Bidirectional Uptake, Transfer, and Transport of Dextran-Based Nanoparticles in Plants for Multidimensional Enhancement of Pesticide Utilization

The development of effective multifunctional nano-delivery approaches for pesticide absorption remains a challenge. Here, a dextran-based pesticide delivery system (MBD) is constructed to deliver tebuconazole for multidimensionally enhancing its effective utilization on tomato plants. Spherical MBD nanoparticles are obtained through two-step esterification of dextran, followed by tebuconazole loading using the Michael addition reaction. Confocal laser scanning microscopy shows that fluorescein isothiocyanate-labeled MBD nanoparticles can be bidirectionally transported in tomato plants and a modified quick, easy, cheap, effective, rugged, and safe-HPLC approach demonstrates the capacity to carry tebuconazole to plant tissues after 24 h of root uptake and foliar spray, respectively. Additionally, MBD nanoparticles could increase the retention of tebuconazole on tomato leaves by up to nearly 2.1 times compared with the tebuconazole technical material by measuring the tebuconazole content retained on the leaves. In vitro antifungal and pot experiments show that MBD nanoparticles improve the inhibitory effect of tebuconazole against botrytis cinerea by 58.4% and the protection against tomato gray molds by 74.9% compared with commercial suspensions. Furthermore, the MBD nanoparticles do not affect the healthy growth of tomato plants. These results underline the potential for the delivery system to provide a strategy for multidimensional enhancement of pesticide efficacy.

Adding Metal Ions to the Bacillus mojavensis D50 Promotes Biofilm Formation and Improves Ability of Biocontrol

Bacillus mojavensis D50, a biocontrol strain, is used to prevent and treat the fungal plant pathogen Botrytis cinerea. Bacillus mojavensis D50's biofilms can affect its colonization; thus, the effects of different metal ions and culture conditions on biofilm formation were determined in this study. The results of medium optimization showed that Ca²⁺ had the best ability to promote biofilm formation. The optimal medium composition for the formation of biofilms contained tryptone (10 g/L), CaCl₂ (5.14 g/L), and yeast extract (5.0 g/L), and the optimal fermentation conditions included pH 7, a temperature of 31.4 °C, and a culture time of 51.8 h. We found that the antifungal activity and abilities to form biofilms and colonize roots were improved after optimization. In addition, the levels of expression of the genes luxS, SinR, FlhA, and tasA were up-regulated by 37.56-, 2.87-, 12.46-, and 6.22-fold, respectively. The soil enzymatic activities which related biocontrol-related enzymes were the highest when the soil was treated by strain D50 after optimization. In vivo biocontrol assays indicated that the biocontrol effect of strain D50 after optimization was improved.

Synergistic Effects of Clonostachys rosea Isolates and Succinate Dehydrogenase Inhibitors Fungicides against Gray Mold on Tomato

Gray mold caused by Botrytis cinerea is a devastating disease in tomatoes. Site-specific fungicide application is still key to disease management; however, chemical control has many drawbacks. Here, the combined application of a biological agent, Clonostachys rosea, with newly developed succinate dehydrogenase inhibitors (SDHI) fungicides showed stronger synergistic effects than the application of SDHI fungicides alone on tomato gray mold control. C. rosea 67-1 has been reported as an efficient biological control agent (BCA) for B. cinerea. Little information is currently available about the combination of C. rosea and fungicides in the control of gray mold. By testing the sensitivity to fungicides with different action mechanisms, C. rosea isolates showed high tolerance to SDHI fungicides (1000 μg mL^-1) on PDA, and the conidial germination rate was almost not affected under 120 μg mL^-1 of fluxapyroxad and fluopyram. In greenhouse experiments, the control effect of the combination of C. rosea and fluxapyroxad or fluopyram against tomato gray mold was significantly increased than the application of BCA or SDHI fungicides alone, and the combination allows a two-fold reduction of both the fungicide and BCA dose. Further, the biomass of B. cinerea and C. rosea on tomato plants was determined by qPCR. For B. cinerea, the trend of detection level for different treatments was consistent with that of the pot experiments, and the lowest biomass of B. cinerea was found when treated with C. rosea combined with fluxapyroxad and fluopyram, respectively. For C. rosea, qPCR assay confirmed its colonization on tomato plants when mixed with fluopyram and fluxapyroxad. These results indicated that combining C. rosea 67-1 with the SDHI fungicides could synergistically increase control efficacy against tomato gray mold.

Discovery of Natural Rosin Derivatives Containing Oxime Ester Moieties as Potential Antifungal Agents to Control Tomato Gray Mold Caused by Botrytis cinerea

Inspired by the application of natural products against pathogenic fungi, two series of dehydroabietyl oxime ester derivatives were synthesized using rosin as a raw material. Based on the evaluation and screening of in vitro antifungal activities against Botrytis cinerea (B. cinerea), Sclerotinia sclerotiorum, Valsa mali, Rhizoctonia solani, Fusarium oxysporum, and Alternaria alternata, compound 4f exhibited the best antifungal activity against B. cinerea, and its EC₅₀ was 0.798 mg/L, which was lower than that of the positive control trifloxystrobin (1.112 mg/L). The in vivo antifungal activity results showed that 4f had satisfactory protective and curative effects on tomato. Physiological and biochemical studies showed that the action mechanism of compound 4f against B. cinerea is to change the morphology and the ultrastructure of the mycelium, increase the permeability of the cell membrane, and cause nucleus and mitochondrial dysfunction, thus leading to apoptosis. In addition, qualitative and quantitative structure-activity relationship studies showed that the inductive and conjugative interactions between compound 4f and the target receptor form an electron transfer process, thereby achieving an antifungal effect. These results indicated that compound 4f, which was derived from the natural product rosin, is a novel potential fungicidal candidate against B. cinerea.

Primary Mode of Action of the Novel Sulfonamide Fungicide against Botrytis cinerea and Field Control Effect on Tomato Gray Mold

Botrytis cinerea is considered an important plant pathogen and is responsible for significant crop yield losses. With the frequent application of commercial fungicides, B. cinerea has developed resistance to many frequently used fungicides. Therefore, it is necessary to develop new kinds of fungicides with high activity and new modes of action to solve the increasingly serious problem of resistance. During our screening of fungicide candidates, one novel sulfonamide compound, N-(2-trifluoromethyl-4-chlorphenyl)-2-oxocyclohexyl sulfonamide (L13), has been found to exhibit good fungicidal activity against B. cinerea. In this work, the mode of action of L13 against B. cinerea and the field control effect on tomato gray mold was studied. L13 had good control against B. cinerea resistant to carbendazim, diethofencarb, and iprodione commercial fungicides in the pot culture experiments. SEM and TEM observations revealed that L13 could cause obvious morphological and cytological changes to B. cinerea, including excessive branching, irregular ramification or abnormal configuration, and the decomposition of cell wall and vacuole. L13 induced more significant electrolyte leakage from hyphae than procymidone as a positive control. L13 had only a minor effect on the oxygen consumption of intact mycelia, with 2.15% inhibition at 50 μg/mL. In two locations over 2 years, the field control effect of L13 against tomato gray mold reached 83% at a rate of 450 g ai ha⁻¹, better than the commercial fungicide of iprodione. Moreover, toxicological tests demonstrated the low toxicological effect of L13. This research seeks to provide technical support and theoretical guidance for L13 to become a real commercial fungicide.

A novel Trichoderma asperellum strain DQ-1 promotes tomato growth and induces resistance to gray mold caused by Botrytis cinerea

Gray mold caused by Botrytis cinerea is a major cause of economic losses during tomato production. In this study, we obtained 23 Trichoderma strains from tomato rhizosphere soil and their inhibitory effects on B. cinerea and the promoting effects on tomato growth were determined. Among them, the inhibition rate of strain DQ-1 on B. cinerea was 88.56%; compared with the control group, after treatment with strain DQ-1, the seeds germination rate and root length of tomato increased by 5.55 and 37.86%. The induced disease resistance of strain DQ-1 was evaluated by pot experiments. The disease incidence (DI) and disease severity index (DSI) of tomato pre-inoculated with strain DQ-1 and then inoculated with B. cinerea were reduced by 38 and 64% compared with the control. Furthermore, we detected the expression levels of tomato disease resistance related genes PR2 and TPX, ethylene pathway related genes ETR1 and CTR1 and jasmonic acid pathway related genes LOX1 and PAL in challenging and non-challenging inoculation treatments. The results showed that the tomato treated with strain DQ-1 triggered the system acquired resistance (SAR) and induced systemic resistance (ISR) pathway, thereby enhancing the disease resistance of tomato. Then the strain DQ-1 was identified as Trichoderma asperellum based on morphological characteristics and phylogenetic information. This study suggests that the novel T. asperellum strain DQ-1 can be a potential candidate for the biological control of gray mold in tomato.

Multiscale Parallel Algorithm for Early Detection of Tomato Gray Mold in a Complex Natural Environment

Plant disease detection technology is an important part of the intelligent agricultural Internet of Things monitoring system. The real natural environment requires the plant disease detection system to have extremely high real time detection and accuracy. The lightweight network MobileNetv2-YOLOv3 model can meet the real-time detection, but the accuracy is not enough to meet the actual needs. This study proposed a multiscale parallel algorithm MP-YOLOv3 based on the MobileNetv2-YOLOv3 model. The proposed method put forward a multiscale feature fusion method, and an efficient channel attention mechanism was introduced into the detection layer of the network to achieve feature enhancement. The parallel detection algorithm was used to effectively improve the detection performance of multiscale tomato gray mold lesions while ensuring the real-time performance of the algorithm. The experimental results show that the proposed algorithm can accurately and real-time detect multiscale tomato gray mold lesions in a real natural environment. The F1 score and the average precision reached 95.6 and 93.4% on the self-built tomato gray mold detection dataset. The model size was only 16.9 MB, and the detection time of each image was 0.022 s.

A Biocontrol Strain of Pseudomonas aeruginosa CQ-40 Promote Growth and Control Botrytis cinerea in Tomato

Botrytis cinerea infection can be very devastating for tomato production, as it can result in a large-scale reduction in tomato fruit production and fruit quality after harvest. Thus, it negatively affects tomato yield and quality. In this study, a biocontrol bacteria CQ-4 was isolated and screened from the rhizosphere soil of tomato plants. Morphological, physiological, and biochemical characteristics and 16S rDNA sequence analysis revealed that it belongs to the species Pseudomonas aeruginosa, which has a strong antagonistic effect against Botrytis cinerea. In addition, the bacterium's antibacterial spectrum is relatively extensive, and antagonistic tests have shown that it also has varying degrees of inhibition on other 12 plant diseases. The growth promotion test showed that the strain has a clear promotion effect on tomato seed germination and seedling growth. The growth-promoting effect on plant height, stem thickness, dry and fresh weight and main root length of tomato seedlings was significantly improved after the seeds were soaked in a bacterial solution of 2.5 × 108 cfu mL-1 concentration. This did not only maintain the nutritional quality of tomato fruits, but also prevents them from rotting. In vitro and pot experiments showed that the strain CQ-4 can effectively control tomato gray mold, and the control effects on tomato leaves and fruits reached 74.4% and 66.0%, respectively. Strain CQ-4 induce plants to up-regulate the activities of four disease-resistant defense enzymes. The peak enzymatic activities of Phenylalanine Ammonia Lyase (PAL), polyphenol oxidase (PPO), peroxidase (POD), and Superoxide Dismutase (SOD) were increased by 35.6%, 37.6%, 46.1%, and 38.4%, respectively, as compared with the control group. This study found that the strain can solubilize phosphorus, fix nitrogen, and produce cellulase, protease, ferrophilin, and other antibacterial metabolites, but it does not produce chitinase, glucanase, and HCN (hydrocyanic acid). This research screened out an excellent Pseudomonas aeruginosa strain that can stably and effectively control tomato gray mold, and it provided theoretical basis for further development and the application of biological agents.

Combined Use of Trichoderma atroviride CCTCCSBW0199 and Brassinolide to Control Botrytis cinerea Infection in Tomato

Tomato gray mold caused by Botrytis cinerea is one of the main diseases of tomato and significantly impacts the yield and quality of tomato fruit. The overuse of chemical fungicides has resulted in the development of fungicide-resistant strains. Biological control is becoming an alternative method for the control of plant diseases to replace or decrease the application of traditional synthetic chemical fungicides and genus Trichoderma is widely used as a biological agent for controlling tomato gray mold. Brassinolide (BR) is a plant-growth-promoting steroid. To enhance the efficiency and stability of Trichoderma activity against B. cinerea, an optimal combination of Trichoderma atroviride CCTCCSBW0199 and BR that controls B. cinerea infection in tomato was identified. Strain CCTCCSBW0199 was found to have antagonistic activity against B. cinerea both in vitro and in vivo. In addition, a fermented culture of chlamydospores and metabolites, or metabolites only of strain CCTCCSBW0199 also reduced growth of B. cinerea. BR reduced growth of B. cinerea and had no effect on the sporulation and growth of Trichoderma spp. An application of metabolites of a Trichoderma sp. + BR reduced gray mold on tomato leaves by approximately 70.0%. Furthermore, the activities of induced defense response-related enzyme, such as peroxidase, superoxide dismutase, catalase, and phenylalanine ammonia-lyase were increased in tomato plants treated with a Trichoderma sp. + BR. Our data suggested that applying a mix of metabolites of T. atroviride CCTCCSBW0199 + BR was effective at reducing gray mold of tomato and may lay a theoretical foundation for the development of novel biofungicides.

Synergistic Effect of Combined Application of a New Fungicide Fluopimomide with a Biocontrol Agent Bacillus methylotrophicus TA-1 for Management of Gray Mold in Tomato

Gray mold caused by Botrytis cinerea can be a severe disease of tomato infecting leaves and fruits of tomato plants. Chemical control is currently the most effective and reliable method; however, application of fungicides has many drawbacks. The combination of biological control agents with newly developed fungicides may be a practicable method to control B. cinerea. Fluopimomide is a newly developed fungicide with a novel mode of action. Bacillus methylotrophicus TA-1, isolated from rhizosphere soil of tomato, is a bacterial strain with a broad spectrum of antimicrobial activities. Little information is currently available about the effect of fluopimomide and its integrated effect on B. cinerea. Therefore, laboratory, pot, and field experiments were carried out to determine the effects of fluopimomide alone and in combination with B. methylotrophicus TA-1 against gray mold on tomato. The in vitro growth of B. methylotrophicus TA-1 was unaffected by 100 mg liter^-1 fluopimomide. Inhibition of B. cinerea mycelial growth was significantly increased under combined treatment of fluopimomide and B. methylotrophicus TA-1. In greenhouse experiments, efficacy against gray mold was significantly greater by an integration of fluopimomide and B. methylotrophicus TA-1 than by either alone; control efficacy of fluopimomide at 50 and 100 g ha^-1 in combination with B. methylotrophicus TA-1 at 10⁸ colony-forming units (cfu) ml^-1 reached 70.16 and 69.32%, respectively, compared with the untreated control. In both field trials during 2017 and 2018, control efficacy was significantly higher for the combination of fluopimomide at 50 and 100 g ha^-1 in combination with B. methylotrophicus TA-1 than for either treatment alone. The results from this study indicated that integration of the new fungicide fluopimomide with the biocontrol agent B. methylotrophicus TA-1 synergistically increased control efficacy of the fungicide against gray mold of tomato.

A Biocontrol Strain of Bacillus subtilis WXCDD105 Used to Control Tomato Botrytis cinerea and Cladosporium fulvum Cooke and Promote the Growth of Seedlings

In this study, a strain named WXCDD105, which has strong antagonistic effects on Botrytis cinerea and Cladosporium fulvum Cooke, was screened out from the rhizosphere of healthy tomato plants. The tomato plants had inhibition diameter zones of 5.00 mm during the dual culture for four days. Based on the morphological and physiological characteristics, the 16S rDNA sequence, and the gyrB gene sequence analysis, the strain WXCDD105 was identified as Bacillus subtilis suBap. subtilis. The results of the mycelial growth test showed that the sterile filtrate of the strain WXCDD105 could significantly inhibit mycelial growth of Botrytis cinerea and Cladosporium fulvum Cooke. The inhibition rates were 95.28 and 94.44%, respectively. The potting experiment showed that the strain WXCDD105 made effective the control of tomato gray mold and tomato leaf mold. The control efficiencies were 74.70 and 72.07%. The antagonistic test results showed that the strain WXCDD105 had different degrees of inhibition on 10 kinds of plant pathogenic fungi and the average inhibition rates were more than 80%. We also found that the strain WXCDD105 stimulated both the seed germination and seedling growth of tomatoes. Using the fermentation liquid of WXCDD105 (10⁸ cfu·mL^−1) to treat the seeds, the germination rate and radicle length were increased. Under the treatment of the fermentation liquid of the strain WXCDD105 (10⁶ cfu·mL^−1), nearly all physiological indexes of tomato seedlings were significantly higher than that of the control groups. This could not only keep the nutritional quality of tomato fruits but also prevent them from rotting. This study provided us with an excellent strain for biological control of tomato gray mold, tomato leaf mold, and tomato growth promotion. This also laid the technical foundation for its application.

Development of a Biofungicide Using a Mycoparasitic Fungus Simplicillium lamellicola BCP and Its Control Efficacy against Gray Mold Diseases of Tomato and Ginseng

To develop a commercial product using the mycoparasitic fungus Simplicillium lamellicola BCP, the scaleup of conidia production from a 5-l jar to a 5,000-l pilot bioreactor, optimization of the freeze-drying of the fermentation broth, and preparation of a wettable powder-type formulation were performed. Then, its disease control efficacy was evaluated against gray mold diseases of tomato and ginseng plants in field conditions. The final conidial yields of S. lamellicola BCP were 3.3 × 10⁹ conidia/ml for a 5-l jar, 3.5 × 10⁹ conidia/ml for a 500-l pilot vessel, and 3.1 × 10⁹ conidia/ml for a 5,000-l pilot bioreactor. The conidial yield in the 5,000-l pilot bioreactor was comparable to that in the 5-l jar and 500-l pilot vessel. On the other hand, the highest conidial viability of 86% was obtained by the freeze-drying method using an additive combination of lactose, trehalose, soybean meal, and glycerin. Using the freeze-dried sample, a wettable powder-type formulation (active ingredient 10%; BCP-WP10) was prepared. A conidial viability of more than 50% was maintained in BCP-WP10 until 22 weeks for storage at 40°C. BCP-WP10 effectively suppressed the development of gray mold disease on tomato with control efficacies of 64.7% and 82.6% at 500- and 250-fold dilutions, respectively. It also reduced the incidence of gray mold on ginseng by 65.6% and 81.3% at 500- and 250-fold dilutions, respectively. The results indicated that the new microbial fungicide BCP-WP10 can be used widely to control gray mold diseases of various crops including tomato and ginseng.