Resistance of dwarf Cocos nucifera L. (Arecaceae) cultivars to Raoiella indica Hirst (Acari: Tenuipalpidae).

The red palm mite Raoiella indica Hirst, 1924 (Acari: Tenuipalpidae) is an important pest of the coconut palm Cocos nucifera L. (Arecaceae) and has caused problems in coconut production worldwide. Research has been carried out aiming at controlling the mite through chemical, biological, alternative, and host plant resistance methods. Identifying coconut palm cultivars resistant to R. indica is important to reduce the problems caused to plantations. Therefore, the objective of this work was to evaluate the performance of R. indica in six dwarf coconut palm cultivars, to identify sources of resistance. The cultivars of the sub-varieties green, red, and yellow evaluated were Brazilian Green Dwarf-Jiqui (BGDJ), Brazilian Red Dwarf-Gramame (BRDG), Cameroon Red Dwarf (CRD), Malayan Red Dwarf (MRD), Brazilian Yellow Dwarf-Gramame (BYDG), and Malayan Yellow Dwarf (MYD). Confinement and free choice tests of R. indica on the cultivars were performed, in which biological parameters and preference were evaluated. Mite performance was different in the cultivars evaluated. In the confinement bioassay, R. indica had the worst performance in the cultivar BGDJ, the best performance in CRD, MRD, and BRDG, and intermediate performance in BYDG and MYD. In the free choice test, the cultivars MRD and MYD were preferred in relation to BGDJ, and CRD was less preferred in relation to BGDJ. Therefore, we considered that the cultivar BGDJ is the most resistant to R. indica, by antibiosis and antixenosis; CRD has resistance by antixenosis; and MRD, BRDG, BYDG, and MYD are susceptible.

Transcriptome analysis of aphid-resistant and susceptible near isogenic lines reveals candidate resistance genes in cowpea (Vigna unguiculata).

BACKGROUND: Cowpea (Vigna unguiculata) is a crucial crop for regions of the world that are prone to both heat and drought; however, the phytotoxic cowpea aphid (Aphis craccivora) impairs plant physiology at low population levels. Both antibiotic and antixenotic forms of resistance to the aphid have been mapped to two quantitative trait loci (QTLs) and near isogenic lines (NILs). The molecular mechanism for this resistance response remains unknown. RESULTS: To understand the genes underlying susceptibility and resistance, two cowpea lines with shared heritage were infested along a time course and characterized for transcriptome variation. Aphids remodeled cowpea development and signaling relative to host plant resistance and the duration of feeding, with resource acquisition and mobilization determining, in part, susceptibility to aphid attack. Major differences between the susceptible and resistant cowpea were identified including two regions of interest housing the most genetic differences between the lines. Candidate genes enabling aphid resistance include both conventional resistance genes (e.g., leucine rich repeat protein kinases) as well as multiple novel genes with no known orthologues. CONCLUSIONS: Our results demonstrate that feeding by the cowpea aphid globally remodels the transcriptome of cowpea, but how this occurs depends on both the duration of feeding and host-plant resistance. Constitutive expression profiles of the resistant genotype link aphid resistance to a finely-tuned resource management strategy that ultimately reduces damage (e.g., chlorosis) and delays cell turnover, while impeding aphid performance. Thus, aphid resistance in cowpea is a complex, multigene response that involves crosstalk between primary and secondary metabolism.

Chemical ecology of Himalayan eggplant variety's antixenosis: identification of geraniol as an oviposition deterrent against the eggplant shoot and fruit borer.

Eggplant (Solanum melongena) suffers severe losses due to a multi-insecticide-resistant lepidopteran pest, shoot and fruit borer (SFB, Leucinodes orbonalis). Heavy and combinatorial application of pesticides for SFB control renders eggplant risky for human consumption. We observed that gravid SFB females do not oviposit on Himalayan eggplant variety RC-RL-22 (RL22). We hypothesized that RL22 contained an antixenosis factor. Females' behavior indicated that the RL22 cue they perceived was olfactory. To identify it, leaf volatile blends of seven eggplant varieties were profiled using solid phase microextraction and gas chromatography mass spectrometry. Seven RL22-specific compounds were detected in the plant headspace. In choice assays, oviposition deterrence efficacies of these candidate compounds were independently tested by their foliar application on SFB-susceptible varieties. Complementation of geraniol, which was exclusively found in RL22, reduced oviposition (> 90%). To validate geraniol's role in RL22's SFB-deterrence, we characterized RL22's geraniol synthase and silenced its gene in planta, using virus-induced gene silencing. Geraniol biosynthesis suppression rendered RL22 SFB-susceptible; foliar geraniol application on the geraniol synthase-silenced plants restored oviposition deterrence. We infer that geraniol is RL22's SFB oviposition deterrent. The use of natural compounds like geraniol, which influence the chemical ecology of oviposition, can reduce the load of hazardous synthetic larvicides.

Assessing common bean genotypes for resistance to Diabrotica speciosa (Coleoptera: Chrysomelidae).

Diabrotica speciosa (Germar) (Coleoptera: Chrysomelidae) is a major pest of common bean (Phaseolus vulgaris L.; Fabales: Fabaceae), and adults can defoliate plants during the whole crop cycle. This study was conducted to evaluate the resistance to D. speciosa in 16 common bean genotypes (14 landraces and 2 cultivars), through three different experiments. In the laboratory, choice and no-choice feeding tests were performed to evaluate the percentage of leaf consumption. In the greenhouse, plant height, numbers of leaves, percentage of injured leaves, percentage of injury per leaf, weight of seeds, and D. speciosa survival were evaluated. Furthermore, trichome density, levels of peroxidase (POD), superoxide dismutase (SOD), and protein content in common bean leaves were assessed. In the laboratory, the genotypes Chumbinho Branco, Dobalde, Manteigado, IPR Tuiuiú, and 90D Mouro were the least consumed by D. speciosa. In the greenhouse, the genotypes Dobalde, Manteigado, and IPR Tuiuiú expressed tolerance to the pest, which was associated with a higher plant height and/or unchanged POD and SOD levels and protein content following insect feeding, and no reduction in seed production. The landrace 90D Mouro exhibited antixenosis and tolerance to D. speciosa, observed as a lower leaf injury, higher trichome density, lower protein contents, higher SOD level and no reduction in seed weight. Overall, we have shown that antixenosis and tolerance can help overcome damages resulting from D. speciosa feeding, with emphasis on four common bean genotypes that may be useful in plant breeding programs aimed at controlling D. speciosa in common bean crops.

Induction of resistance, enzyme activity, and phytochemicals in canola plants treated with abscisic acid elevated based on nutrient availability: a case study on Brevicoryne brassicae L. (Hemiptera: Aphididae).

The cabbage aphid, Brevicoryne brassicae L. (Hemiptera: Aphididae), is one of the important pests of cruciferous plants throughout the world including Iran. In the present study, we grew cultivated canola plants under different fertilizers or distilled water and sprayed them with 100 µM abscisic acid (ABA) or a control solution (NaOH dissolved in water) to study (i) the antibiosis parameters of B. brassicae on these plants; (ii) the antixenosis of B. brassicae adults on these plants; (iii) the plant's peroxidase (POD), polyphenol oxidase (PPO), and phenylalanine ammonia-lyase (PAL) activity; and (iv) the plant's total phenolic and glucosinolate content. The results of antibiosis experiments showed that ABA and fertilizers have a profound and negative effect on the performance of B. brassicae. In the antixenosis experiment, control plants attracted a significantly higher number of adult females in comparison to treated plants. Also, B. brassicae had lower performance and preference when they were reared on the ABA-treated fertilized plants with higher levels of phenolic and glucosinolate content. These results prompted us to hypothesize that fertilizers enable canola plants to trigger a higher level of secondary metabolites. Our findings reveal that the type and level of nutrient availability may have different impacts on how the plant regulates its defense mechanisms.

The Identification of a Quantative Trait Loci-Allele System of Antixenosis against the Common Cutworm (Spodoptera litura Fabricius) at the Seedling Stage in the Chinese Soybean Landrace Population.

Common cutworm (CCW) is an omnivorous insect causing severe yield losses in soybean crops. The seedling-stage mini-tray identification system with the damaged leaf percentage (DLP) as an indicator was used to evaluate antixenosis against CCW in the Chinese soybean landrace population (CSLRP) under three environments. Using the innovative restricted two-stage multi-locus genome-wide association study procedure (RTM-GWAS), 86 DLP QTLs with 243 alleles (2-11/QTL) were identified, including 66 main-effect loci with 203 alleles and 57 QTL-environment interaction loci with 172 alleles. Among the main-effect loci, 12 large-contribution loci (R2 ≥ 1%) explained 25.45% of the phenotypic variation (PV), and 54 small-contribution loci (R2 < 1%) explained 16.55% of the PV. This indicates that the CSLRP can be characterized with a DLP QTL-allele system complex that has not been found before, except for a few individual QTLs without alleles involved. From the DLP QTL-allele matrix, the recombination potentials expressed in the 25th percentile of the DLP of all possible crosses were predicted to be reduced by 41.5% as the maximum improvement and 14.2% as the maximum transgression, indicating great breeding potential in the antixenosis of the CSLRP. From the QTLs, 62 candidate genes were annotated, which were involved in eight biological function categories as a gene network of the DLP. Changing from susceptible to moderate plus resistant varieties in the CSLRP, 26 QTLs had 32 alleles involved, in which 19 genes were annotated from 25 QTL-alleles, including eight increased negative alleles on seven loci and 11 decreased positive alleles on 11 loci, showing the major genetic constitution changes for the antixenosis enhancement at the seedling stage in the CSLRP.

The Bph45 Gene Confers Resistance against Brown Planthopper in Rice by Reducing the Production of Limonene.

Brown planthopper (BPH), a monophagous phloem feeder, consumes a large amount of photoassimilates in rice and causes wilting. A near-isogenic line 'TNG71-Bph45' was developed from the Oryza sativa japonica variety 'Tainung 71 (TNG71) carrying a dominant BPH-resistance locus derived from Oryza nivara (IRGC 102165) near the centromere of chromosome 4. We compared the NIL (TNG71-Bph45) and the recurrent parent to explore how the Bph45 gene confers BPH resistance. We found that TNG71-Bph45 is less attractive to BPH at least partially because it produces less limonene. Chiral analysis revealed that the major form of limonene in both rice lines was the L-form. However, both L- and D-limonene attracted BPH when applied exogenously to TNG71-Bph45 rice. The transcript amounts of limonene synthase were significantly higher in TNG71 than in TNG71-Bph45 and were induced by BPH infestation only in the former. Introgression of the Bph45 gene into another japonica variety, Tainan 11, also resulted in a low limonene content. Moreover, several dominantly acting BPH resistance genes introduced into the BPH-sensitive IR24 line compromised its limonene-producing ability and concurrently decreased its attractiveness to BPH. These observations suggest that reducing limonene production may be a common resistance strategy against BPH in rice.

Induction of resistance against Brevicoryne brassicae by Pseudomonas putida and salicylic acid in canola.

The cabbage aphid, Brevicoryne brassicae L. (Hem: Aphididae), is one of the most serious pests of canola worldwide. In this research, the effects of Pseudomonas putida, salicylic acid (SA), and integrated application of both inducers were studied on the resistance of canola to B. brassicae. In free-choice situation, the number of B. brassicae attracted on canola plants under treatments containing P. putida and SA was significantly lower compared to control plants. In the life table study, pre-adult survival, longevity, reproductive period, and fecundity of this aphid were lowest on plants treated with P. putida + SA. The net reproductive rate (R0), intrinsic rate of population increase (r), and finite rate of increase (λ) of B. brassicae decreased significantly in the following order: control (47.19 offspring, 0.293 and 1.340 day-1), P. putida (16.7 offspring, 0.238 and 1.269 day-1), SA (6.37 offspring, 0.163 and 1.178 day-1), and P. putida + SA (3.24 offspring, 0.112 and 1.119 day-1). Moreover, the beneficial effect of the integrated application of P. putida and SA on plant growth parameters was significantly evident in our study. The highest values of glucosinolates, total phenol, and flavonoids were recorded in P. putida + SA treatment. We concluded that canola plants treated with P. putida + SA are more resistant to the cabbage aphid. These findings demonstrated that SA integrated with P. putida on canola plants act effectively for reducing the population of B. brassicae and can be used in integrated management programs of this pest.

A Genome-Wide View of Transcriptional Responses during Aphis glycines Infestation in Soybean.

Soybean aphid (Aphis glycines Matsumura) is one of the major limiting factors in soybean production. The mechanism of aphid resistance in soybean remains enigmatic as little information is available about the different mechanisms of antibiosis and antixenosis. Here, we used genome-wide gene expression profiling of aphid susceptible, antibiotic, and antixenotic genotypes to investigate the underlying aphid-plant interaction mechanisms. The high expression correlation between infested and non-infested genotypes indicated that the response to aphid was controlled by a small subset of genes. Plant response to aphid infestation was faster in antibiotic genotype and the interaction in antixenotic genotype was moderation. The expression patterns of transcription factor genes in susceptible and antixenotic genotypes clustered together and were distant from those of antibiotic genotypes. Among them APETALA 2/ethylene response factors (AP2/ERF), v-myb avian myeloblastosis viral oncogene homolog (MYB), and the transcription factor contained conserved WRKYGQK domain (WRKY) were proposed to play dominant roles. The jasmonic acid-responsive pathway was dominant in aphid-soybean interaction, and salicylic acid pathway played an important role in antibiotic genotype. Callose deposition was more rapid and efficient in antibiotic genotype, while reactive oxygen species were not involved in the response to aphid attack in resistant genotypes. Our study helps to uncover important genes associated with aphid-attack response in soybean genotypes expressing antibiosis and antixenosis.

Silicon-mediated and constitutive resistance to Rhopalosiphum maidis (Hemiptera: Aphididae) in corn hybrids.

The corn leaf aphid, Rhopalosiphum maidis (Fitch) (Hemiptera: Aphididae), is an important pest of corn, but no corn genotypes resistant to R. maidis are commercially available. Although the ability of silicon to induce plant resistance against some insects is known, the effect of silicon on R. maidis and in corn hybrids with different levels of constitutive resistance is still unknown. This study sought to determine the constitutive resistance of corn hybrids to R. maidis and silicon resistance induction in hybrids with different degrees of constitutive resistance. Field experiments with natural infestations of aphids were conducted in three locations in Brazil (Patos de Minas, Araguari, and Tupaciguara). Greenhouse trials were also used to evaluate the effect of varietal resistance on aphid population growth and identify resistant and susceptible genotypes. Aphid resistance induced by silicon was determined with resistant and susceptible corn hybrids. In the field, the corn hybrids BM8850, AS1625PRO, and DKB310PRO had the greatest proportion of plants infested by R. maidis in all three localities. The hybrids P30F53H, STATUS VIP, BM9288, DAS2B587HX, DKB175PRO, AS1633PRO, and DKB390PRO2 were the least infested in Patos de Minas and Araguari, and P30F53H was the least infested in Tupaciguara. When antibiosis effects were evaluated by aphid population growth, the hybrids AG7088PRO3 and DKB310PRO2 were susceptible, while P30F53YH was resistant. When natural aphid infestation was evaluated, wherein the effects of antibiosis and non-preference could not be discriminated, soil applications of silicon-induced resistance to R. maidis in both susceptible and constitutively resistant corn hybrids.

Evaluation of the resistance effect of QTLs derived from wild soybean (Glycine soja) to common cutworm (Spodoptera litura Fabricius).

Common cutworm (CCW) is a serious herbivorous insect pest of soybean. Previously, we conducted an antixenosis bioassay (measuring feeding preference) with CCW using recombinant inbred lines (RILs) derived from a cross between a wild soybean (Glycine soja) collected in Hiroshima prefecture (JP110755) and the leading cultivar, Fukuyutaka. The analysis revealed quantitative trait loci (QTLs) for antixenosis resistance, qRslx3 and qRslx4. In the present study we developed another RIL population using Fukuyutaka and a different G. soja, collected in Kumamoto prefecture (G406). An analysis revealed an antixenosis resistance QTL on chromosome 7, and the resistant allele of the QTL was derived from G406. The chromosomal position of the QTL was almost the same as that of CCW-2, a previously-reported antibiosis resistance QTL for CCW, detected in a F2 population derived from a cross between Fukuyutaka and a resistant cultivar Himeshirazu. These QTLs could be the same locus; however, G406 and Himeshirazu are likely to possess different alleles, because Himeshirazu allele exhibits no antixenosis effect. We expect that pyramiding of the resistance QTLs derived from G. soja will contribute to the development of CCW resistant cultivars.

Antixenosis and antibiosis response of common bean (Phaseolus vulgaris) to two-spotted spider mite (Tetranychus urticae).

The two-spotted spider mite, Tetranychus uticae Koch (Acari: Tetranychidae), is globally one of the most devastating pests that feed on numerous crops, including common bean (Phaseolus vulgaris L.). This study was aimed to evaluate the effects of genotype and morphological attributes of common bean on T. uticae. Forty common bean accessions were used to investigate antixenosis and antibiosis through assessing mite feeding preference and reproduction under laboratory conditions. Three resistant (i.e., 56, 63, 238) and two susceptible (i.e., 182, 236) accessions, along with cultivars Naz (resistant) and Akhtar (susceptible), were used in a life-table study. Both antixenosis and antibiosis mechanism were observed in all of the accessions, albeit a negative correlation occurred. Significant differences were observed for all traits of T. urticae: developmental time of immature stages, reproduction, adult longevity and life-table parameters. Based on the intrinsic rate of increase, the accessions 56, 63, 182, 238, and cv. Naz impose high antibiotic effects on T. urticae. Although significant variation existed among accessions for morphological factors, only glandular trichomes correlated with mite fecundity and feeding preference.

Medicago truncatula Oleanolic-Derived Saponins Are Correlated with Caterpillar Deterrence.

Plant resistance mechanisms to insect herbivory can potentially be bred into crops as an important strategy for integrated pest management. Medicago truncatula ecotypes inoculated with the rhizobium Ensifer medicae (Sinorhizobium medica) WSM419 were screened for resistance to herbivory by caterpillars of the beet armyworm, Spodoptera exigua, through leaf and whole plant choice studies; TN1.11 and F83005.5 are identified as the least and most deterrent ecotypes, respectively. In response to caterpillar herbivory, both ecotypes mount a robust burst of plant defensive jasmonate phytohormones. Restriction of caterpillars to either of these ecotypes does not adversely affect pest performance. This argues for an antixenosis (deterrence) resistance mechanism associated with the F83005.5 ecotype. Unbiased metabolomic profiling identified strong ecotype-specific differences in metabolite profile, particularly in the content of oleanolic-derived saponins that may act as antifeedants. Compared to the more susceptible ecotype, F83005.5 has higher levels of oleanolic-type zanhic acid- and medicagenic acid-derived compounds. Together, these data support saponin-mediated deterrence as a resistance mechanism of the F83005.5 ecotype and implicates these compounds as potential antifeedants that could be used in agricultural sustainable pest management strategies.

Direct and indirect resistance of sugarcane to Diatraea saccharalis induced by jasmonic acid.

Treating plants with synthetic jasmonic acid (JA) induces a defensive response similar to herbivore attack, and is a potential strategy for integrated pest management. Despite the importance of sugarcane, its JA-induced defences have not yet been studied. We investigated the effects of JA treatment on the direct and indirect resistance of sugarcane to the key-pest and specialist herbivore Diatraea saccharalis and the generalist Spodoptera frugiperda. Indirect defences were examined by testing the attraction of Cotesia flavipes, a sugarcane-borer parasitoid, to JA-induced volatile. The results showed that JA-treated sugarcane did not affect the weight gain of the two larvae. However, in dual-choice assays, both species preferred to feed on mock rather than JA-treated plants. Leaf colorimetric analyses showed that visual cues are unlikely to be involved in larval preference, whereas results from olfactometric assays revealed that D. saccharalis preferred JA-induced over mock plant volatiles. After 48 h of treatment, JA-treated plants emitted a volatile blend attractive to C. flavipes, comprised mainly of sesquiterpenes. However, the parasitoid did not discriminate JA-treated from host-damaged plant volatiles. When the wasps were given a choice between JA-treated and JA-treated + host-damaged plants, they preferred the latter, which emitted a more complex blend, suggesting that JA treatment likely does not hamper host-finding. We concluded that JA induces the emission of volatiles that are attractive to the sugarcane borer parasitoid, as well as an antixenosis type of resistance in sugarcane against the two pests, although neither volatiles nor visual cues alone are involved in the underlying mechanism.

Susceptibility and possible resistance mechanisms in the palm species Phoenix dactylifera, Chamaerops humilis and Washingtonia filifera against Rhynchophorus ferrugineus (Olivier, 1790) (Coleoptera: Curculionidae).

Rhynchophorus ferrugineus, known as the Red Palm Weevil (RPW), is reported as a pest of up to 40 palm species. However, the susceptibility degree and the defense mechanisms of these species against this weevil are still poorly known. In Europe, the RPW is a major pest of Phoenix canariensis while other palm species, including the congeneric Phoenix dactylifera, seem to be less suitable hosts for this insect. The aim of our study was to compare the defensive response of P. dactylifera, Chamaerops humilis and Washingtonia filifera against R. ferrugineus and try to define the mechanisms of resistance that characterize these species. Bioassays were carried out to evaluate the mortality induced on RPW larvae by extracts from the leaf rachis of the studied palm species. Tests at semi-field scale were also conducted, based either on forced palm infestation, with larvae of RPW, or on natural infestation, with adult females. Rachis extracts from C. humilis and W. filifera caused 100% larval mortality after 2 days of exposure, while extracts of P. dactylifera did not impair larval survival. Independently of the effect of the leaf extracts, the weevils were unable to naturally infest the three palm species, although larval survival was high after forced infestation of the plants. We concluded that the observed lack of infestation of P. dactylifera by RPW is due to factors other than antibiosis. In W. filifera and C. humilis, although the presence of antixenosis mechanisms cannot be excluded, resistance to R. ferrugineus seems to rely on the presence of antibiosis compounds.

A scarab beetle (Coleoptera: Scarabaeidae) causes tree mortality, delayed growth, and yield reduction in cacao with genotype-specific susceptibility to herbivory.

BACKGROUND: This study explored the impact of Leucothyreus femoratus, a previously unreported folivorous pest in cacao cultivation, on cacao tree survival, development, and yield. The study was conducted in an experimental cacao plot in the Colombian plains, it featured 20 cacao genotypes in an agroforestry system, with plantain and Mexican sunflower providing temporary shade, and yopo offering permanent shade. RESULTS: We found an infestation rate of 2.9 ± 0.3 adult beetles per cacao tree. L. femoratus larvae were discovered in association with the roots of all plants within the agroforestry arrangement; however, yopo and plantain exhibited the highest incidence of root-feeding larvae among these associated plants. Interestingly, male and female L. femoratus displayed distinct leaf consumption patterns in the laboratory, with females consuming more foliage relative to their body weight. Moreover, field observations highlighted the detrimental impact of L. femoratus herbivory on cacao tree survival and growth, leading to leaf skeletonization, reduced plant height, and stem diameter. Trees with over 50% leaf consumption suffered more than 20% mortality. Additionally, herbivory negatively affected cacao yield, correlating higher leaf surface damage with a decrease in harvested pods. The study also identified varying antixenotic resistance in different cacao genotypes, with some consistently displaying resistance while others showed variable levels during tree establishment and production stages. CONCLUSION: This research underscores the significant role of L. femoratus as a cacao pest, emphasizing its adverse effects on cacao tree survival, development, and yield. Consequently, implementing effective control measures is vital for ensuring sustainable cacao cultivation. © 2023 Society of Chemical Industry.

Role of eggplant trichome in whitefly oviposition and its relevance to biological control under greenhouse conditions.

The combined release of the predatory mite Amblyseius swirskii (Athias-Henriot) and the mirid Nesidiocoris tenuis (Reuter) provides effective biological control of the tobacco whitefly (Bemisia tabaci (Gennadius)) in greenhouse eggplant. However, knowing how plants' trichomes affect pest-predator interactions could improve whitefly management. Here, the effect of two varieties with either the presence or absence of trichomes was assessed on naturally occurring whitefly populations and predator abundance in a first experiment under field conditions. Predator-prey models were developed to assess the effect of trichomes on pest and predator population dynamics under field conditions. In a second semi-field experiment, the occurrence and oviposition preferences of B. tabaci and A. swirskii in the same eggplant varieties were compared. Significantly higher numbers of whitefly and mite, adults and eggs, were found on the hairy variety in both experiments. However, no differences were found in N. tenuis abundance between varieties under field conditions. Predator-prey models showed that whitefly growth rate increased in the hairy variety. N. tenuis and A. swirskii showed different fitness parameters according to the variety, with the former displaying better performance in the hairless variety and the latter in the hairy variety. Both predators effectively controlled the increase in whitefly populations in both varieties. Overall, the findings suggest that the hairless variety is more effective in deterring whiteflies. Additionally, the higher population of A. swirskii on the hairy variety indicates that this predator benefited from both the presence of trichomes and the prey.

Characterisation of aphid antixenosis in aphid-resistant ancestor wheat, Triticum monococcum.

BACKGROUND: Due to the increasing presence of insecticide resistance across cereal aphid populations, new aphid management strategies, including the engineering of host resistance to aphids into commercial wheat varieties, are required. Previous studies have identified ancestor wheat, Triticum monococcum accessions MDR045 and MDR049, with resistance against the grain aphid, Sitobion avenae. To test the hypothesis that resistance can be accounted for by antixenosis (reduced attractiveness of host plants) via the release of repellent volatile organic compounds (VOCs), we explored the response of S. avenae to MDR045 and MDR049 following S. avenae herbivory, using behaviour and electrophysiology experiments. RESULTS: In four-arm olfactometry assays, alate S. avenae showed aphid density-dependent reduced preference to VOC extracts from T. monococcum MDR045 and MDR049. By contrast, alate S. avenae showed aphid density-dependent increased preference to extracts from aphid-susceptible hexaploid wheat, Triticum aestivum var. Solstice and T. monococcum MDR037. Coupled gas chromatography-electroantennography (GC-EAG), using the antennae of alate S. avenae, located 24 electrophysiologically active compounds across all tested accessions. Synthetic blends created from 21 identified EAG-active compounds confirmed bioactivity of corresponding VOC extracts in four-arm olfactometry assays against alate S. avenae. CONCLUSION: Our data suggest that resistance of T. monococcum MDR045 and MDR049 to S. avenae can be at least partially accounted for by antixenosis through antennal perception of specific repellent VOC blends induced by S. avenae feeding behaviour. © 2024 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Characterization and genetic dissection of resistance to spotted alfalfa aphid (Therioaphis trifolii) in Medicago truncatula.

Aphids cause significant yield losses in agricultural crops worldwide. Medicago truncatula, a model legume, cultivated pasture species in Australia and close relative of alfalfa (Medicago sativa), was used to study the defence response against Therioaphis trifolii f. maculate [spotted alfalfa aphid (SAA)]. Aphid performance and plant damage were compared among three accessions. A20 is highly susceptible, A17 has moderate resistance, and Jester is strongly resistant. Subsequent analyses using A17 and A20, reciprocal F1s and an A17×A20 recombinant inbred line (RIL) population revealed that this moderate resistance is phloem mediated and involves antibiosis and tolerance but not antixenosis. Electrical penetration graph analysis also identified a novel waveform termed extended potential drop, which occurred following SAA infestation of M. truncatula. Genetic dissection using the RIL population revealed three quantitative trait loci on chromosomes 3, 6, and 7 involved in distinct modes of aphid defence including antibiosis and tolerance. An antibiosis locus resides on linkage group 3 (LG3) and is derived from A17, whereas a plant tolerance and antibiosis locus resides on LG6 and is derived from A20, which exhibits strong temporary tolerance. The loci identified reside in regions harbouring classical resistance genes, and introgression of these loci in current medic cultivars may help provide durable resistance to SAA, while elucidation of their molecular mechanisms may provide valuable insight into other aphid-plant interactions.

Categories of resistance in cotton genotypes, Gossypium spp. against cotton-melon aphid, Aphis gossypii (Hemiptera: Aphididae).

Cotton-melon aphid, Aphis gossypii Glover (Hemiptera: Aphididae), is emerging as a potential threat to cotton cultivation worldwide. The resistance categories in Gossypium arboreum to A. gossypii still need to be explored. We screened 87 G. arboreum and 20 Gossypium hirsutum genotypes against aphids under natural field conditions. Twenty-six selected genotypes from these 2 species were tested under glasshouse conditions for resistance categories (antixenosis, antibiosis, and tolerance). Resistance categories were assessed by no-choice antibiosis assay, free-choice aphid settling assay, cumulative aphid days using population buildup tests, chlorophyl loss index, and damage ratings. No-choice antibiosis experiment revealed that the G. arboreum genotypes GAM156, PA785, CNA1008, DSV1202, FDX235, AKA2009-6, DAS1032, DHH05-1, GAM532, and GAM216 had a significant adverse effect on aphid development time, longevity, and fecundity. Gossypium arboreum genotypes CISA111 and AKA2008-7 expressed a low level of antixenosis but possessed antibiosis and tolerance. Aphid resistance persisted uniformly at different plant developmental stages studied. The chlorophyl loss percentage and damage rating scores were lower in G. arboreum than in G. hirsutum genotypes, indicating the existence of tolerance in G. arboreum to aphids. Logical relations analysis of resistance contributing factors depicted the presence of antixenosis, antibiosis, and tolerance in the G. arboreum genotypes PA785, CNA1008, DSV1202, and FDX235, indicating their utility for evaluating the mechanisms of resistance and aphid resistance introgression breeding into G. hirsutum to develop commercially cultivated cotton lines.