Reduced Root Galling Research Articles

Phytocytokine StPep1-Secreting Bacteria Suppress Potato Powdery Scab Disease.

Powdery scab is an important potato disease caused by the soilborne pathogen Spongospora subterranea f. sp. subterranea. Currently, reliable chemical control and resistant cultivars for powdery scab are unavailable. As an alternative control strategy, we propose a novel approach involving the effective delivery of a phytocytokine to plant roots by the rhizobacterium Bacillus subtilis. The modified strain is designed to secrete the plant elicitor peptide StPep1. In our experiments employing a hairy root system, we observed a significant reduction in powdery scab pathogen infection when we directly applied the StPep1 peptide. Furthermore, our pot assay, which involved pretreating potato roots with StPep1-secreting B. subtilis, demonstrated a substantial decrease in disease symptoms, including reduced root galling and fewer tuber lesions. These findings underscore the potential of engineered bacteria as a promising strategy for safeguarding plants against powdery scab.

Control of Southern root-knot nematode on tomato using soil amendments

The present results found that organic waste materials were effective against the root-knot nematode that attacks tomatoes under field conditions and significantly reduced root gall indices, nematodes and egg masses compared to the control. Organic soil amendments stimulate the activities of microorganisms that are antagonistic to root-knot nematodes.

Nematicidal activity of <i>Ageratum conyzoides</i> leaf extract against root-knot nematode (<i>Meloidogyne javanica</i>) on eggplant in Jalingo, Nigeria

Devastation of crops by pests is exacerbated by human activities but nature provides remedies that are environmentally friendly. This study was carried out to evaluate the activity of A. conyzoides leaf extract against Meloidogyne javanica on eggplant in Jalingo, Nigeria. Three concentrations (crude extract, 5 ml and 10 ml dilutions) of extract of Ageratum conyzoides as well as control (no application) were applied on juveniles and eggs of M. javanica in petri dishes in the laboratory in 2018 and 10 ml of the same extract was applied into holes at the base of eggplants transplanted into a nematode-infested field in 2018 and 2019. Result of the juvenile mortality test showed that the extract treatments caused the mortality of M. javanica juveniles with crudes extract being highest at 90.3%. Results of the egg hatch inhibition test also showed the extract treatments significantly reduced egg hatch compared to control with crude extract having the highest inhibition of 85.5%. Field experiment in both years indicated that the extract treatments recorded significantly (P˂0.05) better result than control in all parameters in both years. There was reduced root galling and nematode reproduction and by extension final nematode population with attendant high yield in extract-treated plants. It is therefore concluded that A. conyzoides has the potential for use as a bio-pesticide against M. javanica.

A Novel Robust Screening Assay Identifies Pseudomonas Strains as Reliable Antagonists of the Root-Knot Nematode Meloidogyne incognita.

Forty-four bacterial strains isolated from greenhouse soil and beetroots were tested for their antagonistic activity against the plant-parasitic root-knot nematode (RKN) Meloidogyne incognita, which causes significant yield losses in a number of important crops worldwide. Through a novel combination of in vitro and on planta screening assays, Pseudomonas spp. 105 and 108 were identified as the most promising bacterial isolates. Both strains were evaluated for their potential to control different RKN population densities and as root protectants against nematode infestation. Regardless of the application method, both strains significantly reduced root galling caused by M. incognita. These two strains were subjected to whole genome sequencing and de novo genome assembly as a basis for phylogenetic and future functional characterization. Phylogenetic analysis revealed that both Pseudomonas strains cluster within the Pseudomonas fluorescens clade among previously characterized RKN antagonists and Pseudomonas-based biocontrol agents of plant diseases.

Effect of Different Rates, Application Timing, and Combination of Nonfumigant Nematicides in Control of Meloidogyne incognita in Watermelon

The use of plasticulture systems, which consist of raised beds, plastic mulch, and drip irrigation, for watermelon production has increased in the Southern United States in recent decades. The root-knot nematode (RKN), Meloidogyne incognita, is a significant pathogen of watermelon production in plasticulture systems and can cause varying levels of yield loss depending on the nematode population density if not properly controlled. A few new nonfumigant nematicides (fluensulfone, fluazaindolizine, and fluopyram) have emerged in the last decade to help manage RKNs. A 2-year field study was conducted to examine the impact of different rates, application timing (i.e., days before transplanting, at transplanting, and days after transplanting), and combinations of these new nematicides and an older one (oxamyl) in control of RKN in watermelon cultivar Fascination. The nematicide treatments, except for a single-time application of oxamyl in 2019 and 2020, significantly reduced root galling compared with the untreated check. Similarly, all treatments, except a single application of oxamyl in 2020, resulted in a lower soil population level of M. incognita than the untreated check. All nematicide treatments, except a single application of fluensulfone and a two-time application of fluopyram at a half-recommended rate, increased fruit yields when compared with the untreated check. Overall, the drip application of new chemistries, known as 3-F nematicides, has been shown to be a useful option for RKN management in watermelon. At-planting application of fluazaindolizine or fluopyram and two-time applications of oxamyl based on the manufacturer's recommended rate show potential to prevent crop loss.

Screening of the nematicidal potential of some spice extracts against root-knot nematode, Meloidogyne arenaria (Neal, 1889) Chitwood, 1949 (Tylenchida: Meloidogynidae)

Experiments were conducted in the laboratories and greenhouses of Plant Protection Department, Agricultural Faculty, Ondokuz Mayıs University in 2018 and 2019 to investigate the nematicidal effects of aqueous extracts of 13 spices on Meloidogyne arenaria (Neal, 1889) Chitwood, 1949 (Tylenchida: Meloidogynidae). Spice extract concentrations of 0.5, 1 and 2% were tested in laboratory experiments for inhibition of egg hatching, mortality and immobility of second-stage juveniles (J2s). When used at a concentration of 2%, clove, Syzygium aromaticum L. (Myrtales: Myrtaceae) caused the greatest immobility and mortality of J2s. The extracts had a lesser effect on J2s than the egg hatching. For the pot experiment, five effective spices extracts were selected based on the laboratory experiments. These extracts were applied at 2% to 200 g of soil inoculated with 3,000 nematode eggs then susceptible tomato seedlings were transplanted into the soil. Forty-five days after inoculation, the gall index and the quantity of nematode eggs on roots were determined and reproduction factor of nematode calculated. All extracts, except cumin, Cuminum cyminum L. (Apiales: Apiaceae), reduced root gall index and the reproduction factor when compared to control. Basil, Ocimum basilicum L. (Lamiales: Lamiaceae) extract reduced nematode reproduction the greatest degree, followed by turmeric, Curcuma longa L. (Zingiberales: Zingiberaceae) and clove extracts.

Evaluation of bacterial formulations as potential biocontrol agents against the southern root-knot nematode, Meloidogyne incognita

BackgroundBacterial bioagents, Pseudomonas fluorescens, P. putida, Bacillus amyloliquifaciens, and B. megaterium, have management potential against root-knot nematode (RKN), Meloidogyne incognita, in bottle gourd.ResultsField and laboratory experiments were conducted to evaluate the effect of bacterial bioagents Bacillus megaterium 1% WP (2 × 106 CFU/g), B. amyloliquifaciens 1% WP (2 × 108 CFU/g), Pseudomonas putida 1% WP (2 × 108 CFU/g), P. fluorescens 1% WP (2 × 109 CFU/g) on egg hatching and juvenile mortality of root-knot nematode, M. incognita. All the bacterial species inhibited the egg hatching in M. incognita and caused juvenile mortality. The lowest mean egg hatching in 120 h. after treatment was observed in P. putida (20.9% mean egg hatching), followed by P. fluorescens (21.1%), B. amyloliquifaciens (23.7%), and B. megaterium (24.7%) at 4% concentration of the formulated product against (47%) egg hatching in control. The juvenile mortality was found highest (57.1% mean mortality) in P. fluorescens in 120 h. of exposure, followed by P. putida (56.13%), B. megaterium (54.46%), and B. amyloliquifaciens (53.13%) at 4% concentration against 0.46 mean juvenile mortality in control, where distilled water was used. Under field conditions, the bottle gourd seeds that were treated either with B. amyloliquefaciens, B. megaterium, P. fluorescens, or P. putida at 10 g/kg seed along with the application of neem cake (1t/ha) significantly resulted in reduced root gall index and the number of nematode juveniles in soil and roots than the non-treated control.ConclusionThis study revealed that the tested bacterial bioagents, namely B. amyloquefaciens, B. megaterium, P. fluorescens, and P. putida, showed the potential for controlling of root knot nematode (RKN) in the laboratory as well as in field conditions in bottle gourd.

Sensitivity of Meloidogyne enterolobii and M. incognita to fluorinated nematicides.

Meloidogyne enterolobii (Yang and Eisenback) was recently introduced into Louisiana on contaminated sweetpotato planting material. Given the known variation in sensitivity to nematicides within the genus Meloidogyne, there is question as to whether fluorinated nematicides will be as efficacious toward M. enterolobii as they are with M. incognita (Chitwood). Using a series of in vitro and growth cabinet experiments, this study compared the sensitivity of M. enterolobii and M. incognita to four synthetic non-fumigant nematicides (fluopyram, fluensulfone, fluazaindolizine, and oxamyl). Meloidogyne enterolobii had lower sensitivity to nematicides than M. incognita in the majority of the in vitro exposure assays. Similar levels of reduction in root infectivity were observed after nematicide exposure among both nematode species. Fluopyram showed high hatching inhibition for both Meloidogyne species at low concentrations [median effective concentration (EC50 ) values of 0.273 to 0.018 mg L-1 ], whereas fluensulfone showed high root penetration inhibition at low concentrations (EC50 values of 0.151 to 0.065 mg L-1 ) relative to that of other evaluated nematicides. For both Meloidogyne species, each of the four non-fumigant nematicides reduced root galling (58-96% reduction for M. enterolobii, 71-100% reduction for M. incognita) and egg production (63-99% reduction for M. enterolobii, 58-96% reduction for M. incognita) on sweetpotato when applied at the label recommended rate. Fluorinated nematicides and oxamyl show capacity to suppress M. enterolobii on sweetpotato. © 2021 Society of Chemical Industry.

Reducing root galling caused by root knot nematodes in black pepper (<em>Piper nigrum</em> L. cv. ‘Kuching’) through nutrient supplementation

Purpose: Root-knot nematodes (RKN) remain one of the leading causes of economic damage in black pepper (Piper nigrum L.) cultivation worldwide. An experiment was conducted to evaluate the response of black pepper plants to RKN when irrigated with three nutrient solutions; Hoagland solution only, Hoagland solution + 0.005 mM potassium silicate solution, and Hoagland solution + 2 mM salicylic acid solution. Research Method: Plants grown in medium-sized polybags were inoculated with RKN and routinely irrigated with the appropriate nutrient solutions. Presence of foliar symptoms of RKN infection on plants, their aerial growth plus root infestation were assessed. Superoxide anion and hydrogen peroxide production from the plant leaves were also detected after inoculation. Findings: Foliar symptoms of RKN infection started manifesting after 81 days from inoculation. Plants without silicate or salicylic acid supplementation displayed the most severe foliar disorder symptoms, highest root galling and the shortest aerial growth. Plants irrigated with potassium silicate had the highest aerial growth and their leaves showed the least oxidative stress when challenged with RKN. Originality: From present results, soil amendment with potassium silicate is a promising tool for reducing root galling and promoting aerial growth in RKN-infested black pepper fields.

Biocontrol Potential of Cinnamon Bark Extracts and Chitosan Against Meloidogyne incognita Inflicted Disease in Black Pepper Plants

In this study, we aimed to evaluate the nematicidal activity of cinnamon bark extracts (CE) and chitosan (Cs) against Meloidogyne incognita under in vitro, pot, and field conditions. In the pot experiments, CE mixed with Cs effectively inhibited M. incognita infection on black pepper plants. We applied the following formulations, which all significantly reduced the gall index and nematode number in 5 g of root and 100 g of soil: CE:Cs = 5 mg:20 mg, 10 mg:40 mg, and 15 mg:60 mg per pot. In addition, the application of CE:Cs = 32 mg:120 mg, 64 mg:240 mg, and 96 mg:360 mg per plant effectively reduced root gall formation and nematode density in black pepper roots and soil compared with that of the non-treated control under field conditions. Nematode density in the black pepper roots was positively correlated with the percentage of plants with yellow leaves. These results suggest that cinnamon mixed with chitosan may be used as an effective and eco-friendly pesticide against plant parasitic nematodes.

Influence of Rhizopheric H2O2 on Growth, Mineral Absorption, Root Anatomy and Nematode Infection of Ficus deltoidea

Hydrogen peroxide (H2O2) is a broad-range chemical catalyst that is receiving rapidly increasing attention recently due to its role as a signaling molecule in various plant physiological and biochemical processes. A study was carried out to investigate the effects of H2O2 on the plant physiology, root growth, mineral nutrient accumulation, root anatomy, and nematode control of Ficus deltoidea, a slow growing shade tolerant and nematode susceptible medicinal plant. H2O2 at 0 (control), 15, 30, 60, and 90 mM was injected into the root zone of plants weekly. The results showed that the treatment of H2O2 enhanced the accumulation of pigments, photosynthetic characteristics, and quantum yield (Fv/Fm) of F. deltoidea. H2O2 at a 90 mM treatment significantly increased seedling height, leaf number, syconium number, biomass yield, relative water content, leaf dry matter, leaf moisture, and live line fuel moisture of the plant by 1.35-, 3.02-, 3.60-, 5.13-, 1.21-, 1.12-, 1.79- and 1.06-fold, respectively, over the control plant. In addition, root growth, which includes root crown diameter, root length, root volume, root tips, number of roots and root biomass, also exhibited the highest values with an application of 90 mM of H2O2. Heavy metals arsenic (As+) and antimony (Sb+) content in the leaves decreased by 4.08-and 1.63-fold, respectively, in the 60 mM H2O2 treated plant when compared to the control plant. In addition, 90 mM H2O2 was the best treatment for magnesium (Mg2+), calcium (Ca2+), and sodium (Na+) mineral accumulation in the syconium of F. deltoidea. Treatments with 60 mM H2O2 increased magnesium (Mg2+), calcium (Ca2+), and potassium (K+) content in leaves by 14%, 19%, and 15%, respectively, over the control plant. In the study of controlling root-knot nematode, both control and 15 mM treatments produced many root galls, whereas, 60 mM H2O2 treatment produced fewer tiny root galls and 90 mM of H2O2 showed no root gall formation. H2O2 treatments reduced root gall size, root/shoot ratio, and increased the shoot biomass of plants. The treated root developed an epidermal suberin, root periderm, resin duct, cortex, druses, and a well-developed vascular system compared to the control plants. Furthermore, no nematodes were observed in the roots of treated plants with 30–90 mM H2O2. The study concluded that injections of 60–90 mM H2O2 to the root zone weekly improved plant physiology, increased mineral accumulation, root growth and development, reduced root gall formation, improved root cellular structure, and controlled root-knot nematode of F. deltoidea plants.

Nemato-toxic potential of <em>Trichoderma harzianum</em> and <em>T. viride</em> extra-cellular metabolites and <em>Annona glabra</em> crude extraction on <em>Meloidogyne incognita</em> infestation

Root-knot nematode, Meloidogyne incognita (Kofoid and White) is one of the most destructive plant parasitic nematode species in almost all agriculture and horticulture crops in Sri Lanka. Biologically sound controlling measures against this nematode species has been attempted from long past with ambiguous efficacy. This paper highlights the nemato-toxic potential of crude leaf extract of Annona glabra, and extracellular metabolites of Trichoderma harzianum and T. viride on root-knot nematode species, Meloidogyne incognita infesting in spinach plants under semi-field conditions. Results revealed that nematode infested plants treated with T. harzianum extract showed a significantly higher plant growth together with reduced root galling compared to that of T. viride and A. glabra crude extract. Both T. harzianum and T. viride treatments significantly increased the root growth of the nematode infested plants compared to that of A. glabra crude extract. Annona glabra crude leaf extract at the rate of 125 g/L and fungus mycelium of T. viride and T. harzianum at the rate of 140 mg/L and 100 mg/L respectively resulted the highest nemato-toxic potential against M. incognita. This study concludes positive effect of antagonists tested against M. incognita and suggests that activity of lytic enzymes of T. harzianum and T. viride has enhanced the nemato-toxic effect.

Polysulfides Applied as Formulated Garlic Extract to Protect Tomato Plants against the Root-Knot Nematode Meloidogyne incognita.

The devastating root-knot nematode Meloidogyne incognita can cause severe damage to field and greenhouse crops. Due to high economic losses, alternative products are essential to replace banned or strictly regulated nematicides that affect human health and/or the environment. Garlic based products have been previously investigated as environmentally friendly nematicides and their active substances, diallyl polysulfides exist as formulated nematicides on the market. We tested the garlic-based nematicide NEMguard® DE as protective of tomato roots. In vitro evaluation of the lethal concentration (LC) showed strong nematicidal activity with LC50 of 0.8 mg/mL after 96 h and LC90 of 1.5 mg/mL. NEMguard® DE showed protective effect against M. incognita as a single application in small pots and a second application further reduced root galling, significantly. Large greenhouse trials were carried out in two consecutive years to test single and monthly applications of NEMguard® DE. In both years, no controlling effect could be observed on M. incognita. We assume that the silt content of the loamy sandy soil used had an effect on the polysulfides, inhibiting their nematicidal effect. We conclude that further experiments are necessary to investigate the nematicidal potential of NEMguard® DE under different soil compositions or as a different formulation.

Evaluation of fluazaindolizine, a new nematicide for management of Meloidogyne incognita in squash in calcareous soils

The southern root-knot nematode (Meloidogyne incognita) is one of the major problems affecting squash production in Florida and worldwide. Calcareous soils exist in south Florida, and squash in Miami-Dade County is grown in this type of soil. Environmentally friendly and low-toxic non-fumigant nematicides for managing M. incognita are urgently needed. Fluazaindolizine is a new compound that has been evaluated on vegetable crops and proven to be a highly effective non-fumigant nematicide. However, its efficacy against M. incognita in squash and its effect on squash fruit yield in calcareous soils are not documented. Field trials were conducted in 2019 and 2020 to evaluate the effect of fluazaindolizine on root galling and populations of M. incognita in the soil, plant vigor, and fruit yield of squash grown in calcareous soils in south Florida. In both field experiments, all treatments containing fluazaindolizine significantly (p < 0.05) reduced root galling index of squash caused by M. incognita, compared to the untreated control. Fluazaindolizine at 2.24 L/ha (FI 2x) applied at seeding and fluazaindolizine at 1.12 L/ha applied at seeding and again 14 days after seeding (FI 1x + FI 1x) was most effective in reducing root galling index. M. incognita populations were consistently significantly (p < 0.05) reduced by FI 1x + FI 1x in both trials, compared to the untreated control (1054 and 3344 per 100 mL of soil, respectively) with a suppression of 58.4% and 63.6%, respectively. In the 2019 experiment 1, all treatments significantly (p < 0.05) increased squash plant vigor and yield of fruit (except F1 x). In the 2020 experiment 2, there were no significant differences in squash plant vigor and yield between treatments and the untreated control. Results from the field trials indicated that fluazaindolizine was an effective non-fumigant nematicide that could aid in management of M. incognita in squash in calcareous soils of south Florida.

Nematicidal activity of cinnamon bark extracts and chitosan against Meloidogyne incognita and Pratylenchus coffeae

Summary In this study, we aimed to evaluate the nematicidal activity of cinnamon bark extracts (CE) and chitosan (Cs) against Meloidogyne incognita and Pratylenchus coffeae under pot and field conditions. In the pot experiments, CE mixed with Cs effectively inhibited M. incognita and P. coffeae infection on robusta coffee plants. The formulations applied, CE:Cs = 8 mg:30 mg, CE:Cs = 16 mg:60 mg and CE:Cs = 16 mg:60 mg per pot, significantly reduced the gall index and nematode number in 5 g of root and 100 g of soil. In addition, the application of CE:Cs = 48 mg:180 mg CE:Cs = 80 mg:300 mg and CE:Cs = 112 mg:420 mg plant−1 effectively reduced root gall formation and nematode density in roots and soil compared with the non-treated control under field conditions. Nematode density in the roots was positively correlated with the rate of yellow leaf disease. These results suggest that cinnamon mixed with chitosan may be used as an effective eco-friendly pesticide against plant-parasitic nematodes.

Fluazaindolizine mitigates plant-parasitic nematode activity at sublethal dosages

Plant-parasitic nematodes are significant pests for many crops with considerable economic impact worldwide. Alternatives to highly toxic soil fumigants and nematicides are urgently sought after. Fluazaindolizine is a fluorinated nematicide with a novel, unknown mode-of-action and very low mammalian toxicity. The current research investigated the early responses of several plant-parasitic nematode species to the compound by in vitro mortality and parasitism trials with nematode-susceptible host plants. After a 72-h in vitro exposure time, fluazaindolizine exhibited the most potent toxic activity against the second-stage juveniles (J2) of Meloidogyne incognita and Tylenchulus semipenetrans with LC50 values of 177.14 and 355.2 mg L−1, respectively. Pratylenchus brachyurus, J2 of the Heterodera schachtii, and eggs of M. incognita were considerably less sensitive to the nematicide. The fitness of M. incognita J2 was strongly affected when exposed to various concentrations of fluazaindolizine for 12 h before inoculation of cucumber seedlings in soilless seed pouches. The lowest level of 5 mg L−1 reduced root galling, egg mass production, and the number of eggs to about 25% compared to the water control. In another bioassay, H. schachtii J2 were exposed to fluazaindolizine at 100 and 200 mg L−1 for 72 h before used to infest soil with 3-day-old radish seedlings. About 39.8% and 59.6%, respectively, fewer J2 invaded the roots compared to the control. In conclusion, the tested nematode species varied considerably in their in vitro mortality following fluazaindolizine exposure. However, the bioassays demonstrated that parasitism was already severely impacted at non-lethal concentrations and short-term exposure to the nematicide.

Identification of quantitative trait loci underlying resistance and tolerance to the rice root-knot nematode, Meloidogyne graminicola, in Asian rice (Oryza sativa)

Meloidogyne graminicola is one of the most important plant-parasitic nematodes in rice. Breeding for natural resistance and tolerance is considered one of the most economical and sustainable approaches to control this damaging pathogen. Quantitative trait loci (QTL) mapping was carried out in a recombinant inbred line (RIL) population derived from a cross between the Asian rice genotypes IR78877-208-B-1-2 and Dinorado. IR78877-208-B-1-2 is an aerobic rice genotype that is resistant and tolerant to M. graminicola. Dinorado is a traditional upland rice genotype from the Philippines that is characterized by its aroma and prized for its cooking quality. The host response of 300 F4 lines derived from this cross was evaluated in both nematode infested and non-infested concrete beds in the dry seasons of 2013 and 2014. Five genotypes were found consistently resistant while 13 genotypes were consistently partially resistant to M. graminicola. QTL mapping for M. graminicola resistance/tolerance, yield-contributing traits, and yield revealed four main effect QTLs (qJ2RS2.1, qJ2GRT2.1, qJ2RS3.1, and qJ2GRT3.1) associated with reduced nematode reproduction on chromosomes 2 and 3 and two QTLs (qGR3.1 and qGR5.1) associated with reduced root galling on chromosomes 3 and 5. Twenty main effect QTLs associated with yield-contributing traits and yield were also found. Our study further identified co-locating QTLs associated with nematode resistance, yield-contributing traits, and yield on chromosomes 3 and 5. QTLs harboring candidate genes, such as OsBAK1, OsDST, OsIPT4, and DUF26, for higher grain yield and tolerance to abiotic and biotic stress, were identified. These QTLs and the RILs that are consistently resistant and tolerant to M. graminicola, and which are high-yielding in nematode-infested fields, can be utilized in breeding programs to improve the resistance and tolerance of Asian rice to this important pathogen.

Enhancing potato resistance against root-knot nematodes using a plant-defence elicitor delivered by bacteria

The root-knot nematode Meloidogyne chitwoodi is a pest that affects potato production in the Pacific Northwest of the United States. Here, to develop new strategies against M. chitwoodi infection of potato, we engineered Bacillus subtilis to secrete the plant-defence elicitor peptide StPep1. Pre-treatment of potato roots with the bacteria secreting StPep1 substantially reduced root galling, indicating that a bacterial secretion of a plant elicitor is an effective strategy for plant protection.

ACTIVITY OF RUTA GRAVEOLENS L. AGAINST ROOT-KNOT NEMATODES (MELOIDOGYNE spp.)

Two in vitro experiments and two open field trials were carried out to investigate the nematicidal effect of Ruta graveolens on the root-knot nematode Meloidogyne incognita. In the first in vitro experiment the nematode egg masses were immersed for 3 weeks in aqueous leaf extract of rue plants and then subjected to an hatching test in distilled water for five more weeks. In the other in vitro experiment M. incognita egg masses were exposed to the rue extract for 4, 8 and 16 hours and then incubated in distilled water for 8 weeks. Distilled water and a 5 μg/mL an aqueous solution of Fenamiphos or only distilled water were used as controls in the first and second in vitro experiment, respectively. Both hatching tests were carried out in a growth cabinet at 25±2 0C, providing four replicates for each treatment. In the first experiment the hatching from the egg masses treated with rue extracts and Fenamiphos solution resulted significantly lower than that in the untreated control. In the second in vitro experiment, a 8-hour immersion of the egg masses in the rue extract resulted in a final hatch significantly lower than that in distilled water. The nematicidal effect of R. graveolens green manure was investigated in open field condition on tomato and tobacco. Plots amended with rue plant biomass were compared with untreated and Fenamiphos treated plots (3 t/ha). Four replications were provided for each treatment. Crop yield, root gall index and soil nematode population density were recorded at the end of each crop cycle. Soil incorporation with R. graveolens plant materials significantly increased both tomato and tobacco yield and reduced root gall index and soil nematode population density in comparison to the untreated controls. These experiments demonstrated a high suitability of R. graveolens for the development of new sustainable nematicidal products.

Identification and characterization of Javanese root-knot nematode (Meloidogyne javanica) suppressive soils in Florida

In Florida, Javanese root-knot nematode (Meloidogyne javanica) is widely distributed and causes extensive damage to a number of economically important crops. Soil fumigants are commonly used to manage this soilborne pest; however, increasing societal concerns regarding the negative effects of these products on environmental and human health are driving a shift towards more sustainable management options. Of particular interest are naturally occurring nematode suppressive soils. Identifying farming practices and ecological factors that enable suppressive organisms to function and persist in soil will support the implementation of natural biological control. In this study, we evaluated suppressiveness to M. javanica in 12 soils from Florida. Using next-generation sequencing technology, we characterized the bacterial and fungal communities in these soils to further understand how those communities may contribute to nematode suppressive soils. In spring 2018, soil was collected from multiple geographic regions, production systems, and management practices within the state of Florida. In a soil-based suppressiveness assay, soil collected from 7 out of 12 of the sites reduced the recovery of inoculated J2-stage M. javanica relative to that of soil that had been steam-pasteurized. In a plant-based suppressiveness assay, all soils reduced root galling on cucumber by M. javanica relative to that of their steam-pasteurized counterparts. Contrary to other studies on pathogen suppressive soils, enhanced soil bacterial and fungal diversity was not associated with suppressiveness to M. javanica. Differences in soil fungal community composition was a stronger driver of suppressiveness than bacterial community composition, with the fungal orders Xylariales, Mortierellales, and Agaricales showing positive correlation with nematode suppressiveness across 64 % of the sites surveyed. Overall, Florida soils hold considerable potential to naturally regulate M. javanica populations. The use of soil management practices that promote the abundance and activity of suppressive microorganisms may reduce horticultural reliance on soil fumigants.