Nonchemical methods and strategies for nematode management including cultural methods and engineered measures have been recommended as an alternative to methyl bromide (a major soil fumigant), due to its role in the depletion of the ozone layer. Hence, an international agreement has recently been reached calling for its reduced consumption and complete phasing out. This present research evaluates the potential of Ecologic, a biological, marine shell meal chitin material, as a soil amendment management agent for root knot nematode, Meloidogyne incognita, control, and its effect on the growth of Floradel tomato plant, Lycopersicon esculentum. To accomplish this goal, studies were conducted during which, experimental pots were set up in greenhouse environments using sterilized soil inoculated with 5,000 root-knot eggs per 1500 g soil. There were 4 treatments and 5 replications. Treatments were: No chitin; 50 g chitin; 100 g chitin; and 200 g chitin. A two-week wait period following Ecologic amendment preceded Floradel tomato planting to allow breakdown of the chitin material into the soil. Fresh and dry weights of shoot and root materials were taken as growth end-points. A statistically significant difference (p ≤ 0.05) was obtained with regard to the growth rate of L. esculentum at 100 g chitin treatment compared to the control with no chitin. Mean fresh weights of Floradel tomato were 78.0 ± 22.3g, 81.0 ± 20.3g, 109.0 ± 25.4g and 102.0 ± 33.3g at 0, 50, 100 and 200g chitin, respectively. The analysis of root knot nematode concentrations indicated a substantial effect on reproduction rate associated with chitin amendment. Study results showed a significant decrease in both root knot nematode eggs and juveniles (J2) at 100g and 200g Ecologic chitin levels, however, an increase in nematode concentrations was recorded at the 50g Ecologic chitin level (p ≤ 0.05). The mean amounts of J2 population, as expressed per 1500cm3 soil, were 49,933 ± 38,819, 86,050 ± 25248, 103 ± 133 and 103 ± 133 for 0, 50, 100 and 200g chitin, respectively. Similarly, the mean numbers of root knot nematode eggs (per 1500cm3 of soil) were 40,759 ± 36,712, 66,048 ± 39,730, 9,904 ± 16,591 and 9,257 ± 17,204. Root gall rating was also significantly lower (p ≤ 0.05) at the 100g and 200g chitin levels compared to the control. Percent gall ratings were 3.3 ± 1.0%, 3.2 ± 1.0%, 1.0 ± 0.5%, and 1.0% ± 0.6% for amendment levels of 0, 50, 100, and 200g chitin, respectively.
Ecologic chitin; root knot nematode; tomato plant; agricultural management
Oxycom applications increased plant growth and population levels of Meloidogyne incognita on susceptible tomato. A single Oxycom drench at 2,500 ppm applied 7 days prior to inoculation with M. incognita provided remediation of plant growth measured 63 days later. This occurred without reducing nematode population levels. Follow-up drenches at 2,500 ppm at 10-day intervals stunted shoots and roots (P = 0.05). The same application rates at 20-day intervals did not reduce plant growth. Plants receiving multiple drenches had more galls (P = 0.05), females, and second-stage juveniles (J2) per root system compared to plants receiving only the single treatment. Foliar mass and height of plants treated with a single pre-inoculation Oxycom drench were indistinguishable from plants without nematodes. Oxycom treatments activated signaling pathways for plant defense as confirmed by detection of elevated defense gene transcripts in root tissues. The finding of increased reproduction of root-knot nematode without loss of plant growth is consistent with the definition of induced tolerance. Frequency, rate, and timing of applications need further study with other nematodes and various field settings.
Ethylene; growth stimulation; induced resistance; MAPK activation; nematodes; salicylic acid; tolerance
Researchers have indicated that the C₉ fatty acid, pelargonic acid (nonanoic acid), has considerable nematicidal activity that could be increased by derivitization and improved emulsification. Microemulsions of methyl and ethylene glycol esters of pelargonic acid developed by Mycogen Corporation (San Diego, CA) were tested for nematicidal activity against root-knot and soybean cyst nematodes. All treamaents were compared to a deionized water control and a microemulsion "blank" (minus active ingredient). Methyl pelargonate reduced gall numbers at concentrations ≥0.8 μl a.i./liter, and ethylene glycol pelargonate reduced gall numbers at ≥6.4 μl a.i./liter in a laboratory bioassay of Meloidogyne javanica on roots of tomato seedlings. Microscopic observation of treated M. javanica second-stage juveniles suggested that methyl pelargonate was toxic to nematodes at concentrations as low as 0.2 μl a.i./liter. Cysts of Heterodera glycines per gram of root were significantly reduced by weekly soil drenches of methyl pelargonate at 6.4, 3.2, and 1.6 μl a.i./liter compared to controls in one greenhouse experiment. Weekly soil drenches of methyl pelargonate at 4.8 or 3.2 μ1 a.i./liter also significantly reduced the number of eggs produced by M. incognita on soybean in a greenhouse test. In both greenhouse tests with soybean, rates of methyl pelargonate ≥4.8 μl a.i./liter had considerable phytotoxicity. No significant interaction of chemical treatment and different soil mixtures affected the nematode numbers produced or plant vigor observed. Soil drenches with microemulsions of methyl pelargonate at 3.2 μl a.i./liter applied weekly, or as two initial applications, were effective as a nematicide for root-knot and soybean cyst nematodes with negligible effects on plant vigor.
fatty acid; Glycine max; Heterodera glycines; Meloidogyne incognita; Meloidogyne javanica; nematicide; nonanoie acid; pelargonic acid methyl ester; pelargonic acid ethylene glycol ester; phytotoxicity; root-knot nematode; soybean cyst nematode
The effects of a root-knot nematode-resistant tomato cultivar and application of the nematicide ethoprop on root-knot nematode injury to cucumber were compared in a tomato-cucumber double-cropping system. A root-knot nematode-resistant tomato cultivar, Celebrity, and a susceptible cultivar, Heatwave, were grown in rotation with cucumber in 1995 and 1996. Celebrity suppressed populations of Meloidogyne incognita in the soil and resulted in a low root-gall rating on the subsequent cucumber crop. Nematode population densities were significantly lower at the termination of the cucumber crop in plots following Celebrity than in plots following Heatwave. Premium and marketable yields of cucumbers were higher in plots following Celebrity than in plots following Heatwave. Application of ethoprop through drip irrigation at 4.6 kg a.i./ha reduced root galling on the cucumber crop but had no effect on the nematode population density in the soil at crop termination. Ethoprop did not affect cucumber yield. These results indicate that planting a resistant tomato cultivar in a tomato-cucumber double-cropping system is more effective than applying ethoprop for managing M. incognita.
cucumber; cultural control; double crop; Meloidogyne incognita; nematode; root-knot nematode; tomato; trellising
Nematicide/irrigation rate trials were conducted in Texas (TX) in 2009 and 2010 in cotton grown at three irrigation rates, where irrigation rate (base (B), B - 33%, B + 33%) was the main plot and treatment (untreated check, aldicarb, and nematicide seed treatment (NST) and NST + aldicarb) were the subplots. Aldicarb improved cotton lint yield with the base (medium) irrigation rate over the untreated check, but not at the B - 33% and B + 33% irrigation rates. In a second evaluation, 20 tests conducted over 7 yr at the same field in TX and 12 tests conducted over 6 yr at the same field in Alabama (AL) were examined for impact of environmental variables (EV) on the response to NST (containing thiodicarb or abamectin), aldicarb, a nontreated check (CK), insecticide seed treatment (TX only), and a combination of NST + aldicarb + oxamyl (NST/A/O, AL only) on root galls (TX only), early season nematode eggs (AL only), and yield (both sites). Galls/root system were lower with aldicarb-treated plots, than for the CK- or NST-treated plots. As water (irrigation plus rain) in May increased, galls/root system increased for CK or insecticide-only-treated plots, and decreased for NST- and aldicarb-treated plots, suggesting efficacy of nematicides was strongly improved by adequate soil moisture. Nematode reproduction was not affected by EV in either location, though yield was negatively affected by root-knot nematode eggs in AL at 60 d. Yield in both AL and TX was negatively related to temperature parameters and positively related to water parameters. With the addition of EV in TX, chemical treatments went from not significantly different in the absence of EV to aldicarb-treated plots having higher yields than nonnematicide-treated plots in the presence of EV. In AL, NST/A/O-treated plots yielded similar to aldicarb and better than CK or NST in the absence of EV and had significantly higher yields than all other treatments in the presence of most EV.
abamectin; aldicarb; Gossypium hirsutum; Meloidogyne incognita; oxamyl; thiodicarb
The influence of two vesicular-arbuscular mycorrhizal fungi and phosphorus (P) nutrition on penetration, development, and reproduction by Meloidogyne incognita on Walter tomato was studied in the greenhouse. Inoculation with either Gigaspora margarita or Glomus mosseae 2 wk prior to nematode inoculation did not alter infection by M. incognita compared with nonmycorrhizal plants, regardless of soil P level (either 3 μg [low P] or 30 μg [high P] available P/g soil). At a given soil P level, nematode penetration and reproduction did not differ in mycorrhizal and nonmycorrhizal plants. However, plants grown in high P soil had greater root weights, increased nematode penetration and egg production per plant, and decreased colonization by mycorrhizal fungi, compared with plants grown in low P soil. The number of eggs per female nematode on mycorrhizal and nonmycorrhizal plants was not influenced by P treatment. Tomato plants with split root systems grown in double-compartment containers which had either low P soil in both sides or high P in one side and low P in the other, were inoculated at transplanting with G. margarita and 2 wk later one-half of the split root system of each plant was inoculated with M. incognita larvae. Although the mycoorhizal fungus increased the inorganic P content of the root to a level comparable to that in plants grown in high P soil, nematode penetration and reproduction were not altered. In a third series of experiments, the rate of nematode development was not influenced by either the presence of G. margarita or high soil P, compared with control plants grown in low P soil. These data indicate that supplemental P (30 μ/g soil) alters root-knot nematode infection of tomato more than G. mosseae and G. margarita.
Glomus mosseae; Gigaspora margarita; root-knot nematode
The effect of different-colored polyethylene mulches on quantity and spectra of reflected light, plant morphology, and root-knot disease was studied in tomato (Lycopersicon esculentum) grown in simulated planting beds. Tomato plants were inoculated with Meloidogyne incognita at initial populations (Pi) of 0, 1,000, 10,000, or 50,000 eggs/plant, and grown in a greenhouse for 50 days over white, red, or black mulch. Soil temperature was kept constant among the mulch treatments by placing an insulation barrier between the colored mulch and the soil surface. Soil temperature varied less than 0.5 °C between soil chambers at solar noon. Tomatoes grown over white mulch received more reflected photosynthetic light and had greater shoot weights (27%), root weights (32%), and leaf area (20%) than plants grown over black mulch. Plants grown over red mulch received a higher far-red-to-red ratio in the reflected light. Mulch color altered the plant's response to root-knot nematode infection by changing the distribution of mass in axillary shoots. At high Pi, axillary leaf area and leaf weight were greater in tomato grown over white mulch than when grown over red mulch. The root-gall index was lower for plants grown over white mulch than similar plants grown over red mulch.
host-parasite relationship; light quality; Meloidogyne incognita; nematode; photomorphogenesis; plastic mulch; polyethylene; root-knot; tomato
In a greenhouse experiment, the nematicidal effect of some bacterial biofertilizers including the nitrogen fixing bacteria (NFB) Paenibacillus polymyxa (four strains), the phosphate solubilizing bacteria (PSB) Bacillus megaterium (three strains) and the potassium solubilizing bacteria (KSB) B. circulans (three strains) were evaluated individually on tomato plants infested with the root-knot nematode Meloidogyne
incognita in potted sandy soil. Comparing with the uninoculated nematode-infested control, the inoculation with P. polymyxa NFB7, B. megaterium PSB2 and B. circulans KSB2, increased the counts of total bacteria and total bacterial spores in plants potted soil from 1.2 to 2.6 folds estimated 60 days post-inoculation. Consequently, the inoculation with P. polymyxa NFB7 increased significantly the shoot length (cm), number of leaves / plant, shoot dry weight (g) / plant and root dry weight (g) / plant by 32.6 %, 30.8 %, 70.3 % and 14.2 %, respectively. Generally, the majority treatments significantly reduced the nematode multiplication which was more obvious after 60 days of inoculation. Among the applied strains, P. polymyxa NFB7, B. megaterium PSB2 and B. circulans KSB2 inoculations resulted in the highest reduction in nematode population comparing with the uninoculated nematode-infested control. They recorded the highest reduction in numbers of hatched juveniles/root by 95.8 %, females/root by 63.75 % and juveniles/1kg soil by 57.8 %. These results indicated that these bacterial biofertilizers are promising double purpose microorganisms for mobilizing of soil nutrients (nitrogen, phosphate and potassium) and for the biological control of M. incognita.
Paenibacillus polymyxa; Bacillus megaterium; B. circulans; biofertilizers; biocontrol; root-knot nematodes; Meloidogyne incognita
Twelve soil drenches over a period of 30 days with DBCP concentrations of 40 μg/ml did not completely prevent infection of tomato plants by root-knot nematode juveniles. Repeated DBCP drenches of 40 μg/ml halted gall development during the drenches, but 10 days after drenching was discontinued galls were apparent. DBCP drenches at 200 μg/ml prevented tomato root development, and 40 μg/ml slowed it. Ten μg/ml increased the height of root-knot-infected plants, but not their top weights. Treated plants were lanky. Protective drenches of 2.5 to 40 μg/ml of DBCP decreased nematode populations and increased fruitfulness. DBCP as a therapeutant reduced the incidence of galling on new roots and halted increases in gall size on previously infected roots but did not improve fruitfulness or plant size significantly.
The efficacy of the nematode parasite Paecilomyces lilacinus, alone and in combination with phenamiphos and ethoprop, for controlling the root-knot nematode Meloidogyne javanica on tobacco and the ability of this fungus to colonize in soil under field conditions were evaluated for 2 years in microplots. Combinations and individual treatments of the fungus grown on autoclaved wheat seed, M. javanica eggs (76,000 per plot), and nematicides were applied to specified microplots at the time of transplanting tobacco the first year. Vetch was planted as a winter cover crop, and the fungus and nematicides were applied again the second year to specified plots at transplanting time. The fungus did not control the nematode in either year of these experiments. The average root-gall index (0 = no visible galls and 5 = > 100 galls per root system) ranged from 2.7 to 3.9 the first year and from 4.3 to 5.0 the second in nematode-infested plots treated with nematicides. Plants with M. javanica alone or in combination with P. lilacinus had galling indices of 5.0 both years; the latter produced lower yields than all other treatments during both years of the study. Nevertheless, the average soil population densities of P. lilacinus remained high, ranging from 1.2 to 1.3 × 106 propagules/g soil 1 week after the initial inoculation and from 1.6 to 2.3 × 104 propagules/g soil at harvest the second year. At harvest the second year the density of fungal propagules was greatest at the depth of inoculation, 15 cm, and rapidly decreased below this level.
biocontrol; ethoprop; 1,3-dichloropropene; fenamiphos; fungal egg parasite; Meloidogyne javanica; nematicide; Nicotiana tabacum; Paecilomyces lilacinus; root-knot nematode; tobacco; vetch; Vicia vilIosa
Six peppermint (Mentha x piperita) and six spearmint (M. spicata) PI accessions were inoculated with Meloidogyne incognita race 3 and M. arenaria race 2, under greenhouse conditions. No galls formed on roots of any of the plants inoculated with 1,800 eggs/pot. Fewer than two galls per root system formed on three PI accessions of peppermint inoculated with M. incognita at 5,400 eggs/pot. Only one peppermint accession developed galls when inoculated with M. arenaria, whereas none of the spearmint accessions was susceptible to this species. Plant dry weights generally were unaffected by infection with root-knot nematodes at these densities. Growing peppermint and spearmint accessions for 8 or 12 weeks in M. arenaria-infested soil before tomato resulted in 90% reduction of root galls compared with tomato following tomato. Cineole, eugenol, geraniol, linalool, and peppermint oils at 50 and 250 mg oil/kg soil caused no reduction in the number of galls caused by M. arenaria on tomato. At 1,500 mg oil/kg soil, geraniol, eugenol, linalool, and peppermint oils (P =0.05) reduced the number of galls caused by M. arenaria, but the decrease in galling caused by M. incognita was not significant. Geraniol, linalool, and peppermint oil at 1,000 and 1,500 mg were phytotoxic to tomato.
cineole; eugenol; geraniol; linalool; Meloidogyne spp.; nematode; peppermint; peppermint oil; root-knot nematode; spearmint
Increased culturing of a tomato population of Heterodera schachtii (UT1C) on tomato for 480 days (eight inoculation periods of 60 days each) significantly increased virulence to 'Stone Improved' tomato. A synergistic relationship existed between Meloidogyne hapla and H. schaehtii on tomato. A combination of H. schachtii (UTIC) and M. hapla significantly reduced tomato root weights by 65, 64, and 61% below root weights of untreated controls, and single inoculations of M. hapla and H. schachtii, respectively. This corresponded to root reductions of 42, 44, and 46% from a combination of H. schachtii (UT1B) and M. hapla. Antagonism existed between H. schachtii and M. hapla with regard to infection courts and feeding sites. The root-knot galling index dropped from 6.0 with a single inoculation of M. hapla to 4.3 and 3.3 with combined inoculations of M. hapla plus UT1B and M. hapla plus UTIC cyst nematode populations. The pathological virulence of H. schachtii to sugarbeet was not lost by extended culturing on tomato; there were no differences in penetration, maturation, and reproduction between sugarbeet populations continually cultured on sugarbeet and the population continually cultured on tomato.
sugarbeet cyst nematode; northern root-knot nematode; Lycopersicon esculentum; Beta vulgaris; physiological variability; races; synergism; antagonism
Two different defined growth media were used to culture aseptically the root-knot nematode, Meloidogyne incognita, on excised roots of tomato, Lycopersicon esculentum cv 'Marglobe.' One of these media, STW, was a formulation by Skoog, Tsui, and White and the other, MS, a formulation by Murashige and Skoog. From 1 through 4 weeks, inoculated tissues were fractured to observe root infection, giant-cell formation, and nematode development with the scanning electron microscope (SEM). Four weeks after inoculation, the fresh weights of roots and developmental stages of nematodes were recorded. SEM observations indicated that roots cultured on the STW medium had normal growth and infection sites with galls that supported the development of mature females by 4 weeks. Roots cultured on the MS medium were less vigorous and had infection sites with galls containing only one to four syncytialike cells that did not support the development of mature females. Eighty percent of the larvae infecting roots cultured on the MS medium failed to develop into mature females. To determine which factor(s) affected root growth and nematode development, inoculated and uninoculated roots were grown on media consisting of different combinations of the organic and inorganic fractions of the STW and MS formulations. These experiments indicated that the organic fraction of STW was essential for normal root growth; however, the inorganic fraction of MS inhibited normal gall formation and nematode development. Further testing of the inorganic fractions revealed that the high concentration of ammonium nitrate in the MS medium was a factor that inhibited giant-cell formation and nematode development.
ammonium inhibition; Meloidogyne incognita
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
Sugar beet (Beta vulgaris L. cv. Monogerm C.S.F. 1971) seeds sown into Vineland fine sandy loam, infested with 15,500 H. schachtii juveniles/pot, showed little growth during an 11-week test in the greenhouse. Seedlings transplanted at 2, 4, and 6 weeks of age had 32, 30, and 31% less top weight and 71, 68, and 59% less root weight, respectively, compared to controls grown in nematode-free soil. Nematode reproduction in both direct-seeded and transplanted sugar beets was limited and related to root weight. Shoot/root ratios were increased by the nematodes in all nematode-infected beets compared to those grown in soil without nematodes. In contrast to seeding or transplanting sugar beets into nematode-infested Vineland fine sandy loam, an inoculation of Beverly fine sandy loam supporting 0 (seeds), 2-, 4-, and 6-week-old sugar beet seedlings with 7,400 juveniles/pot, followed by 11 weeks of growth in the growth-room, resulted in top weight losses of only 13, 3, 18, and 15% and losses in root weight of 44, 38, 36, and 38%, respectively. Nematode reproduction was high and all shoot/root ratios were increased by the nematode compared to the noninoculated controls. These experiments have shown that sugar beets sown into nematode-infested soil are damaged much more heavily by H. schachtii juveniles than seeds inoculated with the nematode immediately following sowing. Results indicate that an increase in tolerance of sugar beets to attack by H. schachtii does not occur beyond the first 2 weeks of growth and that transplanting damage lowers the tolerance of seedlings to nematode attack.
sugar beet cyst nematode; age tolerance; transplanting damage; host-parasite relationship
The nematicidal activities of ammonium sulfate, chicken litter and chitin, alone or in combination with neem (Azadirachta indica) extracts were tested against Meloidogyne javanica. Soil application of these amendments or the neem extracts alone did not reduce the root galling index of tomato plants or did so only slightly, but application of the amendments in combination with the neem extracts reduced root galling significantly. Soil analysis indicated that the neem extract inhibited the nitrification of the ammonium released from the amendments and extended the persistence of the ammonium concentrations in the soil. In microplot experiments, tomato plants were grown in pots filled with soils from the treated microplots. The galling indices of tomato plants grown in soil treated with ammonium sulfate or chicken litter in combination with the neem extract or a chemical nitrification inhibitor were far lower than those of plants grown in the control soil or in soil treated with chicken litter, neem extract or nitrification inhibitor alone. However, plants grown in the microplots showed only slight reductions in galling, probably because the soil amendments were inadequately mixed compared to their application in the pot experiments. The extended exposure of nematodes to ammonia as a result of nitrification inhibition by the neem extracts appeared to be the cause of the enhanced nematicidal activity of the ammonia-releasing amendments.
ammonia; ammonium sulfate; Azadirachta indica; chicken litter; chitin; neem; nitrification; nitrification inhibitor; soil amendments
Numerous species of soil bacteria which flourish in the rhizosphere of plants or around plant tissues stimulate plant growth and reduce nematode population by antagonistic behavior. These bacteria are collectively known as PGPR (plant growth promoting rhizobacteria). The effects of six isolates of PGPR Pseudomonas putida, Pseudomonas fluorescens, Serratia marcescens, Bacillus amyloliquefaciens, Bacillus subtilis and Bacillus cereus, were studied on tomato plant growth and root knot nematode reproduction after 45 days from nematode infection. The highest number of shoot dry weight/g (43.00 g) was detected in the plant treated with S. marcescens; then P. putida (34.33 g), B. amyloliquefaciens (31.66 g), P. fluorescens (30.0 g), B. subtilis (29.0 g), B. cereus (27.0 g) and nematode alone (untreated) 20 g/plant. While the highest number of plant height was observed when plant was treated with S. marcescens, P. fluorescens, P. putida, B. amyloliquefaciens and P. putida 52.66, 50.66, 48 and 48 cm respectively. No significant differences were seen between previous treatments but only had significant differences compared with untreated plant. The highest number of fruit/plant was observed when plants were treated with S. marcescens (10.66), then B. amyloliquefaciens (8.66), P. putida (8), P. fluorescens (8) and B. cereus (7.66). No significant differences between the last 4 treatments, but all had significant differences compared with untreated plants. The highest weight of plant yield (g) was observed with S. marcescens (319.6 g/plant) and the lowest weight of plant yield was observed in plants treated with nematode alone (untreated). On the other hand, the lowest numbers of J2/10 g of soil (78), galls/root, (24.33) galls/root, egg masses/root (12.66) and egg/egg masses were observed in the plants treated with S. marcescens.
PGPR; Meloidogyne; Biological control; Rhizobacteria; Pseudomonas
Broccoli (Brassica oleracea), carrot (Daucus carota), marigold (Tagetes patula), nematode-resistant tomato (Solanum lycopersicum), and strawberry (Fragaria ananassa) were grown for three years during the winter in a root-knot nematode (Meloidogyne incognita) infested field in Southern California. Each year in the spring, the tops of all crops were shredded and incorporated in the soil. Amendment with poultry litter was included as a sub-treatment. The soil was then covered with clear plastic for six weeks and M. incognita-susceptible tomato was grown during the summer season. Plastic tarping raised the average soil temperature at 13 cm depth by 7°C.The different winter-grown crops or the poultry litter did not affect M. incognita soil population levels. However, root galling on summer tomato was reduced by 36%, and tomato yields increased by 19% after incorporating broccoli compared to the fallow control. This crop also produced the highest amount of biomass of the five winter-grown crops. Over the three-year trial period, poultry litter increased tomato yields, but did not affect root galling caused by M. incognita. We conclude that cultivation followed by soil incorporation of broccoli reduced M. incognita damage to tomato. This effect is possibly due to delaying or preventing a portion of the nematodes to reach the host roots. We also observed that M. incognita populations did not increase under a host crop during the cool season when soil temperatures remained low (< 18°C).
biofumigation; crop rotation; management; Meloidogyne incognita; Solanum lycopersicum
The potential of bacterial antagonists of fungal pathogens to control the root-knot nematode Meloidogyne incognita was investigated under greenhouse conditions. Treatment of tomato seeds with several strains significantly reduced the numbers of galls and egg masses compared with the untreated control. Best performed Bacillus subtilis isolates Sb4-23, Mc5-Re2, and Mc2-Re2, which were further studied for their mode of action with regard to direct effects by bacterial metabolites or repellents, and plant mediated effects. Drenching of soil with culture supernatants significantly reduced the number of egg masses produced by M. incognita on tomato by up to 62% compared to the control without culture supernatant. Repellence of juveniles by the antagonists was shown in a linked twin-pot set-up, where a majority of juveniles penetrated roots on the side without inoculated antagonists. All tested biocontrol strains induced systemic resistance against M. incognita in tomato, as revealed in a split-root system where the bacteria and the nematodes were inoculated at spatially separated roots of the same plant. This reduced the production of egg masses by up to 51%, while inoculation of bacteria and nematodes in the same pot had only a minor additive effect on suppression of M. incognita compared to induced systemic resistance alone. Therefore, the plant mediated effect was the major reason for antagonism rather than direct mechanisms. In conclusion, the bacteria known for their antagonistic potential against fungal pathogens also suppressed M. incognita. Such “multi-purpose” bacteria might provide new options for control strategies, especially with respect to nematode-fungus disease complexes that cause synergistic yield losses.
The antagonistic effects of raw sewage sludge on infection of tomato by Meloidogyne incognita were tested in greenhouse pot experiments. Sludge was mixed with the soil or added on its surface before and after inoculation of tomato plants with nematode eggs. Juvenile penetration was determined 1 and 10 days after inoculation, and 6 weeks later root systems were assessed for nematode reproduction. Fewer juveniles penetrated roots in pots with sludge added to the soil than in unamended control pots. In both experiments, roots were severely galled despite a significant reduction in gall ratings in amended relative to unamended soils. Egg production in treated soil was less (P = 0.05) than in control pots, regardless of whether sludge was incorporated or added 1 day before or after inoculation. In treated pots, RF values (final egg number/inoculation egg number) were strongly reduced. The toxic effects observed on the parasite may result from the ammoniacal nitrogen released in the soil within 7 days after treatment, associated with possible poor host suitability of tomatoes grown in amended substrate and short-lasting compound(s) active after root invasion.
Lycopersicon esculentum; Meloidogyne incognita; nematode; organic amendment; root-knot nematode; tomato; urban waste
Root-knot nematode-susceptible melons (Cantaloupe) were grown in pots with varying levels of Meloidogyne incognita and were compared to susceptible melons that were grafted onto Cucumis metuliferus or Cucurbita moschata rootstocks. In addition, the effect of using melons as transplants in nematode-infested soil was compared to direct seeding of melons in nematode-infested soil. There were no differences in shoot or root weight, or severity of root galling between transplanted and direct-seeded non-grafted susceptible melon in nematode-infested soil. Susceptible melon grafted on C. moschata rootstocks had lower root gall ratings and, at high nematode densities, higher shoot weights than non-grafted susceptible melons. However, final nematode levels were not lower on the grafted than on the non-grafted plants, and it was therefore concluded that grafting susceptible melon on to C. moschata rootstock made the plants tolerant, but not resistant, to the nematodes. Grafting susceptible melons on C. metuliferus rootstocks also reduced levels of root galling, prevented shoot weight losses, and resulted in significantly lower nematode levels at harvest. Thus, C. metuliferus may be used as a rootstock for melon to prevent both growth reduction and a strong nematode buildup in M. incognita-infested soil.
Cucumis melo; Cucumis metuliferus; cucurbita moschata; grafting; Meloidogyne incognita; melon; reproduction; resistance; rootstock
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
Oryzalin (3,5-dinitro-N4,N4-dipropyl-sulfanilamide) and BAS 083 (l,l-dimethylpiperdinium chloride) reduced root-knot infection in tomato roots when respectively applied as a soil drench at 20 ppm and 10,000 ppm. Oryzalin reduced knot counts with various intervals between treatment and inoculation. BAS 083 reduced knot counts only when applied before inoculation. Oryzalin was shown not to be a contact nematicide, and BAS 083 was only a weak one. Neither compound reduced penetration by infective larvae. Postinfection reduction in knot counts by Oryzalin and BAS 083 resulted, in part, from activation of natural defense mechanisms of the host. Giant-cell development in cotton roots inoculated with nematodes was inhibited by Oryzalin. Lateral root development was inhibited by BAS 083.
herbicides; growth regulators; physiology; resistance
A severe root rot of tomato caused by Meloidogyne incognita and Rhizoctonia solani was associated with nutrient mobilization into gall tissue and root exudation. Root decay did not develop when root exudates were continuously removed by leaching. When leachates were collected from M. incognita-infected and control roots and applied to roots of tomatoes inoculated with R. solani alone, roots receiving leachates from M. incognita-infected roots developed a severe rot while roots receiving leachates from control roots were free of decay. During the fourth and fifth weeks following nematode infection, an increased mobilization of ¹⁴C labelled compounds to nematode-infected roots occurred. Higher counts of water soluble nonvolatile ¹⁴C labelled exudates leaked from nematode-infected roots than from control roots at each weekly sampling period. Higher concentrations of Ca, Mg, Na, K, Fe, and Cu were found in exudates from nematode-infected roots than from the control roots. During the first 14 days following nematode infection, carbohydrates were the major organic constituents in exudates leaking from nematode-infected roots. Fourteen days after nematode infection, nitrogenous compounds become the major organic constituents leaking from roots. Shifts in C/N ratio of root exudates from nematode-infected roots were associated with parasitic development of R. solani in tomato roots.
fungus-nematode interactions; Meloidogyne incognita; root exudates; C/N ratios
Two Rotylenchulus reniformis populations (North Carolina and Georgia) were compared on sweetpotato and tomato. 'Beauregard' sweetpotato and 'Better Boy' and 'Marion' tomato were excellent hosts for both R. reniformis populations. On Beauregard sweetpotato, the two populations did not differ in fecundity; however, on both tomato cultivars, the Georgia population reproduced at a higher rate than the North Carolina population (P ≤ 0.05). Meloidogyne javanica reproduction was higher (P ≤ 0.05) on Marion than on Better Boy. Neither population of reniform nematodes suppressed shoot growth of tomato or sweetpotato at any Pi (initial population density). Both populations of R. reniformis, however, restricted storage-root growth of Beauregard sweetpotato but enhanced shoot growth. When the Georgia population was evaluated in microplots with Pi levels of 0, 20,000, or 40,000 R. reniformis/500 cm³ soil, total fruit weights of Better Boy tomato were not affected. In the greenhouse, Marion tomato fresh shoot and fruit growth (weights) was suppressed by M. javanica, but Better Boy was not affected. Root necrosis increased linearly with Pi on Beauregard sweetpotato grown in the greenhouse and became more pronounced as numbers of R. reniformis increased, regardless of the population. The cultivars of tomatoes evaluated were tolerant to the two populations ofR. reniformis in a sandy soil and exhibited no root necrosis. Marion tomato was highly susceptible to M. javanica, while Better Boy was tolerant.
Ipomoea batatas; Lycopersicon esculentum; Meloidogyne javanica; nematode; reniform nematode; root-knot nematode; Rotylenchulus reniformis; sweetpotato; tomato; yield