. arenaria, M. incognito, M. javanico and M. entera/obii) and meiotic (M. f/oridensis) RKN. Ma triggers a hypersensitive-like reaction (HLR) in raot apices and severe nematode attacks induce _ the development of subterminal lateral rootlets replacing primary terminal apices and providing an acive, resist,ance response to HLR damage (1). Sustainability of resistance conferred by Ma has been challenged in multi-year experiments applying a high and continuous nematode inoculum pressure by co-cultivation of RKN-infested susceptible tomato plants together with Prunus plants carrying Ma or, for comparison, with R tomato plants carrying the Mi-l reference gene. Galling and virulent nematode individuals have been observed in Mi-l resistant tomatoes but not in Ma-carrying Prunus plants. The positional cloning of the Ma locus in accession P.2175 has been performed using high resolution mapping developed in two successive steps totalling over 3000 segregants. The Ma locus interval has been reduced to a 32-kb cluster of three TIR-NB-LRR genes (TNLl to TNL3) including a pseudogene (TNL2) and a truncated gene (TNL3). Using A. rhizogenes transformed hairy raots and composite plants (2), the best candidate gene, TNLl, comprising the genomic sequence and the native promoter region (15.3 kb), has been validated as Ma as it conferred the same complete-spectrum and high-Ievel resistance as in the donor accession P.2175. The full-Iength cDNA (2048 aa) of Ma is the longest of ail R genes cloned tc-date. Its TNL structure is extended by a huge Cvterminal post-LRR (PL) region (1088 aa) comprising five repeated PL exons (3).

International audience

International audience; In Prunus spp., resistance genes to root-knot nematodes (RKN), Meloidogyne arenaria, Meloidogyne incognita, Meloidogyne javanica, and Meloidogyne floridensis, confer either a complete spectrum, e.g., the Ma and Rjap genes in Myrobalan and Japanese plums (subgenus Prunophora), respectively, or a more restricted spectrum, e.g., the RMia gene (M. arenaria + M. incognita) in peach (subgenus Amygdalus). We report here characterization data of the RMja gene from the almond Alnem1, another Amygdalus source. The study of its spectrum is hampered by the inability of almond to be propagated by cuttings; we overcame this problem by using F1 and BC1 crosses with previously genotyped Myrobalan plums that conferred their rooting ability to hybrids for simultaneous evaluation to different RKN. As expected from a homozygous dominant resistance, BC1 progenies of Alnem1 segregated for resistance to M. javanica but were uniformly susceptible to M. incognita and M. floridensis, demonstrating that RMja controlled M. javanica but not M. incognita nor M. floridensis. SSR markers covering the Prunus reference map placed RMja on LG7 in the same region as Ma and Rjap and thus showed its independence from the RMia gene (LG2) of the botanically closer peach. The spectrum of this gene allows the theoretical construction of interspecific rootstocks, Myrobalan plum x (almond x peach), which cumulate RMja with Ma and RMia and are protected from each of the predominant RKN affecting Prunus, i.e., M. arenaria, M. incognita, and M. javanica, by at least two genes. This pyramiding strategy should offer to rootstock material an unprecedented guarantee of durable RKN resistance.

International audience; Stone fruit crops Prunus spp. grown under Mediterranean climates are severely damaged by root-knot nematodes (RKN) Meloidogyne spp. and breeding for RKN-resistant rootstocks is a promising control alternative to nematicide ban. Resistance (R) genes that confer different spectra have been identified and mapped in plums (Ma and Rjap), peach (RMia) and almond (RMja). Thus sustainable resistance in Prunus is based on pyramiding of R genes in interspecific rootstock mate rial to take into account the risk of resistance breaking in the durable plant-nematode interaction for perennials. The Ma gene from Myrabalan plum has been shown to confer a complete-spectrum, high-Ievel and heat-stable resistance to both mitotic (M. arenaria, M. incognito, M. javanico and M. enterolobii) and meiotic (M. f/oridensis) RKN. Ma triggers a hypersensitive-like reaction (HLR) in raot apices and severe nematode attacks induce the development of subterminal lateral rootlets replacing primary terminal apices and providing an acive, resist,ance response to HLR damage (1). Sustainability of resistance conferred by Ma has been challenged in multi-year experiments applying a high and continuous nematode inoculum pressure by co-cultivation of RKN-infested susceptible tomato plants together with Prunus plants carrying Ma or, for comparison, with R tomato plants carrying the Mi-l reference gene. Galling and virulent nematode individuals have been observed in Mi-l resistant tomatoes but not in Ma-carrying Prunus plants. The positional cloning of the Ma locus in accession P.2175 has been performed using high resolution mapping developed in two successive steps totalling over 3000 segregants. The Ma locus interval has been reduced to a 32-kb cluster of three TIR-NB-LRR genes (TNLl to TNL3) including a pseudogene (TNL2) and a truncated gene (TNL3). Using A. rhizogenes transformed hairy raots and composite plants (2), the best candidate gene, TNLl, comprising the genomic sequence and the native promoter region (15.3 kb), has been validated as Ma as it conferred the same complete-spectrum and high-Ievel resistance as in the donor accession P.2175. The full-Iength cDNA (2048 aa) of Ma is the longest of ail R genes cloned tc-date. Its TNL structure is extended by a huge Cvterminal post-LRR (PL) region (1088 aa) comprising five repeated PL exons (3)