Biocontrol of root-knot nematode Meloidogyne incognita by the isolates of Pseudomonas on tomato

Biocontrol of root-knot nematode Meloidogyne incognita was studied on tomato using 15 isolates of fluorescent Pseudomonads isolated from pathogen suppressive soils. Pseudomonas aeruginosa (isolates Pa8, Pa9 and Pa3) caused greater inhibitory effect on hatching of M. incognita than other isolates. In addition, isolates Pa8, Pa9 and Pa3 caused greater colonisation of tomato roots and also caused a greater increase in the growth of tomato seedlings. These isolates also caused a greater increase in growth of tomato and higher reduction in galling and nematode multiplication in a green house test than is caused by other isolates. Isolates Pf1, Pf5, Pf6 and Pa13 were unable to increase growth of tomato and caused less reduction in galling and nematode multiplication compared to other isolates. Only 10 isolates produced siderophores on chromo-azurol sulfonate (CAS) agar medium and isolate Pa12 showed greater production of siderophore followed by Pa11, Pa9, Pf10, Pa3 and Pf5. Similarly, isolates Pa14, Pa12, Pf10, Pa9, Pa8, Pa7 and Pa6 produced greater amount of HCN than the other isolates tested. Isolates Pa8 and Pa9 showed greater production of IAA than the other 13 isolates tested. This study suggests that P. aeruginosa isolates Pa8 and Pa9 may be used for the biocontrol of M. incognita on tomato.     

Effect of Iranian strains of Pseudomonas spp. on the control of root-knot nematodes on Pistachios

The role of some Iranian strains of Pseudomonas spp. as biocontrol agents against Meloidogyne incognita and their ability to colonise pistachio roots was investigated. The results of in vitro experiments indicated that all tested bacteria produced significant suppression of M. incognita and showed that all strains were able to kill M. incognita juveniles with strain VUPf428 achieving about 99% mortality at 72 h. The results of in vivo treatments indicated that the best strains that could build high populations in soil infested with nematodes were VUPf5, VUPf52 and VUPf205. These isolates also caused highest reduction in galling and nematode multiplication in a greenhouse test although all strains native to Iran could colonise pistachio roots in pots. Some strains could produce secondary metabolites such as siderophores, proteases and volatile metabolites at high population levels.     

Role of cyanide production by Pseudomonas fluorescens CHA0 in the suppression of root-knot nematode, Meloidogyne javanica in tomato

Summary Pseudomonas fluorescens strain CHA0 produces hydrogen cyanide (HCN), a secondary metabolite that accounts largely for the biocontrol ability of this strain. In this study, we examined the role of HCN production by CHA0 as an antagonistic factor that contributes to biocontrol of Meloidogyne javanica, the root-knot nematode, in situ. Culture filtrate of CHA0, resulting from 1/10-strength nutrient broth yeast extract medium amended with glycine, inhibited egg hatch and caused mortality of M. javanica juveniles in vitro. The bacterium cultured under high oxygen-tension conditions exhibited better inhibitory effects towards nematodes, compared to its cultivation under excess oxygen situation. Growth medium amended with 0.50 or 1.0 mM FeEDDHA further improved hatch inhibition and nematicidal activity of the strain CHA0. Strain CHA77, an HCN-negative mutant, failed to exert such toxic effects, and in this strain, antinematode activity was not influenced by culture conditions. Exogenous cyanide also inhibited egg hatch and caused mortality of M. javanica juveniles in vitro. Strains CHA0 or CHA77 applied in unsterilized sandy-loam soil as drench, caused marked suppression of root-knot disease development incited by M. javanica in tomato seedlings. However, efficacy of CHA77 was noticeably lower compared to its wild type counterpart CHA0. An increased bioavailability of iron following EDTA application in soil substantially improved nematode biocontrol potential of CHA0 but not that of CHA77. Soil infestation with M. javanica eggs resulted in significantly lower nematode population densities and root-knot disease compared to the juveniles used as root-knot disease-inducing agents. Strain CHA0 significantly suppressed nematode populations and inhibited galling in tomato roots grown in soil inoculated with eggs or juveniles and treated with or without EDTA. Strain CHA0 exhibited greater biocontrol potential in soil inoculated with eggs and treated with EDTA. To demonstrate that HCN synthesis by the strain CHA0 acts as the inducing agent of systemic resistance in tomato, efficacy of the strain CHA0 was compared with CHA77 in a split root trial. The split-root experiment, guaranteeing a spatial separation of the inducing agent and the challenging pathogen, showed that HCN production by CHA0 is not crucial in the induction of systemic resistance in tomato against M. javanica, because the HCN-negative-mutant CHA77 induced the same level of resistance as the wild type but exogenous cyanide in the form of KCN failed to trigger the resistance reaction. In the root section where both nematode and the bacterium were present, strain CHA0 reduced nematode penetration to a greater extent than CHA77, suggesting that for effective control of M. javanica, a direct contact between HCN-producing CHA0 and the nematode is essential.     

Biocontrol of wilt disease complex of pea using Pseudomonas fluorescens and Rhizobium sp.

Biocontrol of wilt disease complex of pea caused by the root-knot nematode Meloidogyne incognita and Fusarium oxysporum f. sp. pisi was studied on pea (Pisum sativum L.) using plant growth-promoting rhizobacterium Pseudomonas fluorescens and root nodule bacterium Rhizobium sp. Inoculation of M. incognita and F.oxysporum alone caused significant reductions in plant growth over un-inoculated control. Reduction in plant growth caused by M. incognita was statistically equal to that caused by F. oxysporum. Inoculation of M. incognita plus F. oxysporum together caused a greater reduction in plant growth than the sum of damage caused by these pathogens singly. Inoculation of P. fluorescens and Rhizobium sp. individually or both together increased plant growth in pathogen inoculated and un-inoculated plants. Inoculation of P. fluorescens to pathogen-inoculated plants caused a greater increase in plant growth than caused by Rhizobium sp. Application of Rhizobium plus P. fluorescens caused a greater increase in plant growth than caused by each of them singly. Inoculation of P.fluorescens caused higher reduction in galling and nematode multiplication than caused by Rhizobium sp. Use of Rhizobium plus P. fluorescens caused higher reduction in galling and nematode multiplication than their individual inoculation. Plants inoculated with both pathogens plus Rhizobium showed less nodulation than plants inoculated with single pathogen plus Rhizobium. Inoculation of Rhizobium plus P. fluorescens resulted in higher root-nodulation than inoculated only with Rhizobium. Wilting indices were 4 and 5, respectively, when plants were inoculated with F. oxysporum and F. oxysporum plus M. incognita. Wilting indices were reduced maximum to 1 and 2, respectively, when plants inoculated with F.oxysporum and plants with both pathogens were treated with P. fluorescens plus Rhizobium.     

Fungal root endophytes of tomato from Kenya and their nematode biocontrol potential

The significance of fungal endophytes in African agriculture, particularly Kenya, has not been well investigated. Therefore, the objective of the present work was isolation, multi-gene phylogenetic characterization and biocontrol assessment of endophytic fungi harbored in tomato roots for nematode infection management. A survey was conducted in five different counties along the central and coastal regions of Kenya to determine the culturable endophytic mycobiota. A total of 76 fungal isolates were obtained and characterized into 40 operational taxonomic units based on the analysis of ITS, β-tubulin and tef1α gene sequence data. Among the fungal isolates recovered, the most prevalent species associated with tomato roots were members of the Fusarium oxysporum and F. solani species complexes. Of the three genes utilized for endophyte characterization, tef1α provided the best resolution. A combination of ITS, β-tubulin and tef1α resulted in a better resolution as compared to single gene analysis. Biotests demonstrated the ability of selected non-pathogenic fungal isolates to successfully reduce nematode penetration and subsequent galling as well as reproduction of the root-knot nematode Meloidogyne incognita. Most Trichoderma asperellum and F. oxysporum species complex isolates reduced root-knot nematode egg densities by 35–46 % as compared to the non-fungal control and other isolates. This study provides first insights into the culturable endophytic mycobiota of tomato roots in Kenya and the potential of some isolates for use against the root-knot nematode M. incognita. The data can serve as a framework for fingerprinting potential beneficial endophytic fungal isolates which are optimized for abiotic and biotic environments and are useful in biocontrol strategies against nematode pests in Kenyan tomato cultivars. This information would therefore provide an alternative or complementary crop protection component.     

Interactions of Ralstonia solanacearum and Pectobacterium carotovorum with Meloidogyne incognita on potato

Effect of interactions of Meloidogyne incognita with Ralstonia solanacearum and interaction of M. incognita with Pectobacterium carotovorum were studied in sequential and simultaneous inoculations on potato (Solanum tuberosum). Inoculation of M. incognita caused a lesser reduction in plant growth than caused by R. solanacearum. Inoculation of M. incognita plus R. solanacearum caused a greater reduction in plant growth than the damage caused by either pathogen. Inoculation of M. incognita prior to R. solanacearum resulted in a greater reduction in plant growth than R. solanacearum was inoculated prior to M. incognita. However, inoculation of M. incognita or P. carotovorum caused similar reduction in plant growth. Inoculation of P. carotovorum prior to M. incognita caused lesser reduction in plant growth than simultaneous inoculation of both pathogens. Inoculation of M. incognita caused galling in potato roots but the size of galls was small. Inoculation of P. carotovorum or R. solanacearum with M. incognita had adverse effect on galling and nematode multiplication. Wilting or soft rot index was 3 when R. solanacearum or P. carotovorum was inoculated alone. In other treatments, where R. solanacearum or P. carotovorum was inoculated with M. incognita, wilting or soft rot indices were 5.     

Suppression of the root-knot nematode [Meloidogyne incognita (Kofoid & White) Chitwood] on tomato by dual inoculation with arbuscular mycorrhizal fungi and plant growth-promoting rhizobacteria

Arbuscular mycorrhizal (AM) fungi and plant growth-promoting rhizobacteria (PGPR) have potential for the biocontrol of soil-borne diseases. The objectives of this study were to quantify the interactions between AM fungi [Glomus versiforme (Karsten) Berch and Glomus mosseae (Nicol. & Gerd.) Gerdemann & Trappe] and PGPR [Bacillus polymyxa (Prazmowski) Mace and Bacillus sp.] during colonization of roots and rhizosphere of tomato (Lycopersicon esculentum Mill) plants (cultivar Jinguan), and to determine their combined effects on the root-knot nematode, Meloidogyne incognita, and on tomato growth. Three greenhouse experiments were conducted. PGPR increased colonization of roots by AM fungi, and AM fungi increased numbers of PGPR in the rhizosphere. Dual inoculations of AM fungi plus PGPR provided greater control of M. incognita and greater promotion of plant growth than single inoculations, and the best combination was G. mosseae plus Bacillus sp. The results indicate that specific AM fungi and PGPR can stimulate each other and that specific combinations of AM fungi and PGPR can interact to suppress M. incognita and disease development.     

Pasteuria penetrans for Control of Meloidogyne incognita on Tomato and Cucumber,and M. arenaria on Snapdragon

Meloidogyne incognita and Meloidogyne arenaria are important parasitic nematodes of vegetable and ornamental crops. Microplot and greenhouse experiments were conducted to test commercial formulations of the biocontrol agent Pasteuria penetrans for control of M. incognita on tomato and cucumber and M. arenaria on snapdragon. Three methods of application for P. penetrans were assessed including seed, transplant, and post-plant treatments. Efficacy in controlling galling and reproduction of the two root-knot nematode species was evaluated. Seed treatment application was assessed only for M. incognita on cucumber. Pasteuria treatment rates of a granular transplant formulation ranged from 1.5 × 10⁵ endospores/cm³ to 3 × 10⁵ endospores/cm³ of transplant mix applied at seeding. Additional applications of 1.5 × 10⁵ endospores/cm³ of soil were applied as a liquid formulation to soil post-transplant for both greenhouse and microplot trials. In greenhouse cucumber trials, all Pasteuria treatments were equivalent to steamed soil for reducing M. incognita populations in roots and soil, and reducing nematode reproduction and galling. In cucumber microplot trials there were no differences among treatments for M. incognita populations in roots or soil, eggs/g root, or root condition ratings. Nematode reproduction on cucumber was low with Telone II and with the seed treatment plus post-plant application of Pasteuria, which had the lowest nematode reproduction. However, galling for all Pasteuria treatments was higher than galling with Telone II. Root-knot nematode control with Pasteuria in greenhouse and microplot trials varied on tomato and snapdragon. Positive results were achieved for control of M. incognita with the seed treatment application on cucumber.     

Polarographische Bestimmung von Chlorat-Rückständen im Boden und in der Pflanze

An increase in the inoculum level of root‐knot nematode, Meloidogyne incognita and the reniform nematode, Rotylenchulus reniformis resulted in a relative decrease in plant growth parameters of chickpea. Consequently water absorption capability of roots was impaired. M. incognita caused greater reduction than R. reniformis at the same inoculum level. In concomitant inoculation of M. incognita and R. reniformis there was greater suppression in plant growth of chickpea. The suppression in concomitant inoculations was less than the sum of the suppression caused by the same levels of inoculations of the individual species. The multiplication rate of the nematodes decreased as the inoculum level increased. The results also suggest competition for feeding sites between the two nematode species. The multiplication rate of one species progressively decrease with the increase in the inoculum levels of the other nematode.     

Management of Root-Knot Nematode,Meloidogyne Incognita,by integration of Paecilomyces Lilacinus with organic materials in Chilli

Studies were made to determine the efficacy of Paecilomyces lilacinus in management of root-knot nematode (Meloidogyne incognita) in soil amended with various organic matters. The soil amendments with organic additives except gram and rice husks significantly reduced the multiplication of M. incognita and the root galling caused by root-knot nematode which consequently increased the plant growth. The greatest improvement in plant growth and reduced reproduction factor and root galling was recorded in soil amendment with leaves of Calotropis procera while the least was in kail saw dust. The best protection against M. incognita was observed on the integration of organic additives with P. lilacinus, which resulted increased plant growth and reduced population build-up of nematodes and root gallings. The leaves of C. procera with P. lilacinus were most effective than all other organic materials used among the different integrated approaches. The organic amendments also increased the parasitism of P. lilacinus on M. incognita.     

Interaction between Pseudomonas fluorescens and Meloidogyne incognita on tomato plant as influenced by the different levels of phosphorus

A pot experiment was conducted on tomato (Solanum lycopersicum cv. Pusa Ruby) to assess the effect of different phosphorus (P) levels (0, 125, 250 and 500 mg/pot) and the plant growth promoting rhizobacterium, Pseudomonas fluorescens, on the growth of tomato and on the reproduction of Meloidogyne incognita. Maximum growth of tomato occurred at P rates of 125 mg/kg soil, irrespective of whether plants were uninoculated or inoculated with P. fluorescens or M. incognita or inoculated with both the agents. Nematodes per gram of roots, egg masses per root, eggs per egg mass and galls per root significantly increased by increasing levels of P. P. fluorescens performed better than other treatments and different P levels in improving tomato growth and reducing galling and multiplication of M. incognita.     

Biocontrol of <Emphasis Type="Italic">Meloidogyne javanica</Emphasis> by <Emphasis Type="Italic">Rhizobium</Emphasis> and plant growth-promoting rhizobacteria on lentil

Biocontrol of the root-knot nematode Meloidogyne javanica was studied on lentil using plant growth-promoting rhizobacteria (PGPR) namely Pseudomonas putida, P. alcaligenes, Paenibacillus polymyxa and Bacillus pumilus and root nodule bacterium Rhizobium sp. Pseudomonas putida caused greater inhibitory effect on the hatching and penetration of M. javanica followed by P. alcaligenes, P. polymyxa and B. pumilus. Inoculation of any PGPR species alone or together with Rhizobium increased plant growth both in M. javanica-inoculated and -uninoculated plants. Inoculation of Rhizobum caused greater increase in plant growth than caused by any species of plant growth-promoting rhizobacteria in nematode-inoculated plants. Among PGPR, P. putida caused greater increase in plant growth and higher reduction in galling and nematode multiplication followed by P. alcaligenes, P. polymyxa and B. pumilus. Combined use of Rhizobium with any species of PGPR caused higher reduction in galling and nematode multiplication than their individual inoculation. Use of Rhizobium plus P. putida caused maximum reduction in galling and nematode multiplication followed by Rhizobium plus P. alcaligens. Pseudomonas putida caused greater root colonization and siderophore production followed by P. alcaligenes, P. polymyxa and B. pumilus. Analysis of the protein bands of these four species by SDS-PAGE revealed that P. putida had a different protein band profile compared to the protein profiles of P. alcaligenes, P. polymyxa and B. pumilus. However, the protein profiles of P. acaligenes, P. polymyxa and B. pumilus were similar.     

Screening tomato-associated bacteria for biological control of grey mold on tomato

Aiming at discovering effective biocontrol agents (BCAs) against grey mold on tomato caused by Botrytis cinerea Pers., we selected 819 bacterial isolates from the surface as well as the interior of the roots, stems, and leaves of tomato plants grown in B. cinerea-infested fields. In a dual-culture assay, 116 isolates (14.16%) showed antagonism against B. cinerea and fewer ones against five additional tomato-associated fungal pathogens – Pythium ultimum, Phytophthora capsici, Fusarium oxysporum f. sp. lycopersici, Sclerotinia sclerotiorum and Ralstonia solanacearum. Thirty-one isolates with antagonism to B. cinerea and at least one of the five additional pathogens were assessed for their efficacy in controlling grey mold on tomato in a greenhouse test. Thirteen of them attained the efficacy over 50% and were subjected to the second greenhouse test, in which 12 isolates consistently accomplished the biocontrol efficacy over 50%, with isolates ABc28 and ABc22 achieving the efficacy of 66.71% and 64.90%, respectively. Under greenhouse conditions, the above two as well as isolates ABc2, ABc11 and ABc17 increased tomato biomass by more than 20% in comparison with the control. The 12 antagonistic isolates accomplishing the biocontrol efficacy over 50% in both greenhouse tests were considered potential BCAs against grey mold, which were identified as Pseudomonas spp., Pantoea spp., Bacillus spp. and Chryseobacterium spp. Ten of them were found to produce at least one of the three hydrolytic enzymes (protease, cellulase and chitinase) and/or siderophore, which might be involved in their mechanisms of suppressing the disease. Based on the origin of these 12 strains, the leaf tissue, especially the leaf interior, of tomato plants grown in a B. cinerea-infested field appears to be a good source of potential BCAs against grey mold.     

Effects of dual inoculation of mycorrhiza and endophytic,rhizospheric or parasitic bacteria on the root-knot nematode disease of tomato

The effects of mycorrhisation and inoculation with soil bacteria on the disease caused by Meloidogyne incognita on tomato were studied in pots under greenhouse conditions. Efficacy in promoting plant growth and reducing disease severity and final nematode densities were evaluated for two arbuscular mycorrhizal fungi (AMF; Funneliformis mosseae and Rhizophagus irregularis), three soil bacteria with different living strategies (the endophyte Bacillus megaterium, a rhizospheric Pseudomonas putida and the hyperparasite of nematodes Pasteuria penetrans) and combinations of the fungi and bacteria. In M. incognita-infested plants, F. mosseae increased tomato growth more than R. irregularis, and plants inoculated with B. megaterium presented higher shoot fresh weight than with P. putida or P. penetrans, but dual inoculation did not improve tomato growth more than single inoculations. Disease severity and final nematode densities were reduced by F. mosseae compared to non-mycorrhizal plants. B. megaterium and P. penetrans reduced both the root galling and the final nematode densities compared to treatments without bacteria. P. penetrans reduced final nematode densities more than B. megaterium or P. putida. Dual inoculation of AMF and P. penetrans showed the highest efficacy in reducing the final nematode densities in tomato.     

Effect of plant growth promoting rhizobacteria,nematode parasitic fungi and root-nodule bacterium on root-knot nematodes Meloidogyne javanica and growth of chickpea

Effects of plant growth promoting rhizobacteria (Pseudomonas putida MTCC No. 3604 and Pseudomonas alcaligenes MTCC No. 493) and parasitic fungi (Pochonia chlamydosporia KIA and Paecilomyces lilacinus KIA) were studied, alone and together with Rhizobium sp. (charcoal commercial culture) on the growth of chickpea and multiplication of Meloidogyne javanica. Individually, P. putida 3604, P. alcaligenes 493 and Rhizobium caused a significant increase in the growth of chickpea in both nematode inoculated and uninoculated plants. Inoculation of Rhizobium with a parasitic fungus or with plant growth promoting rhizobaterium caused a greater increase in the growth of plants inoculated with nematodes than caused by either of them singly. Individually, P. lilacinus KIA caused a greater increase in the growth of nematode inoculated plants than caused by P. putida 3604 or P. alcaligenes 493. P. lilacinus KIA caused a greater reduction in galling and nematode multiplication followed by P. chlamydosporia KIA, P. putida 3604 and P. alcaligenes 493. Combined use of P. lilacinus KIA with Rhizobium was better in reducing galling and nematode multiplication than any other treatment. P. putida 3604 caused a greater colonization of root than P. alcaligenes 493 while P. lilacinus KIA was isolated from more nematodes than P. chlamydosporia KIA.     

Biological control of root-knot nematode,Meloidogyne incognita infesting tomato

Talc based formulations of two antagonistic fungi, Acremonium strictum W. Gams and Aspergillus terreus Thom were tested separately and together for their ability to suppress the development of root-knot disease of tomato caused by the root-knot nematode, Meloidogyne incognita Kofoid & White in two consecutive trials (2007–08). Tomato seedlings were each inoculated with M. incognita at 2 infective second stage juveniles /g of soil. M. incognita caused up to 48% reduction in plant growth parameters compared to un-inoculated control. Control efficacy achieved by combined soil application of both fungi, in terms of galls/root system and soil population/50 ml of soil, was 66 and 69% respectively at 60 days of inoculation compared to control. Soil application by individual fungus did not achieve as much effectiveness as the biocontrol agents applied together. The combined treatment was found to have antagonistic effect on M. incognita development and increased plant vigor. Incorporation of fine powder of chickpea pod waste with talc powder was beneficial in providing additional nutrients to both plant and biocontrol agents and increased the activity of the nematophagous fungi in soil. A. strictum and A. terreus were successfully established in the rhizosphere of tomato plants up to the termination of the experiment.     

Effect of seaweed concentrate fromEcklonia maxima (Osbeck) Papenfuss onMeloidogyne incognita infestation on tomato

Seaweed concentrate (SWC), prepared fromEcklonia maxima, when applied as a soil drench to tomato seedlings, significantly increased plant growth and reduced infestation byMeloidogyne incognita. Foliar applied SWC had little effect on plant growth and increased nematode galling. Ashing SWC reduced the suppressive effect on nematode infestation. In anin vitro experiment, SWC lessened infestation of root-knot nematodes on excised roots of a susceptible cultivar of tomato. Application of the same concentrations of SWC to a nematode-resistant cultivar increased the number of egg masses.     

Pseudomonas fluorescens mediated suppression of Meloidogyne incognita infection of cowpea and tomato

Plant growth-promoting rhizobacterium, Pseudomonas fluorescens strain BICC602 suppresses root-knot nematode (Meloidogyne incognita) by enhancing defence mechanism leading to induced systemic resistance in cowpea (Vigna unguiculata) cv. L.Walp. and tomato (Solanum lycopersicum) cv. Pusa Ruby. In cowpea, the soil treatment proved more effective than foliar spray on root galling and eggs in roots. However, which factors are necessary in the induction of resistance response in plants against nematodes by BICC602 is not yet known. Salicylic acid (SA) production by some bacteria acts as endogenous signal for the activation of certain plant defence responses. In a split-root trial with tomato as a host plant and M. incognita as challenging parasite, BICC602 induces systemic resistance in tomato plants. Based on the results, it is assumed that P. fluorescens-induced resistance against M. incognita in cowpea and tomato is made either through SA-dependent or SA-independent transduction pathway.     

The nematicidal potential of local Bacillus species against the root-knot nematode infecting greenhouse tomatoes

Bacillus spp. were isolated from Iranian tomato fields and evaluated for their efficacy against root-knot nematodes, Meloidogyne javanica. The 52 spore-forming bacterium isolates were obtained from tomato rhizosphere following heat treatment. Eight isolates were chosen based on their potency in prevention of M. javanica egg hatch and juvenile mortality and production of proteolytic enzymes in Petri plates. Their ability to form biofilms were also determined in pot experiments. According to phenotypic traits and 16s rDNA sequencing, all selected isolates belonged to Bacillus spp. including B. cereus and B. pumilus. Treatment with bacterial culture filtrates in vitro caused juvenile mortality of 72 to 99% after 48 h. After four days, the percentage of egg hatch ranged from 1.6 to 59% depending on the isolate. Bacillus pumilus (ToIr-MA) and Bacillus sp. (ToIr-10) were found to have significant ability to produce extracellular proteases and to form maximum biofilm, considerably reducing the number of egg masses and root gall index (P = 0.05) in comparison to untreated plants. Application of ToIr-MA and ToIr-10 enhanced the fresh and dry weights of shoot and root systems. There was significant enhancement in dry root weight (45 and 50%) and shoot weight (67 and 75%). Results suggest that these two Bacillus spp. have potential as biocontrol agents against root-knot disease in tomato production.     

Essential oils as soil biofumigants for the control of the root‐knot nematode Meloidogyne incognita on tomato

The effectiveness of soil fumigation with 50, 100 and 200 µL kg^?1 soil of essential oils (EOs) from the plant species Eucalyptus citriodora, Eucalyptus globulus, Mentha piperita, Pelargonium asperum and Ruta graveolens was assessed against the root‐knot nematode Meloidogyne incognita on potted tomato. Plant growth parameters and number of galls, nematode eggs and juveniles on tomato roots were evaluated after two months of maintenance of the treated plants at 25°C in greenhouse. EOs of E. globulus and P. asperum significantly reduced nematode multiplication and gall formation on tomato roots at all the tested rates, whereas the EOs of E. citriodora, M. piperita and R. graveolens were more suppressive at levels greater than 50 µL kg^?1 soil. Biofumigation with EOs of E. globulus and P. asperum resulted also in the largest increase of tomato plant top and root biomass. The five samples of EOs had a different chemical composition as determined by GC and GC‐MS. Structure–activity relationship based on the main constituents of the tested EOs and their nematicidal effect on M. incognita is discussed.