Effect of Crotalaria juncea Amendment on Nematode Communities in Soil with Different Agricultural Histories

Effect of sunn hemp (Crotalaria juncea) hay amendment on nematode community structure in the soil surrounding roots of yellow squash (Cucurbita pepo) infected with root-knot nematodes was examined in two greenhouse experiments. Soils were from field plots treated long-term (LT) with yard-waste compost or no yard-waste compost in LT experiment, and from a short-term (ST) agricultural site in ST experiment. Soils collected were either amended or not amended with C. juncea hay. Nematode communities were examined 2 months after squash was inoculated with Meloidogyne incognita. Amendment increased (P < 0.05) omnivorous nematodes in both experiments but increased only bacterivorous nematodes in ST experiment (P < 0.05), where the soil had relatively low organic matter (<2%). This effect of C. juncea amendment did not occur in LT experiment, in which bacterivores were already abundant. Fungivorous nematodes were not increased by C. juncea amendment in either experiment, but predatory nematodes were increased when present. Although most nematode faunal indices, including enrichment index, structure index, and channel index, were not affected by C. juncea amendment, structure index values were affected by previous soil organic matter content. Results illustrate the importance of considering soil history (organic matter, nutrient level, free-living nematode number) in anticipating changes following amendment with C. juncea hay.     

Influence of Nonhost Plants on Population Decline of Rotylenchulus reniformis

The influence of Chloris gayana, Crotalaria juncea, Digitaria decumbens, Tagetes patula, and a chitin-based soil amendment on Hawaiian populations of Rotylenchulus reniformis was examined. Chloris gayana was a nonhost for R. reniformis. The nematode did not penetrate the roots, and in greenhouse and field experiments, C. gayana reduced reniform nematode numbers at least as well as fallow. Tagetes patula was a poor host for reniform nematode and reduced reniform nematode numbers in soil better than did fallow. Crotalaria juncea was a poor host for R. reniformis, and only a small fraction of the nematode population penetrated the roots. Crotalaria juncea and D. decumbens reduced reniform nematode populations at least as well as fallow. A chitin-based soil amendment, applied at 2.24 t/ha to fallow soil, did not affect the population decline of reniform nematode.     

Non-Traditional Legumes as Potential Soil Amendments for Nematode Control

Dried ground plant tissues from 20 leguminous species were mixed with Meloidogyne incognita-infested soil at 1, 2 or 2.5, and 5% (w/w) and incubated for 1 week at room temperature (21 to 27°C). Tomato (''Rutgers'') seedlings were transplanted into infested soil to determine nematode viability. Most tissues reduced gall numbers below the non-amended controls. The tissue amendments that were most effective include: Canavalia ensiformis, Crotalaria retusa, Indigofera hirsuta, I. nummularifolia, I. spicata, I. suffruticosa, I. tinctoria, and Tephrosia adunca. Although certain tissues reduced the tomato dry weights, particularly at the higher amendment rates (5%), some tissues resulted in greater dry weights. These non-traditional legumes, known to contain bioactive phytochemicals, may offer considerable promise as soil amendments for control of plant-parasitic nematodes. Not only do these legumes reduce root-knot nematodes but some of them also enhance plant height and dry weight.     

Management of Rotylenchulus reniformis in Pineapple,Ananas comosus,by Intercycle Cover Crops

The effects of intercycle cover crops on Rotylenchulus reniformis population densities in pineapple were evaluated in one greenhouse and two field experiments. In the greenhouse, Crotalaria juncea, Brassica napus, and Tagetes erecta were planted for 3 months and then incorporated. These treatments were compared to weedy fallow with or without 1,3-dichloropropene (1,3-D) in three soils (Makawao fallow, Wahiawa fallow, and Wahiawa pineapple) naturally infested with R. reniformis. All cover crop incorporation suppressed R. reniformis numbers in cowpea more than did the weedy treatment in the Makawao (P < 0.05) but not in the Wahiawa soils. Crotalaria juncea treatment increased bacterivorous nematodes and nematode-trapping fungal population densities more than the other treatments in Makawao fallow and Wahiawa pineapple-planted soils. The field trials included the same plants as well as Sinapis alba. Treatments with Crotalaria juncea and 1,3-D maintained lower R. reniformis population densities on pineapple longer than other cover crops or weedy fallow treatments. Crotalaria juncea could have suppressed R. reniformis because it is a poor host and because it enhances nematode-trapping fungi when incorporated into soil. Treatment with 1,3-D reduced microbial activities but produced the greatest pineapple yield.     

Suppression Effects on Pineapple Soil-Borne Pathogens by <i>Crotalaria juncea</i>, Dolomitic Lime and Plastic Mulch Cover on MD-2 Hybrid Cultivar

The development and implementation of sustainable and environmentally friendly agricultural practices are indispensable as alternatives to pesticide use and to keep populations of soil-borne plant pathogens at levels that do not affect crop productivity. The present research evaluates the incidence of soil-borne phytopathogens on the pineapple variety MD-2, which was subjected to different treatments: Incorporation of Crotalaria juncea into the soil (organic amendment), application of dolomitic lime to soil (inorganic amendment), and the use of plastic mulch covering the soil. During the crop cycle (15 months), the following variables were evaluated: plant height (cm), fruit weight (kg·plant⁻¹ ), crop yield (ton·ha⁻¹ ), the bud root disease incidence caused by Phytophthora nicotianae, number of soil phytoparasitic nematodes and colony-forming-units (CFUs) of soil fungi and oomycetes. The results indicate that Crotalaria juncea treatment reduced the pathogen population (nematode and oomycetes) at levels that did not affect crop development, so that yield increased (18–20%). The incorporation of C. juncea into the soil as an organic amendment favors the populations of fungi disease suppressors (Trichoderma-Aspergillus). The phytoparasitic nematodes (Meloidogyne sp., Pratylenchus sp., and Mesocriconema sp.) and oomycetes (Phytophthora spp., and Pythium spp.) showed a reduction of their population levels by effects of organic amendment (C. juncea). The plastic mulch was also effective, probably due to the maintenance of optimal condition to crop growth and weed control. However, the dolomitic lime application had the poorest effect under the conditions of the study area on the variables analyzed. The described observations are characteristics of a system-based approach for the potential management of soil-borne pathogens of pineapple MD-2 in Veracruz, México.     

Evaluation of Asteraceae Plants for Control of Meloidogyne incognita

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.     

Effect of Compost and Manure Soil Amendments on Nematodes and on Yields of Potato and Barley: A 7-Year Study

A 7-year study located in Prince Edward Island, Canada, examined the influence of compost and manure on crop yield and nematode populations. The compost used in this study consisted of cull waste potatoes, sawdust, and beef manure in a 3:3:1 ratio, respectively. No plant-parasitic nematodes were detected in samples collected from windrow compost piles at 5- and 30-cm depths prior to application on field plots. Low population densities of bacterial-feeding nematodes were recovered from compost windrows at the 5-cm depth. Field plots of potato (Solanum tuberosum cv. Kennebec) received compost applied at 16 metric tonnes per hectare, or beef manure applied at 12 metric tonnes per hectare. An adjacent trial with barley (Hordeum vulgare cv. Mic Mac) received only the compost treatment. In both trials the experimental design was a complete randomized block with four replicates. Data averaged over seven growing seasons indicated that population levels of root-lesion nematodes (primarily Pratylenchus penetrans) were higher in root-zone soil in potato plots treated with either compost or manure compared to the untreated control plots. The soil amendments did not affect root-knot nematode (Meloidogyne hapla) population densities in the potato plots, but clover-cyst nematodes (Heterodera trifolii) were more numerous in the root-zone soils of barley treated with compost compared to the untreated plots. Numbers of bacterial-feeding nematodes (primarily Diplogaster lheritieri) were greater in soil in potato plots treated with manure and in soil around barley roots than in untreated plots. Total yields of potato tubers averaged over seven growing seasons increased by 27% in the plots treated with either compost or manure. Grain yields of barley also were increased by 12% when compost was applied. These results indicated that organic amendments increased crop yields, but the impacts on different nematode species varied and usually increased soil population levels.     

Evaluating the predatory potential of carnivorous nematodes against Rotylenchulus reniformis and Meloidogyne incognita

Predatory behavior of a nematode is usually determined through gut content observation or prey delimitation counts. In this experiment, Mononchus and Neoactinolaimus predation of Rotylenchulus reniformis or Meloidogyne incognita was determined using a PCR-based nematode gut content analysis. Soil samples naturally infested with Mononchus were placed in tubes and potential prey nematodes R. reniformis, M. incognita, or a mixture of both were introduced. The gut contents of Mononchus were assayed for the DNA from R. reniformis or M. incognita using PCR specific primers. A higher % of Mononchus tested positive for DNA of R. reniformis than for M. incognita when the prey were added alone. However, when provided with both prey species, Mononchus was tested positive for DNA of M. incognita more frequently than for R. reniformis. Percent Mononchus testing positive for DNA of R. reniformis correlated positively with the abundance of R. reniformis, but this relationship was not observed between Mononchus and M. incognita. Neoactinolaimus was added to aqueous solution containing a mixture of free-living nematodes and R. reniformis. More Neoactinolaimus tested positive for DNA of R. reniformis than other predatory or omnivorous nematodes in the same samples. Based on regression analysis, the presence of fungivorous and other predatory nematodes in the soil could distract Neoactinolaimus from predation on R. reniformis. Our results suggested that Prismatolaimus, Mesodiplogasteroides and Eudorylaimus could also prey on R. reniformis. Although less than 40% of the predatory or omnivorous nematodes tested preyed on R. reniformis, this level of predation could contribute to reducing the population densities of plant-parasitic nematodes in the soil.     

Penetration of Crotalaria juncea,Dolichos lablab,and Sesamum indicum Roots by Meloidogyne javanica

Penetration of Crotalaria juncea (PI 207657 and cv. Tropic Sun) Dolichos lablab cv. Highworth, and Sesamum indicum by juveniles (J2) of Meloidogyne javanica was assessed to investigate the mechanism by which these plants may reduce nematode numbers in the field. Growth chamber experiments were conducted at 25 C, with vials containing 90 g sand infested with 450 J2; tomato (UC 204 C) was included as a susceptible host. Fifteen days after inoculation, roots were stained and the nematodes within stained roots were counted. Both C. juncea lines were highly resistant to penetration, as they contained significantly fewer nematodes per cm of root and per root system than the other plants. Although containing more nematodes per cm of root than C. juncea, S. indicum and D. lablab had significantly fewer nematodes per root system and per cm of root than tomato. Roots were significantly longer in the plants with the lowest nematode penetration. Although C. juncea, D. lablab, and S. indicum may have potential utility as cover or rotation crops in soil infested with M. javanica, further quantitative information on the reproduction of M. javanica and other nematodes in these plants is needed.     

Effects of Rapeseed and Vetch as Green Manure Crops and Fallow on Nematodes and Soil-borne Pathogens

In a rapeseed-squash cropping system, Meloidogyne incognita race 1 and M. javanica did not enter, feed, or reproduce in roots of seven rapeseed cultivars. Both nematode species reproduced at low levels on roots of the third crop of rapeseed. Reproduction of M. incognita and M. javanica was high on squash following rapeseed, hairy vetch, and fallow. The application of fenamiphos suppressed (P = 0.05) root-gall indices on squash following rapeseed, hairy vetch, and fallow; and on Dwarf Essex and Cascade rapeseed, but not Bridger and Humus rapeseed in 1987. The incorporation of 30-61 mt/ha green biomass of rapeseed into the soil 6 months after planting did not affect the population densities of Criconemella ornata, M. incognita, M. javanica, Pythium spp., Rhizoctonia solani AG-4; nor did it consistently increase yield of squash. Hairy vetch supported larger numbers of M. incognita and M. javanica than rapeseed cultivars or fallow. Meloidogyne incognita and M. javanica survived in fallow plots in the absence of a host from October to May each year at a level sufficient to warrant the use of a nematicide to manage nematodes on the following susceptible crop.     

Impact of Soil Texture on the Reproductive and Damage Potentials of Rotylenchulus reniformis and Meloidogyne incognita on Cotton

The effects of soil type and initial inoculum density (Pi) on the reproductive and damage potentials of Meloidogyne incognita and Rotylenchulus reniformis on cotton were evaluated in microplot experiments from 1991 to 1993. The equilibrium nematode population density for R. reniformis on cotton was much greater than that of M. incognita, indicating that cotton is a better host for R. reniformis than M. incognita. Reproduction of M. incognita was greater in coarse-textured soils than in fine-textured soils, whereas R. reniformis reproduction was greatest in a Portsmouth loamy sand with intermediate percentages of clay plus silt. Population densities of M. incognita were inversely related to the percentage of silt and clay, but R. reniformis was favored by moderate levels of clay plus silt (ca. 28%). Both M. incognita races 3 and 4 and R. reniformis effected suppression of seed-cotton yield in all soil types evaluated. Cotton-yield suppression was greatest in response to R. reniformis at high Pi. Cotton maturity, measured as percentage of open bolls at different dates, was affected by the presence of nematodes in all 3 years.     

Nematode Population Fluctuations during Decomposition of Specific Organic Amendments

Population densities of nematodes in field soil without plants were monitored for 10 months following application of organic amendments to pots in a greenhouse. The four treatments consisted of three different kinds of organic amendments: homogeneous crop residues of maize (Zea mays, C:N = 48.0:1), Texas panicum (Panicum texanum, C:N = 32.9:1), or velvetbean (Mucuna pruriens, C:N = 18.6:1), plus a control without any amendment. Plant-parasitic nematodes declined in all treatments due to absence of a food source. Bacterivore numbers increased following amendment application and remained greater than initial population levels until 4 months after application. Fungivore numbers were higher than initial levels until 6 months after amendment application and did not decline below the initial numbers during the course of the experiment. On several sampling dates, the bacterivorous genera Cervidellus and Eucephalobus were most abundant in pots with maize residues. Among the fungivores, Aphelenchoides numbers early in the experiment were greatest in pots amended with velvetbean, whereas numbers of Aphelenchus, Nothotylenchus, and Tylenchidae (mainly Filenchus) were greatest during the latter half of the experiment following the maize amendment. Omnivorous nematodes, particularly Eudorylaimus, showed two peaks in abundance during the course of the experiment. Results provided some evidence that population levels of some genera of bacterivores and fungivores may be affected by specific organic amendments.     

Influence of Soil Temperature on Meloidogyne incognita Resistant and Susceptible Cotton,Gossypium hirsutum

The degree of resistance by a cotton plant to Meloidogyne incognita is affected by soil temperature, particularly in moderately resistant cultivars, The total number of nematodes in the resistant and moderately resistant rools at 35 C was equal to, or greater than, the number in susceptible roots at 20, 25, or 30 C. A shift in numbers to developing and egg-bearing forms of nematodes in the susceptible cultivar as tentperature increased indicates development was affected by temperature rather than by genetic resistance mechanisms. However, the nematode resistant cultivar did not support maturation of nematodes until a soil tempurature of 35 C was attained. This indicated that resistance mechanisms are partially repressed at 35 C and differences in nematode development cannot be explained in terms of accumulated heat units. The moderately resistant cultivar was significantly more sensitive to the effects of high temperature than was the resistant cultivar.     

Effect of Broccoli (Brassica oleracea) Tissue, Incorporated at Different Depths in a Soil Column, on Meloidogyne incognita

Brassicas have been used frequently for biofumigation, a pest-management strategy based on the release of biocidal volatiles during decomposition of soil-incorporated tissue. However, the role of such volatiles in control of plant-parasitic nematodes is unclear. The goal of this study was to determine the direct localized and indirect volatile effects of amending soil with broccoli tissue on root-knot nematode populations. Meloidogyne incognita-infested soil in 50-cm-long tubes was amended with broccoli tissue, which was mixed throughout the tube or concentrated in a 10-cm layer. After three weeks at 28°C, M. incognita populations in the amended tubes were 57 to 80% smaller than in non-amended tubes. Mixing broccoli throughout the tubes reduced M. incognita more than concentrating broccoli in a 10-cm layer. Amending a 10-cm layer reduced M. incognita in the non-amended layers of those tubes by 31 to 71%, probably due to a nematicidal effect of released volatiles. However, the localized direct effect was much stronger than the indirect effect of volatiles. The strong direct effect may have resulted from the release of non-volatile nematicidal compounds. Therefore, when using biofumigation with broccoli to control M. incognita, the tissue should be thoroughly and evenly mixed through the soil layer(s) where the target nematodes occur. Effects on saprophytic nematodes were the reverse. Amended soil layers had much greater numbers of saprophytic nematodes than non-amended layers, and there was no indirect effect of amendments on saprophytic nematodes in adjacent non-amended layers.     

Behavior of Tethered Meloidogyne incognita

The tethered-nematode technique was adapted for use with second-stage juveniles of Meloidogyne incognita. The data demonstrate that M. incognita exhibits the same patterns of behavior as adults of the free-living nematode, Caenorhabditis elegans. The principal differences are that M. incognita is slower and less regular in its behavior than C. elegans. The frequency of normal waves is about 0.2 Hz; that of reversal waves is about 0.06 Hz. Reversal bouts last about 1 minute. In response to a change in NaCl concentration, M. incognita modulates the probability of initiating a reversal bout in the same manner as C. elegans except that it responds more slowly and is repelled instead of attracted.     

Efficacy of Bacillus thuringiensis,Paecilomyces marquandii,and Streptomyces costaricanus with and without Organic Amendments against Meloidogyne hapla Infecting Lettuce

Chitin, wheat mash, or brewery compost were incorporated into unfumigated and methyl bromide-fumigated organic soils placed in microplots formed from cylindrical drainage tiles (0.25 m-diam. clay tile). After 3 weeks, Meloidogyne hapla and cell or spore suspensions of Bacillus thuringiensis, Paecilomyces marquandii, and Streptomyces costaricanus were individually added to the soils of designated microplots. A B. thuringiensis + S. costaricanus combination was also tested. Lettuce seedlings, cv. Montello, were transplanted into the soils 3 to 4 days later. All the bacterial and fungal antagonists applied without a soil amendment, except the B. thuringiensis + S. costaricanus treatment, reduced root galling and increased lettuce head weight in the unfumigated organic soil, but not in the fumigated soil. All three amendments were also effective against M. hapla and reduced root galling in fumigated and unfumigated soils. Wheat mash amendment increased lettuce head weight in the unfumigated soil. In general, no antagonist × amendment interaction was detected. Soil populations of B. thuringiensis were maintained at ≥4.0 log10 colony-forming units/g organic soil during the first 14 days after planting. However, viable cells of B. thuringiensis were not detected after 49 days.     

Effects of Soil Type on the Damage Potential of Meloidogyne incognita on Soybean

Effects of soil type on the reproduction and damage potential of Meloidogyne incognita on soybean, Glycine max (L.) Merr., were determined at five locations in North Carolina, including one site where plots with six soil types were established. M. incognita reproduced readily on a susceptible soybean cultivar in most soil types, with somewhat limited reproduction in muck soils. The relationship between initial population densities and yield varied among soil types and nematode populations. Yield losses were greatest in sandy and muck soil types, with less nematode damage occurring in the clay soil types. A North Carolina and a Georgia population of M. incognita differed greatly in their ability to reproduce on soybean and suppress growth. The North Carolina population had a moderate effect on yield in 1981 and only a slight effect in 1982. In contrast, a Georgia population severely limited soybean growth and yield at lower initial population densities in 1983, Initial population densities of the nematodes and physical and chemical edaphic factors accounted for much of the variation of soybean yield and nematode reproduction.     

Assessing the microbiological,biochemical, soil-physical and hydrological effects of amelioration of degraded soils in semiarid Spain

The way of improving degraded soils fertility and particularly of improving its microbial activity is to add “young” exogenous organic matter that contribute to provide labile organic matter to stimulate the life of the microorganisms existing in the soil. This organic matter will also improve both the retention and hydraulic characteristics of the degraded soils, all this contributing to soil restoration. In this study, the microbiological, biochemical, soil-physical and hydrological effects of the addition of a municipal solid waste compost to a degraded soil in El Campello, SE Spain were evaluated in a field experiment. Soil samples from experimental plots were analyzed 6 and 18 months after soil amendment. In both sampling time treated plots showed significantly higher microbial biomass carbon and dehydrogenase activity values than control, indicating that soil microbial population’s development and activity were stimulated by compost addition, this effect being not ephemeral but lasting in the time. Soil urease activity was not affected by compost addition while protease hydrolysing N-α-benzoil-L-argininamide (BAA) activity was strongly stimulated by the incorporation of compost into the soils. Phosphatase and β-glucosidase activities were also stimulated by the organic amendment, this stimulation being particularly noticeable 18 months after the compost addition. Nevertheless, this increase in soil microbial populations and activity did not result in an increase in soil aggregation and hydrological parameters. This can be due to the high content of carbonates and Ca²⁺ ions in these calcareous soils, that lead to an initially high content of water-stable macroaggregates. Presented at the International Conference on Bioclimatology and Natural Hazards, Poľana nad Detvou, Slovakia, 17–20 September 2007.     

Heavy metal bioavailability in a soil affected by mineral sulphides contamination following the mine spillage at Aznalcóllar (Spain)

A field experiment, lasting 14 months, was carried out in order to assess the effect of organic amendment and lime addition on the bioavailability of heavy metals in contaminated soils. The experiment took place in a soil affected by acid, highly toxic pyritic waste from the Aznalcóllar mine (Seville, Spain) in April 1998. The following treatments were applied (3 plots per treatment): cow manure, a mature compost, lime (to plots having pH < 4), and control without amendment. During the study two crops of Brassica juncea were grown, with two additions of each organic amendment. Throughout the study, the evolution of soil pH, total and available (DTPA-extractable) heavy metals content (Zn, Cu, Mn, Fe, Pb and Cd), electrical conductivity (EC), soluble sulphates and plant growth and heavy metal uptake were followed. The study indicates that: (1) soil acidification, due to the oxidation of metallic sulphides in the soil, increased heavy metal bioavailability; (2) liming succeeded in controlling the soil acidification; and (3) the organic materials generally promoted fixation of heavy metals in non-available soil fractions, with Cu bioavailability being particularly affected by the organic treatments.     

Regenerating Topsoil Functionality in Four Drastically Disturbed Soil Types by Compost Incorporation

The low water-holding capacity and low nutrient levels of roadcuts in northern California cause many of these disturbed areas to remain chronically barren. Yard waste compost was incorporated into four nonvegetated substrates found along roadcuts (decomposed granite [DG], lahar, serpentine, and sandstone) in order to regenerate topsoil infiltration, water-holding capacity, and nutrient availability. Soil physical and chemical properties, as well as the vegetative response of a native perennial grass, were compared between treatments (non-tilled, tilled, and tilled with compost amendment). Tillage and compost addition decreased soil bulk density compared to the non-tilled treatment, and the compost treatment increased the soil carbon and nitrogen contents compared to the non-tilled and tilled treatments. Tillage alone resulted in an increase in saturated hydraulic conductivity in soils that did not contain a large amount of coarse fragments. Tillage also reduced sediment loss in all soils except the DG. Foliar C¹³ content did not predict water stress consistently between treatments. The incorporation of yard waste compost increased plant available water in coarse but not in fine-textured soils, and aboveground plant biomass was significantly greater in the compost treatment than in either of the other treatments. Although the incorporation of yard waste compost generated the greatest revegetation success, tillage alone may be a sufficient treatment if residual soils have adequate nutrient levels.