Host-plant resistance of sorghum: Differential hydrolysis of sorghum pectic substances by polysaccharases of greenbug biotypes (Schizaphis graminum,homoptera: Aphididae)

Pectic substances extracted from different varieties of sorghum are hydrolyzed at differing rates by unfractionated polysaccharases isolated from two biotypes (C, GBC; and E, GBE) of the sorghum pest, Schizaphis graminum (the greenbug). A higher degree of susceptibility of a sorghum variety is associated with a greater rate of hydrolysis of sorghum pectic substances by a greenbug biotype. Increases in the specific activity of polysaccharases on the pectic substances from a resistant sorghum variety are dependent on the duration that a biotype is maintained as a colony on that variety. Polysaccharase activity of GBE on arabinogalactan was significantly greater than GBC. However, there were no differences between the biotypes on the depolymerization of a variety of other plant matrix polysaccharides and a synthetic polysaccharide. The sequence of substrates of increasing refractoriness to hydrolysis are: arabinogalactan < microcrystalline cellulose < xylan < pectin < 2,3-diacetyl pectin < α-1,4-galacturonan. Pectic substances from sorghum varieties resistant to GBC but susceptible to GBE are relatively lower in arabinogalactan with elevated levels of uronic acid (UA) compared to varieties susceptible to both biotypes. A sorghum variety resistant to both GBC and GBE was lowest in levels of arabinogalactan, highest in UA, and highest in fructan content, which in the other varieties occurred only in trace amounts. Pectic composition of rhamnose, xylose, and glucose showed no relationship to resistance. Bound phenolics (potential inhibitors of enzyme activity) were not detected in any of the sorghum pectic substances. The relationship of plant matrix polysaccharides to host-plant aphid biotype compatibility is discussed.     

Phenotypic mechanisms of host resistance against greenbug (Homoptera: Aphididae) revealed by near isogenic lines of wheat

Interactions between biotype E greenbug, Schizaphis graminum (Rondani), and wheat, Triticum aestivum L., were investigated using resistant and susceptible near isogenic lines of the greenbug resistance gene Gb3. In an antixenosis test, the greenbugs preferred susceptible plants to resistant ones when free choice of hosts was allowed. Aphid feeding resulted in quick and severe damage to susceptible plants, which seemed to follow a general pattern spatially and was affected by the position where the greenbugs were initially placed. Symptom of damage in resistant plants resembled senescence. Within-plant distribution of aphids after infestation was clearly different between the two genotypes. Significantly more greenbugs fed on the first (oldest) leaf than on the stem in resistant plants, but this preference was reversed in the susceptible one. After reaching its peak, aphid population on the susceptible plants dropped quickly. All susceptible plants were dead in 10-14 d after infestation due to greenbug feeding. Aphid population dynamics on resistant plants exhibited a multipeak curve. After the first peak, the greenbug population declined slowly. More than 70% of resistant plants were killed 47 d after infestation. Performance of both biotype E and I greenbugs on several Gb3-related wheat germplasm lines were also examined. It seems that the preference-on-stem that was characteristic of biotype E greenbugs on the susceptible plants was aphid biotype- and host genotype-dependent. Results from this study suggested that antixenosis, antibiosis, and tolerance in the resistant plants of wheat might all contribute to resistance against greenbug feeding.     

Effect of virulence genes complementary to the effective resistance genes in sorghum on fitness of the greenbug, <Emphasis Type="Italic">Schizaphis graminum</Emphasis> Rondani (Homoptera,Aphididae)

Analysis of the greenbug (Schizaphis graminum Rond.) — sorghum interaction system confirmed the hypothesis that rare insect virulence was related to reduced fitness. Greenbug clones from the Krasnodar population virulent to resistance genes Sgr5 and Sgr6 revealed lower fecundity in comparison with avirulent ones and were replaced in model populations during reproduction on a susceptible sorghum line. The main role of aphid fecundity was shown to provide higher fitness, reducing the frequency of virulent clones in natural populations.     

Responses of Schizaphis graminum (Homoptera: Aphididae) to leaf excision in resistant and susceptible sorghum

Greenbugs, Schizaphis graminum (Rondani), were reared on intact and excised leaves of varieties of sorghum which differed in their suitability as hosts for this aphid. Aphids grew poorly on intact leaves of three resistant varieties, but grew well on excised leaves of the same varieties. Leaf excision did not affect aphid growth on three susceptible varieties. By electronically monitoring the feeding behaviour of aphids on two resistant and one susceptible variety, significant differences were found in many parameters between aphids assayed on excised vs. intact leaves of only the resistant varieties. Aphids on excised leaves of the resistant varieties, and on excised or intact leaves of the susceptible variety, made fewer probes to the phloem, spending more time ingesting from phloem during each probe, compared to aphids on intact resistant plants. There was a higher level of free amino acids in excised leaves of all varieties, but aphid growth and feeding behaviour improved as a result of excision only on resistant varieties. This observation, coupled with the fact that intact plants of all varieties have similar amino acid levels, indicates that these nutrients are not of primary importance in sorghum suitability to the greenbug. Other explanations for the aphids' responses to excised leaves are discussed.     

The interaction of soybean aphids and soybean cyst nematodes on selected resistant and susceptible soybean lines

Soybean aphids, Aphis glycines Matsumura, and soybean cyst nematodes, Heterodera glycines Ichinohe, are economic pests of soybean, Glycine max (L.) Merr., in the north‐central United States. Combined, these pests may account for 20–50% of yield reductions in a soybean crop. Only limited information is available concerning the interaction of these two pests on soybean production. During the summers of 2006 and 2007, we conducted a field‐experiment near Urbana, IL, to evaluate the effect of resistant and susceptible soybean lines on the development and reproduction of both pests in combination with each other. We also examined how each pest, as well as their interaction, affected the yield of susceptible and resistant soybean lines. Soybean plants grown within caged plots were infested with soybean aphids and soybean cyst nematodes; cumulative aphid days and soybean cyst nematode egg densities were determined at the end of each growing season. Soybean aphids were able to survive on all four soybean lines in both years of this study; however, aphid‐resistant lines generally had fewer cumulative aphid days than aphid‐susceptible lines. Likewise, nematode‐resistant lines typically had fewer eggs than nematode‐susceptible lines. During both years, we failed to observe a significant interaction between these two pests on the reproduction of one another. Yield data from 2006 was inconclusive; however, results from 2007 suggest that yield‐loss when soybean aphids and soybean cyst nematodes occur jointly is not significantly greater than when these two pests occur independently. The relationship between these two pests, and our inability to observe an interaction, are discussed.     

Spatial and temporal distribution of induced resistance to greenbug (Homoptera: Aphididae) herbivory in preconditioned resistant and susceptible near isogenic plants of wheat

Interactions between biotype E greenbugs, Schizaphis graminum (Rodani), and two near isogenic lines of the greenbug resistance gene Gb3 of wheat, Triticum aestivum L., were examined for 62 d after infestation. By comparing aphid performance and host responses on control and greenbug-preconditioned plants, we demonstrated that systemic resistance to greenbug herbivory was inducible in the resistant genotype with varying intensities and effectiveness in different parts of the plants. Preconditioning of susceptible plants resulted in modification of within-plant aphid distribution and reduction of cumulative greenbug densities, but it showed no effect on reducing greenbug feeding damage to host plant. Preconditioning of resistant plants altered greenbug population dynamics by reducing the size and buffering the fluctuation of the aphid population. Preconditioning in the first (oldest) leaf of the resistant plant had no phenotypically detectable effect in the stem and induced susceptibility locally in the first leaf within the first 2 d after infestation. The preconditioning-induced resistance reduced greenbug density, delayed aphid density peaks and extended the life of younger leaves in resistant plants. Expression of induced resistance was spatially and temporally dynamic within the plant, which occurred more rapidly, was longer in duration, and stronger in intensity in younger leaves. Host resistance gene-mediated induced resistance was effective in lowering greenbug performance and reducing damage from greenbug herbivory in host plants. Results from this study supported the optimal defense theory regarding within-plant defense allocation.     

Host race evolution in Schizaphis graminum (Hemiptera: Aphididae): nuclear DNA sequences

The greenbug aphid, Schizaphis graminum (Rondani) was introduced into the United States in the late 1880s, and quickly was established as a pest of wheat, oat, and barley. Sorghum was also a host, but it was not until 1968 that greenbug became a serious pest of it as well. The most effective control method is the planting of resistant varieties; however, the occurrence of greenbug biotypes has hampered the development and use of plant resistance as a management technique. Until the 1990s, the evolutionary status of greenbug biotypes was obscure. Four mtDNA cytochrome oxidase subunit I (COI) haplotypes were previously identified, suggesting that S. graminum sensu lato was comprised of host-adapted races. To elucidate the current evolutionary and taxonomic status of the greenbug and its biotypes, two nuclear genes and introns were sequenced; cytochrome c (CytC) and elongation factor 1-α (EF1-α). Phylogenetic analysis of CytC sequences were in complete agreement with COI sequences and demonstrated three distinct evolutionary lineages in S. graminum. EF1-α DNA sequences were in partial agreement with COI and CytC sequences, and demonstrated two distinct evolutionary lineages. Host-adapted races in greenbug are sympatric and appear reproductively isolated. Agricultural biotypes in S. graminum likely arose by genetic recombination via meiosis during sexual reproduction within host-races. The 1968 greenbug outbreak on sorghum was the result of the introduction of a host race adapted to sorghum, and not selection by host resistance genes in crops.     

Genetic control of different types of the aphid resistance in cereal crops

Inheritance of the two main types of the plant resistance to insects was investigated in the sorghum-greenbug (Schizaphis graminum Rond.) and wheat-bird cherry-oat aphid (Rhopalosiphon padi L.) interaction systems. The data obtained support the hypothesis that antixenosis (avoiding of the plant by the insect, given a choice) and antibiosis (adverse effect of the plant on the insect feeding on it) are pleiotropic manifestations of the same genes. This is confirmed by the following facts. (1) Identical patterns of segregation for antixenosis and antibiosis in different cases of sorghum resistance to the greenbug: monogenic control (gene Sgr4), digenic control (Sgr1, Sgr2 and Sgr7, Sgr8), and complementary action of the genes (Sgr9 and Sgr10). (2) Correlated changes in the levels of antibiosis and antixenosis during long-term reproduction of a greenbug clone on the resistant sorghum variety k-1206 (resistance controlled by one gene). (3) Simultaneous expression of antixenosis and antibiosis in F₃ wheat hybrid families to the bird cherry-oat aphid.     

高粱抗高粱蚜的生化基础

高粱中的可溶性总氮、可溶性总糖和绝大部分游离氨基酸,特别是必需氨基酸,在感性品种中的含量显著地比抗性品种中的含量高.感性品种叶液微偏酸,抗性品种近中性.多元回归分析表明,高梁对高粱蚜Melanaphis sacchari(Zehntner)的抗性与可溶性总氮、可溶性总糖和游离氨基酸的含量呈反相关.     

Tritrophic interaction of parasitoid Lysiphlebus testaceipes (Hymenoptera: Aphidiidae), greenbug, Schizaphis graminum (Homoptera: Aphididae), and greenbug-resistant sorghum hybrids

Interactions of the parasitoid Lysiphlebus testaceipes (Cresson) and the greenbug, Schizaphis graminum (Rondani), on greenbug-resistant 'Cargill 607E' (antibiosis), 'Cargill 797' (primarily tolerance), and -susceptible 'Golden Harvest 510B' sorghum, Sorghum bicolor (L.) Moench, were tested using three levels of biotype I greenbug infestation. The parasitoid infestation rate was 0.5 female and 1.0 male L. testaceipes per plant. For all three greenbug infestation levels, the parasitoid brought the greenbug under control (i.e., prevented the greenbugs from killing the plants) on both resistant hybrids, but it did not prevent heavy leaf damage at the higher greenbug infestation rates. At the low greenbug infestation rate (50 greenbugs per resistant plant when parasitoids were introduced), greenbugs damaged 5 and 18% of the total leaf area on 'Cargill 797' and 'Cargill 607E', respectively, before greenbugs were eliminated. Leaf damage was higher for the intermediate infestation study (120 greenbugs per plant), 21% and 30% leaf area were damaged on the resistant sorghum hybrids 'Cargill 797' and 'Cargill 607E', respectively. At the high greenbug infestation rate (300 greenbugs per plant), heavy damage occurred: 61% on 'Cargill 607E' and 75% on 'Cargill 797'. The parasitoids did not control greenbugs on the susceptible sorghum hybrid 'Golden Harvest 510B'. L. testaceipes provided comparable control on both greenbug-resistant hybrids. This study supports previous studies indicating that L. testaceipes is effective in controlling greenbugs on sorghum with antibiosis resistance to greenbugs. Furthermore, new information is provided indicating that L. testaceipes is also effective in controlling greenbugs on a greenbug-tolerant hybrid.     

Molecular mapping of QTLs for resistance to the greenbug <Emphasis Type="Italic">Schizaphis graminum</Emphasis> (Rondani) in <Emphasis Type="Italic">Sorghum bicolor</Emphasis> (Moench)

Sorghum is a worldwide important cereal crop and widely cultivated for grain and forage production. Greenbug, Schizaphis graminum (Rondani) is one of the major insect pests of sorghum and can cause serious damage to sorghum plants, particularly in the US Great Plains. Identification of chromosomal regions responsible for greenbug resistance will facilitate both map-based cloning and marker-assisted breeding. Thus, a mapping experiment was conducted to dissect sorghum genetic resistance to greenbug biotype I into genomic regions. Two hundred and seventy-seven (277) F(2) progeny and their F(2:3) families from a cross between Westland A line (susceptible parent) and PI550610 (resistant parent) combined with 118 polymorphic simple sequence repeat (SSR) markers were used to map the greenbug resistance QTLs. Composite interval mapping (CIM) and multiple interval mapping (MIM) revealed two QTLs on sorghum chromosome nine (SBI-09) consistently conditioned the resistance of host plant to the greenbug. The two QTLs were designated as QSsgr-09-01 (major QTL) and QSsgr-09-02 (minor QTL), accounting for approximately 55-80%, and 1-6% of the phenotypic variation for the resistance to greenbug feeding, respectively. These resistance QTLs appeared to have additive and partially dominant effects. The markers Xtxp358, Xtxp289, Xtxp67 and Xtxp230 closely flanked the respective QTLs, and can be used in high-throughput marker-assisted selections (MAS) for breeding new resistant parents and producing commercial hybrids.     

高粱抗蚜研究进展

高粱(Sorghum bicolour)是世界上最重要的粮食、饲料、酿造和能源作物之一, 也是C₄植物研究的模式植物。蚜虫是农业生产上的重要害虫, 几乎危害所有的栽培作物。危害高粱的蚜虫主要包括高粱蚜(Melanaphis sacchari)、麦二叉蚜(Schizaphis graminum)和玉米蚜(Rhopalosiphum maidis)。高粱的抗蚜资源尚不丰富且缺乏深入系统的研究。目前研究较多的是麦二叉蚜的抗性遗传方面, 已定位20个抗性QTLs, 单一QTL对抗性差异贡献率最高可达80.3%, 对高粱蚜和玉米蚜的研究尚需进一步加强。高粱的理化特性与其抗蚜性能相关, 故可与育种实践相结合。高粱和蚜虫(Acyrthosiphon pisum)的全基因组测序工作已经完成, 这将有助于蚜虫-植物间的相互作用关系及植物对蚜虫的抗性机制研究。目前已克隆到2个抗蚜基因, 且多个抗蚜基因(位点)已被定位在染色体上。该文重点综述了上述研究成果并对高粱抗蚜的研究前景进行了展望。     

Complementarity of genes for resistance to greenbug [Schizaphis graminum (Rondani)], biotype E,in sorghum [Sorghum bicolor (L.) Moench]

Summary Gene complementarity among various sources of resistance to greenbug biotype E was assessed. Analysis of the F₂ generation of crosses between susceptible and resistant parents (mating 1) and among sources of resistance (mating 2) suggested that resistance in sorghum to greenbug biotype E was complexly inherited and, to some extent, dependent on the nature of both the resistant and susceptible parents. Positive transgressive segregation in the F₂ generations of both matings was found to be due to effective plus factors, contributed by both parents in a cross, which complemented each other. The number of plus factors ranged from one to two in the susceptible parents and from two to five in the resistant parents of mating 1, and from one to five in the parents of mating 2. The consistently significant reciprocal effects shown by Sarvasi and PI264453 indicated that these sources had major factors for resistance in their cytoplasms, which were expressed in all their crosses. The results from this study indicated that the sources of resistance complemented each other to give increased number of F₂ segregates with increased resistance. Thus, it should be possible to increase and diversify resistance of sorghum to greenbug biotype E by accumulating different, effective plus factors from various sources through recurrent selection.Contribution No. 90-106-J from the Kansas Agricultural Experiment Station, Kansas State University, Manhattan, KS 66506, USA     

Blockage of stylet tips as the mechanism of resistance to virus transmission by Aphis gossypii in melon lines bearing the Vat gene

Aphis gossypii is the main virus vector in muskmelon crops. The melon gene Vat confers resistance to non‐persistent virus transmission by this aphid. The mechanism of this resistance is not well understood, but no relationship has been detected between resistance and the probing behaviour of aphids on resistant plants. Results presented here suggest that temporary blockage of aphid stylet tips preventing virus particle release may explain the resistance conferred by Vat gene. We performed experiments in which viruliferous aphids were allowed to probe different sequences of resistant (Vat‐bearing) and/or susceptible melon plants. The results demonstrated that A. gossypii inoculates Cucumber mosaic virus (CMV) efficiently in susceptible plants having previously probed resistant plants, showing that the resistance mechanism is reversible. Furthermore, the infection rate obtained for susceptible plants was the same (25%) regardless of whether the transmitting aphid had come directly from the CMV source or had subsequently probed on resistant plants. This result suggests that virus is not lost from stylet to plant during probing of resistant plants, supporting the temporary blockage hypothesis. We also found that the ability of Myzus persicae to transmit CMV is noticeably reduced after probing on resistant plants, providing evidence that this aphid species also responds to the presence of the Vat gene. Finally, we also found that in probes immediately after virus acquisition M. persicae inoculates resistant plants with CMV more efficiently than susceptible plants, perhaps because the Vat gene product induces increased salivation by this aphid.     

Feeding behavior of aphids on narrow‐leafed lupin (Lupinus angustifolius) genotypes varying in the content of quinolizidine alkaloids

Since the beginning of breeding narrow‐leafed lupins [Lupinus angustifolius L. (Fabaceae)] with a low alkaloid content, susceptibility to several aphid species has increased. Therefore, the probing and feeding behavior of Aphis fabae Scopoli, Aphis craccivora Koch, Acyrthosiphon pisum (Harris), Myzus persicae (Sulzer), and the well‐adapted Macrosiphum albifrons Essig (all Hemiptera: Aphididae) was studied over 12 h on narrow‐leafed lupin genotypes containing varying amounts and compositions of alkaloids. We used the electrical penetration graph (EPG) technique to obtain information on the influence of alkaloid content and composition on the susceptibility to various aphid species. Results indicated that the total time of probing of A. fabae, A. craccivora, A. pisum, and M. persicae increased with a reduced alkaloid content, whereas the alkaloid content had no influence on M. albifrons. Almost all of the individuals (>93%) conducted sieve element phases on the highly susceptible genotype Bo083521AR (low alkaloid content). A reduced occurrence of phloem phases was observed during the 12‐h recording on the alkaloid‐rich cultivar Azuro, especially for A. pisum (37.5%) and A. fabae (55.0%). Furthermore, aphids feeding on genotypes with low alkaloid content had in most cases significantly longer sieve element phases than when feeding on resistant genotypes (Kalya: low alkaloid content, yet resistant; Azuro: high alkaloid content, resistant), whereas M. albifrons showed the longest phloem phase on the alkaloid‐rich cultivar Azuro. As most significant differences were found in phloem‐related parameters, it is likely that the most important plant factors influencing aphid probing and feeding behavior are localized in the sieve elements. The aphids’ feeding behavior on the cultivar Kalya, with a low alkaloid content but reduced susceptibility, indicates that not only the total alkaloid content influences the feeding behavior but additional plant factors have an impact.     

Life history study of multiple clones of insecticide resistant and susceptible greenbug Schizaphis graminum (Homoptera: Aphididae)

Comparative differences and similarities in prereproductive time (d), progeny production in a time equal to d (Md), and intrinsic rate of increase (rm) were established for one susceptible (S) and three resistant (R) strains of the greenbug, Schizaphis graminum (Rondani), reared on sorghum hybrids Dekalb G550E and Cargill 607E. The R strains showed three patterns of elevated esterase activity. Four R1 clones, four R2 clones, one R3 clone, and four S clones were evaluated. The interaction of sorghum hybrid and greenbug strain did not significantly influence any of the parameters measured. However, R1 greenbugs exhibited a significantly longer prereproductive period than the other strains. In addition, the R1 strain had a significantly slower intrinsic rate of increase than the R2 or S greenbug strains, but did not differ significantly from the R3 strain. These results suggest that R1 greenbugs may be less fit than the other strains studied.     

Triticum monococcum lines with distinct metabolic phenotypes and phloem‐based partial resistance to the bird cherry–oat aphid Rhopalosiphum padi

Crop protection is an integral part of establishing food security, by protecting the yield potential of crops. Cereal aphids cause yield losses by direct damage and transmission of viruses. Some wild relatives of wheat show resistance to aphids but the mechanisms remain unresolved. In order to elucidate the location of the partial resistance to the bird cherry–oat aphid, Rhopalosiphum padi, in diploid wheat lines of Triticum monococcum, we conducted aphid performance studies using developmental bioassays and electrical penetration graphs, as well as metabolic profiling of partially resistant and susceptible lines. This demonstrated that the partial resistance is related to a delayed effect on the reproduction and development of R. padi. The observed partial resistance is phloem based and is shown by an increase in number of probes before the first phloem ingestion, a higher number and duration of salivation events without subsequent phloem feeding and a shorter time spent phloem feeding on plants with reduced susceptibility. Clear metabolic phenotypes separate partially resistant and susceptible lines, with the former having lower levels of the majority of primary metabolites, including total carbohydrates. A number of compounds were identified as being at different levels in the susceptible and partially resistant lines, with asparagine, octopamine and glycine betaine elevated in less susceptible lines without aphid infestation. In addition, two of those, asparagine and octopamine, as well as threonine, glutamine, succinate, trehalose, glycerol, guanosine and choline increased in response to infestation, accumulating in plant tissue localised close to aphid feeding after 24 h. There was no clear evidence of systemic plant response to aphid infestation.     

The impact of Meu1-mediated resistance in tomato on longevity, fecundity and behavior of the potato aphid, Macrosiphum euphorbiae

The effect of the tomato resistance gene, Meu1, on feeding, longevity, fecundity and developmental rate of the pink biotype of the potato aphid, Macrosiphum euphorbiae (Thomas) (Hemiptera, Aphididae), was determined using nearly isogenic tomato (Lycopersicon esculentum Mill, Solanaceae) lines. Aphid mortality was significantly higher on resistant plants, with 60% of the aphids dying by the 4th day of exposure. By the 10th day, all the aphids on the resistant plants were dead whereas 100% of the aphids on susceptible plants were alive. Meu1-mediated resistance resulted in significantly decreased fecundity with a ten-fold decrease in the net fertility rate (4.5 and 45.7 progeny per aphid on resistant and susceptible tomato, respectively). A qualitative analysis showed that honeydew was produced by aphids on resistant and susceptible plants, suggesting that aphids initiate feeding on both plant types. However, significantly lower quantities of honeydew were present when aphids were caged on resistant plants. There were also significant differences in aphid location on resistant and susceptible leaves. Experiments evaluating behavior in less than 24 h showed that aphids left resistant leaves after relatively short exposure (3–6 h). Aphids transferred from resistant to susceptible tomato at intervals between 3 h and 24 h resumed feeding as evidenced by presence of honeydew. Although the mechanism by which Meu1-mediated resistance operates is not yet known, our data suggest that resistance factors act rapidly after initiation of feeding and that lower fecundity and longevity are related to reduction in aphid feeding.     

The effect of co-infestation by conspecific and heterospecific aphids on the feeding behaviour of <Emphasis Type="Italic">Nasonovia ribisnigri</Emphasis> on resistant and susceptible lettuce cultivars

Aphid saliva can suppress the blocking of sieve elements, a reaction that plants employ to inhibit aphid feeding, but aphid saliva can also elicit plant defence responses. Such plant responses might affect interactions between different aphid species and intraspecifically, e.g. among different biotypes. The objectives of our study were to investigate if feeding behaviour and performance of two biotypes of the lettuce aphid Nasonovia ribisnigri are affected by (1) feeding by the other biotype and (2) feeding by the green peach aphid Myzus persicae or the potato aphid Macrosiphum euphorbiae. Additionally the effect of feeding in a group was studied. All experiments were performed on both a resistant and an isogenic susceptible lettuce cultivar. Feeding or probing by conspecific or heterospecific aphids had different effects on Nasonovia ribisnigri biotypes. Aphids were only slightly affected by feeding or probing of the same biotype on both susceptible and resistant lettuce. N. ribisnigri virulent biotype Nr:1 suppressed the resistance against Nr:0 in the resistant cultivar. In contrast, defence was induced by Nr:1 against Nr:0 in susceptible lettuce. Co-infestation by M. euphorbiae and M. persicae had minor effects on Nr:0. Defence against Nr:1 was induced on both susceptible lettuce and resistant lettuce by Nr:0 and M. euphorbiae. Additionally, M. persicae induced defence in resistant lettuce against Nr:1. Effectors in the saliva of Nr:1 aphids are likely responsible for the defence suppression in lettuce. Identification of these effectors could lead to a better understanding of the mechanism of virulence in N. ribisnigri.