Evaluation of Allyl Isothiocyanate as a Soil Fumigant for Tomato (Lycopersicon esculentum Mill.) Production

Evaluation of Biopesticides for Management of Bemisia tabaci Middle East-Asia Minor 1 (Hemiptera: Aleyrodidae) in Florida

The sweetpotato whitefly, Bemisia tabaci MEAM1, is a pest known to significantly impact tomato development and yields through direct damage and virus transmission. To manage this pest, the current study compared the effectiveness of various insecticide rotations. Field trials included rotations involving synthetic insecticides, biochemicals, and microbial agents, applied according to their highest labeled concentrations. The results indicated that while standard synthetic insecticides consistently reduced whitefly egg and nymph counts significantly, microbial biopesticide rotations also achieved reductions, although less consistently. This study demonstrated that while traditional chemical treatments remain highly effective, microbial biopesticides containing Beauveria bassiana and Cordyceps javanica present a viable alternative to manage MEAM1 in tomato fields. The data generated in this study provided baseline information for further investigations to determine the potential for optimizing integrated pest management (IPM) and insecticide resistance management (IRM) strategies by incorporating microbial biopesticides in rotations with a variety of modes of action to sustainably manage B. tabaci MEAM1 populations in agricultural settings.

In vitro application of Eruca vesicaria subsp. sativa leaf extracts and associated metabolites reduces the growth of Oomycota species involved in Kiwifruit Vine Decline Syndrome

This study aimed to determine whether leaf extracts from seven Eruca vesicaria subsp. sativa cultivars and their biochemically active compounds (glucosinolates and downstream-derived products) inhibit mycelia growth of three well-known pathogenic oomycetes, Phytopythium chamaehyphon, Phytopythium vexans and Phytophthora citrophthora; being the most significant in the development of Kiwifruit Vine Decline Syndrome (KVDS). Leaf extract quantity of 10, 20 and 30 mg were inoculated in Petri dish (90 mm Ø, each 22 mL of liquid medium - Potato Dextrose Agar), for in vitro bioassays. A pathogen plug was placed in the centre of each plate and the Oomycota colony perimeter was marked 5 days after inoculation. Radial colony growth was measured from 4 marks per plate 5, 10, and 15 days after inoculation, further elaborated with Image J software image analysis. Growth rates for all strains were inhibited by around 67% after 15 days. This was most pronounced when applying the highest concentration of leaf extract. By using Liquid Chromatography Mass Spectrometry (LC-MS) and Gas Chromatography Mass Spectrometry (GC-MS), fifteen glucosinolate compounds, of which glucosativin was found in the highest quantity, were identified. Concentrations of hydrolysis products produced by leaves (erucin and sativin) were also investigated, and were significantly associated with colony radial growth, especially towards Pp. chamaehyphon and Pp. vexans. Three downstream products of glucosinolates (two pure isothiocyanates, AITC and PEITC; and one indole I3C; all commonly present in Brassicaceae) were also tested, and a statistically significant inhibition of growth was observed at the highest concentration (0.6 µL).

Effects of allyl isothiocyanate fumigation on medicinal plant root knot disease control, plant survival, and the soil bacterial community

BACKGROUND

Allyl isothiocyanate (AITC) is a natural product with high volatility that is used as a biofumigant to alleviate soil-borne plant diseases, and problems such as root knot nematodes (RKNs) that necessitate continuous cropping. However, little research has assessed the effects of AITC fumigation on medicinal plants.

RESULTS

AITC significantly reduced the population of RKNs in soil (p < 0.0001) and showed an excellent RKN disease control effect within 6 months after sowing Panax notoginseng (p < 0.0001). The seedling survival rate of 2-year-old P. notoginseng was approximately 1.7-fold higher after soil treatment with AITC (p = 0.1008). 16S rRNA sequencing indicated that the AITC treatment affected bacterial richness rather than diversity in consecutively cultivated (CC) soil. Furthermore, biomarkers with statistical differences between AITC-treated and untreated CC soil showed that Pirellulales (order), Pirellulaceae (family), Pseudomonadaceae (family), and Pseudomonas (genus) played important roles in the AITC-treated group. In addition, the microbiome functional phenotypes predicted using the BugBase tool suggested that AITC treatment is more conducive to improving CC soil through changes in the bacterial community structure. Crucially, our research also suggested that AITC soil treatment significantly increases soil organic matter (p = 0.0055), total nitrogen (p = 0.0054), and available potassium (p = 0.0373), which promotes the survival of a succeeding medicinal plant (Polygonatum kingianum).

CONCLUSION

AITC is an ecologically friendly soil treatment that affects the top 10 bacterial richness but not diversity. It could also provide a basis for a useful agricultural soil management measure to alleviate soil sickness.

Impact of Disruption and Drying Conditions on Physicochemical, Functional and Antioxidant Properties of Powdered Ingredients Obtained from Brassica Vegetable By-Products

Reintroducing waste products into the food chain, thus contributing to circular economy, is a key goal towards sustainable food systems. Fruit and vegetable processing generates large amounts of residual organic matter, rich in bioactive compounds. In Brassicaceae, glucosinolates are present as secondary metabolites involved in the biotic stress response. They are hydrolysed by the enzyme myrosinase when plant tissue is damaged, releasing new products (isothiocyanates) of great interest to human health. In this work, the process for obtaining powdered products from broccoli and white cabbage by-products, to be used as food ingredients, was developed. Residues produced during primary processing of these vegetables were transformed into powders by a process consisting of disruption (chopping or grinding), drying (hot-air drying at 50, 60 or 70 °C, or freeze drying) and final milling. The impact of processing on powders' physicochemical and functional properties was assessed in terms of their physicochemical, technological and antioxidant properties. The matrix response to drying conditions (drying kinetics), as well as the isothiocyanate (sulforaphane) content of the powders obtained were also evaluated. The different combinations applied produced powdered products, the properties of which were determined by the techniques and conditions used. Freeze drying better preserved the characteristics of the raw materials; nevertheless, antioxidant characteristics were favoured by air drying at higher temperatures and by applying a lower intensity of disruption prior to drying. Sulforaphane was identified in all samples, although processing implied a reduction in this bioactive compound. The results of the present work suggest Brassica residues may be transformed into powdered ingredients that might be used to provide additional nutritional value while contributing to sustainable development.

Sorghum cover crop and repeated soil fumigation for purple nutsedge management in tomato production

BACKGROUND

Purple nutsedge (Cyperus rotundus L.) is one of the most common and troublesome weeds. Field research trials were conducted in Florida to evaluate the effects of repeated fumigation and a sorghum sudangrass [Sorghum bicolor S. bicolor var. sudanense (Piper) Stapf.] cover crop on purple nutsedge (Cyperus rotundus L.) populations over time in tomato (Solanum lycopersicum L.) production.

RESULTS

Among the soil fumigants, DMDS + metam potassium was consistently the most effective treatment in terms of in-crop purple nutsedge control. Plots with a sorghum cover crop during the fallow period exhibited higher purple nutsedge density during the tomato growing season as well as higher purple nutsedge shoot and tuber densities during the fallow period compared to the chemical fallow.

CONCLUSION

DMDS + metam potassium was the most effective fumigant for purple nutsedge control. Unexpectedly, a sorghum cover crop during the fallow period was less effective than chemical fallow for purple nutsedge management, and therefore we do not recommend the use of sorghum cover crops for weed management in fields where purple nutsedge is the major weed species.

Long-term effect of fumigation and a sorghum cover crop on broadleaf and grass weeds in plastic-mulched tomato

BACKGROUND

Broadleaf and grass weeds can adversely affect growth and productivity of plastic-mulched tomato (Solanum lycopersicum L.). Two, four-year research trials were conducted in Florida to evaluate the effect of repeated fumigation and chemical fallow versus a sorghum [Sorghum bicolor S. bicolor var. sudanense (Piper) Stapf.] cover crop on broadleaf and grass weeds in tomato plasticulture.

RESULTS

1,3-Dichloropropene (1,3-D) + chloropicrin (Pic), dimethyl disulfide (DMDS) + Pic, and DMDS + metam potassium effectively controlled broadleaf weeds in-crop and reduced densities by 79-98% compared to the non-fumigated control but provided inconsistent control of grass weeds. DMDS + metam potassium was generally the most effective fumigant. During the fallow period, a sorghum cover crop effectively reduced broadleaf weed density than the chemical fallow, while chemical fallow effectively reduced grass weed density than the cover crop. The fallow program did not affect in-crop densities of broadleaf and grass weeds. In some measurements, the evaluated fumigants resulted in taller tomato plants and higher yield compared to the non-fumigated control.

CONCLUSION

We conclude that the evaluated soil fumigants effectively control broadleaf and grass weeds. Planting a sorghum cover crop effectively suppresses broadleaf weeds but not grasses during the fallow period. However, this suppression does not result in reduced weed density in-crop despite the fact that similar weed species were observed in both time periods. © 2020 Society of Chemical Industry.

Deciphering the Behavioral Response of Meloidogyne incognita and Fusarium oxysporum Toward Mustard Essential Oil

Environmental concerns related to synthetic pesticides and the emphasis on the adoption of an integrated pest management concept as a cardinal principle have strengthened the focus of global research and development on botanical pesticides. A scientific understanding of the mode of action of biomolecules over a range of pests is key to the successful development of biopesticides. The present investigation focuses on the in silico protein-ligand interactions of allyl isothiocyanate (AITC), a major constituent of black mustard (Brassica nigra) essential oil (MEO) against two pests, namely, Meloidogyne incognita (Mi) and Fusarium oxysporum f. sp. lycopersici (Fol), that cause severe yield losses in agricultural crops, especially in vegetables. The in vitro bioassay results of MEO against Mi exhibited an exposure time dependent on the lethal concentration causing 50% mortality (LC₅₀) values of 47.7, 30.3, and 20.4 μg ml^-1 at 24, 48, and 72 h of exposure, respectively. The study revealed short-term nematostatic activity at lower concentrations, with nematicidal activity at higher concentrations upon prolonged exposure. Black mustard essential oil displayed excellent in vitro Fol mycelial growth inhibition, with an effective concentration to cause 50% inhibition (EC₅₀) value of 6.42 μg ml^-1. In order to decipher the mechanism of action of MEO, its major component, AITC (87.6%), which was identified by gas chromatography-mass spectrometry (GC-MS), was subjected to in silico docking and simulation studies against seven and eight putative target proteins of Mi and Fol, respectively. Allyl isothiocyanate exhibited the highest binding affinity with the binding sites of acetyl cholinesterase (AChE), followed by odorant response gene-1 (ODR1) and neuropeptide G-protein coupled receptor (nGPCR) in Mi, suggesting the possible suppression of neurotransmission and chemosensing functions. Among the target proteins of Fol, AITC was the most effective protein in blocking chitin synthase (CS), followed by 2,3-dihydroxy benzoic acid decarboxylase (6m53) and trypsinase (1try), thus inferring these as the principal molecular targets of fungal growth. Taken together, the study establishes the potential of MEO as a novel biopesticide lead, which will be utilized further to manage the Mi-Fol disease complex.

New Insights on the Role of Allyl Isothiocyanate in Controlling the Root Knot Nematode Meloidogyne hapla

Biofumigation, although a well-known method, is still controversially debated as a management strategy for plant-parasitic nematodes (PPN). Its controlling effect is attributed to the production of isothiocyanates (ITCs) following the action of myrosinase on glucosinolates (GSLs). Different ITCs are formed from different GSLs, depending on the plant species. To better understand the potential of ITCs, eight cultivars from three Brassicaceae species were investigated as biofumigation crops to control the root knot nematode Meloidogyne hapla. Since results were inconsistent, the nematicidal effect of selected ITCs were further evaluated in vitro. Based on its nematicidal potential, allyl ITC (AITC) was specifically investigated under different soil:sand compositions. A significantly lower nematicidal activity was observed in soil compared to sand. AITC was also evaluated as an additive to the biofumigation in a greenhouse trial. Its supplementation to the biofumigation process with Brassica juncea cv. Terrafit controlled M. hapla, while no control was observed using Raphanus sativus cv. Defender. Thus, the success of biofumigation seems to be strongly dependent on the soil characteristics and the ITC produced during the biofumigation process. Therefore, the supplementation of AITC in combination with the right cover crop can improve the biofumigation process to control M. hapla.

Pest control with drip-applied dimethyl disulfide and chloropicrin in plastic-mulched tomato (Solanum lycopersicum L.)

BACKGROUND

Dimethyl disulfide (DMDS) is used as a preplant soil fumigant for weed and soilborne pathogen control in plasticulture vegetable crops. The objective of this research was to determine the control efficacy of emulsifiable concentrate (EC) formulation of DMDS or DMDS + chloropicrin (Pic) on weed and Fusarium wilt in tomato (Solanum lycopersicum L.) plasticulture.

RESULTS

The effective DMDS rates required to provide 50% (ER₅₀ ) control of purple nutsedge (Cyperus rotundus L.) were 210 and 340 kg ha^-1 at 4 weeks after fumigation (WAF) in fall 2017 and fall 2018, respectively, while these values increased to 348 and >467 kg ha^-1 , respectively, at 12 WAF. The ER₅₀ values of DMDS + Pic were 150 and 240 kg ha^-1 at 4 WAF in fall 2017 and fall 2018, respectively, while these values increased to 255 and 450 kg ha^-1 , respectively, at 12 WAF. DMDS + Pic was generally more effective than DMDS for C. rotundus control. The high rates of DMDS or DMDS + Pic provided adequate C. rotundus control in early season but failed to provide effective control by season end. In addition, DMDS + Pic injections through drip tape effectively reduced Fusarium oxysporum f. sp. lycopersici (FOL) inoculum while DMDS alone was generally ineffective.

CONCLUSION

Injection of the EC formulation of DMDS or DMDS + Pic through drip tape should have been provided a viable option for C. rotundus and Fusarium wilt control in plastic-mulched tomato. However, supplemental weed management actions, such as herbicide applications, may be required to achieve season-long control. © 2019 Society of Chemical Industry.