Wheat Seed Coating with Streptomyces sp. Strain DEF39 Spores Protects against Fusarium Head Blight

Priority actions for Fusarium head blight resistance in durum wheat: Insights from the wheat initiative

Fusarium head blight (FHB), mainly caused by Fusarium graminearum and Fusarium culmorum, is a major wheat disease. Significant efforts have been made to improve resistance to FHB in bread wheat (Triticum aestivum), but more work is needed for durum wheat (Triticum turgidum spp. durum). Bread wheat has ample genetic variation for resistance breeding, which can be readily exploited, while durum wheat is characterized by higher disease susceptibility and fewer valuable resistance sources. The Wheat Initiative - Expert Working Group on Durum Wheat Genomics and Breeding has promoted a scientific discussion to define the key actions that should be prioritized for achieving resistance in durum wheat comparable to that found in bread wheat. Here, a detailed state of the art and novel tools to improve FHB resistance in durum are presented, together with a perspective on the next steps forward. A meta-analysis grouping all quantitative trait loci (QTL) associated with FHB resistance in both bread and durum wheat has been conducted to identify hotspot regions that do not overlap with Rht alleles, which are known to negatively correlate with FHB resistance. A detailed list of QTL related to FHB resistance and deoxynivalenol contamination and durum lines carrying different sources of FHB resistance are provided as a strategic resource. QTL, closely linked markers and durum wheat lines carrying the useful alleles, can be selected to design an effective breeding program. Finally, we highlight the priority actions that should be implemented to achieve satisfactory resistance to FHB in durum wheat.

Biodiversity and Antifungal Activities of Amazonian Actinomycetes Isolated from Rhizospheres of Inga edulis Plants

BACKGROUND

Actinobacteria are major producers of antibacterial and antifungal metabolites and are growing their search for substances of biotechnological interest, especially for use in agriculture, among other applications. The Amazon is potentially rich in actinobacteria; however, almost no research studies exist. Thus, we present a study of the occurrence and antifungal potential of actinobacteria from the rhizosphere of Inga edulis, a native South American plant and one that is economically useful in the whole of the Amazon.

METHODS

Among the 64 actinobacteria strains isolated from the rhizosphere of three Inga edulis plants, 20 strains were selected and submitted to dual-culture assays against five important phytopathogenic fungi and morphological and 16S rRNA gene analyses. Two strains, LaBMicrA B270 and B280, were also studied for production curves of metabolic extracts and antifungal activities, including their minimum inhibitory concentration (MIC) against phytopathogenic fungi.

RESULTS

Among the 20 strains, 90% were identified as Streptomyces and 10% as Kitasatospora. All the strains showed antagonisms against two or more of five phytopathogens: Corynespora cassiicola, Colletotrichum guaranicola, Colletotrichum sp., Pestalotiopsis sp., and Sclerotium coffeicola. Streptomyces spp. strains LaBMicrA B270 and B280 were active against phytopathogens of the guarana plant (Paullinia cupana). Furthermore, AcOEt/2-propanol 9:1 extract from the 10-day strain LaBMicrA B280 cultured medium presented activity against all the phytopathogens tested, with a minimum inhibitory concentration of 125 μg/mL.

CONCLUSIONS

The results revealed various actinomycetes in three rhizospheres of I. edulis in the Amazon and the high potential of metabolic extracts from some of these bacterial strains against phytopathogenic fungi that destroy numerous crops.

Exploration of a multifunctional biocontrol agent Streptomyces sp. JCK-8055 for the management of apple fire blight

Apple fire blight, caused by the bacterium Erwinia amylovora, is a devastating disease of apple and pear trees. Biological control methods have attracted much attention from researchers to manage plant diseases as they are eco-friendly and viable alternatives to synthetic pesticides. Herein, we isolated Streptomyces sp. JCK-8055 from the root of pepper and investigated its mechanisms of action against E. amylovora. Streptomyces sp. JCK-8055 produced aureothricin and thiolutin, which antagonistically affect E. amylovora. JCK-8055 and its two active metabolites have a broad-spectrum in vitro activity against various phytopathogenic bacteria and fungi. They also effectively suppressed tomato bacterial wilt and apple fire blight in in vivo experiments. Interestingly, JCK-8055 colonizes roots as a tomato seed coating and induces apple leaf shedding at the abscission zone, ultimately halting the growth of pathogenic bacteria. Additionally, JCK-8055 can produce the plant growth regulation hormone indole-3-acetic acid (IAA) and hydrolytic enzymes, including protease, gelatinase, and cellulase. JCK-8055 treatment also triggered the expression of salicylate (SA) and jasmonate (JA) signaling pathway marker genes, such as PR1, PR2, and PR3. Overall, our findings demonstrate that Streptomyces sp. JCK-8055 can control a wide range of plant diseases, particularly apple fire blight, through a combination of mechanisms such as antibiosis and induced resistance, highlighting its excellent potential as a biocontrol agent. KEY POINTS: • JCK-8055 produces the systemic antimicrobial metabolites, aureothricin, and thiolutin. • JCK-8055 treatment upregulates PR gene expression in apple plants against E. amylovora. • JCK-8055 controls plant diseases with antibiotics and induced resistance.

Synthetic and Natural Antifungal Substances in Cereal Grain Protection: A Review of Bright and Dark Sides

Molds pose a severe challenge to agriculture because they cause very large crop losses. For this reason, synthetic fungicides have been used for a long time. Without adequate protection against pests and various pathogens, crop losses could be as high as 30-40%. However, concerns mainly about the environmental impact of synthetic antifungals and human health risk have prompted a search for natural alternatives. But do natural remedies only have advantages? This article reviews the current state of knowledge on the use of antifungal substances in agriculture to protect seeds against phytopathogens. The advantages and disadvantages of using both synthetic and natural fungicides to protect cereal grains were discussed, indicating specific examples and mechanisms of action. The possibilities of an integrated control approach, combining cultural, biological, and chemical methods are described, constituting a holistic strategy for sustainable mold management in the grain industry.

Development and application of a novel suspension concentrate for seed coating of rice for controlling bakanae disease and seedling rot disease

The main rice planting areas in the middle and lower reaches of the Yangtze River are primarily affected by two types of rice seedling diseases: bakanae disease and seedling rot disease. These diseases lead to considerable losses. Seed coating technology effectively protects rice from these diseases and mitigates environmental pollution. We determined the antifungal activity of six fungicides, including phenamacril, azoxystrobin, fludioxonil, metconazole, thifluzamide and prothioconazole against Fusarium moniliforme Sheldon and Curvularia lunata in this study. In addition, the impact of fungicides and surfactants on rice seed germination were determined. Furthermore, phenamacril and fludioxonil were selected as the active components of suspension concentrate for seed coating. The antifungal activity of phenamacril against F. moniliforme Sheldon was 0.139 mg/L and fludioxonil against C. lunata was 0.110 mg/L. PEG-2000 was selected as the surfactant due to its promoting effect on rice seedling. Based on the above findings, 6% phenamacril fludioxonil FS was developed via the wet sand grinding method. The toxicity of 6% phenamacril fludioxonil FS to zebrafish was verified, and field experiments were conducted in five different regions of the Yangtze River Basin. The results indicated minimal toxicity of 6% phenamacril fludioxonil FS to zebrafish. Relative to the control agent consisting of 6.25% phenamacril metalaxyl-M FS, 6% phenamacril fludioxonil FS showed better control effect and exhibited superior efficacy in promoting growth and increasing yield in all five regions. Specifically, the control effect of 6% phenamacril fludioxonil FS on bakanae exceeded 84.83% with the highest yield increasing value recorded at 30.48%. Currently, the market offers a limited selection of suspension concentrate for seed coating of rice. The findings of this study may offer a viable alternative formulation and directions for further research concerning the application of suspension concentrate for seed coating of rice.

Update on the state of research to manage Fusarium head blight

Fusarium head blight (FHB) is one of the most devastating diseases of cereal crops, causing severe reduction in yield and quality of grain worldwide. In the United States, the major causal agent of FHB is the mycotoxigenic fungus, Fusarium graminearum. The contamination of grain with mycotoxins, including deoxynivalenol and zearalenone, is a particularly serious concern due to its impact on the health of humans and livestock. For the past few decades, multidisciplinary studies have been conducted on management strategies designed to reduce the losses caused by FHB. However, effective management is still challenging due to the emergence of fungicide-tolerant strains of F. graminearum and the lack of highly resistant wheat and barley cultivars. This review presents multidisciplinary approaches that incorporate advances in genomics, genetic-engineering, new fungicide chemistries, applied biocontrol, and consideration of the disease cycle for management of FHB.

Endophytic Streptomyces population induced by L-glutamic acid enhances plant resilience to abiotic stresses in tomato

Endophyte bacteria, which colonize plants including roots, stem, flower, and fruit, it can derive their nutrients from the host, are recognized for their mutualistic relationship with the host plant. They play a critical role in promoting host growth and modulating abiotic stress. Carbon and nitrogen have a significant impact on bacterial population and secondary metabolite production, which are highly specific in various categories such as bacterial growth regulation, anti-compounds production. Application of L-glutamic acid can significantly enhance Streptomyces globisporus population buildup in plants. However, the effectiveness of this population buildup against abiotic stresses such as salinity and drought has not been investigated. Therefore, in this study, we tested the bacteria and their prebiotic activity against salinity and drought stress in tomato plants. Three different amino acids were treated on the tomato plants, and it was observed that L-asparagine and L-proline had a negative effect on plant growth and phenotype, while L-glutamic acid promoted plant growth and increased bacteria population density. The bacteria were found to colonize the rhizosphere and root endosphere, with colonization being promoted by L-glutamic acid. Additionally, Streptomyces was found to have plant growth promotion effects and provided protection against abiotic stresses. Interestingly, L-glutamic acid reduced the damage caused by salinity stress, but not drought stress. These findings suggest that L-glutamic acid plays a role in providing tolerance to salinity stress with the core microbiota, thus the current study demonstrated their prebiotic activity in the agriculture system.

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.