Root Knot nematode (RKN; Meloidogyne spp.) is one of the most devastating parasites that infect the roots of hundreds of plant
species. RKN cannot live independently from their hosts and are the biggest contributors to the loss of the world's primary foods.
RNAi gene silencing studies have demonstrated that there are fewer galls and galls are smaller when RNAi constructs targeted to
silence certain RKN genes are expressed in plant roots. We conducted a comparative genomics analysis, comparing RKN genes of
six species: Meloidogyne Arenaria, Meloidogyne Chitwoodi, Meloidogyne Hapla, Meloidogyne Incognita, Meloidogyne Javanica, and
Meloidogyne Paranaensis to that of the free living nematode Caenorhabditis elegans, to identify candidate genes that will be lethal to
RKN when silenced or mutated. Our analysis yielded a number of such candidate lethal genes in RKN, some of which have been
tested and proven to be effective in soybean roots. A web based database was built to house and allow scientists to search the data.
This database will be useful to scientists seeking to identify candidate genes as targets for gene silencing to confer resistance in
plants to RKN.
The database can be accessed from http://bioinformatics.towson.edu/RKN/
RKN; Meloidogyne; web based database; RNAi; C. elegans
The role of Pasteuria penetrans in suppressing numbers of root-knot nematodes was investigated in a 7-year monocuhure of tobacco in a field naturally infested with a mixed population of Meloidogyne incognita race 1 and M. javanica. The suppressiveness of the soil was tested using four treatments: autoclaving (AC), microwaving (MW), air drying (DR), and untreated. The treated soil bioassays consisted of tobacco cv. Northrup King 326 (resistant to M. incognita but susceptible to M. javanica) and cv. Coker 371 Gold (susceptible to M. incognita and M. javanica) in pots inoculated with 0 or 2,000 second-stage juveniles of M. incognita race 1. Endospores of P. penetrans were killed by AC but were only slightly affected by MW, whereas most fungal propagules were destroyed or inhibited in both treatments. Root galls, egg masses, and numbers of eggs were fewer on Coker 371 Gold in MW, DR, and untreated soil than in AC-treated soil. There were fewer egg masses than root galls on both tobacco cultivars in MW, DR, and untreated soil than in the AC treatment. Because both Meloidogyne spp. were suppressed in MW soil (with few fungi present) as well as in DR and untreated soil, the reduction in root galling, as well as numbers of egg masses and eggs appeared to have resulted from infection of both nematode species by P. penetrans.
bacterium; biological control; Meloidogyne incognita; M. javanica; nematode; Nicotiana tabacum; Pasteuria penetrans; root-knot nematode; suppressive soil; tobacco
Root-knot nematode is an important pest in agricultural production worldwide. Crop rotation is the only management strategy in some production systems, especially for resource poor farmers in developing countries. A series of experiments was conducted in the laboratory with several leguminous cover crops to investigate their potential for managing a mixture of root-knot nematodes (Meloidogyne arenaria, M. incognita, M. javanica). The root-knot nematode mixture failed to multiply on Mucuna pruriens and Crotalaria spectabilis but on Dolichos lablab the population increased more than 2- fold when inoculated with 500 and 1,000 nematodes per plant. There was no root-galling on M. pruriens and C. spectabilis but the gall rating was noted on D. lablab. Greater mortality of juvenile root-knot nematodes occurred when exposed to eluants of roots and leaves of leguminous crops than those of tomato; 48.7% of juveniles died after 72 h exposure to root eluant of C. spectabilis. The leaf eluant of D. lablab was toxic to nematodes but the root eluant was not. Thus, different parts of a botanical contain different active ingredients or different concentrations of the same active ingredient. The numbers of root-knot nematode eggs that hatched in root exudates of M. pruriens and C. spectabilis were significantly lower (20% and 26%) than in distilled water, tomato and P. vulgaris root exudates (83%, 72% and 89%) respectively. Tomato lacks nematotoxic compounds found in M. pruriens and C. spectabilis. Three months after inoculating plants with 1,000 root-knot nematode juveniles the populations in pots with M. pruriens, C. spectabilis and C. retusa had been reduced by approximately 79%, 85% and 86% respectively; compared with an increase of 262% nematodes in pots with Phaseolus vulgaris. There was significant reduction of 90% nematodes in fallow pots with no growing plant. The results from this study demonstrate that some leguminous species contain compounds that either kill root-knot nematodes or interfere with hatching and affect their capacity to invade and develop within their roots. M. pruriens, C. spectabilis and C. retusa could be used with effect to decrease a mixed field populations of root-knot nematodes.
Crotalaria spectabilis; Crotalaria retusa; Dolichos lablab; Mucuna pruriens; Phaseolus vulgaris; nematicidal compounds; phytoalexins
Eight commonly cultivated Ixora species or cultivars were tested for their suitability as hosts and their level of tolerance to Meloidogyne incognita race 1 and M. javanica in a greenhouse study. Twenty weeks postinoculation with 5,000 eggs per pot, M. incognita race 1 and M. javanica produced galls and formed egg masses on roots of all eight Ixora species or cultivars tested. However, only M. javanica-infected 'Petite Yellow' and 'Maui' had decreases (P ≤ 0.05) in root wet weights, suggesting that the other cultivars were more tolerant to these root-knot nematode species. Differential host suitability to each Meloidogyne species was based on the relative number of galls, galls per gram root weight, egg masses, and second-stage juveniles produced per plant. 'Bonnie Lynn,' 'Maui,' and 'Petite Red' were good to excellent hosts for both Meloidogyne spp. Ixora coccinea was a good host for M. incognita race 1 but less suitable for M. javanica. 'Singapore' and 'Petite Yellow' were poor hosts for M. incognita race 1 but excellent hosts for M. javanica. 'Nora Grant' and I. casei 'Super King' were poor hosts for both species of root-knot nematodes.
host-parasite relationship; Ixora spp.; Meloidogyne incognita race 1; M. javanica; nematode; ornamental; root-knot nematode; woody ornamental
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, F2:3, BC1F1 and F2:7 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.
cotton; Gossypium hirsutum; Meloidogyne incognita; resistance; rkn1; root-knot nematode; phenotypic expression; transgressive segregation
We examined the efficacy of a bacterium for biocontrol of the root-knot nematode (RKN) Meloidogyne hapla in carrot (Daucus carota subsp. sativus) and tomato (Solanum lycopersicum). Among 542 bacterial isolates from various soils and plants, the highest nematode mortality was observed for treatments with isolate C1-7, which was identified as Bacillus cereus based on cultural and morphological characteristics, the Biolog program, and 16S rRNA sequencing analyses. The population density and the nematicidal activity of B. cereus C1-7 remained high until the end of culture in brain heart infusion broth, suggesting that it may have sustainable biocontrol potential. In pot experiments, the biocontrol efficacy of B. cereus C1-7 was high, showing complete inhibition of root gall or egg mass formation by RKN in carrot and tomato plants, and subsequently reducing RKN damage and suppressing nematode population growth, respectively. Light microscopy of RKN-infected carrot root tissues treated with C1-7 showed reduced formation of gall cells and fully developed giant cells, while extensive gall cells and fully mature giant cells with prominent cell wall ingrowths formed in the untreated control plants infected with RKNs. These histopathological characteristics may be the result of residual or systemic biocontrol activity of the bacterium, which may coincide with the biocontrol efficacies of nematodes in pots. These results suggest that B. cereus C1-7 can be used as a biocontrol agent for M. hapla.
Bacillus cereus; biological control; giant cell; Meloidogyne hapla
Several cover crops with potential for use in tropical and subtropical regions were assessed for susceptibility to three common species of root-knot nematode, Meloidogyne arenaria, M. incognita, and M. javanica. Crops were selected based on potential use as organic amendments in anaerobic soil disinfestation (ASD) applications. Nematode juvenile (J2) numbers in soil and roots, egg production, and host plant root galling were evaluated on arugula (Eruca sativa, cv. Nemat), cowpea (Vigna unguiculata, cv. Iron & Clay), jack bean (Canavalia ensiformis, cv. Comum), two commercial mixtures of Indian mustard and white mustard (Brassica juncea & Sinapis alba, mixtures Caliente 61 and Caliente 99), pearl millet (Pennisetum glaucum, cv. Tifleaf III), sorghum-sudangrass hybrid (Sorghum bicolor × S. bicolor var. sudanense, cv. Sugar Grazer II), and three cultivars of sunflower (Helianthus annuus, cvs. 545A, Nusun 660CL, and Nusun 5672). Tomato (Solanum lycopersicum, cv. Rutgers) was included in all trials as a susceptible host to all three nematode species. The majority of cover crops tested were less susceptible than tomato to M. arenaria, with the exception of jack bean. Sunflower cv. Nusun 5672 had fewer M. arenaria J2 isolated from roots than the other sunflower cultivars, less galling than tomato, and fewer eggs than tomato and sunflower cv. 545A. Several cover crops did not support high populations of M. incognita in roots or exhibit significant galling, although high numbers of M. incognita J2 were isolated from the soil. Arugula, cowpea, and mustard mixture Caliente 99 did not support M. incognita in soil or roots. Jack bean and all three cultivars of sunflower were highly susceptible to M. javanica, and all sunflower cultivars had high numbers of eggs isolated from roots. Sunflower, jack bean, and both mustard mixtures exhibited significant galling in response to M. javanica. Arugula, cowpea, and sorghum-sudangrass consistently had low numbers of all three Meloidogyne species associated with roots and are good selections for use in ASD for root-knot nematode control. The remainder of crops tested had significant levels of galling, J2, and eggs associated with roots, which varied among the Meloidogyne species tested.
Anaerobic soil disinfestation; ASD; Brassica juncea & Sinapis alba; Canavalia ensiformis; cover crops; cowpea; Eruca sativa; Helianthus annuus; jack bean; management; Meloidogyne arenaria; M. incognita; M. javanica; mustard; pearl millet; Pennisetum glaucum; root-knot nematodes; sorghum-sudangrass; sunflower; Vigna unguiculata
A greenhouse study was conducted to determine if root necrosis had an effect on the relationship between root-knot nematode gall index and egg mass number. Thirty-four cultigens of Cucumis (14 accessions, 12 cultivars, and six breeding lines of C. sativus, and two accessions of C. metuliferus) were evaluated against four root-knot species (Meloidogyne arenaria race 2, M. incognita race 1, M. incognita race 3, and M. javanica) measuring gall index, root necrosis, and egg mass number. Root necrosis affected the gall index-egg mass relationship. At lower root necrosis values, a stronger relationship existed between gall index and egg mass number than at higher root necrosis values. Root tissue was destroyed by root necrosis, and normal root-knot nematode reproduction would not occur, even though root galling was still observed. The races of M. incognita tested had a greater effect in predisposing C. sativus and C. metuliferus to root necrosis than did M. arenaria race 2 or M. javanica. This study showed that root necrosis had an adverse affect on the relationship between gall index and egg mass number in cucumber.
African horned cucumber; cucumber; Cucumis sativus; Cucumis metuliferus; Meloidogyne arenaria; Meloidogyne incognita; Meloidogyne javanica; nematode; resistance; root-knot nematode
Ten cultivated plants of the family Cruciferae were evaluated for susceptibility to Meloidogyne arenaria race 1, M. incognita races 1 and 3, and M. javanica in a series of four separate greenhouse tests. After 62-64 days, or 1,032-1,072 degree days (10 C base), several of the crops evaluated showed moderate to severe levels of galling (> 3.0 on 0-5 scale) and moderate numbers of egg masses (>2.0 on 0-5 scale) in response to each of the nematode species and races. Among the plants tested, collard (Brassica oleracea var. acephala) cv. Georgia Southern was the least susceptible (fewest galls and egg masses) to each of the four nematode isolates. Similar low levels of infection were obtained with broccoli (B. oleracea var. botrytis) cv. De Cicco in response to M. incognita race 1 and M. arenaria. Numbers of second-stage juveniles hatched from eggs per root system were variable in the test with M. arenaria, but lowest on collard for each of the other nematodes. Some commonly grown crucifers are hosts to several different species and races of Meloidogyne, which should be considered if these crops are included in cropping systems.
Brassica chinensis; Brassica napus; Brassica oleracea; Brassica rapa; broccoli; cabbage; canola; cauliflower; chinese cabbage; collard; host-plant resistance; Meloidogyne arenaria; Meloidogyne incognita; Meloidogyne javanica; mustard; nematode; radish; Raphanus sativus; Sinapis alba; turnip
Responses of 17 Prunus rootstocks or accessions (11 from the subgenus Amygdalus and 6 from the subgenus Prunophora) were evaluated against 11 isolates of Meloidogyne spp. including one M. arenaria, four M. incognita, four M. javanica, one M. hispanica, and an unclassified population from Florida. Characterization of plant response to root-knot nematodes was based on a gall index rating. Numbers of females and juveniles plus eggs in the roots were determined for 10 of the rootstocks evaluated against one M. arenaria, one M. incognita, one M. javanica, and the Florida isolate. These 10 rootstocks plus Nemaguard and Nemared were retested by growing three different rootstock genotypes together in containers of soil infested individually with each of the above four isolates. Garfi and Garrigues almonds, GF.305 and Rutgers Red Leaf peaches, and the peach-almond GF.677 were susceptible to all isolates. Differences in resistance were detected among the other rootstocks of the subgenus Amygdalus. The peach-almond GF.557 and Summergrand peach were resistant to M. arenaria and M. incognita but susceptible to M. javanica and the Florida isolate. Nemaguard, Nemared, and its two hybrids G x N no. 15 and G x N no. 22 were resistant to all but the Florida isolate. In the subgenus Prunophora, Myrobalan plums P.1079, P.2175, P.2980, and P.2984; Marianna plum 29C; and P. insititia plum AD.101 were resistant to all isolates. Thus, two different genetic systems of RKN resistance were found in the subgenus Amygdalus: one system acting against M. arenaria and M. incognita, and another system also acting against M. javanica. Prunophora rootstocks bear a complete genetic system for resistance also acting against the Florida isolate. The hypotheses on the relationships between these systems and the corresponding putative genes of resistance are presented.
Amygdalus; Meloidogyne arenaria; Meloidogyne incognita; Meloidogyne javanica; Prunophora; Prunus amygdalus; Prunus cerasifera; Prunus persica; resistance
Experiments were conducted in the greenhouse to assess root galling and egg production of three root-knot nematode species, Meloidogyne arenaria, M. incognita, and M. javanica, on several weeds common to Florida agricultural land. Weeds evaluated were Amaranthus retroflexus (redroot pigweed), Cyperus esculentus (yellow nutsedge), Eleusine indica (goosegrass), Portulaca oleracea (common purslane), and Solanum americanum (American black nightshade). Additionally, although it is recommended as a cover crop in southern regions of the U.S., Aeschynomene americana (American jointvetch) was evaluated as a weed following the detection of root galling in a heavy volunteer infestation of an experimental field in southeastern Florida. Weeds were propagated from seed and inoculated with 1000 nematode eggs when plants reached the two true-leaf stage. Tomato (Solanum lycopersicum ‘Rutgers’) was included as a positive control. Aeschynomene americana and P. oleracea roots supported the highest number of juveniles (J2) and had the highest number of eggs/g of root for all three species of Meloidogyne tested. However, though P. oleracea supported very high root levels of the three nematode species tested, its fleshy roots did not exhibit severe gall symptoms. Low levels of apparent galling, combined with high egg production, increase the potential for P. oleracea to support populations of these three species of root-knot nematodes to a degree that may not be appropriately recognized. This research quantifies the impact of P. oleracea as a host for M. arenaria, M. incognita, and M. javanica compared to several other important weeds commonly found in Florida agricultural production, and the potential for A. americana to serve as an important weed host of the three species of root-knot nematode tested in southern regions of Florida.
Aeschynomene americana; Amaranthus retroflexus; Cyperus esculentus; Eleusine indica; Florida; host status; nematode reproduction; Portulaca oleracea; root-knot nematodes; Solanum americanum
Root-knot nematodes (RKN) are obligatory plant parasitic worms that establish and maintain an intimate relationship with their host plants. During a compatible interaction, RKN induce the redifferentiation of root cells into multinucleate and hypertrophied giant cells essential for nematode growth and reproduction. These metabolically active feeding cells constitute the exclusive source of nutrients for the nematode. Detailed analysis of glutathione (GSH) and homoglutathione (hGSH) metabolism demonstrated the importance of these compounds for the success of nematode infection in Medicago truncatula. We reported quantification of GSH and hGSH and gene expression analysis showing that (h)GSH metabolism in neoformed gall organs differs from that in uninfected roots. Depletion of (h)GSH content impaired nematode egg mass formation and modified the sex ratio. In addition, gene expression and metabolomic analyses showed a substantial modification of starch and γ-aminobutyrate metabolism and of malate and glucose content in (h)GSH-depleted galls. Interestingly, these modifications did not occur in (h)GSH-depleted roots. These various results suggest that (h)GSH have a key role in the regulation of giant cell metabolism. The discovery of these specific plant regulatory elements could lead to the development of new pest management strategies against nematodes.
Parasitic nematodes are microscopic worms that cause major diseases of plants, animals and humans. During compatible interactions, root-knot nematodes (RKN) induce the formation of galls in which redifferentiation of root cells into multinucleate and hypertrophied giant cells is essential for nematode growth and reproduction. The importance of glutathione (GSH), a major antioxidant molecule involved in plant development, in plant microbe interaction and in abiotic stress response, was analyzed during the plant-RKN interaction. Our analyses demonstrated that the gall development and functioning are characterized by an adapted GSH metabolism and that depletion of GSH content impairs nematode reproduction and modified sex ratio. This phenotype is linked to specific modifications of carbon metabolism which do not occur in uninfected roots indicating a peculiar metabolism of this neoformed organ. This first metabolomic analysis during the plant-RKN interaction highlights the regulatory role played by GSH in this pathogenic interaction and completes our vision of the role of GSH during plant-pathogen interactions. RKN sex ratio modification has previously been observed under unfavorable nematode feeding conditions suggesting that the GSH-redox system could be a general sensor of gall fitness in natural conditions.
The southern root-knot nematode (RKN, Meloidogyne incognita) is a major soil-inhabiting plant parasite that causes significant yield losses in cotton (Gossypium spp.). Progeny from crosses between cotton genotypes susceptible to RKN produced segregants in subsequent populations which were highly resistant to this parasite. A recombinant inbred line (RIL) population of 138 lines developed from a cross between Upland cotton TM-1 (G. hirsutum L.) and Pima 3–79 (G. barbadense L.), both susceptible to RKN, was used to identify quantitative trait loci (QTLs) determining responses to RKN in greenhouse infection assays with simple sequence repeat (SSR) markers. Compared to both parents, 53.6% and 52.1% of RILs showed less (P<0.05) root-galling index (GI) and had lower (P<0.05) nematode egg production (eggs per gram root, EGR). Highly resistant lines (transgressive segregants) were identified in this RIL population for GI and/or EGR in two greenhouse experiments. QTLs were identified using the single-marker analysis nonparametric mapping Kruskal-Wallis test. Four major QTLs located on chromosomes 3, 4, 11, and 17 were identified to account for 8.0 to 12.3% of the phenotypic variance (R2) in root-galling. Two major QTLs accounting for 9.7% and 10.6% of EGR variance were identified on chromosomes 14 and 23 (P<0.005), respectively. In addition, 19 putative QTLs (P<0.05) accounted for 4.5–7.7% of phenotypic variance (R2) in GI, and 15 QTLs accounted for 4.2–7.3% of phenotypic variance in EGR. In lines with alleles positive for resistance contributed by both parents in combinations of two to four QTLs, dramatic reductions of >50% in both GI and EGR were observed. The transgressive segregants with epistatic effects derived from susceptible parents indicate that high levels of nematode resistance in cotton may be attained by pyramiding positive alleles using a QTL mapping approach.
Twelve ornamental bedding plant cultivars were grown in soil infested with isolates of Meloidogyne incognita race 1, M. javanica, or M. arenaria race 1 in a series of tests in containers in a growth room. Root galling (0-5 scale) and eggs/plant were evaluated 8-10 weeks after soil infestation and seedling transplantation. Snapdragon, Antirrhinum majus cv. First Ladies, was extensively galled and highly susceptible (mean gall rating ≥4.2 and ≥14,500 eggs/plant), and Celosia argentea cv. Century Mix and Coleus blumei cv. Rainbow were susceptible (>1,500 eggs/plant) to all three Meloidogyne isolates. Response of Petunia x hybrida varied with cultivar and nematode isolate. Little or no galling or egg production from any Meloidogyne isolate was observed on Ageratum houstonianum cv. Blue Mink, Lobularia maritima cv. Rosie O'Day, or Tagetes patula cv. Dwarf Primrose. Galling was slight (mean rating ≤2.0) but varied with nematode species on Dianthus chinensis cv. Baby Doll Mix, Salvia splendens cv. Bonfire, and Vinca rosea cv. Little Bright Eye. Verbena × hybrida cv. Florist was heavily infected (gall rating >4.0 and ≥7,900 eggs/plant) by M. javanica and M. arenaria but was nearly free of galling from M. incognita. Zinna elegans cv. Scarlet was nearly free of galling from M. incognita and M. arenaria but was susceptible (mean gall rating = 2.9; 3,400 eggs/plant) to M. javanica.
Ageratum houstonianum; Antirrhinum majus; Celosia argentea; Coleus blumei; Dianthus chinensis; flowers; Lobularia maritima; Meloidogyne arenaria; Meloidogyne incognita; Meloidogyne javanica; nematode; ornamental; Petunia x hybrida; Salvia splendens; Tagetes patula; Verbena × hybrida; Vinca rosea; Zinnia elegans
Of the 56 species and 43 genera of Asteraceae tested, 9 were highly resistant or immune to Meloidogyne incognita and did not form root galls. Twenty-six species and six cultivars had 25% or fewer roots galled and were considered moderately resistant to M. incognita. Pre-planting Cosmos bipinnatus (F190), Gaillardia pulchella, Tagetes erecta, Tithonia diversifolia, or Zinnia elegans (F645) reduced root galling and M. incognita J2 in and around Ipomoea reptans. Amendment of soils with roots, stems, or leaves of G. pulchella was effective in controlling M. incognita on I. reptans. Tissue extracts of G. pulchella were lethal to various plant-parasitic nematodes but were innocuous to free-living nematodes. Root exudates of G. pulchella were lethal to J2 of M. incognita and were inhibitory to the hatch of eggs at the concentration of 250 ppm or higher. Gaillardia pulchella could be used to manage M. incognita as a rotation crop, a co-planted crop, or a soil amendment for control of root-knot nematode.
antagonistic plants; Asteraceous plants; Ipomoea repans; root exudates; rotation; soil amendment; tissue extracts
The root-knot nematode (RKN) is one of the most damaging agricultural pests.Effective biological control is need for controlling this destructive pathogen in organic farming system. During October 2010 to 2011, the nematicidal effects of the Syncephalastrum racemosum fungus and the nematicide, avermectin, alone or combined were tested against the RKN (Meloidogyne incognita) on cucumber under pot and field condition in China. Under pot conditions, the application of S. racemosum alone or combined with avermectin significantly increased the plant vigor index by 31.4% and 10.9%, respectively compared to the M. incognita-inoculated control. However, treatment with avermectin alone did not significantly affect the plant vigor index. All treatments reduced the number of root galls and juvenile nematodes compared to the untreated control. Under greenhouse conditions, all treatments reduced the disease severity and enhanced fruit yield compared to the untreated control. Fewer nematodes infecting plant roots were observed after treatment with avermectin alone, S. racemosum alone or their combination compared to the M. incognita-inoculated control. Among all the treatments, application of avermectin or S. racemosum combined with avermectin was more effective than the S. racemosum treatment. Our results showed that application of S. racemosum combined with avermectin not only reduced the nematode number and plant disease severity but also enhanced plant vigor and yield. The results indicated that the combination of S. racemosum with avermectin could be an effective biological component in integrated management of RKN on cucumber.
Several potential cover crops were evaluated for their susceptibility to Meloidogyne arenaria race 1, M. incognita race 1, and M. javanica in a series of five greenhouse experiments. No galls or egg masses were observed on roots of castor (Ricinus communis), cowpea (Vigna unguiculata cv. Iron Clay), crotalaria (Crotalaria spectabilis), or American jointvetch (Aeschynomene americana). Occasional egg masses (rating ≤1.0 on 0-5 scale) were observed on marigold (Tagetes minuta) in one test with M. incognita, on sesame (Sesamum indicum cv. Paloma) in a test with M. arenaria, and on sunn hemp (Crotalaria juncea cv. Tropic Sun) in 1 of 2 tests with M. incognita; otherwise, these crops were free of egg masses. Numbers of second-stage juveniles (J2) hatched from eggs per root system were low (≤10/pot) for the abovementioned crops. Egg-mass levels and numbers of hatched J2 of M. incognita on pearl millet (Pennisetum typhoides, Tifleaf II hybrid) were comparable to those on a susceptible tomato (Lycopersicon esculentum cv. Rutgers). In a test with M. arenaria, egg mass levels and numbers of J2 on Japanese millet (Echinochloa frumentacea) were similar to those on tomato. Japanese millet was susceptible to each of the nematode isolates tested. However, several of the crops evaluated were very poor hosts or non-hosts of the nematode isolates, including several legumes (cowpea, crotalaria, jointvetch, sunn hemp) that have potential use in both nematode and nitrogen management.
Aeschynomene americana; castor; cowpea; Crotalaria juncea; Crotalaria spectabilis; Echinochloa frumentacea; host-plant resistance; jointvetch; marigold; Meloidogyne arenaria; Meloidogyne incognita; Meloidogyne javanica; millet; nematode; nematode management; Pennisetum glaucum; Pennisetum typhoides; Ricinus communis; sesame; Sesamum indicum; sunn hemp; sustainable agriculture; Tagetes minuta; Vigna unguiculata
The effects of soil temperature and initial inoculum density (Pi) of Meloidogyne incognito and M. javanica on growth of wheat (Triticum aestivum cv. Anza) and nematode reproduction were studied in controlled temperature baths in the glasshouse. Nematode reproduction was directly proportional to temperature between 14 and 30 C for M. incognita and between 18 and 26 C for M. javanica. Reproduction rates (Pf/Pi, where Pf = final number of eggs) for Pi's of 3,000, 9,000, and 30,000 eggs/plant were greatest at each temperature when Pi = 3,000. Maximum M. incognita reproduction rate (Pf/Pi = 51.12) was at 30 C. At 26 C, M. javanica reproduction (Pf/Pi = 14.82, 9.02, and 4.23 for Pi = 3,000, 9,000, and 30,000, respectively) was about half that of M. incognita when Pi = 3,000 or 9,000 but similar when Pi = 30,000. Reproduction of both species was depressed between 14 and 18 C. Shoot and root growth and head numbers were inversely related to soil temperature between 14 and 30 C but were not affected by the Pi of M. incognita when 7 d old seedlings were inoculated. When newly germinated seedlings were inoculated with M. incognita or M. javanica, the Pi did not affect shoot and root fresh weights, shoot/root ratio, and tillering, but it did reduce root dry weight (M. javanica at 26 C) and increase shoot dry weight (M. incognita at 18-22 C). The optimum temperature range is lower for wheat growth than for nematode reproduction. Wheat cv. Anza is a good host for M. incognita and M. javanica, but it is tolerant to both species.
temperature; root-knot nematodes; tolerance; population dynamics
The influence of solutions of ascorbic acid, thiamine, L-arginine, and L-gtutamic acid on egg hatch, juvenile survival, and development and reproduction of Meloidogyne incognita in susceptible and resistant tomatoes was studied. Maximum inhibition of egg hatch occurred at 2,000, 4,000, and 2,000 ppm for ascorbic acid, L-arginine, and L-glutamic acid, respectively. Larval survival was significantly reduced by concentrations of 2,000 ppm ascorbic acid and 1,000 ppm of L-arginine. Maximum inhibition of egg hatch and mortality of juveniles was achieved at a concentration of 4,000 ppm of ascorbic acid and L-arginine. L-glutamic acid and thiamine had respective moderate and minimal toxic effects. Foliar sprays of ascorbic acid, L-arginine, or L-glutamic acid suppressed the numbers of root galls, females, and egg masses on the susceptible tomato cultivar Tropic. Ascorbic acid and L-arginine had highly significant effects when applied to foliage before inoculation with nematodes. Thiamine had little effect. All sprays suppressed the numbers of root galls and females in roots of the resistant cultivar VFN8 when treatments were applied before inoculation. They were not, however, effective as post-inoculation treatments. Growth of a susceptible cultivar was improved by post-inoculation and pre-inoculation treatments when compared with the control plants which had neither nematode infection nor chemical treatment. No positive growth response to chemical treatment was seen in resistant control plants.
amino acid; Meloidogyne incognita; tomato; vitamin
We have developed a simple PCR assay protocol for detection of the root-knot nematode (RKN) species Meloidogyne arenaria, M. incognita, and M. javanica extracted from soil. Nematodes are extracted from soil using Baermann funnels and centrifugal flotation. The nematode-containing fraction is then digested with proteinase K, and a PCR assay is carried out with primers specific for this group of RKN and with universal primers spanning the ITS of rRNA genes. The presence of RKN J2 can be detected among large numbers of other plant-parasitic and free-living nematodes. The procedure was tested with several soil types and crops from different locations and was found to be sensitive and accurate. Analysis of unknowns and spiked soil samples indicated that detection sensitivity was the same as or higher than by microscopic examination.
Detection; diagnosis; Meloidogyne arenaria; Meloidogyne incognita; Meloidogyne javanica; PCR; root-knot nematode; soil
Seven-day-old seedlings of two cultivars (Cristalina and UFV ITM1) of Glycine max were inoculated with 0, 3,000, 9,000, or 27,000 eggs of Meloidogyne incognita race 3 or M. javanica and maintained in a greenhouse. Thirty days later, plants were exposed to ¹⁴CO₂ for 4 hours. Twenty hours after ¹⁴CO₂ exposure, the root fresh weight, leaf dry weight, nematode eggs per gram of root, total and specific radioactivity of carbohydrates in roots, and root carbohydrate content were evaluated. Meloidogyne javanica produced more eggs than M. incognita on both varieties. A general increase in root weight and a decrease in leaf weight with increased inoculum levels were observed. Gall tissue appeared to account for most of the root mass increase in seedlings infected with M. javanica. For both nematodes there was an increase of total radioactivity in the root system with increased levels of nematodes, and this was positively related to the number of eggs per gram fresh weight and to the root fresh weight, but negatively related to leaf dry weight. In most cases, specific radioactivities of sucrose and reducing sugars were also increased with increased inoculum levels. Highest specific radioactivities were observed with reducing sugars. Although significant changes were not observed in endogenous levels of carbohydrates, sucrose content was higher than reducing sugars. The data show that nematodes are strong metabolic sinks and significantly change the carbon distribution pattern in infected soybean plants. Carbon partitioning in plants infected with nematodes may vary with the nematode genotype.
carbohydrates; carbon partitioning; Glycine max; Meloidogyne incognita; Meloidogyne javanica; nematode; photoassimilate translocation; root growth; soybean
Two Hawaiian isolates of Steinernema feltiae MG-14 and Heterohabditis indica MG-13, a French isolate of S. feltiae SN, and a Texan isolate of S. riobrave TX were tested for their efficacy against the root-knot nematode, Meloidogyne javanica, in the laboratory and greenhouse. Experiments were conducted to investigate the effects of treatment application time and dose on M. javanica penetration in soybean, and egg production and plant development in tomato. Two experiments conducted to assess the effects of entomopathogenic nematode application time on M. javanica penetration demonstrated that a single application of 10⁴ S. feltiae MG-14 or SN infective juveniles per 100 cm³ of sterile soil, together with 500 (MG-14) or 1,500 (SN) second-stage juveniles of M. javanica, reduced root penetration 3 days after M. javanica inoculation compared to that of a water treatment. Entomopathogenic nematode infective juveniles applied to assess the effects on M. javanica egg production did not demonstrate a significant reduction compared to that of the water control treatment. There was no dose response effect by Steinernema spp. On M. javanica root penetration or egg production. Steinernema spp. did not affect the growth or development of M. javanica-infected plants, but H. indica MG-13-treated plants had lower biomass than untreated plants infected with M. javanica. Infective juveniles of S. riobrave TX, S. feltiae SN, and MG-14 but not those of H. indica MG-13 were found inside root cortical tissues of M. javanica-infected plants. Entomopathogenic nematode antagonism to M. javanica on soybean or tomato was insufficient in the present study to provide a consistent level of nematode suppression at the concentrations of infective juveniles applied.
behavior; heterorhabditis; Meloidogyne javanica; root penetration; Steinernema; suppression
Guardian peach rootstock was evaluated for susceptibility to Meloidogyne incognita race 3 (Georgia-peach isolate) and M. javanica in the greenhouse. Both commercial Guardian seed sources produced plants that were poor hosts of M. incognita and M. javanica. Reproduction as measured by number of egg masses and eggs per plant, eggs per egg mass, and eggs per gram of root were a better measure of host resistance than number of root galls per plant. Penetration, development, and reproduction of M. incognita in Guardian (resistant) and Lovell (susceptible) peach were also studied in the greenhouse. Differences in susceptibility were not attributed to differential penetration by the infectivestage juveniles (J2) or the number of root galls per plant. Results indicated that M. incognita J2 penetrated Guardian roots and formed galls, but that the majority of the nematodes failed to mature and reproduce.
host-parasitic relationship; Meloidogyne incognita; Meloidogyne javanica; nematode; peach; Prunus persica; resistance; root-knot nematode; rootstock
This study sought to control the root-knot nematode (RKN) Meloidogyne incognita using benign organo-chemicals. Second-stage juveniles (J2) of RKN were exposed to dilutions (1.0%, 0.5%, 0.2%, and 0.1%) of acetic acid (AA), lactic acid (LA), and their mixtures (MX). The nematode bodies were disrupted severely and moderately by vacuolations in 0.5% of MX and single organic acids, respectively, suggesting toxicity of MX may be higher than AA and LA. The mortality of J2 was 100% at all concentrations of AA and MX and only at 1.0% and 0.5% of LA, which lowered slightly at 0.2% and greatly at 0.1% of LA. This suggests the nematicidal activity of MX may be mostly derived from AA together with supplementary LA toxicity. MX was applied to chili pepper plants inoculated with about 1,000 J2, for which root-knot gall formations and plant growths were examined 4 weeks after inoculation. The root gall formation was completely inhibited by 0.5% MX and standard and double concentrations of fosthiazate; and inhibited 92.9% and 57.1% by 0.2% and 0.1% MX, respectively. Shoot height, shoot weight, and root weight were not significantly (P ≤ 0.05) different among all treatments and the untreated and non-inoculated controls. All of these results suggest that the mixture of the organic acids may have a potential to be developed as an eco-friendly nematode control agent that needs to be supported by the more nematode control experiments in fields.
control; Meloidogyne incognita; nematode mortality; organic acids; root gall formation
The survival of eggs of the root-knot nematode Meloidogyne javanica was studied in a series of experiments comparing the infectivity of egg masses (EM) to that of separated eggs (SE). The EM or SE were placed in the centers of pots containing citrus orchard soil and incubated for 24 hours, 10 days, or 20 days. Following each incubation time, 10-day-old tomato plants were planted in each pot, and 3 to 4 weeks later the plants were harvested and the galling indices determined. In the EM treatments, galling indices of ca. 4.0 to 5.0 were recorded after all three incubation periods; in the SE treatments, the infectivity gradually declined to trace amounts by 20 days. Incubating EM and SE for 2 weeks in four different soil types showed the same pattern in all the soil types: EM caused heavy infection of the test plants while the infection rate from the SE was extremely low. Incubating EM and SE in soil disinfested with formaldehyde resulted in comparable galling indices in most treatments. In petri dish experiments, 100 mg of natural soil was spread at the perimeter of a Phytagel surface and EM or SE of M. incognita were placed in the center. Light microscopy revealed that within 5 to 10 days the SE were attacked by a broad spectrum of microorganisms and were obliterated while the eggs within the EM remained intact. Separated eggs placed within sections of gelatinous matrix (GM) were not attacked by the soil microorganisms. When selected microbes were placed on Phytagel surfaces with EM of M. incognita, electron microscopy demonstrated that at least some microbes colonized the GM. As the major difference between the EM and the SE was the presence of the GM, the GM may serve as a barrier to the invasion of some microorganisms.
biological control; Burkholderia cepacia; egg; electron microscopy; gelatinous matrix; Meloidogyne; Mortierella sp.; nematode; root-knot nematode