Infection of Powdery Mildew Reduces the Fitness of Grain Aphids (Sitobion avenae) Through Restricted Nutrition and Induced Defense Response in Wheat

New genetic resources for aphid resistance were identified from a newly developed wheat mutant library

Reports on development of resilient wheat mutants to aphid infestation-causing heavy losses to wheat production in many parts of the world, are scanty. The present study aimed to identify genetic diversity of wheat mutants in terms of varying degree of resistance to aphid infestation which can help protect wheat crop, improve yields and enhance food security. Resistance response to aphid infestation was studied on newly developed 33 wheat mutants, developed through irradiating seed of an elite wheat cultivar "Punjab-11" with gamma radiations, during three normal growing seasons at two sites. Data on various traits including aphid count per plant, biochemical traits, physiological traits and grain yield was recorded. Meteorological data was also collected to unravel the impact of environmental conditions on aphid infestation on wheat plants. Minimum average aphid infestation was found on Pb-M-2725, Pb-M-2550, and Pb-M-2719 as compared to the wild type. High yielding mutants Pb-M-1323, Pb-M-59, and Pb-M-1272 supported the moderate aphid infestation. The prevailing temperature up to 25 °C showed positive correlation (0.25) with aphid count. Among biochemical traits, POD (0.34), TSP (0.33), TFA (0.324) exhibited a high positive correlation with aphid count. In addition, CAT (0.31), TSS (0.294), and proline content (0.293) also showed a positive correlation with aphid count. However, all physiological traits depicted negative correlation with aphid count, while, a very weak correlation (0.12) was found between mean aphid count and grain yield. In PCA biplots, the biochemical variables clustered together with aphid count, while physiological variables grouped with grain yield. Biochemical parameters contributed most, towards first dimension of the PCA (48.6%) as compared to the physiological variables (13%). The FAMD revealed that mutant lines were major contributor towards total variation; Pb-M-1027, Pb-M-1323, Pb-M-59 were found to be the most diverse lines. The PCA revealed that biochemical parameters played a significant role in explaining variations in aphid resistance, emphasizing their importance in aphid defense mechanisms. The identified mutants can be utilized by the international wheat community for getting insight into the molecular circuits of resistant mechanism against aphids as well as for designing new KASP markers. This study also highlights the importance of considering both genetic and environmental factors in the development of resilient wheat varieties and pave the way for further investigations into the molecular mechanisms underpinning aphid resistance in wheat.

Prior Infection by Colletotrichum spinaciae Lowers the Susceptibility to Infection by Powdery Mildew in Common Vetch

Anthracnose (Colletotrichum spinaciae) and powdery mildew (Erysiphe pisi) are important diseases of common vetch (Vicia sativa) and often co-occur in the same plant. Here, we evaluate how C. spinaciae infection affects susceptibility to E. pisi, using sterilized and non-sterilized field soil to test the effect of resident soil microorganisms on the plant's immune response. Plants infected with C. spinaciae (C+) exhibited a respective 41.77~44.16% and 72.37~75.27% lower incidence and severity of powdery mildew than uninfected (C-) plants. Moreover, the net photosynthetic rate, transpiration rate, and stomatal conductance were higher in the C- plants than in the C+ plants prior to infection with powdery mildew. These differences were not recorded following powdery mildew infection. Additionally, the activities of superoxide dismutase, polyphenol oxidase, and catalase were higher in the C+ plants than in the C- plants. The resident soil microbiota did not affect the plant responses to both pathogens. By uncovering the mechanistic basis of plant immune response, our study informs integrated disease management in a globally important forage crop.

Single, but not dual, attack by a biotrophic pathogen and a sap-sucking insect affects the oak leaf metabolome

Plants interact with a multitude of microorganisms and insects, both below- and above ground, which might influence plant metabolism. Despite this, we lack knowledge of the impact of natural soil communities and multiple aboveground attackers on the metabolic responses of plants, and whether plant metabolic responses to single attack can predict responses to dual attack. We used untargeted metabolic fingerprinting (gas chromatography-mass spectrometry, GC-MS) on leaves of the pedunculate oak, Quercus robur, to assess the metabolic response to different soil microbiomes and aboveground single and dual attack by oak powdery mildew (Erysiphe alphitoides) and the common oak aphid (Tuberculatus annulatus). Distinct soil microbiomes were not associated with differences in the metabolic profile of oak seedling leaves. Single attacks by aphids or mildew had pronounced but different effects on the oak leaf metabolome, but we detected no difference between the metabolomes of healthy seedlings and seedlings attacked by both aphids and powdery mildew. Our findings show that aboveground attackers can have species-specific and non-additive effects on the leaf metabolome of oak. The lack of a metabolic signature detected by GC-MS upon dual attack might suggest the existence of a potential negative feedback, and highlights the importance of considering the impacts of multiple attackers to gain mechanistic insights into the ecology and evolution of species interactions and the structure of plant-associated communities, as well as for the development of sustainable strategies to control agricultural pests and diseases and plant breeding.

Biological Control of Plant Diseases: An Evolutionary and Eco-Economic Consideration

Biological control is considered as a promising alternative to pesticide and plant resistance to manage plant diseases, but a better understanding of the interaction of its natural and societal functions is necessary for its endorsement. The introduction of biological control agents (BCAs) alters the interaction among plants, pathogens, and environments, leading to biological and physical cascades that influence pathogen fitness, plant health, and ecological function. These interrelationships generate a landscape of tradeoffs among natural and social functions of biological control, and a comprehensive evaluation of its benefits and costs across social and farmer perspectives is required to ensure the sustainable development and deployment of the approach. Consequently, there should be a shift of disease control philosophy from a single concept that only concerns crop productivity to a multifaceted concept concerning crop productivity, ecological function, social acceptability, and economical accessibility. To achieve these goals, attempts should make to develop “green” BCAs used dynamically and synthetically with other disease control approaches in an integrated disease management scheme, and evolutionary biologists should play an increasing role in formulating the strategies. Governments and the public should also play a role in the development and implementation of biological control strategies supporting positive externality.

Genome-Wide Identification of Neuropeptides and Their Receptors in an Aphid Endoparasitoid Wasp, Aphidius gifuensi

In insects, neuropeptides and their receptors not only play a critical role in insect physiology and behavior but also are the potential targets for novel pesticide discoveries. Aphidius gifuensis is one of the most important and widespread aphid parasitoids, and has been successfully used to control aphid. In the present work, we systematically identified neuropeptides and their receptors from the genome and head transcriptome of A. gifuensis. A total of 35 neuropeptide precursors and 49 corresponding receptors were identified. The phylogenetic analyses demonstrated that 35 of these receptors belong to family-A, four belong to family-B, two belong to leucine-rich repeat-containing GPCRs, four belong to receptor guanylyl cyclases, and four belong to receptor tyrosine kinases. Oral ingestion of imidacloprid significantly up-regulated five neuropeptide precursors and four receptors whereas three neuropeptide precursors and eight receptors were significantly down-regulated, which indicated that these neuropeptides and their receptors are potential targets of some commercial insecticides. The RT-qPCR results showed that dopamine receptor 1, dopamine receptor 2, octopamine receptor, allatostatin-A receptor, neuropeptides capa receptor, SIFamide receptor, FMRFamide receptor, tyramine receptor and short neuropeptide F predominantly were expressed in the head whilst the expression of ion transport peptide showed widespread distribution in various tissues. The high expression levels of these genes suggest their important roles in the central nervous system. Taken together, our study provides fundamental information that may further our understanding of neuropeptidergic signaling systems in the regulation of the physiology and behavior of solitary wasps. Furthermore, this information could also aid in the design and discovery of specific and environment-friendly insecticides.

Interaction between the Bird Cherry-Oat Aphid (Rhopalosiphum padi) and Stagonospora Nodorum Blotch (Parastagonospora nodorum) on Wheat

Simple Summary

The bird cherry-oat aphid and the fungal plant pathogen causing stagonospora nodorum blotch (SNB) are common pests of wheat. Plants are under constant attack by multiple pests and diseases but there are limited studies on the interaction between several pests on wheat. We therefore conducted controlled greenhouse and laboratory experiments to determine how these pests affected each other on a wheat plant. We found that aphid feeding predisposed wheat to fungal disease, but that aphids preferred and reproduced better on leaves that had not been infected by the fungal pathogen. These results are important to understand the interactions between multiple pests on wheat and how to develop new control strategies in future integrated pest management (IPM).

Abstract

Wheat plants are under constant attack by multiple pests and diseases. Until now, there are no studies on the interaction between the aphid Rhopalosiphum padi and the plant pathogenic fungus Parastagonospora nodorum causal agent of septoria nodorum blotch (SNB) on wheat. Controlled experiments were conducted to determine: (i) The preference and reproduction of aphids on P. nodorum inoculated and non-inoculated wheat plants and (ii) the effect of prior aphid infestation of wheat plants on SNB development. The preference and reproduction of aphids was determined by releasing female aphids on P. nodorum inoculated (SNB+) and non-inoculated (SNB−) wheat leaves. The effect of prior aphid infestation of wheat plants on SNB development was determined by inoculating P. nodorum on aphid-infested (Aphid+) and aphid free (Aphid−) wheat plants. Higher numbers of aphids moved to and settled on the healthy (SNB−) leaves than inoculated (SNB+) leaves, and reproduction was significantly higher on SNB− leaves than on SNB+ leaves. Aphid infestation of wheat plants predisposed the plants to P. nodorum infection and colonization. These results are important to understand the interactions between multiple pests in wheat and hence how to develop new strategies in future integrated pest management (IPM).

Effect of Different Combinations of Phosphorus and Nitrogen Fertilization on Arbuscular Mycorrhizal Fungi and Aphids in Wheat

While chemical fertilizers can be used to increase crop yield, the abuse of fertilizers aggravates environmental pollution and soil degradation. Understanding the effects of chemical fertilizers on the interaction between arbuscular mycorrhizal fungi (AMF) and pest insects is of great benefit to crop and environmental protection, because AMF can enhance the nutrition absorption and insect resistance of crops. This study tested the effect of different levels of phosphorus, nitrogen, and their interactions on AMF, secondary metabolites, Sitobion avenae in garden, as well as the wheat traits in field. The results showed that AMF colonization on roots in the P0N1 treatment (0 g P/pot, 1.3083 g N/pot in the garden, and 0 g P/plot, 299.84 g N/plot) was the highest in both the garden and the field. The abundance of aphid was reduced in the P0N1 treatment, and there were negative relationships between aphids and AMF and phenolics, but a positive relationship between AMF and phenolics. Our results indicated that a change in the ratio of phosphorus to nitrogen affects the relationship among AMF, aphid abundance, and metabolites. The results also suggested an approach to save chemical fertilizers that could improve crop health and protect the agroecosystem against pollution at the same time.

Previous Aphid Infestation Induces Different Expression Profiles of Genes Associated with Hormone-Dependent Responses in Near-Isogenic Winter Wheat Lines

Hormone-dependent responses in host plants induced by herbivore infestation have species-specific effects. This study focused on determining the relative expression profiles of the genes associated with hormone-dependent pathways in two near-isogenic wheat lines when attacked by cereal aphids. Infestation with Rhopalosiphum padi Linnaeus (Hemiptera: Aphididae) and/or Sitobion avenae Fabricius (Hemiptera: Aphididae) significantly upregulated the expression of marker genes related to the salicylic acid (SA)- and jasmonic acid (JA)-dependent pathways in the tested lines. In the resistant line 35-E4, previous infestation with R. padi significantly increased the relative expression of plant pathogenesis-related protein 1 at all sampling times but did not have a significant effect on the expression of the phenylalanine ammonia-lyase (PAL) gene. In addition, the expression levels of the lipoxygenase (LOX) and allene oxide synthase (AOS) genes immediately increased after the aphid attack. In susceptible line 35-A20, infestation with either R. padi or S. avenae led to significantly increased expression levels of the AOS and PAL genes. Moreover, sequential aphid infestation induced higher expression of AOS compared with a single-species aphid infestation, whereas the expression of the PAL gene was antagonistically affected by sequential aphid infestation. Overall, these results showed that aphid infestation induced SA- and JA-dependent responses in host plants. However, the expression profiles of these genes in resistant and susceptible host lines were significantly different.

Changes in oak (Quercus robur) photosynthesis after winter moth (Operophtera brumata) herbivory are not explained by changes in chemical or structural leaf traits

Insect herbivores have the potential to change both physical and chemical traits of their host plant. Although the impacts of herbivores on their hosts have been widely studied, experiments assessing changes in multiple leaf traits or functions simultaneously are still rare. We experimentally tested whether herbivory by winter moth (Operophtera brumata) caterpillars and mechanical leaf wounding changed leaf mass per area, leaf area, leaf carbon and nitrogen content, and the concentrations of 27 polyphenol compounds on oak (Quercus robur) leaves. To investigate how potential changes in the studied traits affect leaf functioning, we related the traits to the rates of leaf photosynthesis and respiration. Overall, we did not detect any clear effects of herbivory or mechanical leaf damage on the chemical or physical leaf traits, despite clear effect of herbivory on photosynthesis. Rather, the trait variation was primarily driven by variation between individual trees. Only leaf nitrogen content and a subset of the studied polyphenol compounds correlated with photosynthesis and leaf respiration. Our results suggest that in our study system, abiotic conditions related to the growth location, variation between tree individuals, and seasonal trends in plant physiology are more important than herbivory in determining the distribution and composition of leaf chemical and structural traits.

Effect of Sublethal Doses of Imidacloprid on the Biological Performance of Aphid Endoparasitoid Aphidius gifuensis (Hymenoptera: Aphidiidae) and Influence on Its Related Gene Expression

The integrated pest management (IPM) strategy was developed and used in combination with pesticides and beneficial biological control agents. To further develop IPM efficiency, it is important to evaluate the side effects of pesticides on biological control agents. Aphidius gifuensis is one of the most important aphid natural enemies and has been successfully used to control Myzys persicae and other aphid species. Imidacloprid (IMD) is a popular pesticide used worldwide and is highly toxic to non-target arthropods. Here, we investigated the short-term sublethal toxicity of IMD in Aphidius gifuensis and its impact on the biological performance and gene expression of this parasitoid. We found that sublethal IMD doses had a significant negative effect on the life history traits of female A. gifuensis, including shortening the lifespan and lowering parasitic capacity. Moreover, exposure to sublethal IMD also adversely affected the response of A. gifuensis to aphid-infested plant volatiles. Based on the transcriptome analysis, we found that the exposure to sublethal IMD doses significantly affected expression of genes involved in the central nervous system, energy metabolism, olfactory, and detoxification system of A. gifuensis. RT-qPCR also revealed that short term expose to sublethal IMD doses significantly induced the gene expression of genes related to the central nervous system (nAChRa7, nAChRa9, TbH, OAR1, NFR, TYR, and DAR1), olfactory system (OR28 and IR8a1), and detoxification system (CYP49p3, CYP6a2, and POD), while it suppressed the expression of genes involved in the central nervous system (nAChRa4 and nAChRb1), olfactory system (Orco1, IR8a2, and GR1), and detoxification system (GST2). Furthermore, exposure to sublethal doses of IMD also significantly increased the activities of CarEs and POD, whereas we observed no influence on the activities of CAT, GST, and SOD. Our results indicate that sublethal IMD doses might adversely affect the biological performance of A. gifuensis by altering gene expression related to the function of olfactory, nervous, energy metabolism, and detoxification systems. Thus, how the use of pesticides directly affect insect population should be considered when used in conjunction with natural pest parasitoids in IPM strategies.

Probing behaviors and their plasticity for the aphid Sitobion avenae on three alternative host plants

Insects may develop different behavioral phenotypes in response to heterogeneous environments (e.g., host plants), but the plasticity of their feeding behaviors has been rarely explored. In order to address the issue, clones of the English grain aphid, Sitobion avenae (Fabricius), were collected from wheat, and their probing behaviors were recorded on three plants. Our results demonstrated that S. avenae individuals on the alternative plants (i.e., barley and oat) tended to have higher frequency of non-probing (Np), increased duration of the pathway phase, increased phloem salivation, and decreased phloem ingestion (E2), compared to those on the source plant (i.e., wheat), showing the resistance of barley and oat to this aphid's feeding. This aphid showed apparently high extents of plasticity for all test probing behaviors on barley or oat. Positive selection for higher extents of plasticity in E2 duration was identified on barley and oat. The factor 'clone' alone explained 30.6% to 70.1% of the total variance for each behavioral plasticity, suggesting that the divergence of probing behavior plasticity in S. avenae had a genetic basis. This aphid's fitness correlated positively with the plasticity of Np frequency and E2 frequency. Some behaviors and their corresponding plasticities (e.g., the frequency of xylem ingestion and its plasticity) were found to be correlated characters, probably reflecting the limits for the evolution of higher extents of behavioral plasticity in this aphid. The differential probing behaviors and their plasticity in S. avenae can have significant implications for the adaptation and management of aphids on different plants.