The plant response induced in wheat ears by a combined attack of Sitobion avenae aphids and Fusarium graminearum boosts fungal infection and deoxynivalenol production

Effect of the mycotoxins enniatin B and deoxynivalenol on the wheat aphid Sitobion avenae and on the predatory lacewing Chrysoperla carnea

BACKGROUND

Fusarium species are responsible for Fusarium head blight (FHB) in wheat, resulting in yield losses and mycotoxin contamination. Deoxynivalenol (DON) and enniatins (ENNs) are common mycotoxins produced by Fusarium, affecting plant, animal and human health. Although DON's effects have been widely studied, limited research has explored the impact of ENNs on insects. This study examines the influence of DON and enniatin B (ENB), both singularly and in combination, on the wheat aphid Sitobion avenae and one of its predators, the lacewing Chrysoperla carnea.

RESULTS

When exposed to DON (100 mg L-1) or DON + ENB (100 mg L-1), S. avenae exhibited significantly increased mortality compared to the negative control. ENB (100 mg L-1) had no significant effect on aphid mortality. DON-treated aphids showed increasing mortality from 48 to 96 h. A dose-response relationship with DON revealed significant cumulative mortality starting at 25 mg L-1. By contrast, C. carnea larvae exposed to mycotoxins via cuticular application did not show significant differences in mortality when mycotoxins were dissolved in water but exhibited increased mortality with acetone-solubilized DON + ENB (100 mg L-1). Feeding C. carnea with aphids exposed to mycotoxins (indirect exposure) did not impact their survival or predatory activity. Additionally, the impact of mycotoxins on C. carnea was observed only with acetone-solubilized DON + ENB.

CONCLUSIONS

These findings shed light on the complex interactions involving mycotoxins, aphids and their predators, offering valuable insights for integrated pest management strategies. Further research should explore broader ecological consequences of mycotoxin contamination in agroecosystems. © 2024 Society of Chemical Industry.

Impact of Enniatin and Deoxynivalenol Co-Occurrence on Plant, Microbial, Insect, Animal and Human Systems: Current Knowledge and Future Perspectives

Fusarium mycotoxins commonly contaminate agricultural products resulting in a serious threat to both animal and human health. The co-occurrence of different mycotoxins in the same cereal field is very common, so the risks as well as the functional and ecological effects of mycotoxins cannot always be predicted by focusing only on the effect of the single contaminants. Enniatins (ENNs) are among the most frequently detected emerging mycotoxins, while deoxynivalenol (DON) is probably the most common contaminant of cereal grains worldwide. The purpose of this review is to provide an overview of the simultaneous exposure to these mycotoxins, with emphasis on the combined effects in multiple organisms. Our literature analysis shows that just a few studies on ENN-DON toxicity are available, suggesting the complexity of mycotoxin interactions, which include synergistic, antagonistic, and additive effects. Both ENNs and DON modulate drug efflux transporters, therefore this specific ability deserves to be explored to better understand their complex biological role. Additionally, future studies should investigate the interaction mechanisms of mycotoxin co-occurrence on different model organisms, using concentrations closer to real exposures.

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.

UAV-Based Thermal, RGB Imaging and Gene Expression Analysis Allowed Detection of Fusarium Head Blight and Gave New Insights Into the Physiological Responses to the Disease in Durum Wheat

Wheat is one of the world's most economically important cereal crop, grown on 220 million hectares. Fusarium head blight (FHB) disease is considered a major threat to durum (Triticum turgidum subsp. durum (Desfontaines) Husnache) and bread wheat (T. aestivum L.) cultivars and is mainly managed by the application of fungicides at anthesis. However, fungicides are applied when FHB symptoms are clearly visible and the spikes are almost entirely bleached (% of diseased spikelets > 80%), by when it is too late to control FHB disease. For this reason, farmers often react by performing repeated fungicide treatments that, however, due to the advanced state of the infection, cause a waste of money and pose significant risks to the environment and non-target organisms. In the present study, we used unmanned aerial vehicle (UAV)-based thermal infrared (TIR) and red-green-blue (RGB) imaging for FHB detection in T. turgidum (cv. Marco Aurelio) under natural field conditions. TIR and RGB data coupled with ground-based measurements such as spike's temperature, photosynthetic efficiency and molecular identification of FHB pathogens, detected FHB at anthesis half-way (Zadoks stage 65, ZS 65), when the percentage (%) of diseased spikelets ranged between 20% and 60%. Moreover, in greenhouse experiments the transcripts of the key genes involved in stomatal closure were mostly up-regulated in F. graminearum-inoculated plants, demonstrating that the physiological mechanism behind the spike's temperature increase and photosynthetic efficiency decrease could be attributed to the closure of the guard cells in response to F. graminearum. In addition, preliminary analysis revealed that there is differential regulation of genes between drought-stressed and F. graminearum-inoculated plants, suggesting that there might be a possibility to discriminate between water stress and FHB infection. This study shows the potential of UAV-based TIR and RGB imaging for field phenotyping of wheat and other cereal crop species in response to environmental stresses. This is anticipated to have enormous promise for the detection of FHB disease and tremendous implications for optimizing the application of fungicides, since global food crop demand is to be met with minimal environmental impacts.

The Effect of Fusarium verticillioides Fumonisins on Fatty Acids, Sphingolipids, and Oxylipins in Maize Germlings

Fusarium verticillioides causes multiple diseases of Zea mays (maize) including ear and seedling rots, contaminates seeds and seed products worldwide with toxic chemicals called fumonisins. The role of fumonisins in disease is unclear because, although they are not required for ear rot, they are required for seedling diseases. Disease symptoms may be due to the ability of fumonisins to inhibit ceramide synthase activity, the expected cause of lipids (fatty acids, oxylipins, and sphingolipids) alteration in infected plants. In this study, we explored the impact of fumonisins on fatty acid, oxylipin, and sphingolipid levels in planta and how these changes affect F. verticillioides growth in maize. The identity and levels of principal fatty acids, oxylipins, and over 50 sphingolipids were evaluated by chromatography followed by mass spectrometry in maize infected with an F. verticillioides fumonisin-producing wild-type strain and a fumonisin-deficient mutant, after different periods of growth. Plant hormones associated with defense responses, i.e., salicylic and jasmonic acid, were also evaluated. We suggest that fumonisins produced by F. verticillioides alter maize lipid metabolism, which help switch fungal growth from a relatively harmless endophyte to a destructive necrotroph.

Presence of the Weakly Pathogenic Fusarium poae in the Fusarium Head Blight Disease Complex Hampers Biocontrol and Chemical Control of the Virulent Fusarium graminearum Pathogen

Fusarium head blight (FHB) in wheat (Triticum aestivum L.) is caused by a consortium of mutually interacting Fusarium species. In the field, the weakly pathogenic F. poae often thrives on the infection sites of the virulent F. graminearum. In this ecological context, we investigated the efficacy of chemical and biocontrol agents against F. graminearum in wheat ears. For this purpose, one fungicide comprising prothioconazole + spiroxamine and two bacterial biocontrol strains, Streptomyces rimosus LMG 19352 and Rhodococcus sp. R-43120 were tested for their efficacy to reduce FHB symptoms and mycotoxin (deoxynivalenol, DON) production by F. graminearum in presence or absence of F. poae. Results showed that the fungicide and both actinobacterial strains reduced FHB symptoms and concomitant DON levels in wheat ears inoculated with F. graminearum. Where Streptomyces rimosus appeared to have direct antagonistic effects, Rhodococcus and the fungicide mediated suppression of F. graminearum was linked to the archetypal salicylic acid and jasmonic acid defense pathways that involve the activation of LOX1, LOX2 and ICS. Remarkably, this chemical- and biocontrol efficacy was significantly reduced when F. poae was co-inoculated with F. graminearum. This reduced efficacy was linked to a suppression of the plant's intrinsic defense system and increased levels of DON. In conclusion, our study shows that control strategies against the virulent F. graminearum in the disease complex causing FHB are hampered by the presence of the weakly pathogenic F. poae. This study provides generic insights in the complexity of control strategies against plant diseases caused by multiple pathogens.

At the scene of the crime: New insights into the role of weakly pathogenic members of the fusarium head blight disease complex

Plant diseases are often caused by a consortium of pathogens competing with one another to gain a foothold in the infection niche. Nevertheless, studies are often limited to a single pathogen on its host. In Europe, fusarium head blight (FHB) of wheat is caused by multiple Fusarium species, including Fusarium graminearum and F. poae. Here, we combined a time series of (co)inoculations, monitored by multispectral imaging, transcriptional, and mycotoxin analyses, to study the temporal interaction between both species and wheat. Our results showed coinoculation of F. graminearum and F. poae inhibited symptom development but did not alter mycotoxin accumulation compared to a single inoculation with F. graminearum. In contrast, preinoculation of F. poae reduced both FHB symptoms and mycotoxin levels compared to a single F. graminearum infection. Interestingly, F. poae exhibited increased growth in dual infections, demonstrating that this weak pathogen takes advantage of its co-occurrence with F. graminearum. Quantitative reverse transcription PCR revealed that F. poae induces LOX and ICS gene expression in wheat. We hypothesize that the early induction of salicylic and jasmonic acid-related defences by F. poae hampers a subsequent F. graminearum infection. This study is the first to report on the defence mechanisms of the plant involved in a tripartite interaction between two species of a disease complex and their host.

The modulation of stomatal conductance and photosynthetic parameters is involved in Fusarium head blight resistance in wheat

Fusarium head blight (FHB) is one of the most devastating fungal diseases affecting grain crops and Fusarium graminearum is the most aggressive causal species. Several evidences shown that stomatal closure is involved in the first line of defence against plant pathogens. However, there is very little evidence to show that photosynthetic parameters change in inoculated plants. The aim of the present study was to study the role of stomatal regulation in wheat after F. graminearum inoculation and explore its possible involvement in FHB resistance. RT-qPCR revealed that genes involved in stomatal regulation are induced in the resistant Sumai3 cultivar but not in the susceptible Rebelde cultivar. Seven genes involved in the positive regulation of stomatal closure were up-regulated in Sumai3, but it is most likely, that two genes, TaBG and TaCYP450, involved in the negative regulation of stomatal closure, were strongly induced, suggesting that FHB response is linked to cross-talk between the genes promoting and inhibiting stomatal closure. Increasing temperature of spikes in the wheat genotypes and a decrease in photosynthetic efficiency in Rebelde but not in Sumai3, were observed, confirming the hypothesis that photosynthetic parameters are related to FHB resistance.

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.

Green leaf volatile production by plants: a meta-analysis

666 I. Introduction 667 II. Biosynthesis 667 III. Meta-analysis 669 IV. The type of stress influences the total amount of GLVs released 669 V. Herbivores can modulate the wound-induced release of GLVs 669 VI. Fungal infection greatly induces GLV production 672 VII. Monocots and eudicots respond differentially to different types of stress 673 VIII. The type of stress does not influence the proportion of GLVs per chemical class 673 IX. The type of stress does influence the isomeric ratio within each chemical class 674 X. GLVs: from signal perception to signal transduction 676 XI. GLVs influence the C/N metabolism 677 XII. Interaction with plant hormones 678 XIII. General conclusions and unanswered questions 678 Acknowledgements 679 References 679 SUMMARY: Plants respond to stress by releasing biogenic volatile organic compounds (BVOCs). Green leaf volatiles (GLVs), which are abundantly produced across the plant kingdom, comprise an important group within the BVOCs. They can repel or attract herbivores and their natural enemies; and they can induce plant defences or prime plants for enhanced defence against herbivores and pathogens and can have direct toxic effects on bacteria and fungi. Unlike other volatiles, GLVs are released almost instantly upon mechanical damage and (a)biotic stress and could thus function as an immediate and informative signal for many organisms in the plant's environment. We used a meta-analysis approach in which data from the literature on GLV production during biotic stress responses were compiled and interpreted. We identified that different types of attackers and feeding styles add a degree of complexity to the amount of emitted GLVs, compared with wounding alone. This meta-analysis illustrates that there is less variation in the GLV profile than we presumed, that pathogens induce more GLVs than insects and wounding, and that there are clear differences in GLV emission between monocots and dicots. Besides the meta-analysis, this review provides an update on recent insights into the perception and signalling of GLVs in plants.

Reduced phloem uptake of Myzus persicae on an aphid resistant pepper accession

BACKGROUND

The green peach aphid (GPA), Myzus persicae, is economically one of the most threatening pests in pepper cultivation, which not only causes direct damage but also transmits many viruses. Breeding aphid resistant pepper varieties is a promising and environmentally friendly method to control aphid populations in the field and in the greenhouse. Until now, no strong sources of resistance against the GPA have been identified. Therefore the main aims of this study were to identify pepper materials with a good level of resistance to GPA and to elucidate possible resistance mechanisms.

RESULTS

We screened 74 pepper accessions from different geographical areas for resistance to M. persicae. After four rounds of evaluation we identified one Capsicum baccatum accession (PB2013071) as highly resistant to M. persicae, while the accessions PB2013062 and PB2012022 showed intermediate resistance. The resistance of PB2013071 resulted in a severely reduced uptake of phloem compared to the susceptible accession, as determined by Electrical Penetration Graph (EPG) studies. Feeding of M. persicae induced the expression of callose synthase genes and resulted in callose deposition in the sieve elements in resistant, but not in susceptible plants.

CONCLUSIONS

Three aphid resistant pepper accessions were identified, which will be important for breeding aphid resistant pepper varieties in the future. The most resistant accession PB2013071 showed phloem-based resistance against aphid infestation.

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

In natural ecological systems, plants are often simultaneously attacked by both insects and pathogens, which can affect each other's performance and the interactions can be extended to higher trophic levels, such as parasitoids. The English grain aphid (Sitobion avenae) and powdery mildew (Blumeria graminis f. sp. tritici) are two common antagonists that pose a serious threat to wheat production. Numerous studies have investigated the effect of a single factor (insect or pathogen) on wheat production. However, investigation on the interactions among insect pests, pathogens, and parasitoids within the wheat crop system are rare. Furthermore, the influence of the fungicide, propiconazole, has been found to imitate the natural ecosystem. Therefore, this study investigated the effects of B. graminis on the biological performance of grain aphids and the orientation behavior of its endoparasitic wasp Aphidius gifuensis in the wheat system. Our findings indicated that B. graminis infection suppressed the feeding behavior, adult and nymph weight, and fecundity and prolonged the developmental time of S. avenae. We found that wheat host plants had decreased proportions of essential amino acids and higher content of sucrose following aggravated B. graminis infection. The contents of Pro and Gln increased in the wheat plant tissues after B. graminis infection. In addition, B. graminis infection elicited immune responses in wheat: increase in the expression of defense genes, content of total phenolic compounds, and activity of three related antioxidant enzymes. Moreover, co-infection of B. graminis and S. avenae increased the attraction to A. gifuensis compare to that after infestation with aphids alone. In conclusion, our results indicated that B. graminis infection adversely affected the performance of S. avenae in wheat through restricted nutrition and induced defense response. Furthermore, the preference of parasitoids in such an interactive environment might provide an important basis for pest management control.

Fusarium Toxins in Cereals: Occurrence, Legislation, Factors Promoting the Appearance and Their Management

Fusarium diseases of small grain cereals and maize cause significant yield losses worldwide. Fusarium infections result in reduced grain yield and contamination with mycotoxins, some of which have a notable impact on human and animal health. Regulations on maximum limits have been established in various countries to protect consumers from the harmful effects of these mycotoxins. Several factors are involved in Fusarium disease and mycotoxin occurrence and among them environmental factors and the agronomic practices have been shown to deeply affect mycotoxin contamination in the field. In the present review particular emphasis will be placed on how environmental conditions and stress factors for the crops can affect Fusarium infection and mycotoxin production, with the aim to provide useful knowledge to develop strategies to prevent mycotoxin accumulation in cereals.