Aphid-resistant Cultivars Research Articles

Invasive sorghum aphid: A decade of research on deciphering plant resistance mechanisms and novel approaches in breeding for sorghum resistance to aphids

AbstractDuring the last decade, the sorghum aphid (Melanaphis sorghi), previously identified as sugarcane aphid (Melanaphis sacchari), became a serious pest of sorghum, spreading to all sorghum‐producing regions in the United States, Mexico, and South America, where crop losses of 50%–100% have been reported. Developing sorghum cultivars with resistance to this insect is the most sustainable strategy for long‐term pest management. To design cultivars with aphid resistance, comprehensively understanding the mechanisms underlying aphid survival, host plant resistance, and aphid–sorghum interactions is critical. In this review, we summarize the comprehensive efforts to characterize the aphid populations as well as their interaction with sorghum plants via hormonal pathways that trigger various genes including leucine rich repeats, WRKY transcription factors, lipoxygenases, calmodulins, and others. We discuss efforts made during the last decade to identify specific genomic regions and candidate genes that confer aphid resistance, as well as describe recent successes and potential challenges in breeding for aphid resistance. Furthermore, we discuss the use of disruptive technologies like high‐throughput phenotyping, artificial intelligence, or machine learning for developing aphid resistant sorghum cultivars. Integration of these new technologies has the potential to accelerate the development and design of novel traits that confer durable aphid resistance in new sorghum cultivars to defend sorghum against new aphid genotype development.

Aphid-resistant alfalfa cultivar minimizes the survival of spotted alfalfa aphid through upregulating plant defense compounds

The spotted alfalfa aphid, Therioaphis trifolii, is one of the most important pests of alfalfa, Medicago sativa. Previous studies have revealed a significant difference in aphid numbers between the aphid-susceptible cultivar WL343 and the aphid-resistant cultivar Zhongmu No.1. To explore the reasons for this phenomenon, we constructed life tables for T. trifolii reared on these two alfalfa cultivars, and analyzed the changes in jasmonic acid (JA), salicylic acid (SA), secondary metabolites (total phenolic compounds, tannic acid, total flavonoids, and saponin), the activities of catalase (CAT), superoxide dismutase (SOD), and peroxidase (POD) in both cultivars following the introduction of aphids. In addition, we measured the gastric toxicity of M. sativa secondary metabolites (tannic acid and saponin) against T. trifolii. Results revealed a lower fitness of T. trifolii on the resistant cultivar compared to the susceptible cultivar. The concentrations of JA, phenolic compounds, tannic acid, flavonoids, saponin, and the activities of CAT, SOD, and POD in the resistant cultivar were significantly higher than those in the susceptible cultivar. Subsequently, it was confirmed that tannic acid and saponin have direct gastric toxicity against T. trifolii. This indicated that the aphid-resistant cultivar inhibited aphid growth and fecundity by producing more defense substances, i.e., JA, secondary metabolites, and enhanced activities of protective enzymes including tannic acid and saponin found in alfalfa leaves directly associated with toxicity to T. trifolii, while reducing the content of SA. This study provides important support for breeding insect-resistant varieties while elucidating plant-resistant responses to insect herbivory.

Comprehensive Assessment of Aphid (Lipaphis erysimi (Kalt.) Resistance in Mustard Cultivars

The study focuses on mustard (Brassica spp.) crops, crucial rabi oilseed crops in India. This study aimed to assess the susceptibility of 45 mustard crop cultivars to Lipaphis erysimi Kaltenbach, commonly known as the mustard aphid, a significant biotic stressor affecting Indian mustard (Brassica juncea). The necessity of this study lies in the importance of identifying aphid-resistant cultivars to enhance pest management strategies and improve mustard crop yields. Field experiments were conducted at Jawaharlal Nehru Krishi Vishwavidyalaya in Jabalpur, Madhya Pradesh, India during the rabi season, using a Randomized Block Design. The study utilized a mean aphid index-based scoring scheme to categorize the cultivars into different susceptibility levels, ranging from highly resistant to highly susceptible. The classification was determined based on normal distribution values, including highly resistant (HR), resistant (R), moderately resistant (MR), moderately susceptible (MS), susceptible (S), and highly susceptible (HS). The results revealed that none of the cultivars fell into the highly resistant category, but five cultivars demonstrated resistance, with mean aphid index values below 0.34. Thirty cultivars were classified as moderately resistant, displaying mean aphid index values between 0.34 and 0.66. Six cultivars exhibited moderate susceptibility (mean aphid index between 0.66 and 0.82), while four cultivars were categorized as susceptible (mean aphid index between 0.82 and 0.98). Notably, none of the cultivars were highly susceptible. The study underscores the importance of identifying aphid-resistant cultivars to enhance pest management strategies and improve mustard crop yields. The results provide valuable insights into the susceptibility levels of different cultivars, guiding farmers in selecting appropriate varieties for cultivation. The research also emphasizes the significance of environmentally friendly pest management options, considering the potential risks associated with pesticide use. Overall, this study contributes to the development of sustainable Integrated Pest Management (IPM) techniques for Indian mustard cultivation.

Feeding behavior and life-history parameters of Therioaphis trifolii (Hemiptera: Aphididae) on 2 alfalfa cultivars.

Alfalfa, Medicago sativa, is a link connecting crop production and animal husbandry and plays a dominant role in the development of the livestock sector. The productivity of alfalfa is adversely affected by aphids' feeding damage and their capacity to transmit viral plant pathogens. To increase alfalfa forage yield, it is imperative to control pest insects and use resistant varieties. The aim of this study was to identify the mechanism of M. sativa resistance to aphids by examining changes in the physiology, feeding behavior, and life history of the pests. The leaves of Gannong No. 5 (HA-3, aphid-resistant cultivar) had denser, longer trichome and thicker cortical parenchyma cell, and greater xylem thicknesses than those of Hunter River (Hu, aphid-susceptible cultivar). Nonprobing behaviors suggested that the spotted alfalfa aphid, Therioaphis trifolii, became more active in searching for suitable feeding sites on HA-3 than on Hu plants. Additionally, T. trifolii showed shorter durations for salivating into sieve elements and ingesting phloem sap on HA-3 plants. Life-table analysis showed that T. trifolii on HA-3 had longer developmental duration, higher mortality rate, and lower fecundity, net reproductive rate, intrinsic rate of increase, finite rate of increase and gross reproduction rate values than that on Hu plants. Moreover, relative fitness was significantly reduced in T. trifolii on HA-3 plants. The results of this study provided a basis for developing better control strategies for T. trifolii and studying the mechanisms of alfalfa resistance to aphids.

Evaluation of promising safflower accessions/breeding lines toaphid, Uroleucon compositae

Identification of stable resistant sources for aphids is essential for development of aphid resistant safflower cultivars. Among the different lines evaluated, a high oleic acid line, BC2-F6-38-9-4-OL was found consistently tolerant to aphid. Another nine accessions were confirmed moderately tolerant.

Markers of resistance to pea aphid, Acyrthosiphon pisum Harris in Pisum sativum L. accessions

One of the major insect pests in Pisum sativum L. (is Acyrthosiphon pisum Harris (Hemiptera: pests in Pisum sativum L. (Hemiptera: Aphididae) is Acyrthosiphon pisum Harris (Hemiptera: Aphididae). An effective strategy for aphid control is the resistant host plant use. The current study aimed to identify resistance mechanisms and assess biochemical and morphological markers of pea aphid resistance in pea accessions. Meteorological variables affected the pea aphid density, which positively correlated with temperature, while precipitation amount and humidity negatively impacted. The aphid number was significantly and positively associated with the leaf area and the nitrogen content but negatively correlated with calcium and phosphorus levels. The pea aphid-resistant cultivars L 123-7-11, L 128-1and L 125-5 had small leaf areas, and high phosphorus and calcium content but a low nitrogen level. In the mutual influence of the plant indicators, phosphorus concentration had the highest negative impact on pea aphid density, followed by calcium. The plant marker inclusion in the pea breeding process is an efficient tool for a substantial selection program improvement for aphid resistance. Therefore, resistant host plants are essential tools promoting considerable selection program improvement for aphid resistance in the P. sativum breeding process and helping develop sustainable and environmentally friendly agriculture.

Aphids on Aphid-Susceptible Cultivars Have Easy Access to Turnip Mosaic Virus, and Effective Inoculation on Aphid-Resistant Cultivars of Oilseed Rape (Brassica napus).

Plant viruses improve transmission efficiency by directly and indirectly influencing vector behavior, but the impact of plant cultivars on these modifications is rarely studied. Using electropenetrography (EPG) technology, a comparative study of the effects of turnip mosaic virus (TuMV) infection on quantitative probing behaviors of the cabbage aphid (Brevicoryne brassicae) was conducted on two oilseed rape cultivars ('Deleyou6' and 'Zhongshuang11'). Compared to mock-inoculated plants, cabbage aphids on infected plants increased the frequency of brief probing, cell penetration, and salivation. Additionally, aphids on infected 'Deleyou6' prolonged cell penetration time and decreased ingestion, but not on infected 'Zhongshuang11', suggesting that aphids were more likely to acquire and vector TuMV on the aphid-susceptible cultivar 'Deleyou6' than on resistant cultivars. TuMV also affected aphid probing behavior directly. Viruliferous aphids reduced the pathway duration, secreted more saliva, and ingested less sap than non-viruliferous aphids. In comparison with non-viruliferous aphids, viruliferous aphids started the first probe earlier and increased brief probing and cell penetration frequencies on the aphid-resistant cultivar 'Zhongshuang11'. Based on these observations, viruliferous aphids can be inoculated with TuMV more efficiently on 'Zhongshuang11' than on 'Deleyou6'. Although aphid resistance and TuMV infection may influence aphid probing behavior, oilseed rape resistance to aphids does not impede TuMV transmission effectively.

Metabolite profile variation of chili pepper genotypes for resistance to aphids infestation

The cotton aphids (CA) were reported to reduce chili pepper production in tropical area and transmits several viruses. Using resistant cultivars can reduce the number of insecticide sprays and maintain natural enemies. The research objective was to evaluate aphid infestation in seven chili pepper genotypes and investigate secondary metabolite profiles under aphid infestation. Seven chili pepper genotypes belonging to the species Capsicum annuum L. were used in this study. The experiment was conducted using a four-replication randomized complete block design. We used a no-choice clip cage test to evaluate the chili pepper genotype. The evaluation was carried out under greenhouse conditions. Each plant was infested with one aphid using a wet brush in an insect-proof cage about five weeks after sowing. The resistance level was determined after seven days of infection (7 DAI) by counting the number of aphids. Gas chromatography-mass spectrophotometry (GC-MS) was used to perform untargeted metabolomic studies. The results showed that IPB C20 and IPB C367 genotypes had low aphid infestation, while IPB C313 showed the highest aphid infestation. Untargeted metabolomics using GC-MS detected 16 metabolites in the control plant and 27 in the treatment. Principal component analysis (PCA) (PC1 = 62% and PC2 = 23%) can used to differentiate metabolites among resistant genotypes, susceptible genotypes, and control plants. Chili pepper resistance to aphid infestation was antibiosis with numerous potential metabolite chemicals, such as fluorobenzoic acid, which strongly connected with decreased aphid colonies at 7 DAI. This study will be useful for pest control and will aid in the developing of aphid-resistant cultivars.

The Efficacy of Biological Control for the Suppression of the Pea Aphid (Acyrthosiphon Pisum): Does the Resistance of Alfalfa Cultivars Matter?

The pea aphid, Acyrthosiphon pisum Harris, is a major pest of alfalfa in northwestern China. However, the roles of different groups of natural enemies in combination with aphid-resistant cultivars in the suppression of the pea aphid have not been clarified under field conditions. In this study, we used experimental cages to better understand the top-down (natural enemies) and bottom-up (nine alfalfa cultivars) biological processes, as well as the individual roles of the two processes, in the control of the pea aphid. There was a significant difference in resistance among cultivar classes revealed when natural enemies were excluded. The functional contribution of top-down suppression was higher than the bottom-up process, with natural enemies significantly suppressing aphid populations, regardless of the resistance level of different alfalfa cultivars. The mean biological efficacies of predators, parasitoids, and mixed populations of natural enemies were 85%, 42%, and 88%, respectively. Overall, our study indicated that natural enemies play a critical role in suppressing aphid populations, especially in the summer, whereas cultivar resistance did not combine effectively with natural enemies to inhibit the growth of aphids. Conservation biological control (CBC) can be implemented in the alfalfa production regions in northwestern China to reduce the overreliance on insecticides for the control of pests and mitigate their harmful effects on humans, ecosystems, and biodiversity.

Transcriptomic profiling of cotton leaves in response to cotton aphid damage

Cotton aphid (Aphis gossypii Glover) is regarded as one of the most harmful insect pests for cotton production. They are usually capable of causing severe yield loss through sucking plant sap, secreting honeydew and transmitting plant viral diseases. However, the molecular mechanism of the interaction between cotton and cotton aphids remains unclear currently. Therefore, the RNA-Seq study of cotton leaves was performed in response to cotton aphid damage at different time points (0 h, 6 h, 12 h, 24 h, 48 h and 72 h). A total of 9, 103 new genes were identified, and 7, 510 of them were annotated functionally. Based on the comparison results, the gene expression was analyzed according to the expression amount of genes in different samples. 24,793 differentially expressed genes (DEGs) were authenticated in all and their functional annotation and enrichment analysis were conducted. Compared with 0 h (without aphid damage, CK), the amount of down-regulated DEGs was largely more than that of the up-regulated DEGs at different time points under cotton aphid attack except for 48 h. As revealed by the functional annotation of DEGs, these genes are involved in all kinds of plant biological processes, including various resistance to abiotic and biotic stress, hormone metabolism, signaling transduction and transcriptional regulation. The results revealed the molecular mechanism of the interaction between cotton and cotton aphids and would facilitate the development of plant aphid-resistant cultivars.

Investigation of Metabolic Resistance to Soybean Aphid (Aphis glycines Matsumura) Feeding in Soybean Cultivars.

Simple SummaryThis project examined the interaction between soybean aphids and Ontario-grown soybean cultivars to determine which leaf metabolites were most associated with aphid resistance. Tolerance and resistance were determined by measuring the growth and reproduction of aphids and leaf feeding damage over 10-day and 4-week infestation periods. Chromatographic techniques were used for the analysis of legume-specific plant natural products and isoflavonoids, and high-resolution mass spectrometry was used for the identification of free amino acids in aphid-resistant, tolerant, and susceptible soybean cultivars. There was a low correlation between isoflavonoid leaf concentrations and aphid resistance in the soybean varieties studied; however, the aphid-resistant cultivars were determined to have lower free amino acid concentrations, indicating that lower nutrient quality could be responsible for the resistance observed. Identifying these cultivars is important for managing aphid populations and provides an additional tool for soybean integrated pest management.Soybean aphid (Aphis glycines) is a major soybean (Glycine max) herbivore pest in many soybean growing regions. High numbers of aphids on soybean can cause severe reductions in yield. The management of soybean aphids includes monitoring, insecticide applications when required, and the use of resistant cultivars. Soybean aphid-resistant soybean varieties are associated with genes that confer one or more categories of resistance to soybean aphids, including antibiosis (affects survival, growth, and fecundity), antixenosis (affects behaviour such as feeding), and tolerance (plant can withstand greater damage without economic loss). The genetic resistance of soybean to several herbivores has been associated with isoflavonoid phytoalexins; however, this correlation has not been observed in soybean varieties commonly grown in southern Ontario, Canada. Isoflavonoids in the leaves of 18 cultivars in the early growth stage were analyzed by HPLC and the concentration by fresh weight was used to rate the potential resistance to aphids. Greenhouse and growth cabinet trials determined that the cultivars with greater resistance to aphids were Harosoy 63 and OAC Avatar. The most susceptible cultivar was Maple Arrow, whereas Pagoda and Conrad were more tolerant to aphid feeding damage. Overall, there was a low correlation between the number of aphids per leaf, feeding damage, and leaf isoflavonoid levels. Metabolite profiling by high-resolution LC-MS determined that the most resistant cultivar had on average lower levels of certain free amino acids (Met, Tyr, and His) relative to the most susceptible cultivar. This suggests that within the tested cultivars, nutritional quality stimulates aphid feeding more than isoflavonoids negatively affect aphid feeding or growth. These findings provide a better understanding of soybean host plant resistance and suggest ways to improve soybean resistance to aphid feeding through the breeding or metabolic engineering of leaf metabolites.

A major-effect genetic locus, ApRVII, controlling resistance against both adapted and non-adapted aphid biotypes in pea.

A genome-wide association study for pea resistance against a pea-adapted biotype and a non-adapted biotype of the aphid, Acyrthosiphon pisum, identified a genomic region conferring resistance to both biotypes. In a context of reduced insecticide use, the development of cultivars resistant to insect pests is crucial for an integrated pest management. Pea (Pisum sativum) is a crop of major importance among cultivated legumes, for the supply of dietary proteins and nitrogen in low-input cropping systems. However, yields of the pea crop have become unstable due to plant parasites. The pea aphid (Acyrthosiphon pisum) is an insect pest species forming a complex of biotypes, each one adapted to feed on one or a few related legume species. This study aimed to identify resistance to A. pisum and the underlying genetic determinism by examining a collection of 240 pea genotypes. The collection was screened against a pea-adapted biotype and a non-adapted biotype of A. pisum to characterize their resistant phenotype. Partial resistance was observed in some pea genotypes exposed to the pea-adapted biotype. Many pea genotypes were completely resistant to non-adapted biotype, but some exhibited partial susceptibility. A genome-wide association study, using pea exome-capture sequencing data, enabled the identification of the major-effect quantitative trait locus ApRVII on the chromosome 7. ApRVII includes linkage disequilibrium blocks significantly associated with resistance to one or both of the two aphid biotypes studied. Finally, we identified candidate genes underlying ApRVII that are potentially involved in plant-aphid interactions and marker haplotypes linked with aphid resistance. This study sets the ground for the functional characterization of molecular pathways involved in pea defence to the aphids but also is a step forward for breeding aphid-resistant cultivars.

Chili pepper genotypes assay approach for resistance to Aphis gossypii (Hemiptera: Aphididae)

The cotton aphid (Aphis gossypii), is one of the most devastating insect pests for chili pepper that damages the crop and transmits several viruses. Thus far, there is no commercial chili cultivar with effective resistance to cotton aphids (CA). The present study aimed to develop a reliable and practical screening protocol in chili peppers for aphids resistance in the tropical areas. Three no-choice test methods i.e., seedling cage, detached leaf, and clip cage tests have been developed. The experiment was conducted in a randomized complete block design (RCBD) with four replications in a greenhouse at the Gunung Putri, Bogor, West Java, Indonesia. Seven chili pepper genotypes belong to the species Capsicum annuum L. provided by the Department of Agronomy and Horticulture, IPB University, Bogor, Indonesia were used in this study. Chili pepper resistance to aphids was observed through the number of aphids progeny, and aphids fecundity among the genotypes. Two chili genotypes consistently showed low infestation while other genotypes showed the highest infestation with three screening methods. All the methods have a high heritability value (90%–91%), indicating that the evaluated chili genotypes could be used to determine effective screening methods. The correlation between the detached leaf and clip cage tests was significant (r = 0.84, P ≤ 0.05). Therefore, the clip cage test could be used as a reliable and practical screening test for the assay of chili peppers resistance to CA infestation. These information will be helpful in the development of aphid resistant cultivars in the future.

The Source of Rag5-Mediated Resistance to Soybean Aphids Is Located in the Stem.

The soybean aphid (Aphis glycines) continues to threaten soybean production in the United States. A suite of management strategies, such as planting aphid-resistant cultivars, has been successful in controlling soybean aphids. Several Rag genes (resistance against A. glycines) have been identified, and two are currently being deployed in commercial soybean cultivars. However, the mechanisms underlying Rag-mediated resistance are yet to be identified. In this study, we sought to determine the nature of resistance conferred by the Rag5 gene using behavioral, molecular biology, physiological, and biochemical approaches. We confirmed previous findings that plants carrying the Rag5 gene were resistant to soybean aphids in whole plant assays, and this resistance was absent in detached leaf assays. Analysis of aphid feeding behaviors using the electrical penetration graph technique on whole plants and detached leaves did not reveal differences between the Rag5 plants and Williams 82, a susceptible cultivar. In reciprocal grafting experiments, aphid populations were lower in the Rag5/rag5 (Scion/Root stock) chimera, suggesting that Rag5-mediated resistance is derived from the shoots. Further evidence for the role of stems comes from poor aphid performance in detached stem plus leaf assays. Gene expression analysis revealed that biosynthesis of the isoflavone kaempferol is upregulated in both leaves and stems in resistant Rag5 plants. Moreover, supplementing with kaempferol restored resistance in detached stems of plants carrying Rag5. This study demonstrates for the first time that Rag5-mediated resistance against soybean aphids is likely derived from stems.

Volatiles inheriting from Crossostephium chinense act as repellent weapons against aphids in Chrysanthemum lavandulifolium cultivars

Chrysanthemum lavandulifolium is a kind of medicinal plant with large industrial scale and widely cultivated in southern China. Chrysanthemum aphids (Macrosiphoniella sanborni) seriously restricted the development of C. lavandulifolium industry. In this study, in order to breed aphid resistant cultivars, we introduced a potential aphid resistant germplasm Crossostephium chinense to participate in breeding, and the role of volatiles in this process was analyzed. Nine true hybrids were obtained by distant hybridization combined with embryo rescue. The aphid resistance and behavioral effects of their volatiles on aphids were tested. All hybrids behaved stronger resistance and repellency than C. lavandulifolium. The repellency of H1, H2 and H11 was significantly higher than other hybrids. Forty-seven major volatiles were detected in the parent and hybrid leaves by using solid phase micro extraction-gas chromatography-mass spectrometry (SPME-GC–MS). H1, H2 and H11 can be separated from other plant materials by PCA analysis, 15 volatiles such as 1, 2-Oxidolinalool were identified as their characteristic difference compounds. Methacrolein was demonstrated to be a repellent compound to aphids by using standard chemical. These findings may lead to novel control strategies against M. sanborni of C. lavandulifolium and its relative species.

Susceptibility of Certain Egyptian Wheat Cultivars to Greenbug, Schizaphis graminum (Rondani) (Homoptera: Aphididae) Infestation

The greenbug (Schizaphis graminum) (Homoptera: Aphididae) is a major aphid species attacking cereal crops and responsible for viral disease transmission of the plant. Host plant resistance is a strong pillar in Integrated Pest Management (IPM) for reducing the damage of this pest. This study was carried out at Plant Protection Department, Faculty of Agriculture, Al-Azhar University, Cairo, Egypt during 2019-2020 to study the susceptibility of five Egyptian wheat cultivars (Beni Suef 5, Gimmiza 11, Giza 168, Misr 1 and Sids 12) to greenbug infestation. The results indicated that in the host preference (free choose) experiment, Sids 12 cultivar was resistant (R) against aphid, while Giza 168 and Misr 1 were moderately resistant (MR) cultivars, on contrast Beni Suef 5 and Gimmiza 11 were susceptible (S) for aphid infestation. The nymphs fed on Beni Suef 5 cultivar had significantly shorter developmental time (7.6 days), highest survival (96.1%) and shorter adult longevity (9.7 days) with average offspring 45.8 aphids/ female, than other four wheat cultivars, while nymphs reared on Sids 12 had significantly longest developmental time (9.2 days), lowest survival (86.3%) and longest adult longevity (12.2 days) with average offspring 31.4 aphids/female. Feedingof S. graminum on tested wheat cultivars leaves significantly reduces the growth parameters (shoot length, wet and dry weights) and photosynthetic pigments content. Results from this study are important for plant breeding programs that have the objective of producing aphid resistant cultivars.

Resistance among selected wild soybean and associated soybean accessions against two virulent colonies of Aphis glycines (Hemiptera: Aphididae)

The soybean aphid (Aphis glycines) is an important pest of soybean (Glycine max). Wild soybean (Glycine soja; also known as ‘soja’) has many useful traits, including some accessions with aphid resistance that may be incorporated into modern soybean cultivars. The objective of this work was to evaluate 76 selected soja accessions and 14 associated soybean accessions for resistance against two virulent colonies of soybean aphid in environmental-chamber experiments. In free-choice tests, soja accessions PI 407175, PI 407190, PI 407206, PI 407240, PI 507624 and PI 562558 were resistant against the Accrue colony, and PI 407191wf and PI 597458 C were resistant against the Volga16 colony. None of the soybean test accessions except the resistant check, PI 437696, showed resistance against either colony in free-choice tests. In no-choice tests, soja accession PI 507624 showed strong resistance against the Accrue colony; whereas PI 407240 and PI 407190 had intermediate aphid levels; PI 597458 C showed strong resistance to Volga16 aphids, and PI 407191wf had an intermediate level of resistance. Based on results from both sets of tests, soja accessions PI 507624 and PI 597458 C may be strong candidates in breeding programs to develop aphid-resistant soybean cultivars.

Stability of Sources of Resistance to Cowpea Aphid (Aphis craccivoraKoch, Hemiptera: Aphididae) across Major Cowpea Production Zones in Ghana

Aphids (Aphis craccivoraKoch) are an important vegetative stage pest of cowpea in Africa. The use of resistant cultivars is among the best management option for this pest, but the success of this strategy is influenced by the stability of the resistant genotype to the cowpea aphid biotypes present in the major cowpea growing areas in a country. This work, therefore, aimed at identifying cultivars/genotypes with stable resistance to aphid infestation across different cowpea growing ecologies in Ghana and estimating yield loss due to aphid infestation at the seedling stage. To ascertain the stability of aphid-resistant cultivars/genotypes, four cultivars/genotypes (SARC1-57-2, SARC1-91-1, IT97K-499-35, and Zaayura) and a susceptible check (Apagbaala) were tested across 18 locations in Ghana. An on-station experiment was used to quantify yield losses due to aphid attack at the seedling stage in the five cultivars/genotypes mentioned above together with 5 additional cultivars/genotypes [i.e., IT99K-573-3-2-1, IT99K-573-1-1, Padituya, Resistant BC4F3(Zaayura//(Zaayura × SARC1-57-2)), and Susceptible BC4F3(Zaayura//(Zaayura × SARC1-57-2))]. The results showed that SARC1-57-2 was stable in all ecologies, in terms of its resistance to aphids; it had high vigour score (3.8 ± 0.03) and low plant mortality (3.7 ± 0.22%) compared to the susceptible genotypes. The number of days to flowering and maturity were significantly higher in aphid-infested plants than in the uninfested ones. Grain yield loss was estimated to range between 3.8 and 32.8%. Except for SARC1-57-2, Resistant BC4F3,and Padituya, the remaining cultivars/genotypes sustained significant yield losses under aphid infestation. Thus, the aphid-resistance gene in SARC1-57-2 is stable against aphids. This resistance genotype can be incorporated into cowpea improvement programmes to breed for aphid-resistant cultivars. Also, the cultivation of such improved cultivars will reduce pesticide usage in cowpea production.

Resistance of Soybean Plant Introductions to Three Colonies of Soybean Aphid (Hemiptera: Aphididae) Biotype 4.

Soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), infestations of soybean, Glycine max (L.) Merr. (Fabales: Fabaceae), and the associated yield loss have led to a large dependence on insecticidal management in soybean throughout the Midwestern United States. However, several populations of pyrethroid-resistant soybean aphids have recently been found in Iowa, Minnesota, North Dakota and South Dakota, which highlights the importance of alternative management approaches. One such alternative method is host-plant resistance, which uses naturally occurring plant defenses in crop cultivars to reduce the potential for yield loss from a pest population. Current soybean aphid-resistant cultivars do not protect against all soybean aphids due to the presence of virulent biotypes. In particular, soybean aphid biotype 4 is virulent to Rag1 and Rag2 resistance genes both individually and in combination. However, we hypothesized that resistance to biotype 4 may exist in previously identified, but uncharacterized resistant soybean plant introductions (PIs). To test this, we evaluated 51 previously identified but uncharacterized soybean aphid-resistant PIs for their resistance to colonies of soybean aphid biotype 4 collected in separate site-years (Lomira, WI 2013; Volga, SD 2015, 2016). Free-choice tests identified 14 PIs with putative resistance to 'Lomira13', two to 'Volga15', and eight to 'Volga16' soybean aphid colonies. Follow-up, no-choice tests corroborated two to three resistant PIs per colony, and PI 437696, which was resistant to each of the three colonies and could aid in breeding efforts and an integrated approach to soybean aphid management.

New source of resistance to Aphis gossypii in Tunisian melon accessions using phenotypic and molecular marker approaches

Aphis gossypii (Glover) is one of the major pests of melon crops as well as an efficient vector of non-persistent virus such as Cucumber Mosaic Virus and Zucchini Yellow Mosaic Virus among others. Host-plant resistance is one of the best strategies that can be used to control this pest. In this study 14 Tunisian melon accessions were screened to identify new sources of resistance/tolerance to Aphis gossypii using phenotypic and molecular approaches. Antixenosis, antibiosis and tolerance tests were carried out to phenotype those accessions which were also analyzed by molecular markers linked to the Vat gene which confers resistance to both A. gossypii colonization and virus transmission. Results evidenced that only the accession TUN-7 showed antixenosis, antibiosis and tolerance (no leaf curling), at a similar level to that of the resistant control PI414723. Although plants of the accession TUN-13 did not show leaf curling either, the presence of the Vat gene was only detected in TUN-7; its fruit characteristics, of Ananas type, makes this accession as a valuable source of resistance to this aphid that can be used in breeding programs to develop new aphid resistant melon cultivars.