Molecular mapping of resistance gene to English grain aphid (Sitobion avenae F.) in Triticum durum wheat line C273

Integrated genome-wide association study and QTL mapping reveals qSa-3A associated with English grain aphid, Sitobion avenae (Fabricius) resistance in wheat

BACKGROUND

The English grain aphid, Sitobion avenae (Fabricius), is a devastating pest impacts yield and quality in wheat (Triticum aestivum L.). Breeding resistant wheat varieties and detecting resistance genes are important strategies to control aphid.

RESULTS

In this study, we evaluated the number of aphids per spike, the rate of thousand kernel weight decrease and aphid index based on three classic resistance mechanisms (antibiosis, tolerance and antixenosis), and detected SNPs/QTLs for resistance to S. avenae in a natural population of 163 varieties with 20 689 high-quality single-nucleotide polymorphism (SNP) markers and recombinant inbred line (RIL) population of 164 lines with 3627 diversity arrays technology (DArT) markers. Results showed that 83 loci significantly associated with S. avenae antibiosis and 182 loci significantly associated with S. avenae tolerance were detected by genome-wide association study (GWAS), explaining 6.47-15.82% and 8.36-35.61% of the phenotypic variances, respectively. The wsnp_Ku_c4568_8243646 detected in two periods was localized at 34.52 Mb on chromosome 3AS. Then, we confirmed a stable QSa.haust-3A.2 explained 11.19-20.10% of the phenotypic variances in two periods with S. avenae antixenosis in the physical interval of 37.49-37.50 Mb on chromosome 3A in the RIL population. Therefore, a narrow region in the physical interval of 34.52-37.50 Mb on chromosome 3AS was named as qSa-3A, which was a new locus between wsnp_Ku_c4568_8243646 and QSa.haust-3A.2 associated with S. avenae resistance.

CONCLUSION

We found qSa-3A was a new locus associated with S. avenae resistance. The results could be applied in gene cloning and genetic improvement of S. avenae resistance in wheat. © 2023 Society of Chemical Industry.

Wheat as a new host for potato aphid Macrosiphum euphorbiae Thomas (Hemiptera: Aphididae) and construction of its age-stage two-sex life tables

Wheat (Triticum aestivum L.) is the major global staple food crop that meets the food security demands of various nations across the continents. The recent reduction in wheat production is attributed to several biotic and abiotic factors especially, temperature and rainfall patterns, and pest occurrence. Among insect pests, aphid species are emerging as new pests of economic importance in India and elsewhere. The present investigation identified a new association of Macrosiphum euphorbiae Thomas with the wheat crop. Life table parameters were studied for M. euphorbiae and Rhopalosiphum padi fed on wheat foliage. The total nymphal duration and life cycle duration, respectively, of R. padi (4.76 ± 0.54 and 9.71 ± 1.38 days) and M. euphorbiae (5.84 ± 0.69 and 9.96 ± 1.31 days) were significantly different for these species. The fecundity of the two aphid species was 23.95 ± 8.67 and 11.6 ± 4.10 progeny/female, respectively. Age-specific survival rate (lx), age-specific fecundity (fx), and population age-specific fecundity (mx) were higher in R. Padi compared to M. euphorbiae. Reproductive value (Vxj) was high in R. padi and the duration of reproduction was less, while these parameters showed an opposite trend in M. euphorbiae. The gross reproduction rate (GRR) was found higher in R. Padi (29.17 offspring/adult lifetime) compared to M. euphorbiae (19.58 offspring/adult lifetime). The M. euphorbiae being a pest of solanaceous crops seems to have shifted to a new host, i.e., wheat. This new adaptation strategy to survive for long periods on a wheat crop might pose a serious threat to wheat crop cultivation in near future.

Genome-wide identification and characterization of lipoxygenase genes related to the English grain aphid infestation response in wheat

44 wheat LOX genes were identified by silico genome-wide search method. TaLOX5, 7, 10, 24, 29, 33 were specifically expressed post aphid infestation, indicating their participation in wheat-aphid interaction. In plants, LOX genes play important roles in various biological progresses including seed germination, tuber development, plant vegetative growth and most crucially in plant signal transduction, stress response and plant defense against plant diseases and insects. Although LOX genes have been characterized in many species, the importance of the LOX family in wheat has still not been well understood, hampering further improvement of wheat under stress conditions. Here, we identified 44 LOX genes (TaLOXs) in the whole wheat genome and classified into three subfamilies (9-LOXs, Type I 13-LOXs and Type II 13-LOXs) according to phylogenetic relationships. The TaLOXs belonging to the same subgroup shared similar gene structures and motif organizations. Synteny analysis demonstrated that segmental duplication events mainly contributed to the expansion of the LOX gene family in wheat. The results of protein-protein interaction network (PPI) and miRNA-TaLOXs predictions revealed that three TaLOXs (TaLOX20, 22 and 37) interacted mostly with proteins related to methyl jasmonate (MeJA) signaling pathway. The expression patterns of TaLOXs in different tissues (root, stem, leaf, spike and grain) under diverse abiotic stresses (heat, cold, drought, drought and heat combined treatment, and salt) as well as under diverse biotic stresses (powdery mildew pathogen, Fusarium graminearum and stripe rust pathogen) were systematically analyzed using RNA-seq data. We obtained aphid-responsive candidate genes by RNA-seq data of wheat after the English grain aphid infestation. Aphid-responsive candidate genes, including TaLOX5, 7, 10, 24, 29 and 33, were up-regulated in the wheat aphid-resistant genotype (Lunxuan144), while they were little expressed in the susceptible genotype (Jimai22) during late response (48 h and 72 h) to the English grain aphid infestation. Meanwhile, qRT-PCR analysis was used to validate these aphid-responsive candidate genes. The genetic divergence and diversity of all the TaLOXs in bread wheat and its relative species were investigated by available resequencing data. Finally, the 3D structure of the TaLOX proteins was predicted based on the homology modeling method. This study not only systematically investigated the characteristics and evolutionary relationships of TaLOXs, but also provided potential candidate genes in response to the English grain aphid infestation and laid the foundation to further study the regulatory roles in the English grain aphid infestation of LOX family in wheat and beyond.

Influence of Bacterial Secondary Symbionts in Sitobion avenae on Its Survival Fitness against Entomopathogenic Fungi, Beauveria bassiana and Metarhizium brunneum

The research was focused on the ability of wheat aphids Sitobion avenae, harboring bacterial secondary symbionts (BSS) Hamiltonella defensa or Regiella insecticola, to withstand exposure to fungal isolates of Beauveria bassiana and Metarhizium brunneum. In comparison to aphids lacking bacterial secondary symbionts, BSS considerably increased the lifespan of wheat aphids exposed to B. bassiana strains (Bb1022, EABb04/01-Tip) and M. brunneum strains (ART 2825 and BIPESCO 5) and also reduced the aphids' mortality. The wheat aphid clones lacking bacterial secondary symbionts were shown to be particularly vulnerable to M. brunneum strain BIPESCO 5. As opposed to wheat aphids carrying bacterial symbionts, fungal pathogens infected the wheat aphids lacking H. defensa and R. insecticola more quickly. When treated with fungal pathogens, bacterial endosymbionts had a favorable effect on the fecundity of their host aphids compared to the aphids lacking these symbionts, but there was no change in fungal sporulation on the deceased aphids. By defending their insect hosts against natural enemies, BSS increase the population of their host society and may have a significant impact on the development of their hosts.

Genetic Resources of Cereal Crops for Aphid Resistance

The genetic resources of cereal crops in terms of resistance to aphids are reviewed. Phytosanitary destabilization led to a significant increase in the harmfulness of this group of insects. The breeding of resistant plant genotypes is a radical, the cheapest, and environmentally safe way of pest control. The genetic homogeneity of crops hastens the adaptive microevolution of harmful organisms. Both major and minor aphid resistance genes of cereal plants interact with insects differentially. Therefore, rational breeding envisages the expansion of the genetic diversity of cultivated varieties. The possibilities of replenishing the stock of effective resistance genes by studying the collection of cultivated cereals, introgression, and creating mutant forms are considered. The interaction of insects with plants is subject to the gene-for-gene relationship. Plant resistance genes are characterized by close linkage and multiple allelism. The realizing plant genotype depends on the phytophage biotype. Information about the mechanisms of constitutional and induced plant resistance is discussed. Resistance genes differ in terms of stability of expression. The duration of the period when varieties remain resistant is not related either to its phenotypic manifestation or to the number of resistance genes. One explanation for the phenomenon of durable resistance is the association of the virulence mutation with pest viability.

Identification of Differentially Expressed Genes in Resistant Tetraploid Wheat (Triticum turgidum) under Sitobion avenae (F.) Infestation

The grain aphid Sitobion avenae (Fabricius) is one of the most destructive pests of wheat (Triticum aestivum). Deployment of resistant wheat germplasm appears as an excellent solution for this problem. Elite bread wheat cultivars only have limited resistance to this pest. The present study was carried out to investigate the potential of the tetraploid wheat (Triticum turgidum) variety Lanmai, which showed high resistance to S. avenae at both seedling and adult plant stages, as a source of resistance genes. Based on apterous adult aphids’ fecundity tests and choice bioassays, Lanmai has been shown to display antixenosis and antibiosis. Suppression subtractive hybridization (SSH) was employed to identify and isolate the putative candidate defense genes in Lanmai against S. avenae infestation. A total of 134 expressed sequence tags (ESTs) were identified and categorized based on their putative functions. RT-qPCR analysis of 30 selected genes confirmed their differential expression over time between the resistant wheat variety Lanmai and susceptible wheat variety Polan305 during S. avenae infestation. There were 11 genes related to the photosynthesis process, and only 3 genes showed higher expression in Lanmai than in Polan305 after S. avenae infestation. Gene expression analysis also revealed that Lanmai played a critical role in salicylic acid and jasmonic acid pathways after S. avenae infestation. This study provided further insights into the role of defense signaling networks in wheat resistance to S. avenae and indicates that the resistant tetraploid wheat variety Lanmai may provide a valuable resource for aphid tolerance improvement in wheat.

Prevalent Pest Management Strategies for Grain Aphids: Opportunities and Challenges

Cereal plants in natural ecological systems are often either sequentially or simultaneously attacked by different species of aphids, which significantly decreases the quality and quantity of harvested grain. The severity of the damage is potentially aggravated by microbes associated with the aphids or the coexistence of other fungal pathogens. Although chemical control and the use of cultivars with single-gene-based antibiosis resistance could effectively suppress grain aphid populations, this method has accelerated the development of insecticide resistance and resulted in pest resurgence. Therefore, it is important that effective and environmentally friendly pest management measures to control the damage done by grain aphids to cereals in agricultural ecosystems be developed and promoted. In recent decades, extensive studies have typically focused on further understanding the relationship between crops and aphids, which has greatly contributed to the establishment of sustainable pest management approaches. This review discusses recent advances and challenges related to the control of grain aphids in agricultural production. Current knowledge and ongoing research show that the integration of the large-scale cultivation of aphid-resistant wheat cultivars with agricultural and/or other management practices will be the most prevalent and economically important management strategy for wheat aphid control.

Wheat-Fusarium graminearum Interactions Under Sitobion avenae Influence: From Nutrients and Hormone Signals

The English grain aphid Sitobion avenae and phytopathogen Fusarium graminearum are wheat spike colonizers. "Synergistic" effects of the coexistence of S. avenae and F. graminearum on the wheat spikes have been shown in agroecosystems. To develop genetic resistance in diverse wheat cultivars, an important question is how to discover wheat-F. graminearum interactions under S. avenae influence. In recent decades, extensive studies have typically focused on the unraveling of more details on the relationship between wheat-aphids and wheat-pathogens that has greatly contributed to the understanding of these tripartite interactions at the ecological level. Based on the scientific production available, the working hypotheses were synthesized from the aspects of environmental nutrients, auxin production, hormone signals, and their potential roles related to the tripartite interaction S. avenae-wheat-F. graminearum. In addition, this review highlights the relevance of preexposure to the herbivore S. avenae to trigger the accumulation of mycotoxins, which stimulates the infection process of F. graminearum and epidemic of Fusarium head blight (FHB) in the agroecosystems.

Defence gene expression and phloem quality contribute to mesophyll and phloem resistance to aphids in wild barley

Aphids, including the bird cherry-oat aphid (Rhopalosiphum padi), are significant agricultural pests. The wild relative of barley, Hordeum spontaneum 5 (Hsp5), has been described to be partially resistant to R. padi, with this resistance proposed to involve higher thionin and lipoxygenase gene expression. However, the specificity of this resistance to aphids and its underlying mechanistic processes are unknown. In this study, we assessed the specificity of Hsp5 resistance to aphids and analysed differences in aphid probing and feeding behaviour on Hsp5 and a susceptible barley cultivar (Concerto). We found that partial resistance in Hsp5 to R. padi extends to two other aphid pests of grasses. Using the electrical penetration graph technique, we show that partial resistance is mediated by phloem- and mesophyll-based resistance factors that limit aphid phloem ingestion. To gain insight into plant traits responsible for partial resistance, we compared non-glandular trichome density, defence gene expression, and phloem composition of Hsp5 with those of the susceptible barley cultivar Concerto. We show that Hsp5 partial resistance involves elevated basal expression of thionin and phytohormone signalling genes, and a reduction in phloem quality. This study highlights plant traits that may contribute to broad-spectrum partial resistance to aphids in barley.

Resistance of Wheat Accessions to the English Grain Aphid Sitobion avenae

The English grain aphid, Sitobion avenae, is a major pest species of wheat crops; however, certain varieties may have stronger resistance to infestation than others. Here, we investigated 3 classical resistance mechanisms (antixenosis, antibiosis, and tolerance) by 14 wheat varieties/lines to S. avenae under laboratory and field conditions. Under laboratory conditions, alatae given the choice between 2 wheat varieties, strongly discriminated against certain varieties. Specifically, the 'Amigo' variety had the lowest palatability to S. avenae alatae of all varieties. 'Tm' (Triticum monococcum), 'Astron,' 'Xanthus,' 'Ww2730,' and 'Batis' varieties also had lower palatability than other varieties. Thus, these accessions may use antibiosis as the resistant mechanism. In contrast, under field conditions, there were no significant differences in the number of alatae detected on the 14 wheat varieties. One synthetic line (98-10-30, a cross between of Triticum aestivum (var. Chris) and Triticum turgidum (var. durum) hybridization) had low aphid numbers but high yield loss, indicating that it has high antibiosis, but poor tolerance. In comparison, 'Amigo,' 'Xiaoyan22,' and some '186Tm' samples had high aphid numbers but low yield loss rates, indicating they have low antibiosis, but good tolerance. Aphid population size and wheat yield loss rates greatly varied in different fields and years for '98-10-35,' 'Xiaoyan22,' 'Tp,' 'Tam200,' 'PI high,' and other '186Tm' samples, which were hybrid offspring of T. aestivum and wheat related species. Thus, these germplasm should be considered for use in future studies. Overall, S. avenae is best adapted to 'Xinong1376,' because it was the most palatable variety, with the greatest yield loss rates of all 14 wheat varieties. However, individual varieties/lines influenced aphid populations differently in different years. Therefore, we strongly recommend a combination of laboratory and long-term field experiments in targeted planting regions to identify varieties/lines that consistently show high resistance to S. avenae infestation.

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

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

Expression of potential resistance genes to the English grain aphid, Sitobion avenae, in wheat, Triticum aestivum

The English grain aphid, Sitobion avenae (F.) (Homoptera: Aphididae), is a dominant and destructive pest in wheat, Triticum estivum L. (Poales: Poaceae), production regions in China and other grain-growing areas worldwide. Patterns of gene expression of the S. avenae-resistant synthetic wheat line 98-10-35, the S. avenae-susceptible line1376, and their hybrid population, and the differences in segments between 98-10-35/1376 F₃ resistant plants and resistant parents of 98-10-35, as well as those between the F3 resistant and susceptible populations, were examined with differential display reverse transcription PCR. The results showed that five patterns of differential expression were detected between the progeny and its resistant parents: 1) The gene was silenced in one of the parents; 2) Special expression showed in the progeny; 3) Expression was consistent with the resistant parents; 4) Up expression showed in the progeny but not in the parents; 5) Down expression showed in the progeny but not in the parents. Paired t-test results were not significant; however, the probability value (0.9158) indicated that gene expression on the RNA level were consistent with resistant bands found in F3 resistant individuals and resistant parents, as well as the F₃ resistant and susceptible populations. For both the F₃ of 98-10-35/1376 and the parents, the total number of amplified bands was 202, with an average of 25.3 per primer. The number of differential bands was 116, with an average of 14.5 per primer amplified and a polymorphism ratio of 56.3%. In the present study, differential expression genes in the resistant line 98-10-35 were all up-regulated. Among them, gene expression of resistant groups in the F₃ population was in agreement with patterns 2, 3, and 4. However, the susceptible line 1376 did not have this gene expression on the RNA level. This pattern is expected to be used to select and analyze target genes from the same F₃ population and the resistant parents. The results suggest that it can be employed as a new method for molecular assisted breeding.