Biological silicon nanoparticles maximize the efficiency of nematicides against biotic stress induced by Meloidogyne incognita in eggplant

Nemours effective management tactics were used to reduce world crop losses caused by plant-parasitic nematodes. Nowadays the metallic nanoparticles are easily developed with desired size and shape. Nanoparticles (NPs) technology becomes a recognized need for researchers. Ecofriendly and biosafe SiNPs are developed from microorganisms. Recently, silicon nanoparticles (SiNPs) have gained novel pesticide properties against numerous agricultural pests. This study assessed the biosynthesis of SiNPs from Fusarium oxysporum SM5. The obtained SiNPs were spherical with a size of 45 nm and a negative charge of −25.65. The nematocidal effect of SiNPs against egg hatching and second-stage juveniles (J2) of root-knot nematode (RKN) (Meloidogyne incognita) was evaluated on eggplant,Solanum melongena L. plants. In vitro, all tested SiNPs concentrations significantly (p ≤ 0.05) inhibited the percentage of egg hatching at a different time of exposure than control. Meanwhile, after 72 h, the percent mortality of J2 ranged from 87.00 % to 98.50 %, with SiNPs (100 and 200 ppm). The combination between SiNPs and the half-recommended doses (0.5 RD) of commercial nematicides namely,  fenamiphos (Femax 40 % EC)^R, nemathorin (Fosthiazate 10 % WG) ^R, and fosthiazate (krenkel 75 % EC) ^R confirmed the increase of egg hatching inhibition and J2 mortality after exposure to SiNPs (100 ppm) mixed with 0.5 RD of synthetic nematicides. The findings suggest that the combination between SiNPs, and 0.5 RD of nematicides reduced nematode reproduction, gall formation, egg masses on roots and final population of J2 in the soil. Therefore, improving the plant growth parameters by reducing the M. incognita population.     

Predicting Damage of Meloidogyne incognita on Watermelon

Quantitative growth response of watermelon (Citrullus lanatus) sensitive to Meloidogyne incognita is poorly understood. Determination of soil population densities of second-stage juveniles (J2) of M. incognita with Baermann funnel extraction often is inaccurate at low soil temperatures. In greenhouse experiments, three sandy soils were inoculated with dilution series of population densities of eggs or J2 of M. incognita and planted in small containers to watermelon ‘Royal Sweet’ or subjected to Baermann funnel extraction. After five weeks of incubation in the greenhouse bioassay plants in egg-inoculated soils, gall numbers on watermelon roots related more closely to inoculated population densities than J2 counts after Baermann funnel extraction. In April 2004, perpendicularly-inserted tubes (45-cm diameter, 55-cm deep) served as microplots where two methyl bromide-fumigated sandy soils were inoculated with egg suspensions of M. incognita at 0, 100, 1,000 or 10,000 eggs/100 cm³ of soil in 15-cm depth. At transplanting of 4-week old watermelon seedlings, soils were sampled for the bioassay or for extraction of J2 by Baermann funnel. In the Seinhorst function of harvested biomass in relation to nematode numbers, decline of biomass with increasing population densities of M. incognita was accurately modeled by the inoculated eggs (R² = 0.93) and by the counts of galls on the bioassay roots (R² = 0.98); but poorly by J2 counts (R² = 0.68). Threshold levels of watermelon top dry weight to M. incognita were 122 eggs/100 cm³ soil, 1.6 galls on bioassay roots, or 3.6 J2/100 cm³ of soil. Using the bioassay in early spring for predicting risk of nematode damage appeared useful in integrated pest management systems of watermelon.     

Effects of Inoculum Level and Time of Microcoleus vaginatus on Control of Meloidogyne incognita on Tomato

Application of Microcoleus vaginatus, a blue-green alga (Cyanobacterium) at different levels along with Meloidogyne incognita, second stage larvae, in the rhizosphere of tomato plants; showed that the plant growth as well as yield of tomato were increased and gall formations and nematode populations decreased with the increase in inoculum level of M. vaginatus. An inoculum level of 20 ml endospores suspension of M. vaginatus (2.4 × 10⁶ endospores per ml) per plant was optimum to reduce nematode attack with a population density of 1000 larvae per kg soil. Plant growth and yield of fruits were greatly suppressed and gall formations on roots, and nematode populations in soil were increased when M. incognita larvae added five days prior to M. vaginatus inoculation. On the other hand, when M. vaginatus inoculated ten days before nematode inoculation, suppressive effect of M. incognta on plants was reduced and their population density as well as gall formations were also decreased significantly. The efficacy of simultaneous inoculation of both nematode and M. vaginatus was lied in between two treatments discussed above.     

Bio-activity of fungal culture filtrates against root-knot nematode egg hatch and juvenile motility and their effects on growth of mung bean (Vigna radiata L. Wilczek) infected with the root-knot nematode,Meloidogyne incognita

Culture filtrates of selected soil fungi, namely Aspergillus flavus, Aspergillus fumigatus, Aspergillus niger, Fusarium oxysporum, Penicillium vermiculatum and Rhizopus nigricans exhibited variable response to egg hatching and mortality of the root-knot nematode, Meloidogyne incognita. Higher concentrations of the culture filtrates of all the fungi inhibited egg hatching and proved to be toxic to the juveniles of M. incognita. In addition, development of the gall and multiplication of M. incognita were also found adversely affected in varying degrees on all the plants of Vigna radiata treated with the filtrates. The culture filtrate of A. niger showed highest toxicity to the nematode than those of any other fungus tested. Soil drench application of the culture filtrates gave better seedling growth and least nematode multiplication in comparison to seed soaking treatment.     

Post-transcriptional gene silencing of root-knot nematode in transformed soybean roots

RNAi constructs targeted to four different genes were examined to determine their efficacy to reduce galls formed by Meloidogyne incognita in soybean roots. These genes have high similarity with essential soybean cyst nematode (Heterodera glycines) and Caenorhabditis elegans genes. Transformed roots were challenged with M. incognita. Two constructs, targeted to genes encoding tyrosine phosphatase (TP) and mitochondrial stress-70 protein precursor (MSP), respectively, strongly interfered with M. incognita gall formation. The number of galls formed on roots transformed with constructs targeting the M. incognita TP and MSP genes was reduced by 92% and 94.7%, respectively. The diameter of M. incognita inside these transformed roots was 5.4 and 6.5 times less than the diameter of M. incognita found inside control plants transformed with the empty vector. These results indicate that silencing the genes encoding TP and MSP can greatly decrease gall formation and shows a promising solution for broadening resistance of plants against this plant-parasitic nematode.     

Identification of Sources of Resistance to Four Species of Root-knot Nematodes in Tobacco

Resistance to the southern root-knot nematode, Meloidogyne incognita races 1 and 3, has been identified, incorporated, and deployed into commercial cultivars of tobacco, Nicotiana tabacum. Cultivars with resistance to other economically important root-knot nematode species attacking tobacco, M. arenaria, M. hapla, M. javanica, and other host-specific races of M. incognita, are not available in the United States. Twenty-eight tobacco genotypes of diverse origin and two standard cultivars, NC 2326 (susceptible) and Speight G 28 (resistant to M. incognita races 1 and 3), were screened for resistance to eight root-knot nematode populations of North Carolina origin. Based on root gall indices at 8 to 12 weeks after inoculation, all genotypes except NC 2326 and Okinawa were resistant to M. arenaria race 1, and races 1 and 3 of M. incognita. Except for slight root galling, genotypes resistant to M. arenaria race 1 responded similarly to races 1 and 3 of M. incognita. All genotypes except NC 2326, Okinawa, and Speight G 28 showed resistance to M. javanica. Okinawa, while supporting lower reproduction of M. javanica than NC 2326, was rated as moderately susceptible. Tobacco breeding lines 81-R-617A, 81-RL- 2K, SA 1213, SA 1214, SA 1223, and SA 1224 were resistant to M. arenaria race 2, and thus may be used as sources of resistance to this pathogen. No resistance to M. hapla and only moderate resistance to races 2 and 4 of M. incognita were found in any of the tobacco genotypes. Under natural field infestations of M. arenaria race 2, nematode development on resistant tobacco breeding lines 81-RL-2K, SA 1214, and SA 1215 was similar to a susceptible cultivar with some nematicide treatments; however, quantity and quality of yield were inferior compared to K 326 plus nematicides.     

Influence of Glomus intraradices and Soil Phosphorus on Meloidogyne incognita Infecting Cucumis melo

The interaction among Glomus intraradices, Meloidogyne incognita, and cantaloupe was studied at three soil phosphorus (P) levels in a greenhouse. All plants grew poorly in soil not amended with P, regardless of mycorrhizal or nematode status. In soil amended with 50 μg P /g soil, M. incognita suppressed the growth of nonmycorrhizal plants by 84%. In contrast, growth of mycorrhizal plants inoculated with M. incognita was retarded by only 21%. A similar trend occurred in plants grown in soil with 100 μg P /g soil. Mycorrhizal infection had no effect on the degree of root-knot gall formation and did not affect the number of nematode eggs per egg mass. Mineral levels in plant shoots generally declined as soil P levels increased and were not significantly influenced by G. intraradices or M. incognita.     

Expression of a nematode symbiotic bacterium-derived protease inhibitor protein in tobacco enhanced tolerance against Myzus persicae

Fusion proteins of a protease inhibitor from an entomopathogenic nematode symbiotic bacterium (PIN1) and green fluorescent protein (GFP) were expressed in tobacco (Nicotiana tobacum cv. Samsun NN). The PIN1-GFP protein expressed under the control of the CaMV-35S promoter was detected in leaves of transgenic tobacco plants. The effect of PIN1 on anti-pest activity for Myzus persicae was tested by feeding neonate aphids on three independent homozygous lines. For nymphs fed on PIN1-GFP-expressing plants, no effects on insect survival were observed but average insect weight and fecundity were significantly reduced. The aphid biomass was decreased by 30–35?% compared to those reared on control plants. The effects of PIN1 on M. persicae were correlated with the decrease of the leucine aminopeptidase and total protease activities of whole insect extracts. Furthermore, an increase in polyphenoloxidase activity was observed in PIN1-GFP-expressing plants. These results revealed that the transgenic expression of PIN1 in tobacco enhanced tolerance against aphids. Key message This study suggests that entomopathogenic nematode symbiotic bacterium is another valuable resource of protease inhibitors which can be engineered into plants for insect pest management.     

Population Development of Meloidogyne incognita on Soybean Defoliated by Pseudoplusia includens

Greenhouse studies examined population densities of Meloidogyne incognita race 4 on soybean (Glycine max ''Davis'') defoliated by larvae of soybean looper (Pseudoplusia indudens (Walker)). Plants were defoliated over a 2-week period beginning 5 weeks after seedlings were transplanted. Four groups of plants were infested with nematodes (5,000 eggs/pot) at 2-week intervals to allow harvesting of plants at 0, 2, 4, and 6 weeks postdefoliation (WPD). Plants in each group were harvested 4 weeks after nematode infestation. Root and nodule weights of defoliated plants were suppressed at 0 WPD, but differences were not detectable at 2, 4, and 6 WPD. Population densities of M. incognita were similar on defoliated and control plants at 0 WPD but were greater on defoliated plants at 4 and 6 WPD. Percentage hatching of eggs produced on the latter plants also was higher. Effects of insect-induced defoliation on development of M. incognita remained detectable even after soybean plant growth apparently returned to normal.     

Utility of Host Delivered RNAi of Two FMRF Amide Like Peptides,flp-14 and flp-18, for the Management of Root Knot Nematode,Meloidogyne incognita

Root knot nematode, Meloidogyne incognita, is an obligate sedentary endoparasite that infects a large number of crop species and causes substantial yield losses. Non-chemical based control strategies for these nematodes are gaining importance. In the present study, we have demonstrated the significance of two FMRFamide like peptide genes (flp-14 and flp-18) for infection and development of resistance to M. incognita through host-derived RNAi. The study demonstrated both in vitro and in planta validation of RNAi-induced silencing of the two genes cloned from J2 stage of M. incognita. In vitro silencing of both the genes interfered with nematode migration towards the host roots and subsequent invasion into the roots. Transgenic tobacco lines were developed with RNAi constructs of flp-14 and flp-18 and evaluated against M. incognita. The transformed plants did not show any visible phenotypic variations suggesting the absence of any off-target effects. Bioefficacy studies with deliberate challenging of M. incognita resulted in 50-80% reduction in infection and multiplication confirming the silencing effect. We have provided evidence for in vitro and in planta silencing of the genes by expression analysis using qRT-PCR. Thus the identified genes and the strategy can be used as a potential tool for the control of M. incognita. This is the first ever report that has revealed the utility of host delivered RNAi of flps to control M. incognita. The strategy can also be extended to other crops and nematodes.     

Host Plant Resistance as an Alternative to Methyl Bromide for Managing Meloidogyne incognita in Pepper

Pre-plant soil fumigation with methyl bromide and host resistance were compared for managing the southern root-knot nematode (Meloidogyne incognita) in pepper. Three pepper cultivars (Carolina Cayenne, Keystone Resistant Giant, and California Wonder) that differed in resistance to M. incognita were grown in field plots that had been fumigated with methyl bromide (98% CH₃Br : 2% CCl₃NO₂ [w/w]) before planting or left untreated. Carolina Cayenne is a well-adapted cayenne-type pepper that is highly resistant to M. incognita. The bell-type peppers Keystone Resistant Giant and California Wonder are intermediate to susceptible and susceptible, respectively. None of the cultivars exhibited root galling in the methyl bromide fumigated plots and nematode reproduction was minimal (<250 eggs/g fresh root), indicating that the fumigation treatment was highly effective in controlling M. incognita. Root galling of Carolina Cayenne and nematode reproduction were minimal, and fruit yields were not reduced in the untreated plots. The root-galling reaction for Keystone Resistant Giant was intermediate (gall index = 2.9, on a scale of 1 to 5), and nematode reproduction was moderately high. However, yields of Keystone Resistant Giant were not reduced in untreated plots. Root galling was severe (gall index = 4.3) on susceptible California Wonder, nematode reproduction was high, and fruit yields were reduced (P ≤ 0.05) in untreated plots. The resistance exhibited by Carolina Cayenne and Keystone Resistant Giant provides an alternative to methyl bromide for reducing yield losses by southern root-knot nematodes in pepper. The high level of resistance of Carolina Cayenne also suppresses population densities of M. incognita.     

Expression and Regulation of the Arabidopsis thaliana Cel1 Endo 1,4 �� Glucanase Gene During Compatible Plant-Nematode Interactions

The root-knot nematode Meloidogyne incognita is an obligate endoparasite of plant roots and stimulates elaborate modifications of selected root vascular cells to form giant cells for feeding. An Arabidopsis thaliana endoglucanase (Atcel1) promoter is activated in giant cells that were formed in Atcel1::UidA transgenic tobacco and Arabidopsis plants. Activity of the full-length Atcel1 promoter was detected in root and shoot elongation zones and in the lateral root primordia. Different 5’ and internal deletions of regions of the 1,673 bp Atcel1 promoter were each fused to the UidA reporter gene and transformed in tobacco, and roots of the transformants were inoculated with M. incognita to assay for GUS expression in giant cells and noninfected plant tissues. Comparison of the Atcel1 promoter deletion constructs showed that the region between −1,673 and −1,171 (fragment 1) was essential for Atcel1 promoter activity in giant cells and roots. Fragment 1 alone, however, was not sufficient for Atcel1 expression in giant cells or roots, suggesting that cis-acting elements in fragment 1 may function in consort with other elements within the Atcel1 promoter. Root-knot nematodes and giant cells developed normally within roots of Arabidopsis that expressed a functional antisense construct to Atcel1, suggesting that a functional redundancy in endoglucanase activity may represent another level of regulatory control of cell wall-modifying activity within nematode feeding cells.     

Nutsedge Counts Predict Meloidogyne incognita Juvenile Counts in an Integrated Management System

The southern root-knot nematode (Meloidogyne incognita), yellow nutsedge (Cyperus esculentus) and purple nutsedge (Cyperus rotundus) are important pests in crops grown in the southern US. Management of the individual pests rather than the pest complex is often unsuccessful due to mutually beneficial pest interactions. In an integrated pest management scheme using alfalfa to suppress nutsedges and M. incognita, we evaluated quadratic polynomial regression models for prediction of the number of M. incognita J2 in soil samples as a function of yellow and purple nutsedge plant counts, squares of nutsedge counts and the cross-product between nutsedge counts . In May 2005, purple nutsedge plant count was a significant predictor of M. incognita count. In July and September 2005, counts of both nutsedges and the cross-product were significant predictors. In 2006, the second year of the alfalfa rotation, counts of all three species were reduced. As a likely consequence, the predictive relationship between nutsedges and M. incognita was not significant for May and July. In September 2006, purple nutsedge was a significant predictor of M. incognita. These results lead us to conclude that nutsedge plant counts in a field infested with the M. incognita-nutsedge pest complex can be used as a visual predictor of M. incognita J2 populations, unless the numbers of nutsedge plants and M. incognita are all very low.     

Phenotypic Expression of rkn1-Mediated Meloidogyne incognita Resistance in Gossypium hirsutum Populations

The root-knot nematode Meloidogyne incognita is a damaging pest of cotton (Gossypium hirsutum) worldwide. A major gene (rkn1) conferring resistance to M. incognita was previously identified on linkage group A03 in G. hirsutum cv. Acala NemX. To determine the patterns of segregation and phenotypic expression of rkn1, F₁, F₂, F_2:3, BC₁F₁ and F_2:7 recombinant inbred lines (RIL) from intraspecific crosses between Acala NemX and a closely related susceptible cultivar Acala SJ-2 were inoculated in greenhouse tests with M. incognita race 3. The resistance phenotype was determined by the extent of nematode-induced root galling and nematode egg production on roots. Suppression of root galling and egg production was highly correlated among individuals in all tests. Root galling and egg production on heterozygous plants did not differ from the susceptible parent phenotype 125 d or more after inoculation, but were slightly suppressed with shorter screening (60 d), indicating that rkn1 behaved as a recessive gene or an incompletely recessive gene, depending on the screening condition. In the RIL, rkn1 segregated in an expected 1 resistant: 1 susceptible ratio for a major resistance gene. However, within the resistant class, 21 out of 34 RIL were more resistant than the resistant parent Acala NemX, indicating transgressive segregation. These results suggest that rkn1-based resistance in G. hirsutum can be enhanced in progenies of crosses with susceptible genotypes. Allelism tests and molecular genetic analysis are needed to determine the relationship of rkn1 to other M. incognita resistance sources in cotton.     

Fine mapping QMi-C11 a major QTL controlling root-knot nematodes resistance in Upland cotton

The identification and utilization of a high-level of host plant resistance is the most effective and economical approach to control root-knot nematode (Meloidogyne incognita). In an earlier study, we identified a major quantitative trait locus (QTL) for resistance to root-knot nematode in the M-120 RNR Upland cotton line (Gossypium hirsutum L.) of the Auburn 623 RNR source. The QTL is located in a 12.9-cM interval flanked by the two SSR markers CIR069 and CIR316 on the distal segment of chromosome 11. To construct a fine map around the target region, a bulked segregation analysis was performed using two DNA pools consisting of five individuals, with each being homozygous for the two parental alleles. From a survey of 1,152 AFLP primer combinations, 9 AFLP markers closely linked to the target region were identified. By screening an additional 1,221 F₂ individuals developed from the initial mapping population, the Mi-C11 locus was delimited to a 3.6-cM interval flanked by the SSR marker CIR069 and the AFLP marker E14M27-375. These results further elucidate the genetic fine structure of the Mi-C11 locus and provide the basis for map-based isolation of the nematode resistance gene in M-120 RNR.