Management of Root-knot Nematode (Meloidogyne incognita) on Pittosporum tobira Under Greenhouse, Field, and On-farm Conditions in Florida

Plant-Parasitic Nematodes and their Effects on Ornamental Plants: A Review

Worldwide, the ornamental plant industry is estimated to be valued at $70 billion, with the United States' ornamental plant industry valued at $4.8 billion in 2020. Ornamental plants are cultivated for numerous reasons worldwide, such as decorative, medicinal, social, and utility purposes, making the ornamental field a high growth industry. One of the main pathogen groups affecting the yield and growth of the ornamental plant industry is plant-parasitic nematodes, which are microscopic roundworms that feed on plant parts causing significant yield loss. There are many kinds of plant-parasitic nematodes that affect ornamental plants, with the main genera being Meloidogyne spp., Aphelenchoides spp., Paratylenchus spp., Pratylenchus spp., Helicotylenchus spp., Radopholus spp., Xiphinema spp., Trichodorus spp., Paratrichodorus spp., Rotylenchulus spp., and Longidorus spp. The aim of this review is to focus on the effects, hosts, and symptoms of these major plant-parasitic nematodes on ornamental plants and synthesize current management strategies in the ornamental plant industry.

High killing rate of nematode and promotion of rice growth by synthetic volatiles from Bacillus strains due to enhanced oxidative stress response

The plant parasitic nematode Aphelenchoides besseyi is a major pest that poses serious threats to different vegetables and crop plants. In the present study, volatiles isolated from Bacillus spp. were utilized as green biocontrol agents to overcome nematodes. In in vitro experiment, Bacillus spp. GBSC56, SYST2, and FZB42 showed the strongest nematicidal activity with killing rates of 80.78%, 75.69%, and 60.45%, respectively, as compared with control. The selected synthetic volatile organic compounds (VOCs), namely albuterol, benzaldehyde (BDH), 1,2-benzisothiazol-3(2H)-one (1,2-HIT), dimethyl disulfide (DMDS), 2-undecanone (2-UD), and 1,3-propanediole (1,3-PD), exhibited strong nematicidal activity, with A. besseyi killing rate of 85.58%, 82.65%, 81.75%, 80.36%, 84.45%, and 82.36%, respectively, at 400 μg/mL. Microscopic analysis proved that the rapid mortality was due to the production of reactive oxygen species (ROS). Molecular docking attributed this ROS production to the nematicidal effect of synthetic VOCs on NADH DEHYDROGENASE SUBUNIT 2, which is known to play a critical role in the suppression of ROS in nematode models. In a greenhouse experiment, the Bacillus strains GBSC56, SYST2, and FZB42 and their synthetic VOCs significantly improved the physiological parameters in terms of growth promotion traits. In addition, selected genes related to growth promotion and defense genes showed a significant upregulation of their expression in rice seedlings treated with those synthetic VOCs. Overall, these findings revealed that the selected Bacillus strains and their synthetic VOCs possess high potential against A. besseyi. Moreover, this study also sheds new light on the mechanisms by which specific Bacillus nematicidal VOCs influence important genes involved in rice plant growth promotion and could effectively be used to suppress plant parasitic nematodes.

Nematicidal Activity of Burkholderia arboris J211 Against Meloidogyne incognita on Tobacco

Root-knot nematode (Meloidogyne incognita) is the most widespread nematode affecting Solanaceae crops. Due to the lack of effective measures to control this nematode, its management can be achieved, using biocontrol agents. This study investigated in vitro efficacy of the antagonistic bacterial strain J211 isolated from tobacco rhizosphere soil against M. incognita, and further assessed its role in controlling nematodes, both in pot and field trials. Phylogenetic analysis of the 16S rRNA gene sequence of strain J211 assigned to Burkholderia arboris. Culture filtrates B. arboris J211 exhibited anematicidal activity against the second-stage juveniles (J2s) of M. incognita, with a 96.6% mortality after 24 h exposure. Inoculation of J211 in tobacco roots significantly reduced the root galling caused by M. incognita, both in pot and field trials. Meanwhile, plant growth-promoting (PGP) traits results showed that J211 had outstanding IAA-producing activity, and the IAA production reached 66.60 mg L⁻¹. In the field study, B. arboris J211 also promoted tobacco growth and increase flue-cured tobacco yield by 8.7–24.3%. Overall, B. arboris J211 as a high-yielding IAA nematicidal strain effectively controlled M. incognita and improved tobacco yield making it a promising alternative bionematocide.

Entomopathogenic Fungi Biodiversity in the Soil of Three Provinces Located in Southwest China and First Approach to Evaluate Their Biocontrol Potential

Entomopathogenic fungi (EF), who represent active agents to control insect natural populations, usually persist in terrestrial habitats. Southwest area in China has various climate conditions and abundant plant biodiversity (crop, forest, grassy, orchard and arable areas). Nevertheless, the potential of soil-inhabitant EF as insect pest biocontrol agents, is unknown. In this study, first the EF biodiversity from soil of three provinces (Guizhou, Sichuan, and Yunnan) was surveyed. Then, the virulence of 29 isolated strains against Bemesia tabaci and Spodoptera litura was assessed. After analyzing 212 soil samples, 497 isolated fungi were identified. Out of them, 490 isolates were classified in 45 species of 24 genera, whereas the other seven isolates, belonging to Paecilomyces and Purpureocillium genera, were not identified under species level. Furthermore, the EF biodiversity from soil of Sichuan, Yunan, and Guizhou areas, analyzed by Shannon Wiener Index (SWI) was rated at 2.98, 1.89, and 2.14, while SWIs-biodiversity in crop, forest, grassy, orchard and arable areas was rated at 2.88, 2.74, 3.05, 2.39, and 2.47. SWI data suggested that soil from Sichuan area and grassy had higher EF biodiversity compared with other analyzed provinces and areas. Virulence bioassay results indicated that, out of the 29 isolates tested, 24 were pathogenic against B. tabaci and S. litura, resulting in mortality rates >10%. In conclusion, this study reports the EF distribution and biodiversity in soil from three provinces located at Southwest China, whereas their potential use as a tool for the B. tabaci and S. litura biocontrol must be further investigated.

Organic or conventional production system and nutrient rate affect the nematode community in carrot production

Organic and conventional production are common in horticulture crops and each system may exert a different influence on the soil ecosystem, particularly the nematode community. Crop nutrient rate is an important choice in both production systems. The objectives of this study were to assess the impacts of (i) organic and conventional production systems and (ii) nutrient rate in both systems on the nematode community in carrot production. To investigate these objectives, field studies in organic and conventional production - which included fumigation with 1,3-dichloropropene - were conducted in North-Central Florida. In both production systems, nutrient rate treatments were 168, 224, 280, 336, and 392 kg N/ha. Poultry litter was the nitrogen source in organic production whereas synthetic, inorganic fertilizer was used in conventional production. All nematode trophic groups were consistently more abundant in organic than conventional production. The nematode community was more diverse and had greater trophic structure in organic production. Greater rates of organic nutrients increased enrichment opportunists (bacterivores and fungivores), but inconsistently across years. Conventional production had similar results except that only moderate nutrient rates increased fungivore abundances. Extreme enrichment opportunists (Rhabditis spp.) drove bacterivore trends in organic production whereas moderate enrichment opportunists (Cephalobus spp.) drove trends in conventional production. Nutrient rates did not affect omnivore-predators, herbivores, nematode community diversity, or structure in either system. In summary, type of production system, organic or conventional, exerts a strong influence on the nematode community, but nutrient rate has less consistent effects in horticulture production.

N-alkyl isatin derivatives: Synthesis, nematicidal evaluation and protein target identifications for their mode of action

Meloidogyne incognita is an economically dominant pathogen infesting a wide range of crops curbing their growth and productivity. Deregistration of frontline nematicides has necessitated exploration of innovative and novel class of structurally diverse nematicides with streamlined activity. In this context, N-alkylated derivatives of isatin known for their remarkable biological profile were synthesized, characterized and evaluated in vitro for their antinemic character followed by in silico studies for their mode of action and toxicological studies for their fitness as agrochemical. The antinemic evaluation was carried by egg hatch inhibition and juvenile mortality and its effect on egg hatching. Compounds 1 and 2a exhibited nematicidal potential and significantly decreased egg hatching and increased juvenile mortality. For egg hatch inhibition LC₅₀ and LC₉₅ values for 1 were found to be 0.125 and 1.380 mg/ml and for compound 2a, 0.457 and 8.511 mg/ml respectively. For juvenile mortality LC₅₀ and LC₉₅ values for 1 were found to be 0.109 and 0.776 mg/ml and for 2a, 0.190 and 1.380 mg/ml respectively. For insights into the mode of action of the synthesized molecules, in silico studies for the targeted effects were conducted which revealed novel interaction with pathogenic protein - Aspartyl protease. Computational studies on the drug-ability and potential toxicity of the selected compounds revealed they belonged to class IV and are safe. With good reasons, our compounds hold value for their exploration in agrochemical industry and thus, this study identifies a new scaffold with useful level of nematicidal activity for its use in agriculture industry.

From Old-Generation to Next-Generation Nematicides

The phaseout of methyl bromide and the ban on, or withdrawal of, other toxic soil fumigants and non-fumigant nematicides belonging to the organophosphate and carbamate groups are leading to changes in nematode-control strategies. Sustainable nematode-control methods are available and preferred, but not always effective enough, especially for cash crops in intensive agriculture. A few non-fumigant nematicides, which have a relatively high control efficacy with a low toxicity to non-target organisms, have been released to the market or are in the process of being registered for use. Fluensulfone, fluopyram, and fluazaindolizine are the three main and most promising next-generation nematicides. In this paper, several aspects of these non-fumigant nematicides are reviewed, along with a brief history and problems of old-generation nematicides.

New reduced-risk agricultural nematicides - rationale and review

The last decade has seen a sharp increase in nematicide research in the agricultural industry. As a result, several new synthetic nematicides have become available to growers, and several more are expected in the near future. This new interest in nematicides is directly related to the growing demand for safer and more selective products, and the increasing regulatory pressure on many of the traditional nematicides. This has led to a ban of several widely used fumigant (e.g. methyl bromide) and non-fumigant (e.g. aldicarb) nematicides. The loss of traditional nematicides, combined with a lack of replacement products and awareness of the damage that nematodes can cause, has not only raised concern among growers, but has also created new opportunities for the crop protection industry. Nematicides have become a priority, and many companies are now allocating significant research dollars to discover new nematicides. The new nematicides are very different from previous products: (i) they are more selective, often only targeting nematodes, and (ii) they are less toxic, and safer to use. This review article describes these new developments by discussing the challenges that are associated with finding new nematicides, reviewing the nature, characteristics, and efficacy of new nematicides, and discussing the impact they could have on future nematode management.

Dysregulation of endocrine disruption, apoptosis and the transgenerational toxicity induced by spirotetramat

Spirotetramat (SPT) is a new tetronic acid derivative insecticide used to control scales and aphids; the potential for endocrine disruptor effects in fish could not be finalized with the available data. In this study, zebrafish were selected to assess the endocrine-disrupting effects. Significant decrease of plasma estradiol (E2), testosterone (T) and 11-ketotestosterone (11-KT) were observed in both male and female following the spirotetramat exposure; the vitellogenin (VTG) level in females significantly decreased. The expression of the hypothalamic-pituitary-gonad (HPG) axis genes fshr, lhr and esr1 showed significant increase in the gonads, which expression in males is higher than in females. In addition, the activities of capspase-3 and caspase-9 significantly decreased in both males and females liver, while the capspase-3 and caspase-9 were increased in male testis, the mRNA expression levels of genes expression related to the apoptosis pathway were also significantly altered after the spirotetramat exposure. Additionally, we found the parental zebrafish exposed to spirotetramat induced the development delay of its offspring. Above all, the adverse effects induced by spirotetramat suggesting that spirotetramat is a potential exogenous hazardous agent.

Nematicidal activity of 5-iodoindole against root-knot nematodes

Multi-drug resistance in nematodes is a serious problem as lately several resistant phenotypes have emerged following the intermittent usage of synthetic nematicides. Contemporary research continues to focus on developing and/or repurposing small molecule inhibitors that are eco-friendly. Here, we describe the repurposing of the indole derivative, 5-iodoindole, as a nematicide for the root-knot nematode, Meloidogyne incognita. 5-Iodoindole effectively killed juveniles and freshly hatched juveniles by inducing multiple vacuole formation. Notably, at higher dosage (50 μg/mL), 5-iodoindole induced rapid juvenile death within 6 h. Microscopic analysis confirmed that the rapid death was due to the generation of reactive oxygen species (ROS). Computational docking attributed this ROS production to the antagonistic effect of 5-iodoindole on glutathione S-transferase (GST), which is known to play a critical role in the suppression of ROS in nematode models. Furthermore, 5-iodoindole also effectively reduced the gall formations and eggs masses of M. incognita on Solanum lycopersicum roots in pot experiments, and importantly it did not harm the physiological properties of the plant. Overall, the study provides valuable insights on the use of 5-iodoindole as an alternate measure to control root-knot nematodes. Overall, our findings suggest the efficacy of 5-iodoindole should be studied under field conditions.

Biodiversity of Entomopathogenic Fungi in the Soils of South China

The southern part of China, located in tropical and south subtropical areas has unique natural environments, but the distributions of entomopathogenic fungi (EFs) in the soil are not clear. In this research, 198 soil samples were collected from the four Provinces (Autonomous Region) of South China. The results indicated that a total of 292 fungal isolates were obtained from 176 soil samples. Then, based on the morphological and rDNA-ITS sequences analysis, 213 EFs isolates of 19 species in 12 genera were identified. Furthermore, Purpureocillium lilacinum with 75 isolates was recognized as the absolutely dominant EF species, while Isaria javanica, Metarhizium anisopliae, and Beauveria bassiana (respectively with 29, 26, and 26 isolates) were the richer species. The data also indicated that Guangxi Province has the best EFs diversity with the Shannon–Wiener index (SWI) of 2.29, the soils covered with grass had the best EFs diversity with the 2.14 SWI, while the orchard and fallow land had the lowest SWI of 1.52, which suggested that the diversity of plants and insects on ground, as well as the massive application of broad-spectrum fungicides, affect the EFs diversity in the soil. Finally, the rare species, Nectria mauritiicola and Scopulariopsis brumptii were first reported about their entomopathogenic activities against Bemisia tabaci. Our experiment will give new insights to the understanding of EFs distribution characteristics and their biodiversity conservation.

Human Pathogenic Paecilomyces from Food

Paecilomyces spp. and Byssochlamys spp. are heat-resistant fungi important to industry because they can cause food and beverage spoilage, incurring economic loss. The consequences of food or beverage fungal colonization is the loss of nutritional value, structure and taste, and the possibility of producing toxic secondary metabolites that may result in medical problems. Furthermore, these fungi can infect animals and humans and it is unknown if contaminated foods may be fomites. P. variotii is the principal agent of food spoilage or contamination and it is most frequently associated with human hyalohyphomycosis with clinical manifestations including peritonitis, cutaneous and disseminated infections, among others. Byssochlamys spp. had not been identified as a cause of systemic infection until the case of a dog with a fungal infection, after immunosuppressive therapy. P. variotii has clinical importance because it causes severe infection in immunosuppressed patients and also because the number of immunocompetent infected patients is increasing. This review draws attention to the ability of these species to grow at high temperatures, to colonize food products, and to cause human disease.

Microbial biopesticides for invertebrate pests and their markets in the United States

Microbial pesticides based on bacteria, fungi and viruses or their bioactive compounds have long been developed as alternatives for synthetic pesticides to control invertebrate pests. However, concern for environmental and human health from excessive reliance on chemical pesticides, changes in residue standards, and increased demand for organically grown produce has contributed to a considerable growth in their use in recent years. There are currently 356 registered biopesticide active ingredients in the U.S., including 57 species and/or strains of microbes or their derivatives, labelled for use against pestiferous insects, mites and nematodes. Strains of Bacillus thuringiensis for Lepidoptera remain the most popular products, but newer bacterial strains and their metabolites have been developed against a wider range of arthropods for use on fruit, vegetable and ornamental crops. Currently, ten fungal species/strains are registered against thrips, whiteflies, aphids, or other sucking pests and plant parasitic nematodes in greenhouse, nursery and field crops, while five nucleopolyhedroviruses and three granuloviruses are registered for Lepidoptera in field and greenhouse grown vegetables and ornamentals, tree fruit and nuts, forestry, and stored products. Many of these products are organic listed and most have 4 h or less reentry and no pre-harvest restrictions. Investment by multinational companies, advances in screening, industrial fermentation and storage of new microorganisms, are increasing the market share for microbials. Here, we summarize the market for microbial-based pesticides labelled for invertebrates in the U.S. We cover current uses and recent advances that further advance their use in additional markets in the coming decades.

Field efficacy of furfural as a nematicide on turf

A commercial formulation of furfural was recently launched in the United States as a turfgrass nematicide. Three field trials evaluated efficacy of this commercial formulation on dwarf bermudagrass putting greens infested primarily with Belonolaimus longicaudatus, Meloidogyne graminis, or both these nematodes, and in some cases with Mesocriconema ornatum or Helicotylenchus pseudorobustus. In all these trials, furfural improved turf health but did not reduce population densities of B. longicaudatus, M. graminis, or the other plant-parasitic nematodes present. In two additional field trials, efficacy of furfural at increasing depths in the soil profile (0 to 5 cm, 5 to 10 cm, and 10 to 15 cm) against B. longicaudatus on bermudagrass was evaluated. Reduction in population density of B. longicaudatus was observed in furfural-treated plots for depths below 5 cm on several dates during both trials. However, no differences in population densities of B. longicaudatus were observed between the furfural-treated plots and the untreated control for soil depth of 0 to 5 cm during either trial. These results indicate that furfural applications can improve health of nematode-infested turf and can reduce population density of plant-parasitic nematodes in turf systems. Although the degree to which turf improvement is directly caused by nematicidal effects is still unclear, furfural does appear to be a useful nematode management tool for turf.