Effective and Sustained Control of Soil-Borne Plant Diseases by Biodegradable Polyhydroxybutyrate Mulch Films Embedded with Fungicide of Prothioconazole

PHB Production by Bacillus megaterium LSRB 0103 Using Cornstarch and Urea

Polyhydroxybutyrates (PHBs) are biopolymers that are good green alternative for synthetic carbon-based polymers, and are also one of the most researched members of the Polyhydroxyalkanoates (PHA) family. In this study, a gram-positive bacterial strain Bacillus megaterium LSRB 0103 was isolated from Pallikaranai Marshland, Chennai, India. Primary screening using Sudan Black dye revealed the presence of intracellular PHB granules. Minimal Davis Media (MDM) which was used or PHB production gave a yield of 0.7107 g/L. Subsequently, using response surface methodology (RSM), a central composite design (CCD) model was designed for media optimization having cornstarch, urea, and pH as independent variables. The findings of the CCD model were fitted into a second-order polynomial equation. The RSM model predicted the maximum PHB yield of 0.93 g/L, at these independent variable levels, cornstarch, 5 g/L; urea, 2.1 g/L; and pH 7.0; while the experimental PHB yield was 0.94 g/L, with a percentage error of 1.1%. This study is the first-time report of production of PHB by Bacillus megaterium using cornstarch and urea as substrate.

A biodegradable oxidized starch/carboxymethyl chitosan film coated with pesticide-loaded ZIF-8 for tomato fusarium wilt control

Film mulching is one of the most important methods to control soil-borne diseases. However, the traditional mulch may cause microplastic pollution and soil ecological damage. Herein, a biodegradable film was developed using oxidized starch and carboxymethyl chitosan and incorporated ZIF-8 carrying fludioxonil to sustainably control soil-borne disease. The microstructure, mechanical properties, optical properties, and water barrier properties of the composite films (Flu@ZIF-8-OS/CMCS) were investigated. The results show that Flu@ZIF-8-OS/CMCS had a smooth and uniform surface and excellent light transmittance. The excellent mechanical properties of the films were verified by tensile strength, elongation at break and Young's modulus. Higher contact angle and lower water vapor permeability indicate water retention capacity of the soil was improved through using Flu@ZIF-8-OS/CMCS. Furthermore, the release properties, biological activity, degradability and safety to soil organisms of Flu@ZIF-8-OS/CMCS was determined. The addition of ZIF-8 significantly improved the film's ability to retard the release of Flu, while the Flu@ZIF-8-OS/CMCS has good soil degradability. In vitro antifungal assays and pot experiments demonstrated excellent inhibitory activity against Fusarium oxysporum f. sp. Lycopersici. Flu@ZIF-8-OS/CMCS caused only 13.33 % mortality of earthworms within 7 d. This research provides a new approach to reducing microplastic pollution and effectively managing soil-borne diseases.

Nano-Micro Core-Shell Fibers for Efficient Pest Trapping

Insect sex pheromones as an alternative to chemical pesticides hold promising prospects in pest control. However, their burst release and duration need to be optimized. Herein, pheromone-loaded core-shell fibers composed of degradable polycaprolactone and polyhydroxybutyrate were prepared by coaxial electrospinning. The results showed that this core-shell fiber had good hydrophobic performance and thermal stability, and the light transmittance in the ultraviolet band was only below 40%, which provided protection to pheromones. The core-shell structure alleviated the burst release of pheromone in the fiber and extended the release time to about 133 days. In the field, the pheromone-loaded core-shell fibers showed the same continuous and efficient trapping of Spodoptera litura as the commercial carriers. More importantly, the electrospun fibers combined with biomaterials had a degradability unmatched by commercial carriers. The structure design strategy provides ideas for the innovative design of pheromone carriers and is a potential tool for the management of agricultural pests.

Role of Fungi in Imparting General Disease Suppressiveness in Soil from Organic Field

Soil microbial communities are key players responsible for imparting suppressive potential to the soil against soil-borne phytopathogens. Fungi have an immense potential to inhibit soil-borne phytopathogens, but the fungal counterpart has been less explored in this context. We assessed the composition of fungal communities in soil under long-term organic and conventional farming practice, and control soil. The disease-suppressive potential of organic field was already established. A comparative analysis of the disease suppressiveness contributed by the fungal component of soil from conventional and organic farms was assessed using dual culture assays. The quantification of biocontrol markers and total fungi was done; the characterization of fungal community was carried out using ITS-based amplicon sequencing. Soil from organic field exhibited higher disease-suppressive potential than that from conventional farming, against the pathogens selected for the study. Higher levels of hydrolytic enzymes such as chitinase and cellulase, and siderophore production were observed in soil from the organic field compared to the conventional field. Differences in community composition were observed under conventional and organic farming, with soil from organic field exhibiting specific enrichment of key biocontrol fungal genera. The fungal alpha diversity was lower in soil from the organic field compared to the conventional field. Our results highlight the role of fungi in contributing to general disease-suppressive ability of the soil against phytopathogens. The identification of fungal taxa specifically associated with organic farming can aid in understanding the mechanism of disease suppression under such a practice, and can be exploited to induce general disease suppressiveness in otherwise conducive soil.

Construction and formulation optimization of prothioconazole nanoemulsions for the control of Fusarium graminearum: Enhancing activity and reducing toxicity

In this study, the optimal emulsifier for prothioconazole nanoemulsions was initially screened based on appearance, microscopic observation, mean droplet size and polydispersity index (PDI). In addition, the BoxBehnken design method is adopted, and the optimal formula is screened with an emulsification time, emulsifier content, and solvent content as a single factor. On this basis, the nanoemulsion meets FAO standards for various indicators. The contact angle of droplets on wheat leaves was significantly reduced. This nanoemulsion also showed good inhibitory activity against Fusarium graminearum (EC₅₀ =1.94 mg L^-1), low acute toxicity to zebrafish (LC₅₀ =26.35 mg L^-1) and good biosafety to BEAS-2B cells. The nanoemulsion reduced the adverse effects of pesticide on wheat seed germination and growth. This study can help promote the design and manufacture of stable, efficient and safe agricultural nanoemulsions, and is expected to benefit the sustainable development of green plant protection.

Resistance risk assessment of Fusarium pseudograminearum from wheat to prothioconazole

Fusarium crown rot (FCR), primarily caused by Fusarium pseudograminearum, poses significant threats to cereal crops worldwide. Prothioconazole is a demethylation inhibitor (DMI) fungicide used to control FCR. However, the risk of resistance in F. pseudograminearum to prothioconazole has not yet been evaluated. In this study, the sensitivity of a total of 255 F. pseudograminearum strains obtained from Henan Province, China to prothioconazole were determined by the mycelial growth inhibition. The results showed that the effective concentration to 50% growth inhibition (EC₅₀) of these strains ranged from 0.4228 μg/mL to 2.5284 μg/mL, with a mean EC₅₀ value of 1.0692 ± 0.4527 μg/mL (mean ± SD). Thirty prothioconazole-resistant mutants were obtained out of six selected sensitive parental strains by means of fungicide taming. The resistant mutants exhibited defects in vegetative growth, conidia production, and pathogenicity on wheat seedlings compared to their parental strains. Under ion, cell wall, and temperature stress conditions but not osmotic stress, all the mutants exhibited decreased growth rates compared with their parental strains, which was consistent with the control treatment. Cross-resistance test showed that there was a cross-resistance relationship between prothioconazole and four DMI fungicides, including prochloraz, metconazole, tebuconazole and hexaconazole, but no cross-resistance was observed between prothioconazole and carbendazim, phenamacril, fludioxonil, or azoxystrobin. Although no site mutation occurred on Cyp51a and Cyp51b genes, the constitutive expression level of the Cyp51a gene was significantly increased in all mutants. After being treated with prothioconazole, the Cyp51a and Cyp51b genes were significantly increased in both the resistant mutants and their parents. These results suggested that the resistance to prothioconazole of the mutants may be attributed to the changes of the relative expression level of Cyp51a and Cyp51b genes. Taken together, these results could provide a theoretical basis for the scientific use of prothioconazole in the field and fungicide resistance management strategies.

Effectiveness of slow-release fungicide formulations for suppressing potato pathogens

BACKGROUND

For the first time, the biological activity of slow-release fungicide formulations for suppressing potato pathogens deposited in a degradable poly-3-hydroxybutyrate/sawdust base has been obtained and investigated.

RESULTS

The slow-release fungicide formulations (azoxystrobin, azoxystrobin + mefenoxam, and difenoconazole) were studied in vitro and in vivo in comparison with commercial analogues. In in vitro cultures of phytopathogens, the deposited fungicides showed an inhibitory effect comparable to commercial analogues, limiting the growth of colonies of Phytophthora infestans, Alternaria longipes, Rhizoctonia solani and Fusarium solan (2.0-2.3 times relative to the negative control). In laboratory experiments, the use of deposited fungicides was accompanied by earlier germination and more active growth of potatoes against the background of a decrease in the area of plant damage and an increase in yield. In the field experiment, the deposited fungicides suppressed the development of Phytophthora and Alternariosis in the rhizosphere during the entire growing season and reduced the area of plant damage by pathogens by 10-15%, which is two times less than in the groups of plants treated with commercial preparations. The higher biological activity of the embedded fungicides ensured the maximum number of tubers undamaged by pathogens and the total yield of 22-23 t ha^-1 , which exceeded the yields in the groups with commercial fungicides (18.4-20.8 t ha^-1 ).

CONCLUSION

The slow-release fungicide formulations deposited in a degradable P(3HB)/sawdust base are effective in protecting potatoes from pathogens and increasing yields and have an advantage over commercial counterparts. © 2022 Society of Chemical Industry.

Polymers Use as Mulch Films in Agriculture-A Review of History, Problems and Current Trends

The application of mulch films for preserving soil moisture and preventing weed growth has been a part of agricultural practice for decades. Different materials have been used as mulch films, but polyethylene plastic has been considered most effective due to its excellent mechanical strength, low cost and ability to act as a barrier for sunlight and water. However, its use carries a risk of plastic pollution and health hazards, hence new laws have been passed to replace it completely with other materials over the next few years. Research to find out about new biodegradable polymers for this purpose has gained impetus in the past few years, driven by regulations and the United Nations Organization's Sustainable Development Goals. The primary requisite for these polymers is biodegradability under natural climatic conditions without the production of any toxic residual compounds. Therefore, biodegradable polymers developed from fossil fuels, microorganisms, animals and plants are viable options for using as mulching material. However, the solution is not as simple since each polymer has different mechanical properties and a compromise has to be made in terms of strength, cost and biodegradability of the polymer for its use as mulch film. This review discusses the history of mulching materials, the gradual evolution in the choice of materials, the process of biodegradation of mulch films, the regulations passed regarding material to be used, types of polymers that can be explored as potential mulch films and the future prospects in the area.

Degradable Poly(3-hydroxybutyrate)-The Basis of Slow-Release Fungicide Formulations for Suppressing Potato Pathogens

Three-component slow-release fungicide formulations with different modes of action of the active ingredients for suppressing potato pathogens were constructed for the first time. The difenoconazole, mefenoxam, prothioconazole, and azoxystrobin fungicides were embedded in the degradable polymer P(3HB)/birch wood flour blend and examined using SEM, IR spectroscopy, X-ray analysis, DTA, and DSC. Results showed that no chemical bonds were established between the components and that they were physical mixtures that had a lower degree of crystallinity compared to the initial P(3HB), which suggested different crystallization kinetics in the mixtures. The degradation behavior of the experimental formulations was investigated in laboratory micro-ecosystems with pre-characterized field soil. The slow-release fungicide formulations were prolonged-action forms with a half-life of at least 50-60 d, enabling gradual and sustained delivery of the active ingredients to plants. All slow-release fungicide formulations had a strong inhibitory effect on the most common and harmful potato pathogens (Phytophthorainfestans, Alternarialongipes, Rhizoctoniasolani, and Fusariumsolani).

Systemic fungicidal activity of phenazine-1-carboxylic acid-valine conjugate against tobacco sore shin and its translocation and accumulation in tobacco (Nicotiana tabacum L.)

BACKGROUND

Tobacco sore shin caused by Rhizoctonia solani Kühn is a major soil-borne fungal disease of tobacco, gradually causing infected stems to become thin and dry, leading to great losses to China's tobacco industry. Fungicides with phloem mobility are needed for application to foliage to effectively control root or vascular system pathogens. In this study, phenazine-1-carboxylic acid-valine conjugate (PCA-Val) with strong phloem mobility was tested for control of tobacco sore shin. In vitro fungicidal activity, systemicity, and in vivo efficacy of PCA-Val against R. solani in tobacco seedling were evaluated.

RESULTS

In vitro fungicidal activity of PCA-L-Val against R. solani was lower than that of PCA or PCA-D-Val, but the in vivo protective activity and curative activity of PCA-L-Val was the highest among these chemicals tested. The systemicity tests in tobacco seedlings revealed that PCA did not possess phloem mobility, while PCA-L-Val and PCA-D-Val exhibited strong phloem mobility and could be transported and accumulated in the lower part of the seedling as well as throughout the phloem. In addition, we also found that, just like reported hormone amino acid conjugates, PCA-L-Val could be hydrolyzed by tobacco seedlings, to release free PCA.

CONCLUSIONS

The current research results indicated that PCA-L-Val possess good phloem transport in tobacco and promising in vivo antifungal activity against R. solani, which can be used as a phloem-mobile fungicide against tobacco sore shin in production practice.