Mapping of A1 conferring resistance to the aphid Amphorophora idaei and dw (dwarfing habit) in red raspberry (Rubus idaeus L.) using AFLP and microsatellite markers

Known and Potential Invertebrate Vectors of Raspberry Viruses

The estimated global production of raspberry from year 2016 to 2020 averaged 846,515 tons. The most common cultivated Rubus spp. is European red raspberry (Rubus idaeus L. subsp. idaeus). Often cultivated for its high nutritional value, the red raspberry (Rubus idaeus) is susceptible to multiple viruses that lead to yield loss. These viruses are transmitted through different mechanisms, of which one is invertebrate vectors. Aphids and nematodes are known to be vectors of specific raspberry viruses. However, there are still other potential raspberry virus vectors that are not well-studied. This review aimed to provide an overview of studies related to this topic. All the known invertebrates feeding on raspberry were summarized. Eight species of aphids and seven species of plant-parasitic nematodes were the only proven raspberry virus vectors. In addition, the eriophyid mite, Phyllocoptes gracilis, has been suggested as the natural vector of raspberry leaf blotch virus based on the current available evidence. Interactions between vector and non-vector herbivore may promote the spread of raspberry viruses. As a conclusion, there are still multiple aspects of this topic that require further studies to get a better understanding of the interactions among the viral pathogens, invertebrate vectors, and non-vectors in the raspberry agroecosystem. Eventually, this will assist in development of better pest management strategies.

NLR1 is a strong candidate for the Rm3 dominant green peach aphid (Myzus persicae) resistance trait in peach

The green peach aphid (GPA), Myzus persicae, is a polyphagous, sap-sucking aphid and a vector of many plant viruses. In peach, Prunus persica, three individual dominant GPA resistance loci have been genetically defined (Rm1-3), but knowledge of the underlying genes is limited. In this study, we focused on the Rm3 locus. Bulk segregant analysis (BSA) mapping in segregating progeny populations delimited Rm3 to an interval spanning 160 kb containing 21 genes on chromosome 1. RNA-seq data provided no evidence of candidate genes, but chromosomal structural variations were predicted around a nucleotide-binding site-leucine-rich repeat (NLR) gene (ppa000596m) within the Rm3 fine-mapping interval. Following bacterial artificial chromosome (BAC) library construction for a GPA-resistant peach cultivar and the sequencing of three target BAC clones, a chromosomal structural variation encompassing two novel TIR-NLR-class disease resistance (R) protein-coding genes was identified, and the expressed NLR gene (NLR1) was identified as a candidate for M. persicae resistance. Consistent with its proposed role in controlling GPA resistance, NLR1 was only expressed in the leaves of resistant peach phenotypes. A molecular marker that was designed based on the NLR1 sequence co-segregated with the GPA-resistant phenotype in four segregating populations, 162 peach cultivars, and 14 wild relatives, demonstrating the dominant inheritance of the Rm3 locus. Our findings can be exploited to facilitate future breeding for GPA-resistance in peach.

Morphological and anatomical adaptations to dry, shady environments in Adiantum reniforme var. sinense (Pteridaceae)

The natural distribution of the rare perennial fern Adiantum reniforme var. sinense (Pteridaceae), which is endemic to shady cliff environments, is limited to small areas of Wanzhou County, Chongqing, China. In this study, we used brightfield and epifluorescence microscopy to investigate the anatomical structures and histochemical features that may allow this species to thrive in shady, dry cliff environments. The A. reniforme var. sinense sporophyte had a primary structure and a dictyostele. The plants of this species had an endodermis, sclerenchyma layers and hypodermal sterome, reflecting an adaption to dry cliff environments. Blades had a thin cuticle and isolateral mesophyll, suggesting a tolerance of shady environments. These characteristics are similar to many sciophyte ferns such as Lygodium japonicum and Pteris multifida. Thus, the morphological and anatomical characteristics of A. reniforme var. sinense identified in this study are consistent with adaptations to shady, dry cliff environments.

[Molecular markers in the genetic diversity studies of representatives of the genus Rubus L. and prospects of their application in breeding]

Род Rubus L. (семейство Rosaceae Juss.), по оценкам разных систематиков, состоит из 12–16 подродов, объединяющих ~750 видов. Самые крупные по числу видов подроды – Idaeobatus (Focke) Focke, к которому относятся малины, и типовой подрод Rubus (=Eubatus Focke), включающий виды ежевик. Представители рода Rubus обладают высокой пищевой и хозяйственной ценностью, а также лекарственными свойствами. Селекционные исследования направлены на расширение генетического разнообразия и создание новых сортов малин и ежевик, устойчивых к биотическим и абиотическим стрессорам и отличающихся высоким качеством плодов. Современные селекционно-генетические программы все шире включают достижения молекулярной генетики и геномики. В данной статье представлен обзор фундаментальных и прикладных исследований генетического разнообразия культивируемых и дикорастущих видов рода Rubus, выполненных на основе методов молекулярного маркирования. Рассмотрены основные типы молекулярных маркеров (RFLP, RAPD, SSR, ISSR, AFLP, SCAR, SSCP, ретротранспозонные маркеры и т. д.) и области их применения в изучении представителей рода Rubus. Приведены результаты работ по использованию методов ДНК-маркирования для решения самых разных задач, включая: исследование межвидового и внутривидового генетического разнообразия, филогенетических связей видов и надвидовых таксонов, выяснение спорных вопросов систематики, генотипирование и уточнение родословных сортов малин и ежевик, изучение сомаклональной изменчивости и др. Наиболее важным результатом в практическом плане является создание насыщенных молекулярно-генетических карт для разных видов малин и ежевик, на которых локализованы многочисленные гены и QTL, детерминирующие различные хозяйственно ценные признаки. В то же время необходимо отметить, что число маркеров, перспективных для проведения эффективного молекулярного скрининга, пока еще недостаточно.

Genetic and genomic resources for Rubus breeding: a roadmap for the future

Rubus fruits are high-value crops that are sought after by consumers for their flavor, visual appeal, and health benefits. To meet this demand, production of red and black raspberries (R. idaeus L. and R. occidentalis L.), blackberries (R. subgenus Rubus), and hybrids, such as Boysenberry and marionberry, is growing worldwide. Rubus breeding programmes are continually striving to improve flavor, texture, machine harvestability, and yield, provide pest and disease resistance, improve storage and processing properties, and optimize fruits and plants for different production and harvest systems. Breeders face numerous challenges, such as polyploidy, the lack of genetic diversity in many of the elite cultivars, and until recently, the relative shortage of genetic and genomic resources available for Rubus. This review will highlight the development of continually improving genetic maps, the identification of Quantitative Trait Loci (QTL)s controlling key traits, draft genomes for red and black raspberry, and efforts to improve gene models. The development of genetic maps and markers, the molecular characterization of wild species and germplasm, and high-throughput genotyping platforms will expedite breeding of improved cultivars. Fully sequenced genomes and accurate gene models facilitate identification of genes underlying traits of interest and enable gene editing technologies such as CRISPR/Cas9.

Enhancement of Glen Moy x Latham raspberry linkage map using GbS to further understand control of developmental processes leading to fruit ripening

BACKGROUND

The changing climate is altering timing of key fruit ripening processes and increasing the occurrence of fruit defects. To improve our understanding of the genetic control of raspberry fruit development an enhanced genetic linkage map was developed and used to examine ripening phenotypic data.

RESULTS

In this study we developed an enhanced genetic linkage map for the raspberry cvs. Glen Moy x Latham reference mapping population using genotyping by sequencing (GbS). Alignment to a newly sequenced draft reference genome of red raspberry, cultivar (cv.) Glen Moy, identified 8019 single nucleotide polymorphisms (SNPs). After stringent filtering to take account of read coverage over all the progeny individuals, association with a single chromosome, heterozygosity and marker regression mapping, 2348 high confidence SNPs were retained and integrated with an existing raspberry genetic map. The linkage map contained many more SNPs segregating in Latham than in Glen Moy. This caused difficulties in quantitative trait loci (QTL) mapping with standard software and a novel analysis based on a hidden Markov model was used to improve the mapping. QTL mapping using the newly generated dense genetic map not only corroborated previously identified genetic locations but also provided additional genetic elements controlling fruit ripening in raspberry.

CONCLUSION

The high-density GbS map located the QTL peaks more precisely than in earlier studies, aligned the QTLs with Glen Moy genome scaffolds, narrowed the range of potential candidate genes to these regions that can be utilised in other populations or in gene expression studies to confirm their role and increased the repertoire of markers available to understand the genetic control of fruit ripening traits.

Genotyping-by-sequencing in an orphan plant species Physocarpus opulifolius helps identify the evolutionary origins of the genus Prunus

BACKGROUND

The Rosaceae family encompasses numerous genera exhibiting morphological diversification in fruit types and plant habit as well as a wide variety of chromosome numbers. Comparative genomics between various Rosaceous genera has led to the hypothesis that the ancestral genome of the family contained nine chromosomes, however, the synteny studies performed in the Rosaceae to date encompass species with base chromosome numbers x = 7 (Fragaria), x = 8 (Prunus), and x = 17 (Malus), and no study has included species from one of the many Rosaceous genera containing a base chromosome number of x = 9.

RESULTS

A genetic linkage map of the species Physocarpus opulifolius (x = 9) was populated with sequence characterised SNP markers using genotyping by sequencing. This allowed for the first time, the extent of the genome diversification of a Rosaceous genus with a base chromosome number of x = 9 to be performed. Orthologous loci distributed throughout the nine chromosomes of Physocarpus and the eight chromosomes of Prunus were identified which permitted a meaningful comparison of the genomes of these two genera to be made.

CONCLUSIONS

The study revealed a high level of macro-synteny between the two genomes, and relatively few chromosomal rearrangements, as has been observed in studies of other Rosaceous genomes, lending further support for a relatively simple model of genomic evolution in Rosaceae.

Developing expressed sequence tag libraries and the discovery of simple sequence repeat markers for two species of raspberry (Rubus L.)

BACKGROUND

Due to a relatively high level of codominant inheritance and transferability within and among taxonomic groups, simple sequence repeat (SSR) markers are important elements in comparative mapping and delineation of genomic regions associated with traits of economic importance. Expressed sequence tags (ESTs) are a source of SSRs that can be used to develop markers to facilitate plant breeding and for more basic research across genera and higher plant orders.

METHODS

Leaf and meristem tissue from 'Heritage' red raspberry (Rubus idaeus) and 'Bristol' black raspberry (R. occidentalis) were utilized for RNA extraction. After conversion to cDNA and library construction, ESTs were sequenced, quality verified, assembled and scanned for SSRs.  Primers flanking the SSRs were designed and a subset tested for amplification, polymorphism and transferability across species. ESTs containing SSRs were functionally annotated using the GenBank non-redundant (nr) database and further classified using the gene ontology database.

RESULTS

To accelerate development of EST-SSRs in the genus Rubus (Rosaceae), 1149 and 2358 cDNA sequences were generated from red raspberry and black raspberry, respectively. The cDNA sequences were screened using rigorous filtering criteria which resulted in the identification of 121 and 257 SSR loci for red and black raspberry, respectively. Primers were designed from the surrounding sequences resulting in 131 and 288 primer pairs, respectively, as some sequences contained more than one SSR locus. Sequence analysis revealed that the SSR-containing genes span a diversity of functions and share more sequence identity with strawberry genes than with other Rosaceous species.

CONCLUSION

This resource of Rubus-specific, gene-derived markers will facilitate the construction of linkage maps composed of transferable markers for studying and manipulating important traits in this economically important genus.

A genetic linkage map of black raspberry (Rubus occidentalis) and the mapping of Ag(4) conferring resistance to the aphid Amphorophora agathonica

We have constructed a densely populated, saturated genetic linkage map of black raspberry and successfully placed a locus for aphid resistance. Black raspberry (Rubus occidentalis L.) is a high-value crop in the Pacific Northwest of North America with an international marketplace. Few genetic resources are readily available and little improvement has been achieved through breeding efforts to address production challenges involved in growing this crop. Contributing to its lack of improvement is low genetic diversity in elite cultivars and an untapped reservoir of genetic diversity from wild germplasm. In the Pacific Northwest, where most production is centered, the current standard commercial cultivar is highly susceptible to the aphid Amphorophora agathonica Hottes, which is a vector for the Raspberry mosaic virus complex. Infection with the virus complex leads to a rapid decline in plant health resulting in field replacement after only 3-4 growing seasons. Sources of aphid resistance have been identified in wild germplasm and are used to develop mapping populations to study the inheritance of these valuable traits. We have constructed a genetic linkage map using single-nucleotide polymorphism and transferable (primarily simple sequence repeat) markers for F1 population ORUS 4305 consisting of 115 progeny that segregate for aphid resistance. Our linkage map of seven linkage groups representing the seven haploid chromosomes of black raspberry consists of 274 markers on the maternal map and 292 markers on the paternal map including a morphological locus for aphid resistance. This is the first linkage map of black raspberry and will aid in developing markers for marker-assisted breeding, comparative mapping with other Rubus species, and enhancing the black raspberry genome assembly.

Plant resistance to aphid feeding: behavioral, physiological, genetic and molecular cues regulate aphid host selection and feeding

Aphids damage major world food and fiber crops through direct feeding and transmission of plant viruses. Fortunately, the development of many aphid-resistant crop plants has provided both ecological and economic benefits to food production. Plant characters governing aphid host selection often dictate eventual plant resistance or susceptibility to aphid herbivory, and these phenotypic characters have been successfully used to map aphid resistance genes. Aphid resistance is often inherited as a dominant trait, but is also polygenic and inherited as recessive or incompletely dominant traits. Most aphid-resistant cultivars exhibit constitutively expressed defenses, but some cultivars exhibit dramatic aphid-induced responses, resulting in the overexpression of large ensembles of putative aphid resistance genes. Two aphid resistance genes have been cloned. Mi-1.2, an NBS-LRR gene from wild tomato, confers resistance to potato aphid and three Meloidogyne root-knot nematode species, and Vat, an NBS-LRR gene from melon, controls resistance to the cotton/melon aphid and to some viruses. Virulence to aphid resistance genes of plants occurs in 17 aphid species--more than half of all arthropod biotypes demonstrating virulence. The continual appearance of aphid virulence underscores the need to identify new sources of resistance of diverse sequence and function in order to delay or prevent biotype development.

Plant-aphid interactions with a focus on legumes

Sap-sucking insects such as aphids cause substantial yield losses in agriculture by draining plant nutrients as well as vectoring viruses. The main method of control in agriculture is through the application of insecticides. However, aphids rapidly evolve mechanisms to detoxify these, so there is a need to develop durable plant resistance to these damaging insect pests. The focus of this review is on aphid interactions with legumes, but work on aphid interactions with other plants, particularly Arabidopsis and tomato is also discussed. This review covers advances on the plant side of the interaction, including the identification of major resistance genes and quantitative trait loci conferring aphid resistance in legumes, basal and resistance gene mediated defence signalling following aphid infestation and the role of specialised metabolites. On the aphid side of the interaction, this review covers what is known about aphid effector proteins and aphid detoxification enzymes. Recent advances in these areas have provided insight into mechanisms underlying resistance to aphids and the strategies used by aphids for successful infestations and have significant impacts for the delivery of durable resistance to aphids in legume crops.

Genetic map of the primocane-fruiting and thornless traits of tetraploid blackberry

Blackberry primocane fruiting, fruiting on first-year canes, has the potential to expand blackberry production both seasonally and geographically. The incorporation of the primocane-fruiting trait into cultivars with desirable horticultural attributes is challenging due to its recessive nature and tetrasomic inheritance. Molecular marker-assisted selection has high potential to facilitate incorporation, because breeders already use morphological marker-assisted selection of seedlings without marginal cotyledonary hairs to identify progeny that will be thornless when mature. The development of a genetic linkage map with these two traits is the first step to utilizing molecular markers in breeding for thornless primocane-fruiting blackberry cultivars. A full-sib family segregating for thornlessness and primocane fruiting, from a cross between 'APF-12' and 'Arapaho', was used to construct the first genetic map of tetraploid blackberry. Segregation patterns of several dominant markers and the two phenotypic traits fit those expected uniquely with tetrasomic inheritance (e.g., 5:1, 11:1 and 35:1). Some loci showed significant double reduction frequencies, but genotypes that could have originated only from double reduction were not found. The map consists of seven linkage groups (LG) in each parent, consistent with the basic number of chromosomes (2n = 4x = 28). Naming of LG1-LG6 followed that of the recently revised system for raspberry using SSR markers in common between blackberry and raspberry, and LG7 was tentatively defined by default. The loci controlling primocane fruiting and thornlessness were not linked to each other; thornless/thorny, the S Locus, was mapped on LG4, and the primocane-/floricane-fruiting locus, named in this work the F Locus, on LG7.

Saturated linkage map construction in Rubus idaeus using genotyping by sequencing and genome-independent imputation

BACKGROUND

Rapid development of highly saturated genetic maps aids molecular breeding, which can accelerate gain per breeding cycle in woody perennial plants such as Rubus idaeus (red raspberry). Recently, robust genotyping methods based on high-throughput sequencing were developed, which provide high marker density, but result in some genotype errors and a large number of missing genotype values. Imputation can reduce the number of missing values and can correct genotyping errors, but current methods of imputation require a reference genome and thus are not an option for most species.

RESULTS

Genotyping by Sequencing (GBS) was used to produce highly saturated maps for a R. idaeus pseudo-testcross progeny. While low coverage and high variance in sequencing resulted in a large number of missing values for some individuals, a novel method of imputation based on maximum likelihood marker ordering from initial marker segregation overcame the challenge of missing values, and made map construction computationally tractable. The two resulting parental maps contained 4521 and 2391 molecular markers spanning 462.7 and 376.6 cM respectively over seven linkage groups. Detection of precise genomic regions with segregation distortion was possible because of map saturation. Microsatellites (SSRs) linked these results to published maps for cross-validation and map comparison.

CONCLUSIONS

GBS together with genome-independent imputation provides a rapid method for genetic map construction in any pseudo-testcross progeny. Our method of imputation estimates the correct genotype call of missing values and corrects genotyping errors that lead to inflated map size and reduced precision in marker placement. Comparison of SSRs to published R. idaeus maps showed that the linkage maps constructed with GBS and our method of imputation were robust, and marker positioning reliable. The high marker density allowed identification of genomic regions with segregation distortion in R. idaeus, which may help to identify deleterious alleles that are the basis of inbreeding depression in the species.

Saturated linkage map construction in Rubus idaeus using genotyping by sequencing and genome-independent imputation

BACKGROUND

Rapid development of highly saturated genetic maps aids molecular breeding, which can accelerate gain per breeding cycle in woody perennial plants such as Rubus idaeus (red raspberry). Recently, robust genotyping methods based on high-throughput sequencing were developed, which provide high marker density, but result in some genotype errors and a large number of missing genotype values. Imputation can reduce the number of missing values and can correct genotyping errors, but current methods of imputation require a reference genome and thus are not an option for most species.

RESULTS

Genotyping by Sequencing (GBS) was used to produce highly saturated maps for a R. idaeus pseudo-testcross progeny. While low coverage and high variance in sequencing resulted in a large number of missing values for some individuals, a novel method of imputation based on maximum likelihood marker ordering from initial marker segregation overcame the challenge of missing values, and made map construction computationally tractable. The two resulting parental maps contained 4521 and 2391 molecular markers spanning 462.7 and 376.6 cM respectively over seven linkage groups. Detection of precise genomic regions with segregation distortion was possible because of map saturation. Microsatellites (SSRs) linked these results to published maps for cross-validation and map comparison.

CONCLUSIONS

GBS together with genome-independent imputation provides a rapid method for genetic map construction in any pseudo-testcross progeny. Our method of imputation estimates the correct genotype call of missing values and corrects genotyping errors that lead to inflated map size and reduced precision in marker placement. Comparison of SSRs to published R. idaeus maps showed that the linkage maps constructed with GBS and our method of imputation were robust, and marker positioning reliable. The high marker density allowed identification of genomic regions with segregation distortion in R. idaeus, which may help to identify deleterious alleles that are the basis of inbreeding depression in the species.

Construction of black (Rubus occidentalis) and red (R. idaeus) raspberry linkage maps and their comparison to the genomes of strawberry, apple, and peach

The genus Rubus belongs to the Rosaceae and is comprised of 600-800 species distributed world-wide. To date, genetic maps of the genus consist largely of non-transferable markers such as amplified fragment length polymorphisms. An F(1) population developed from a cross between an advanced breeding selection of Rubus occidentalis (96395S1) and R. idaeus 'Latham' was used to construct a new genetic map consisting of DNA sequence-based markers. The genetic linkage maps presented here are constructed of 131 markers on at least one of the two parental maps. The majority of the markers are orthologous, including 14 Rosaceae conserved orthologous set markers, and 60 new gene-based markers developed for raspberry. Thirty-four published raspberry simple sequence repeat markers were used to align the new maps to published raspberry maps. The 96395S1 genetic map consists of six linkage groups (LG) and covers 309 cM with an average of 10 cM between markers; the 'Latham' genetic map consists of seven LG and covers 561 cM with an average of 5 cM between markers. We used BLAST analysis to align the orthologous sequences used to design primer pairs for Rubus genetic mapping with the genome sequences of Fragaria vesca 'Hawaii 4', Malus × domestica 'Golden Delicious', and Prunus 'Lovell'. The alignment of the orthologous markers designed here suggests that the genomes of Rubus and Fragaria have a high degree of synteny and that synteny decreases with phylogenetic distance. Our results give unprecedented insights into the genome evolution of raspberry from the putative ancestral genome of the single ancestor common to Rosaceae.

Molecular bases of plant resistance to arthropods

Arthropod-resistant crops provide significant ecological and economic benefits to global agriculture. Incompatible interactions involving resistant plants and avirulent pest arthropods are mediated by constitutively produced and arthropod-induced plant proteins and defense allelochemicals synthesized by resistance gene products. Cloning and molecular mapping have identified the Mi-1.2 and Vat arthropod resistance genes as CC-NBS-LRR (coiled coil-nucleotide binding site-leucine rich repeat) subfamily NBS-LRR resistance proteins, as well as several resistance gene analogs. Genetic linkage mapping has identified more than 100 plant resistance gene loci and linked molecular markers used in cultivar development. Rice and sorghum arthropod-resistant cultivars and, to a lesser extent, raspberry and wheat cultivars are components of integrated pest management (IPM) programs in Asia, Australia, Europe, and North America. Nevertheless, arthropod resistance in most food and fiber crops has not been integrated due primarily to the application of synthetic insecticides. Plant and arthropod genomics provide many opportunities to more efficiently develop arthropod-resistant plants, but integration of resistant cultivars into IPM programs will succeed only through interdisciplinary collaboration.

How agro-ecological research helps to address food security issues under new IPM and pesticide reduction policies for global crop production systems

Drivers behind food security and crop protection issues are discussed in relation to food losses caused by pests. Pests globally consume food estimated to feed an additional one billion people. Key drivers include rapid human population increase, climate change, loss of beneficial on-farm biodiversity, reduction in per capita cropped land, water shortages, and EU pesticide withdrawals under policies relating to 91/414 EEC. IPM (Integrated Pest Management) will be compulsory for all EU agriculture by 2014 and is also being widely adopted globally. IPM offers a 'toolbox' of complementary crop- and region-specific crop protection solutions to address these rising pressures. IPM aims for more sustainable solutions by using complementary technologies. The applied research challenge now is to reduce selection pressure on single solution strategies, by creating additive/synergistic interactions between IPM components. IPM is compatible with organic, conventional, and GM cropping systems and is flexible, allowing regional fine-tuning. It reduces pests below economic thresholds utilizing key 'ecological services', particularly biocontrol. A recent global review demonstrates that IPM can reduce pesticide use and increase yields of most of the major crops studied. Landscape scale 'ecological engineering', together with genetic improvement of new crop varieties, will enhance the durability of pest-resistant cultivars (conventional and GM). IPM will also promote compatibility with semiochemicals, biopesticides, precision pest monitoring tools, and rapid diagnostics. These combined strategies are urgently needed and are best achieved via multi-disciplinary research, including complex spatio-temporal modelling at farm and landscape scales. Integrative and synergistic use of existing and new IPM technologies will help meet future food production needs more sustainably in developed and developing countries, in an era of reduced pesticide availability. Current IPM research gaps are identified and discussed.

Mapping and validation of QTLs for resistance to aphids and whiteflies in melon

Aphis gossypii and Bemisia tabaci are severe hemipteran pests of melon crops and breeding for resistance to both insects is required to reduce pesticide use. Resistance was evaluated for its effect on behaviour and biotic potential of both hemipterans in a population of recombinant inbred lines (RILs) derived from the cross Védrantais x PI 161375. Insect variability was considered using two A. gossypii clones and two B. tabaci populations. Two additive QTLs affected the whiteflies. Four additive QTLs and two couples of epistatic QTLs affected the aphids. Amongst them, a major QTL affects both behaviour and biotic potential of A. gossypii and therefore a same R gene induces both antixenosis and antibiosis. This major QTL colocalizes with the Vat gene belonging to the NBS-LRR gene family. No loci affected both aphids and whiteflies contrary to what was observed for the Mi1.2 gene, a NBS-LRR gene in tomato. Original populations with different allelic compositions at QTLs affecting A. gossypii were built by one inter-crossing of RILs used for the mapping process. The genetic background was shown homogeneous between these populations what allowed validating QTLs and investigating the effect of allelic combinations at QTLs. Effects of QTLs were stronger than expected and some QTLs had a wider spectrum than expected. This strategy of validation appeared rapid and low cost.

Resistance to aphid vectors of virus disease

The majority of plant viruses rely on vectors for their transmission and completion of their life cycle. These vectors comprise a diverse range of life forms including insects, nematodes, and fungi with the most common of these being insects. The geographic range of many of these vectors is continually expanding due to climate change. The viruses that they carry are therefore also expanding their range to exploit novel and naïve plant hosts. There are many forms of naturally occurring vector resistance ranging from broad nonhost resistance to more specific types of inducible resistance. Understanding and exploiting the many and varied forms of natural resistance to virus vectors is therefore extremely important for current and future agricultural production systems. To demonstrate the range and extent of these resistance mechanisms, this chapter will primarily focus on aphids to highlight key developments appropriate to plant-insect-virus interactions.