Tomato Spotted Wilt Virus Resistance Research Articles

Development of novel specific molecular markers for the Sw-5b gene to assist with tomato spotted wilt virus-resistant tomato breeding

Tomato spotted wilt virus (TSWV) is a plant pathogen that causes devastating tomato yield losses worldwide. The Sw-5b gene is one of the most effective resistance genes for TSWV control in tomato plants, and has been widely used in resistance breeding. Molecular markers are specific DNA sequences with known locations on the chromosome; they are indispensable tools in marker-assisted selection, which detects the presence of target genes to expedite breeding. We developed gene-specific molecular markers for Sw-5b to facilitate the accurate distinction of resistance (Sw-5bR) and susceptibility (Sw-5bS) alleles of Sw-5b. Using these markers, we successfully detected Sw-5b and determined its genotype (homozygous Sw-5bR, heterozygous Sw-5bR/S, or homozygous Sw-5bS) in six tomato varieties. Then we successfully applied these markers to 46 commercial tomato cultivars to detect and determine the genotype of Sw-5b. The results revealed a striking absence of the Sw-5bR gene and high TSWV susceptibility among most of the analyzed commercial cultivars. With the assistance of the novel Sw-5b-specific molecular markers, we generated a TSWV-resistant and homozygous Sw-5bR Micro-Tom tomato line, demonstrating the practical application of these markers in plant breeding. In summary, we developed novel gene-specific molecular markers for Sw-5b, and applied them to distinguish Sw-5b alleles for TSWV resistance or susceptibility. This marker set provides a valuable tool for breeding TSWV-resistant tomato varieties.

Field Screening for Tomato Spotted Wilt and White Mold (Stem Rot) Resistance among Peanut Genotypes

White mold (WM), stem rot, and southern blight are common names for the same soilborne peanut (Arachis hypogaea L.) disease caused by Athelia rolfsii (Curzi) C. C. Tu & Kimbr. = Sclerotium rolfsii Sacc. Tomato spotted wilt is a systemic foliar peanut disease caused by Tomato spotted wilt virus (TSWV). The objective of this study was to screen several currently available peanut genotypes (cultivars and breeding lines) for combined general field resistance to both of these diseases. Results from these field tests showed significant differences (P≤0.05) among the peanut genotypes evaluated for combined resistance to both WM and TSWV. The overall three-year (2018-20) average found that ‘Georgia-12Y’ had among the lowest percent incidence of mid-season TSWV, mid-late season TSWV+WM, late-season WM+TSWV, WM after digging, and the highest pod yield compared to other runner-type peanut cultivars. FloRun ‘331’ was found to have comparable WM resistance as Georgia-12Y, however it was also found to be susceptible to TSWV. ‘Georgia-14N’ was found to have moderate TSWV and WM resistance similar to ‘Georgia-07W’, and it also has a high-level of root-knot nematode (RKN) resistance.

Integrative analysis of the transcriptome and metabolome reveals the response mechanism to tomato spotted wilt virus

Tomato spotted wilt virus (TSWV) is an important virus that has rapidly spread throughout the world. TSWV seriously hinders the production of tomato (Solanum lycopersicum) and other plants. In order to discover more new genes and metabolites related to TSWV resistance in tomato plants, the genes and metabolites related to the resistance of tomato plants inoculated with TSWV were identified and studied herein. The tomato TSWV-resistance line YNAU335 (335) and TSWV-susceptible lines NO5 and 96172I (961) were used as the transcriptome and metabolome research materials. Transcriptomic and metabolomic techniques were used to analyze the gene and metabolite response mechanisms to TSWV inoculation. A total of 3 566, 2 951, and 2 674 differentially expressed genes (DEGs) were identified in lines 335, NO5, and 961, respectively. Meanwhile, 208, 228, and 273 differentially accumulated metabolites (DAMs) were identified in lines 335, NO5, and 961, respectively. In line 335, the number of DEGs was the highest, but the number of DAMs was lowest. Furthermore, 903 DEGs and 94 DAMs were common to the response to TSWV in the three inbred lines. The 903 DEGs and 94 DAMs were mainly enriched in the plant hormone signal transduction and flavonoid synthesis pathways. In addition, many nucleotide-binding site-leucine-rich repeat genes and transcription factors were found that might be involved in the TSWV response. These results provide new insights into TSWV resistance mechanisms.

Mapping and functional characterization of the tomato spotted wilt virus resistance gene SlCHS3 in Solanum lycopersicum.

The online version contains supplementary material available at 10.1007/s11032-022-01325-5.

A new NLR gene for resistance to Tomato spotted wilt virus in tomato (Solanum lycopersicum).

A typical NLR gene, Sl5R-1, which regulates Tomato spotted wilt virus resistance, was fine mapped to a region less than 145kb in the tomato genome. Tomato spotted wilt is a viral disease caused by Tomato spotted wilt virus (TSWV), which is a devastating disease that affects tomato (Solanum lycopersicum) production worldwide, and the resistance provided by the Sw-5 gene has broken down in some cases. In order to identify additional genes that confer resistance to TSWV, the F2 population was mapped using susceptible (M82) and resistant (H149) tomato lines. After 3years of mapping, the main quantitative trait locus on chromosome 05 was narrowed to a genomic region of 145kb and was subsequently identified by the F2 population, with 1971 plants in 2020. This region encompassed 14 candidate genes, and in it was found a gene cluster consisting of three genes (Sl5R-1, Sl5R-2, and Sl5R-3) that code for NBS-LRR proteins. The qRT-PCR and virus-induced gene silencing approach results confirmed that Sl5R-1 is a functional resistance gene for TSWV. Analysis of the Sl5R-1 promoter region revealed that there is a SlTGA9 transcription factor binding site caused by a base deletion in resistant plants, and its expression level was significantly up-regulated in infected resistant plants. Analysis of salicylic acid (SA) and jasmonic acid (JA) levels and the expression of SA- and JA-regulated genes suggest that SlTGA9 interacts or positively regulates Sl5R-1 to affect the SA- and JA-signaling pathways to resist TSWV. These results demonstrate that the identified Sl5R-1 gene regulates TSWV resistance by its own promoter interacting with the transcription factor SlTGA9.

Resistance Response of the Recently Discovered Species Nicotiana mutabilis to Potato virus Y (PVY) and Tomato spotted wilt virus (TSWV) Compared to Other Sources of Resistance

Nicotiana mutabilis is a recently discovered species within the genus Nicotiana. The aim of the present study was to evaluate its resistance to Potato virus Y (PVY) and Tomato spotted wilt virus (TSWV). Molecular analysis was performed to detect the Va gene determining susceptibility to PVY and the SCAR marker associated with resistance to TSWV. Resistance tests were carried out under greenhouse conditions through artificial inoculation with one TSWV and two PVY isolates. In order to confirm the presence of the viruses in plants, DAS-ELISA tests were performed using antibodies against PVY and TSWV. The results indicated the absence of the PVY susceptibility gene and the presence of the TSWV resistance gene in the genome of N. mutabilis. This species was considered tolerant to the two PVY isolates tested because, despite the positive DAS-ELISA results, the infected plants showed vein clearing and chlorotic spots but no vein necrosis. As a result of TSWV inoculation, N. mutabilis showed a hypersensitive response; however, after four months, 30% of the inoculated plants showed systemic infection. This species extends the genetic variation in the genus Nicotiana and, because of its tolerance to PVY and partial resistance to TSWV, it may be a potential source of resistance to these viruses.

Phenotypic characterization of Tomato spotted wilt virus resistance breaking isolate in tomatoes

Domateste lekeli solgunluk virüsü (Tomato spotted wilt virus-TSWV), dünya genelinde ekonomik anlamda büyük kayıplar meydana getiren virüslerden biridir. Son zamanlara kadar domateslerde Sw-5 geni vasıtasıyla bu hastalık ile mücadele edilmekteydi. 2016-2019 yılları arasında Antalya ili ve ilçelerinde domates yetiştiriciliği yapılan seralarda Sw-5 geni barındıran çeşitler üzerinde TSWV’a ait simptomların geliştiği gözlemlenmiştir. Bu izolatların PCR çalışmaları ile bitkilerin Sw-5 geni içerdiği ve RT-PCR (Revers-Transkriptaz Polimeraz Zincir Reaksiyonu) çalışmaları ile de simptomların TSWV’a ait olduğu doğrulandıktan sonra izolatın ismi TSWVAntRB olarak belirlenmiştir. Yapılan gözlemlemeler sonucunda TSWVAntRB izolatının farklı simptomolojik karakterlere sahip olduğu tespit edilmiştir. Bu farklılıklarının belirlenebilmesi için TSWVAntRB izolatının, bitkiler üzerine mekanik inokulasyonu 5 tekerrürlü olacak şekilde gerçekleştirilmiştir. Mekanik inokulasyon çalışmalarında; Sw-5 geni içeren 4 adet ticari çeşit, bir adet dayanıklılık kaynağı olarak bilinen Solanum peruvianum ve bir adet hassas çeşit kullanılmıştır. Sw-5 dayanımını kırmayan (NRB) izolatında şimdiye kadar yaprakta sadece nekrotik lekelenmeler meydana gelirken, Sw-5 dayanımını kıran (RB) izolatında yaprak üzerinde de halkalı lekelenmelerin meydana geldiği belirlenmiştir. Aynı zamanda bazı çeşitler üzerinde ilk simptomlar meyve dönemine kadar gizli kaldığı ve meyve salkımında bazen bir veya iki meyve üzerinde simptomlar meydana getirdiği gözlemlenmiştir. Çalışmada simptom şiddetinin hava sıcaklığı ile ilişkili olduğu saptanmış ve TSWVAntRB izolatının simptomolojik özellikleri her açıdan incelenmiştir.

A recombination bin-map identified a major QTL for resistance to Tomato Spotted Wilt Virus in peanut (Arachis hypogaea)

Tomato spotted wilt virus (TSWV) is a devastating disease to peanut growers in the South-eastern region of the United States. Newly released peanut cultivars in recent years are crucial as they have some levels of resistance to TSWV. One mapping population of recombinant inbred line (RIL) used in this study was derived from peanut lines of SunOleic 97R and NC94022. A whole genome re-sequencing approach was used to sequence these two parents and 140 RILs. A recombination bin-based genetic map was constructed, with 5,816 bins and 20 linkage groups covering a total length of 2004 cM. Using this map, we identified three QTLs which were colocalized on chromosome A01. One QTL had the largest effect of 36.51% to the phenotypic variation and encompassed 89.5 Kb genomic region. This genome region had a cluster of genes, which code for chitinases, strictosidine synthase-like, and NBS-LRR proteins. SNPs linked to this QTL were used to develop Kompetitive allele specific PCR (KASP) markers, and the validated KASP markers showed expected segregation of alleles coming from resistant and susceptible parents within the population. Therefore, this bin-map and QTL associated with TSWV resistance made it possible for functional gene mapping, map-based cloning, and marker-assisted breeding. This study identified the highest number of SNP makers and demonstrated recombination bin-based map for QTL identification in peanut. The chitinase gene clusters and NBS-LRR disease resistance genes in this region suggest the possible involvement in peanut resistance to TSWV.

Population structure and association mapping to detect QTL controlling tomato spotted wilt virus resistance in cultivated peanuts

Tomato spotted wilt (TSW) is a serious virus disease of peanut in the United States. Breeding for TSWV resistance would be facilitated by the implementation of marker-assisted selection in breeding programs; however, genes associated with resistance have not been identified. Association mapping is a type of genetic mapping that can exploit relationships between markers and traits in many lineages. The objectives of this study were to examine genetic diversity and population structure in the U.S. peanut mini-core collection using simple sequence repeat (SSR) markers, and to conduct association mapping between SSR markers and TSWV resistance in cultivated peanuts. One hundred and thirty-three SSR markers were used for genotyping 104 accessions. Four subpopulations, generally corresponding to botanical varieties, were classified by population structure analysis. Association mapping analysis indicated that five markers: pPGPseq5D5, GM1135, GM1991, TC23C08, and TC24C06, were consistently associated with TSW resistance by the Q, PCA, Q+K, and PCA+K models. These markers together explained 36.4% of the phenotypic variance. Moreover, pPGPseq5D5 and GM1991 were associated with both visual symptoms of TSWV and ELISA values with a high R2. The potential of these markers for use in a marker-assisted selection program to breed peanut for resistance to TSWV is discussed.

Registration of ‘Georgia‐17SP’ Peanut

‘Georgia‐17SP’ (Reg. No. CV‐137, PI 687138) is a new high‐yielding, high‐oleic, Tomato spotted wilt virus (TSWV)‐resistant, large‐seeded, US spanish market‐type peanut (Arachis hypogaea L. subsp. hypogaea var. hypogaea) cultivar that was released by the Georgia Agricultural Experiment Station in 2017. It was developed at the University of Georgia, Coastal Plain Experiment Station, Tifton, GA. Georgia‐17SP originated from a cross made between ‘Georgia‐02C’ × F4 (‘Georgia‐01R’ × ‘COAN’). Pedigree selection was practiced within the early segregating generations. Performance testing began in the F4:6 generation with the advanced pure‐line selection, GA 082549, the experimental designation of Georgia‐17SP. During 7 yr (2010–2016) averaged over two planting‐date tests in Georgia, Georgia‐17SP had significantly less total disease incidence and greater pod yield, total sound mature kernels grade, and dollar value return per hectare compared with the spanish‐type cultivars ‘Georgia Browne’, ‘Georgia‐04S’, ‘Tamspan 90’, ‘Tamnut OL06’, ‘Pronto’, ‘Spanco’, and ‘OLin’. Georgia‐17SP was also found to have similar percentage of fancy pods but a larger percentage of jumbo seed size as compared to these other spanish‐type check cultivars. Georgia‐17SP combines high yield, grade, and dollar value with TSWV resistance and the high‐oleic trait for longer shelf‐life and improved oil quality of peanut and peanut products.

Transgressive Segregation and Long-Term Consistency for High TSWV Field Resistance in the ‘Georgia-06G’ Peanut Cultivar

Tomato spotted wilt disease caused by tomato spotted wilt virus (TSWV) is a major peanut (Arachis hypogaea L.) production problem in the United States. TSWV has become endemic since the mid-1980s in the southeastern U.S. peanut production area. ‘Georgia-06G’ is a large-seeded, TSWV-resistant, runner-type peanut cultivar, whereas ‘Georgia Greener’ is a sister line with a smaller seed size than Georgia-06G. Both Georgia-06G and Georgia Greener have greater TSWV general field resistance with higher yields, total sound mature kernels grade, and dollar values than the parents (‘Georgia Green’ and ‘C-99R’), which shows transgressive segregation for these desirable quantitative traits. Therefore, the objective of this 12-year study was to evaluate the higher TSWV host-plant resistance found in the Georgia-06G over time compared with many other runner- and virginia-type peanut cultivars and advanced breeding lines. Despite yearly variability in TSWV and total disease incidence, the data indicate that Georgia-06G exhibited long-term high TSWV and total disease field resistance at midseason and late season, respectively. Georgia-06G was also found to have among the highest pod yield and dollar value every year. The higher general TSWV field resistance of Georgia-06G appears to be consistent across many years and locations, similar to the moderate TSWV resistance in Georgia Green.

Biochemical analysis of NSs from different tospoviruses

Tospoviruses suppress antiviral RNA interference by coding for an RNA silencing suppressor (NSs) protein. Previously, using NSs-containing crude plant and insect cell extracts, the affinity of NSs for double-stranded (ds)RNA molecules was demonstrated by electrophoretic mobility shifts assays (EMSAs). While NSs from tomato spotted wilt virus (TSWV) and groundnut ringspot virus (GRSV) were able to bind small and long dsRNA molecules, the one from tomato yellow ring virus (TYRV), a distinct Asian tospovirus, only bound small dsRNA. Here, using bacterially expressed and purified NSs from GRSV and TYRV, it is shown that they are both able to bind to small and long dsRNA. Binding of siRNAs by NSs revealed two consecutive shifts, i.e. a first shift at low NSs concentrations followed by a second larger one at higher concentrations. When NSs of TSWV resistance inducing (RI) and resistance breaking (RB) isolates were analyzed using extracts from infected plants only a major siRNA shift was observed. In contrast, plant extracts containing the respective transiently expressed NSs proteins showed only the lower shift with NSsRI but no shift with NSsRB. The observed affinity for RNA duplexes, as well as the two-stepwise shift pattern, is discussed in light of NSs as a suppressor of silencing and its importance for tospovirus infection.

Registration of ‘Georgia‐16HO’ Peanut

‘Georgia‐16HO’ (Reg. No. CV‐133, PI 680617) is a new high‐yielding, high‐oleic, Tomato spotted wilt virus (TSWV)‐resistant, large‐seeded, runner‐type peanut (Arachis hypogaea L. subsp. hypogaea var. hypogaea) cultivar released by the Georgia Agricultural Experiment Station in 2016. It was developed at the University of Georgia, Coastal Plain Experiment Station, Tifton, GA. Georgia‐16HO originated from a cross made between ‘Georgia‐07W’ and ‘Florida‐07’. Pedigree selection was practiced within the early segregating generations. Performance testing began in the F4:6 generation with the advanced pure‐line selection, GA 112720, the experimental designation of Georgia‐16HO. During 3 yr (2013–2015) averaged over 23 multiple location tests in Georgia, Georgia‐16HO had significantly less TSWV and total disease incidence and greater pod yield, total sound mature kernel grade, and dollar value return per hectare compared with the high‐oleic, runner‐type cultivars ‘FloRun ‘107”, Florida‐07, and ‘TUFRunner ‘727”. Georgia‐16HO was also found to have a larger percentage of jumbo runner seed size as compared to two of the large‐seeded, high‐oleic, runner‐type check cultivars, Florida‐07 and TUFRunner ‘727’. Georgia‐16HO combines high dollar value and TSWV resistance with the high‐oleic trait for longer shelf life and improved oil quality of peanut and peanut products.

Divergent evolution of multiple virus-resistance genes from a progenitor in Capsicum spp.

Plants have evolved hundreds of nucleotide-binding and leucine-rich domain proteins (NLRs) as potential intracellular immune receptors, but the evolutionary mechanism leading to the ability to recognize specific pathogen effectors is elusive. Here, we cloned Pvr4 (a Potyvirus resistance gene in Capsicum annuum) and Tsw (a Tomato spotted wilt virus resistance gene in Capsicum chinense) via a genome-based approach using independent segregating populations. The genes both encode typical NLRs and are located at the same locus on pepper chromosome 10. Despite the fact that these two genes recognize completely different viral effectors, the genomic structures and coding sequences of the two genes are strikingly similar. Phylogenetic studies revealed that these two immune receptors diverged from a progenitor gene of a common ancestor. Our results suggest that sequence variations caused by gene duplication and neofunctionalization may underlie the evolution of the ability to specifically recognize different effectors. These findings thereby provide insight into the divergent evolution of plant immune receptors.

Identification of major QTLs underlying tomato spotted wilt virus resistance in peanut cultivar Florida-EP(TM) '113'.

BackgroundSpotted wilt caused by tomato spotted wilt virus (TSWV) is one of the major peanut (Arachis hypogaea L.) diseases in the southeastern United States. Occurrence, severity, and symptoms of spotted wilt disease are highly variable from season to season, making it difficult to efficiently evaluate breeding populations for resistance. Molecular markers linked to spotted wilt resistance could overcome this problem and allow selection of resistant lines regardless of environmental conditions. Florida-EPTM ‘113’ is a spotted wilt resistant cultivar with a significantly lower infection frequency. However, the genetic basis is still unknown. The objective of this study is to map the major quantitative trait loci (QTLs) linked to spotted wilt resistance in Florida-EPTM ‘113’.ResultsAmong 2,431 SSR markers located across the whole peanut genome screened between the two parental lines, 329 were polymorphic. Those polymorphic markers were used to further genotype a representative set of individuals in a segregating population. Only polymorphic markers on chromosome A01 showed co-segregation between genotype and phenotype. Genotyping by sequencing (GBS) of the representative set of individuals in the segregating population also depicted a strong association between several SNPs on chromosome A01 and the trait, indicating a major QTL on chromosome A01. Therefore marker density was enriched on the A01 chromosome. A linkage map with 23 makers on chromosome A01 was constructed, showing collinearity with the physical map. Combined with phenotypic data, a major QTL flanked by marker AHGS4584 and GM672 was identified on chromosome A01, with up to 22.7 % PVE and 9.0 LOD value.ConclusionA major QTL controlling the spotted wilt resistance in Florida-EPTM ‘113’ was identified. The resistance is most likely contributed by PI 576638, a hirsuta botanical-type line, introduced from Mexico with spotted wilt resistance. The flanking markers of this QTL can be used for further fine mapping and marker assisted selection in peanut breeding programs.Electronic supplementary materialThe online version of this article (doi:10.1186/s12863-016-0435-9) contains supplementary material, which is available to authorized users.

Development of a Single-nucleotide Polymorphism Marker for the Sw-5b Gene Conferring Disease Resistance to Tomato spotted wilt virus in Tomato

Tomato spotted wilt virus (TSWV) causes one of the most destructive viral diseases that threatens global tomato production. Sw-5b was reported as the resistance gene effective against TSWV. The objective of this research was to develop a single-nucleotide polymorphism (SNP) marker to distinguish tomato cultivars resistant to TSWV from susceptible cultivars for marker-assisted breeding. First, we determined genotypes for TSWV resistance in 32 commercial tomato cultivars using the previously reported Sw-5b gene-based marker. Then, DNA sequences of Sw-5b alleles in tomato cultivars showing resistant or susceptible genotypes were analyzed; a single SNP was found to distinguish tomato cultivars resistant to TSWV from susceptible cultivars. Based on the confirmed SNP, a SNP primer pair was designed. Using this new SNP sequence and high-resolution melting analysis, the same 32 tomato cultivars were screened. The results were perfectly correlated with those from screening with the Sw-5b gene-based marker. These results indicate that the SNP maker developed in this study will be useful for better tracking of resistance to TSWV in tomato breeding.

Registration of ‘Georgia-14N’ Peanut

‘Georgia-14N’ (Reg. No. CV-126, PI 674169) is a new high-yielding, high-oleic, Tomato spotted wilt virus (TSWV)–resistant, root-knot nematode (RKN) [Meloidogyne arenaria (Neal) Chitwood race 1]–resistant, small-seeded, runner-type peanut (Arachis hypogaea L. subsp. hypogaea var. hypogaea) cultivar that was released by the Georgia Agricultural Experiment Station in 2014. It was developed at the University of Georgia, Coastal Plain Experiment Station, Tifton, GA. Georgia-14N originated from a cross made between ‘Georgia-02C’ × F4 (‘Georgia-01R’ × ‘COAN’). Pedigree selection was practiced within the early-segregating generations. Performance testing began in the F4:6 generation with the advanced pure-line selection GA 082522, the experimental designation of Georgia-14N. During 3 yr (2011–2013) averaged over 29 multiple location tests without nematode pressure in Georgia, Georgia-14N had significantly less TSWV and total disease incidence, higher yield, grade, and dollar value return per hectare compared with ‘Tifguard’. Georgia-14N was also found to have a smaller runner seed size compared with the larger runner-type check cultivar Tifguard. Georgia-14N combines high yield, TSWV resistance and RKN resistance with smaller seed size and the high-oleic trait for longer shelf-life and improved oil quality of peanut and peanut products.

Stability of TSWV General Field Resistance in the ‘Georgia Green’ Peanut Cultivar

There are mainly two types of host-plant disease resistance. General or horizontal resistance is usually controlled by several genes each acting with minor additive effects, and specific or vertical resistance is usually controlled by one or two genes with a dominant major effect. In most cases, general resistance may not provide as high a level of control as specific; however, general type of resistance is usually more desirable for long-term stability. Therefore, the objective of this 13-year study was to determine the stability of the general disease resistance to tomato spotted wilt (TSW), caused by Tomato spotted wilt virus (TSWV), found in the peanut (Arachis hypogaea L.) cultivar ‘Georgia Green', as indicated by comparisons with the highly susceptible ‘Florunner’ cultivar. The general host-plant TSWV resistance of Georgia Green was found to have consistently lower TSW at mid-season and total disease (primarily TSW and any soilborne disease) incidence at late season, respectively, and higher pod yield compared to Florunner across all 13 years without any genotype-by-year (G×Y) interaction for these variables. Consequently, the general TSWV-resistance of Georgia Green was found to be highly stable across many years, and should be utilized for progress in breeding improved TSWV-resistant peanut cultivars. Accepted for publication 11 May 2015. Published 18 May 2015.

Host Plant Resistance Against Tomato spotted wilt virus in Peanut (Arachis hypogaea) and Its Impact on Susceptibility to the Virus, Virus Population Genetics, and Vector Feeding Behavior and Survival

Tomato spotted wilt virus (TSWV) severely affects peanut production in the southeastern United States. Breeding efforts over the last three decades resulted in the release of numerous peanut genotypes with field resistance to TSWV. The degree of field resistance in these genotypes has steadily increased over time, with recently released genotypes exhibiting a higher degree of field resistance than older genotypes. However, most new genotypes have never been evaluated in the greenhouse or laboratory against TSWV or thrips, and the mechanism of resistance is unknown. In this study, TSWV-resistant and -susceptible genotypes were subjected to TSWV mechanical inoculation. The incidence of TSWV infection was 71.7 to 87.2%. Estimation of TSWV nucleocapsid (N) gene copies did not reveal significant differences between resistant and susceptible genotypes. Parsimony and principal component analyses of N gene nucleotide sequences revealed inconsistent differences between virus isolates collected from resistant and susceptible genotypes and between old (collected in 1998) and new (2010) isolates. Amino acid sequence analyses indicated consistent differences between old and new isolates. In addition, we found evidence for overabundance of nonsynonymous substitutions. However, there was no evidence for positive selection. Purifying selection, population expansion, and differentiation seem to have influenced the TSWV populations temporally rather than positive selection induced by host resistance. Choice and no-choice tests indicated that resistant and susceptible genotypes differentially affected thrips feeding and survival. Thrips feeding and survival were suppressed on some resistant genotypes compared with susceptible genotypes. These findings reveal how TSWV resistance in peanut could influence evolution, epidemiology, and management of TSWV.

An integrated genetic linkage map of cultivated peanut (Arachis hypogaea L.) constructed from two RIL populations

Construction and improvement of a genetic map for peanut (Arachis hypogaea L.) continues to be an important task in order to facilitate quantitative trait locus (QTL) analysis and the development of tools for marker-assisted breeding. The objective of this study was to develop a comparative integrated map from two cultivated × cultivated recombinant inbred line (RIL) mapping populations and to apply in mapping Tomato spotted wilt virus (TSWV) resistance trait in peanut. A total of 4,576 simple sequence repeat (SSR) markers from three sources: published SSR markers, newly developed SSR markers from expressed sequence tags (EST) and from bacterial artificial chromosome end-sequences were used for screening polymorphisms. Two cleaved amplified polymorphic sequence markers were also included to differentiate ahFAD2A alleles and ahFAD2B alleles. A total of 324 markers were anchored on this integrated map covering 1,352.1 cM with 21 linkage groups (LGs). Combining information from duplicated loci between LGs and comparing with published diploid maps, seven homoeologous groups were defined and 17 LGs (A1-A10, B1-B4, B7, B8, and B9) were aligned to corresponding A-subgenome or B-subgenome of diploid progenitors. One reciprocal translocation was confirmed in the tetraploid-cultivated peanut genome. Several chromosomal rearrangements were observed by comparing with published cultivated peanut maps. High consistency with cultivated peanut maps derived from different populations may support this integrated map as a reliable reference map for peanut whole genome sequencing assembling. Further two major QTLs for TSWV resistance were identified for each RILs, which illustrated the application of this map.