Silvio Tundo

Fusarium graminearum , the main causal agent of Fusarium head blight of wheat, secretes endoxylanases to hydrolyse xylan, a major component of hemicellulose. Mutants of the highly expressed FGSG_03624 ( xylB ) gene previously showed a disease severity level similar to wild‐type (WT) in wheat spikes. In this study, in contrast, three independent deletion mutants of FGSG_10999 ( xylA ), a second highly expressed endoxylanase gene, were significantly impaired in disease severity. Surprisingly, a knock‐out mutant of xylA in the ΔxylB genetic background (ΔΔxylB+A) exhibited virulence comparable to that of ΔxylB and WT. The ΔxylA mutant shared with ΔΔxylB+A a marked reduction in xylanase activity during in vitro growth, and also with ΔxylB a decreased fungal biomass and deoxynivalenol (DON) accumulation in infected spikes. In contrast to ΔΔxylB+A and ΔxylB, ΔxylA revealed down‐regulation of some endoxylanase and effector genes during spike infection. In addition, when grown on a wheat spike medium, the culture filtrate of ΔxylA showed a significant reduction in total protein secretion and a more severe impairment in necrotizing activity in Nicotiana benthamiana infiltrated leaves compared with ΔxylB and ΔΔxylB+A culture filtrates. When a deletion mutant of xylB was generated in the ΔxylA genetic background, the ΔΔxylA+B mutant displayed severely reduced virulence, similar to that of the parental ΔxylA. Altogether, these results demonstrate that xylA plays a critical role in F. graminearum pathogenicity through unexpected pleiotropic, network‐level alterations, as also supported by the partial restoration observed by complementing the xylA gene in ΔxylA, highlighting the strong influence of genetic background on phenotypic outcomes.

Pomegranate dieback is a disease whose etiology remains only partially understood. In this study, surveys were carried out in orchards located in the Apulia, Basilicata, and Veneto regions from 2016 to 2020 with the objective to identify pathogens involved in pomegranate dieback. Six fungal species were isolated from symptomatic trees and identified through morphological and molecular analyses. In addition to the known pomegranate pathogens Neofusicoccum parvum, Diaporthe eres and D. foeniculina, new fungal species, including Neopestalotiopsis rosae, Sporothrix stenoceras, and one belonging to the Xenoacremonium genus, were identified. This study represents the first report of their association with pomegranate plants exhibiting dieback symptoms. When artificially inoculated on pomegranate trees, these fungi caused wood browning, proving their pathogenicity. All fungal species exhibited optimal growth in the temperature range 25–30 °C, although D. eres and N. roseae showed a good adaptability in the range 5–10 °C. Since some of the identified pathogens were isolated from the same trees, cross-pairing assays were conducted, revealing that these fungi can coexist within the same ecological niche while maintaining their viability. Given the need for sustainable management options against these co-occurring pathogens, biological control strategies were evaluated. In vitro experiments demonstrated that both Bacillus and Trichoderma biological control agents (BCAs) inhibit the investigated pomegranate pathogens, highlighting their potential inclusion in integrated management strategies targeting these newly identified fungal pathogens.

Cultivation of pomegranate ( Punica granatum ) is threatened by the emerging pathogens Coniella granati and Phytophthora palmivora . Whether these microorganisms increase their damage due to simultaneous infection and abiotic stress in pomegranate is unknown. Amylo‐X LC is an effective biofungicide based on Bacillus amyloliquefaciens but its efficacy to protect pomegranate from C . granati and P. palmivora if plants are under abiotic stress has not been tested. Therefore, the effects of drought, waterlogging and co‐infection on the aggressiveness of these two pathogens and the efficacy of Amylo‐X LC were evaluated. Pomegranate trees were subjected to regular watering, drought and waterlogging conditions, treated with Amylo‐X LC, and individually or simultaneously inoculated in the stem by C . granati and P. palmivora . Drought experienced by trees limited P. palmivora , while waterlogging favoured C . granati . In combined infections, the presence of P. palmivora amplified the damage caused by C . granati in trees subjected to regular watering and drought. Amylo‐X LC proved effective in preventing P. palmivora damage and did not allow the synergistic effect of P. palmivora on C . granati to occur in trees under regular watering and drought. Drought further reduced P. palmivora lesions in plants pretreated with Amylo‐X LC compared to those under regular watering. The impact of abiotic stress in pomegranate during C . granati and P. palmivora infections and the efficacy of B. amyloliquefaciens as a potential agent against pomegranate dieback were discussed. We conclude that further efforts to evaluate the efficacy of biological control agents on crops exposed to different environmental scenarios are needed.

The challenges posed to modern agriculture such as climate change, depleting groundwater resources, and increased global population (Ivanovish et al 2023; Khatri et al 2024), underscore the urgent need for innovative and sustainable strategies to mitigate plant stress. Plants face a multitude of biotic and abiotic stressors, which can severely affect their growth, development, and productivity. Despite these challenges, plants have evolved complex defense mechanisms that are tightly regulated at various molecular levels (Zandalinas et al., 2021;Zandalinas & Mittler, 2022). However, the ways in which biotic and abiotic stresses together influence plant responses at molecular level remain poorly understood. This Research Topic includes comprehensive studies exploring the interplay between biotic and abiotic stresses, with a particular focus on how abiotic stress can either enhance or reduce plant susceptibility to pathogens and pests. The collection includes a balanced mix of original research and review articles, with an emphasis on molecular and multi-omic approaches. Some studies underscore the critical role of transcription factors and kinases in regulating integrative plant responses, utilizing a variety of omics and molecular studies a more 35 applied emphasizing the importance of in situ measurements for practical 36

Plasmopara viticola, the agent of grapevine downy mildew, causes enormous economic damage, and its control is primarily based on the use of synthetic fungicides. The European Union policies promote reducing reliance on synthetic plant protection products. Biocontrol agents such as Trichoderma spp. constitute a resource for the development of biopesticides. Trichoderma spp. produce secondary metabolites such as peptaibols, but the poor water solubility of peptaibols limits their practical use as agrochemicals. To identify new potential bio-inspired molecules effective against P. viticola, various water-soluble peptide analogs of the peptaibol trichogin were synthesized. In grapevine leaf disk assays, the peptides analogs at a concentration of 50 μM completely prevented P. viticola infection after zoosporangia inoculation. Microscopic observations of one of the most effective peptides showed that it causes membrane lysis and cytoplasmic granulation in both zoosporangia and zoospores. Among the effective peptides, 4r was selected for a 2-year field trial experiment. In the vineyard, the peptide administered at 100 μM (equivalent to 129.3 g/ha) significantly reduced the disease incidence and severity on both leaves and bunches, with protection levels similar to those obtained using a cupric fungicide. In the second-year field trial, reduced dosages of the peptide were also tested, and even at the peptide concentration reduced by 50 or 75%, a significant decrease in the disease incidence and severity was obtained at the end of the trial. The peptide did not show any phytotoxic effect. Previously, peptide 4r had been demonstrated to be active against other fungal pathogens, including the grapevine fungus Botrytis cinerea. Thus, this peptide may be a candidate for a broad-spectrum fungicide whose biological properties deserve further investigation.

The Thinopyrum elongatum Fhb7E locus has been proven to confer outstanding resistance to Fusarium Head Blight (FHB) when transferred into wheat, minimizing yield loss and mycotoxin accumulation in grains. Despite their biological relevance and breeding implications, the molecular mechanisms underlying the resistant phenotype associated with Fhb7E have not been fully uncovered. To gain a broader understanding of processes involved in this complex plant–pathogen interaction, we analysed via untargeted metabolomics durum wheat (DW) rachises and grains upon spike inoculation with Fusarium graminearum (Fg) and water. The employment of DW near-isogenic recombinant lines carrying or lacking the Th. elongatum chromosome 7E region including Fhb7E on their 7AL arm, allowed clear-cut distinction between differentially accumulated disease-related metabolites. Besides confirming the rachis as key site of the main metabolic shift in plant response to FHB, and the upregulation of defence pathways (aromatic amino acid, phenylpropanoid, terpenoid) leading to antioxidants and lignin accumulation, novel insights were revealed. Fhb7E conferred constitutive and early-induced defence response, in which specific importance of polyamine biosynthesis, glutathione and vitamin B₆ metabolisms, along with presence of multiple routes for deoxynivalenol detoxification, was highlighted. The results suggested Fhb7E to correspond to a compound locus, triggering a multi-faceted plant response to Fg, effectively limiting Fg growth and mycotoxin production.

Black rot caused by the Gram-negative bacterial pathogen Xanthomonas campestris pv. campestris (Xcc) is considered one of the most destructive diseases affecting crucifers. Xcc is a seedborne pathogen able to infect the host at any growth stage. The management of the pathogen mainly relies on the use of copper-based products with possible negative effects on human health and the environment. Searching for protection alternatives is crucial for achieving a sustainable management of Xcc. Trichoderma spp. has been largely used as a biocontrol agent against several phytopathogens. Among Trichoderma species, Trichoderma longibrachiatum produces the peptaibol trichogin GA IV, a secondary metabolite with antimicrobial activity against Gram-positive bacteria, as well as filamentous and yeast-like fungi. In this work, we tested, at micromolar concentrations, 25 synthetic analogs of the peptaibol trichogin GA IV for their bacteriostatic and bactericidal activity toward the bacterium Xcc. One of the most effective peptides (4r) was also tested against the Gram-negative bacteria Xanthomonas arboricola, Pseudomonas corrugata, Pseudomonas savastanoi pv. savastanoi, Agrobacterium tumefaciens, Ralstonia solanacearum, and Erwinia carotovora subsp. carotovora, as well as the Gram-positive bacterium Bacillus subtilis. The peptide 4r reduced black rot symptoms on cauliflower plants when administered both before and 24 h after inoculation with Xcc. The cytotoxic activity of the peptide 4r was also evaluated towards suspensions of tobacco cells by Evans Blue assay.

Xylanase inhibitors (XIs) are plant cell wall proteins largely distributed in monocots that inhibit the hemicellulose degrading activity of microbial xylanases. XIs have been classified into three classes with different structures and inhibition specificities, namely Triticum aestivum xylanase inhibitors (TAXI), xylanase inhibitor proteins (XIP), and thaumatin-like xylanase inhibitors (TLXI). Their involvement in plant defense has been established by several reports. Additionally, these inhibitors have considerable economic relevance because they interfere with the activity of xylanases applied in several agro-industrial processes. Previous reviews highlighted the structural and biochemical properties of XIs and hypothesized their role in plant defense. Here, we aimed to update the information on the genomic organization of XI encoding genes, the inhibition properties of XIs against microbial xylanases, and the structural properties of xylanase-XI interaction. We also deepened the knowledge of XI regulation mechanisms in planta and their involvement in plant defense. Finally, we reported the recently studied strategies to reduce the negative impact of XIs in agro-industrial processes and mentioned their allergenicity potential.

The negative impact of using conventional fungicides in plant disease protection has increased the interest in safer alternatives such as plant secondary metabolites, generally having a better toxicological profile. However, cultivation conditions and plant material strongly affect the quality and quantity of secondary metabolites obtained from field grown plants, limiting the standardization needed for industrial production. Plant cell culture technology can provide highly homogeneous biomasses with specific chemical characteristics. A phytocomplex with high rosmarinic acid content (10.12% w/w) was obtained from a selected cell line of Salvia officinalis and was tested against the grapevine downy mildew pathogen, Plasmopara viticola. Grapevine leaf discs were sprayed with the phytocomplex at 5 g/L and then inoculated with P. viticola sporangia. Sporulation level on each disc was assessed after 7 days with an image processing software. The phytocomplex reduced by 95% the sporulation level compared to the control and was also more effective than rosmarinic acid alone, used at the same concentration found in the phytocomplex. Persistence of the phytocomplex was also assessed: when applied 5 days before inoculation, it reduced by 90% the sporulation level compared to the control. These results highlight the possibility to take advantage of cell culture techniques to produce safer pesticides with high quality standards.