Influence of Pratylenchus vulnus and Meloidogyne hapla on the Growth of Rootstocks of Rose

Pratylenchus vulnus is involved in a desease of Rosa noisettiana ''Manetti'' rose rootstock characterized by darkening of roots, death of feeder roots, and stunting of entire plants. The disease is more severe when plants are grown in silt loam soil than when they are grown in sandy loam soil. The nematodes reproduce best in silt loam soil at 20 C. Meloidogyne hapla did not affect the growh of Manetti. Rosa sp. ''Dr. Huey'', Manetti, and R. odorata rose rootstocks were found to be goos hosts for P. vulnus whereas R. multiflora was less suitable. M. hapla reproduced well on R. odorata, Dr. Huey, and R. multiflora, but not on Manetti.     

Interaction of Fusarium oxysporum f. sp. ciceri and Meloidogyne javanica on Cicer arietinum

Interaction of Meloidogyne javanica and Fusarium oxysporum f. sp. ciceri was studied on Fusarium wilt-susceptible (JG 62 and K 850) and resistant (JG 74 and Avrodhi) chickpea cultivars. In greenhouse experiments, inoculation of M. javanica juveniles prior to F. oxysporum f. sp. ciceri caused greater wilt incidence in susceptible cultivars and induced vascular discoloration in roots of resistant cultivars. Nematode reproduction was greatest (P = 0.05) at 25 °C. Number of galls and percentage of root area galled increased when the temperature was increased from 15 °C to 25 °C. Wilt incidence was greater at 20 °C than at 25 °C. Chlorosis of leaves and vascular discoloration of plants did not occur at 15 °C. The nematode enhanced the wilt incidence in wilt-susceptible cultivars only at 25 °C. Interaction between the two pathogens on shoot and root weights was significant only at 20 °C, and F. o. ciceri suppressed the nematode density at this temperature. Wilt incidence was greater in clayey (48% clay) than in loamy sand (85% sand) soils. The nematode caused greater plant damage on loamy sand than on clayey soil. Fusarium wilt resistance in Avrodhi and JG 74 was stable in the presence of M. javanica across temperatures and soil types.     

Non-pathogenic Fusarium solani represses the biosynthesis of nematicidal compounds in vitro and reduces the biocontrol of Meloidogyne javanica by Pseudomonas fluorescens in tomato

AIMS: The aim of the present investigation was to determine the influence of various Fusarium solani strains on the production of nematicidal agent(s) in vitro and biocontrol of Meloidogyne javanica in tomato by Pseudomonas fluorescens strains CHA0 and CHA0/pME3424. METHODS AND RESULTS: Culture filtrates (CF) of P. fluorescens strain CHA0 and its diacetylphloroglucinol-overproducing derivative CHA0/pME3424 caused substantial mortality of M. javanica juveniles in vitro. Bacterial growth medium amended with the growth medium of F. solani repressed the nematicidal activity of the bacteria. Methanol extract of F. solani CF resulting from Czapek's Dox liquid (CDL) medium without zinc amendment repressed the nematicidal activity of the bacteria while the CF obtained from CDL medium amended with zinc did not. Conidial suspension of F. solani strain Fs5 (repressor strain for the biosynthesis of nematicidal compounds in P. fluorescens) reduced biocontrol potential of the bacterial inoculants against M. javanica in tomato while strain Fs3 (non-repressor) did not. CONCLUSIONS: Fusarium solani strains with increased nematicidal activity repress the biosynthesis of nematicidal compounds by P. fluorescens strains in vitro and greatly alter its biocontrol efficacy against root-knot nematode under natural conditions. SIGNIFICANCE AND IMPACT OF THE STUDY: Fusarium solani strains are distributed worldwide and found in almost all the agricultural fields which suggest that some mycotoxin-producing strains will also be found in almost any soil sample taken. Besides the suppressive effect of these metabolite-producing strains on the production of nematicidal compound(s) critical in biocontrol, F. solani strains may also affect the performance of mycotoxin-sensitive biocontrol bacteria effective against plant-parasitic nematodes.     

Effects of Environments,Meloidogyne incognita Inoculum Levels,and Glycine max Genotype on Root-knot Nematode-Soybean Interactions in Field Microplots

Five soybean cultivars (Braxton, Gordon, Jeff, Bragg, and Wright) resistant to Meloidogyne incognita (Mi) and three susceptible cultivars (Coker 156, GaSoy 17, and Coker 237) were grown at two locations for four seasons in microplots with increasing initial soil population densities (Pi) of Mi. The resistant cultivars and Coker 156 yielded better than GaSoy 17 and Coker 237 at all Pi. Yield response was dependent on environmental conditions and at one location was stimulated on Braxton, Gordon, Jeff, and Bragg by low Pi. Although Mi reproduced well on all cultivars, the pattern of reproduction differed. Population densities of Mi leveled off after 90 days on GaSoy 17 and Coker 237 but were still increasing after 120 days on the resistant cultivars; population densities were lower on resistant than on the susceptible cultivars. The population density of Mi on Coker 156 after 120 days was intermediate between those on the other susceptible and on the resistant cultivars. Mi population densities followed the same pattern under varying environmental conditions.     

Selective transport of zinc, manganese, nickel, cobalt and cadmium in the root system and transfer to the leaves in young wheat plants

BACKGROUND AND AIMS: The uptake, translocation and redistribution of the heavy metals zinc, manganese, nickel, cobalt and cadmium are relevant for plant nutrition as well as for the quality of harvested plant products. The long-distance transport of these heavy metals within the root system and the release to the shoot in young wheat (Triticum aestivum 'Arina') plants were investigated. METHODS: After the application of 65Zn, 54Mn, 63Ni, 57Co and 109Cd for 24 h to one seminal root (the other seminal roots being excised) of 54-h-old wheat seedlings, the labelled plants were incubated for several days in hydroponic culture on a medium without radionuclides. KEY RESULTS: The content of 65Zn decreased quickly in the labelled part of the root. After the transfer of 65Zn from the roots to the shoot, a further redistribution in the phloem from older to younger leaves was observed. In contrast to 65Zn, 109Cd was released more slowly from the roots to the leaves and was subsequently redistributed in the phloem to the youngest leaves only at trace levels. The content of 63Ni decreased quickly in the labelled part of the root, moving to the newly formed parts of the root system and also accumulating transiently in the expanding leaves. The 54Mn content decreased quickly in the labelled part of the root and increased simultaneously in leaf 1. A strong retention in the labelled part of the root was observed after supplying 57Co. CONCLUSIONS: The dynamics of redistribution of 65Zn, 54Mn, 63Ni, 57Co and 109Cd differed considerably. The rapid redistribution of 63Ni from older to younger leaves throughout the experiment indicated a high mobility in the phloem, while 54Mn was mobile only in the xylem and 57Co was retained in the labelled root without being loaded into the xylem.     

Effect of soil texture and its organic content on the efficacy of Trichoderma harzianum (MIAU 145 C) in controlling Meloidogyne javanica and stimulating the growth of kidney beans

The efficiency of Trichoderma harzianum (MIAU 145 C) in promoting kidney bean (cv. Goli) growth in different soil texture (sandy loam, loam and clay loam) and organic matter content (0.5 and 2% of leaf litter) was assessed in a factorial experiment in the absence of Meloidogyne javanica. In another factorial experiment, the effect of soil texture, soil organic content and control measure (no control, 10?ml of T. harzianum containing 10⁶ spore ml^?1 and 2?mg ai cadusafos kg^?1 soil) was determined on nematode-infected kidney bean’s growth, fungus controlling activity and M. javanica reproduction. Except for the shoot length, the fungus improved plant growth. Clay loam was not a proper soil type for the cultivation of kidney bean plants (even in the soil without nematode), but the plant grew better in sandy loam and loam soil. The presence of leaf litter in the soil enhanced plant growth, increased fungal efficiency and increased nematode reproduction. It seems that T. harzianum can activate the plant defence system in sandy loam soil. T. harzianum was more effective in sandy loam or loam soil containing 2% organic matter (leaf litter) and reduced the reproduction factor of the nematode in the tested soil textures equally to the chemical nematicide treatment.     

Effects of boron and calcium nutrition on the establishment of the Rhizobium leguminosarum–pea (Pisum sativum) symbiosis and nodule development under salt stress

The effects of modifying boron (B) and calcium (Ca²⁺) concentrations on the establishment and development of rhizobial symbiosis in Pisum sativum plants grown under salt stress were investigated. Salinity almost completely inhibited the nodulation of pea plants by Rhizobium leguminosarum bv. viciae 3841. This effect was prevented by addition of Ca²⁺ during plant growth. The capacity of root exudates derived from salt‐treated plants to induce Rhizobium nod genes was not significantly decreased. However, bacterial adsorption to roots was highly inhibited in plants grown with 75 mM NaCl. Moreover, R. leguminosarum 3841 did not grow in minimal media containing such salt concentration. High Ca²⁺ levels enhanced both rhizobial growth and adsorption to roots, and increased nodule number in the presence of high salt. Nevertheless, the nodules developed were not functional unless the B concentration was also increased. Because B has a strong effect on infection and cell invasion, these processes were investigated by fluorescence microscopy in pea nodules harbouring a R. leguminosarum strain that expresses green fluorescent protein. Salt‐stressed plants had empty nodules and only those treated with high B and high Ca²⁺ developed infection threads and exhibited enhanced cell and tissue invasion by Rhizobium. Overall, the results indicate that Ca²⁺ promotes nodulation and B nodule development leading to an increase of salt tolerance of nodulated legumes.     

Chemical partitioning of iron,cadmium, nickel and chromium in contaminated soils of south-eastern Nigeria

Abstract

Selected heavy metals Fe, Cd, Ni and Cr were studied in contaminated soil samples collected from south-eastern Nigeria. Geochemical differentiation into different chemical fractions, using Ma and Rao six-step sequential chemical extraction procedure, was carried out to assess the potential mobility and bioavailability of the heavy metals in the soil profiles. The residual fraction was the most important phase for the four heavy metals with the following average percentage values 74.43 for Fe, 37.69 for Cd, 70.11 for Ni and 62.47 for Cr. The carbonate fraction contained an appreciable proportion of Fe, Cd and Ni with the average percentage values of 16.29, 14.86 and 10.47 respectively, while organic fraction was of next importance for Cr with an average percentage value of 27.14. The Fe-Mn oxide fraction also contained 15.86% of Cd. Relatively low amounts of the metals were associated with water soluble and exchangeable fractions. The mobility factors for the metals in all the sites ranged from 8.55 to 40.04 for Fe, 8.66 to 56.58 for Cd, 12.74 to 30.19 for Ni and 0.82 to 7.22 for Cr. The generally low values of mobility factors coupled with significantly high levels of association of the metals with the residual fraction, indicate that the metals do not pose any environmental risk nor hazard.     

Root-zone modeling of heavy metal uptake and leaching in the presence of organic ligands

We present a mechanistic model which describes root uptake and leaching of heavy metals in the plant root zone, accounting for solution- and surface-complexation, (kinetic) mineral dissolution, heavy metal diffusion towards the root, root uptake, root exudation, ligand degradation and convective-dispersive transport of the soluble species. The model was used to simulate the influence of EDTA addition on Cu transport and plant uptake and the effect of oxalate exudation by roots on Cu transport and bioavailability using parameter values from the literature. In the simulations we assumed that free Cu²⁺ is the bioavailable form. Under slightly acidic conditions (pH 6) the model predicted that EDTA stabilizes Cu while at a slightly alkaline pH (pH 7.5), EDTA mobilizes Cu. The addition of EDTA approximately halved the cumulative Cu uptake after 360 days at pH 4.5, and reduced the uptake by a factor of 100 and 1000 at pH 6 and 7.5, respectively. Although the total dissolved concentration was increased, plant uptake was reduced by the formation of bio-inavailable complexes. The exudation of oxalate resulted in a decrease of the Cu concentration breaking through below the root zone, due to sorption of Cu-oxalate. In the presence of dissolved organic carbon (DOC), the exudation of oxalate increased Cu leaching considerably at pH 6 and 7.5. In the absence of DOC, the exudation of oxalate reduced Cu uptake due to the formation and adsorption of Cu-oxalate on goethite surface sites. Exudation of oxalate in the presence of DOC resulted in a further decrease of Cu uptake. Oxalate gradually takes over from DOC in binding Cu due to simultaneous production of oxalate and leaching of DOC. The simulations show that addition or exudation of ligands does not necessarily increase the solubility, transport and bioavailability of metals. Depending on the conditions (mainly the pH), also reduced transport and uptake can be observed, either by formation of ternary surface complexes or reduction of free metal concentration. The model can be easily extended to include further processes.     

Rhizosphere strain of <Emphasis Type="Italic">Pseudomonas chlororaphis</Emphasis> capable of degrading naphthalene in the presence of cobalt/nickel

Combination of genetic systems of degradation of polyaromatic hydrocarbons, resistance to heavy metals, and promotion of plant growth/protection is one of the approaches to the creation of polyfunctional strains for phytoremediation of soils after co-contamination with organic pollutants and heavy metals. A plant-growth-promoting rhizosphere strain Pseudomonas chlororaphis PCL1391 (pBS216^*, pBS501) has been obtained, in which the nah operon of plasmid pBS216 provides naphthalene biodegradation and the cnr-like operon of plasmid pBS501 provides resistance to cobalt and nickel due to the extrusion of heavy metal cations from the cells. In the presence of 100 μM of nickel, the viability, growth rate, and naphthalene biodegradation efficiency of the resistant strain PCL1391 (pBS216^*, pBS501) were much higher as compared with the sensitive PCL1391 (pBS216). During the growth of the resistant strain, in contrast to the sensitive strain, nickel (100 μM) had no inhibiting effect on the activity of the key enzymes of naphthalene biodegradation. Original Russian Text ? T.V. Siunova, T.O. Anokhina, A.V. Mashukova, V.V. Kochetkov, A.M. Boronin, 2007, published in Mikrobiologiya, 2007, Vol. 76, No. 2, pp. 212–218.     

Studies on the nodulation of strain-specific resistant pea lines using single,mixed and delayed inoculation by Rhizobium leguminosarum

Symbiotic interactions between peas and Rhizobium leguminosarum were investigated by inoculating four pea lines, three of which are strain-specific resistant to the European strain 311d, with various combinations of two strains of Rhizobium, 311d and Tom⁺⁺. The strains were almost equally good to infect the susceptible European cultivar Hero when added singly inoculated. After mixed inoculation (1:1 proportion) strain analysis by ELISA revealed that the nodules were preferentially formed by 311d, although some Tom⁺⁺ nodules were also found mainly on the upper part of the root. Our conclusion is that Tom⁺⁺ is less compatible in comparison with 311d. In addition, we found that as the Hero plants emerged, they were becoming more resistant towards infection with not adapted bacteria. The strain-specific resistant lines from Afghanistan belong to two different systems: Afgh. I, completely resistant to 311d and highly nodulating with Tom⁺⁺, and Afgh. III, incompletely resistant to 311d and poorly nodulating with Tom⁺⁺. Mixed inoculations resulted in nodule depressions, as compared to single inoculations with Tom⁺⁺ ranging from 87% to 14%. The ability of 311d to block infection sites on the roots were found to depend on the degree of symbiotic adaptation between Afgh. I and Tom⁺⁺, respectively Afgh. III and Tom⁺⁺. Strain analysis after double strain inoculation of Afgh. I plants revealed that some nodules were induced by strain 311d. Thus, the presence of Tom⁺⁺ in this case influences the degree of host resistance. However, in Afgh. III plants the resistance towards nodulation were unaffected by the presence of Tom⁺⁺. We suggest that the degree of symbiotic adaptation may change the barrier of resistance towards infection.     

Effect of Temperature on Growth, Development and Reproduction of Meloidogyne hapla in Lettuce

Temperature was an important factor in growth, development and reproduction of Meloidogyne hapla in lettuce. Growth, as measured by increase in diameter of females, was not appreciably different at the intermediate (21.1 C night and 26.7 C day) and high (26.7 C night and 32.2 C day) temperature regimes, but was considerably less at the low temperature regime (15.5 C night and 21.1 C day) than at the two higher temperature regimes. Second-stage female larvae developed into adults 14 days after inoculation at the high, 18 days at the intermediate and 34 days at the low temperature regime. Eggs were observed 20 days after inoculation at the high, 26 days at the intermediate and 54 days at the low temperature regime. Number of eggs and larvae after 6 weeks was greater at the high than at the intermediate temperature regime and no eggs or larvae occurred at the low temperature regime during the observed 6 weeks.     

Leaching of Cd,Zn, Pb,and Cu in Packed and Undisturbed Columns of Soils Affected by the Spill from a Pyrite Mine in the South of Spain

A study has been made of the leaching of Cd, Zn, Pb, and Cu in three representative soils within the zone affected by the spill from a pyrite mine in Aznalcollar (Sevilla, Spain) employing packed soil columns. According to the breakthrough and cumulative leaching curves, the relative mobilities of the different toxic elements in the columns are as follows: Cd> Zn> Cu> Pb. The effect of leaching on the distribution of metals as a function of depth using intact soil cores was also studied. The results showed that the soils themselves have a good capacity for immobilizing the soluble fraction of the elements from the spilled mud. This capacity varied as follows: clayey soil with a high carbonate content > clayey soil with a moderate carbonate content > sandy-clay loam soil with a low carbonate content. However, sandy soils with a low carbonate content could pose a risk to groundwater if initial contamination was high. These results could be considered during the evaluation of remedial technologies for the immobilization of soil metals.     

Response to carbon-starvation in Pseudomonas aeruginosa strain IE-6S+: analysis of general cross protection,production of some nematocidal compounds in vitro,and the biological control of Meloidogyne javanica in tomato

Adaptation to nutrient-limited conditions by repeated culture on soil agar media was found to induce resistance to osmotic, oxidation, thermal and pH stress as well as carbon-limited culture conditions in Pseudomonas aeruginosa strain IE-6S⁺. Culture filtrate of the resistant strains obtained from 10% strength King's medium B (KMB) caused greater (32–54%) mortality of Meloidogyne javanica juveniles compared with their parental strain. When 10% strength KMB was amended with 1% (w/v) glucose, the ability to cause nematode mortality was substantially enhanced by adapted strains, while activity of the parental strain was repressed. Two of the four starved bacteria IE-6S⁺PBK1 and IE-6S⁺KUC2 grown in KMB liquid medium amended with glucose synthesized salicylic acid (5.1 and 5.8 g ml^–1, respectively) and hydrogen cyanide (picrate paper turned yellow to brownish red for both strains) in greater quantities compared to wild type strain (SA = 4.4 g ml^–1, picrate paper turned orange-yellow). Neither wild type strain IE-6S⁺ nor its adapted strains were capable of utilizing tomato root exudates as a sole carbon source. Strains adapted to carbon-limiting conditions exhibited enhanced colonization in the rhizosphere and inner root tissues of tomato compared to their exponentially growing counterpart. Pre-adapted bacterial inoculants applied in the soil also caused greater (15%) reduction in nematode penetration compared to the parental strain or controls.     

Non-Carcinogenic Risk Assessment of Heavy Metals and Fluoride in Some Water Wells in the Al-Baha Region,Saudi Arabia

On a global scale, pathogenic contamination of drinking water poses the most significant health risk to humans. However, significant risks to human health may also result from exposure to nonpathogenic, toxic contaminants that are often ubiquitous in waters. The purpose of this study is to determine the levels of heavy metal and fluoride contaminants in water wells used in the Al-Baha region, Saudi Arabia, to evaluate if the levels of metals will have non-carcinogenic effects. Samples were collected from private wells in the area and were analyzed for chemical contamination using approved methods of collection and analysis. Chromium, manganese, zinc, iron, and fluoride were detected in all samples, and were selected for toxicological evaluation. Exposure through ingestion and dermal contact were the scenarios proposed in this study. Chronic daily intakes (CDIs) were estimated for both routes and then compared with health guideline values. The non-cancer risk estimations show that manganese, chromium, and zinc individually have oral Hazard Quotient (HQ) values less than a value of one. Iron and fluoride were found to have oral HQ values greater than 1 in some samples. Also, on considering the additive effect of the contaminants we found that some samples have Hazard Index (HI) values greater than 1, which indicates that there is a concern for chronic non-cancer adverse health effects in case of oral and dermal routes of exposure to water from these wells.     

Nematodes as Sentinels of Heavy Metals and Organic Toxicants in the Soil

Field and laboratory research has repeatedly shown that free-living soil nematodes differ in their sensitivity to soil pollution. In this paper, we analyze whether nematode genera proved sensitive or tolerant toward heavy metals and organic pollutants in six long-term field experiments. We discuss overlaps between nematode physiological responses to heavy metals and to organic pollutants, which may explain why nematodes can exhibit co-tolerance toward several contaminants. We propose a simple method for separating direct effects of soil contamination on nematode populations from indirect effects mediated through the food chain. Finally, we analyze the extent to which nematodes exhibited consistent responses across the experiments analyzed. Our results show that (a) indirect effects of pollution were generally strong; (b) fewer nematode genera were tolerant than sensitive; (c) many genera, including practically all Adenophorea, exhibited a common response pattern to contaminants; and (d) several genera of the Secernentea exhibited differential tolerance toward particular pollutants. We conclude that bioindication of soil contamination should preferentially be based on tolerant, and less on sensitive, nematodes. We provide a list of nematode genera that may potentially serve as differential bioindicators for specific soil contaminants.     

Effect of cadmium and nickel on photosynthesis and the enzymes of the photosynthetic carbon reduction cycle in pigeonpea (Cajanus cajan L.)

The effect of Cd²⁺ and Ni²⁺ on the rate of photosynthesis and activities of key enzymes of the photosynthetic carbon reduction cycle was examined in leaves from pigeonpea (Cajanus cajan L., cv. UPAS-120) grown in nitrogen free sand culture. Two different concentrations of Cd²⁺ and Ni²⁺ were applied through the rooting medium at two growth stages. The application of Cd²⁺ and Ni²⁺ (0.5 and 1.0 mM) at an early vegetative stage (30 days after sowing) resulted in about 50% and 32% reduction in net photosynthesis, respectively. However, enzyme activities were decreased to different levels (2–61%) depending upon the enzyme and the concentration of the metal ion.These concentrations (0.5 and 1.0 mM of Cd²⁺ and Ni²⁺) had no effect when applied at a later vegetative stage i.e. 70 days after sowing. However, when the concentration of Cd²⁺ was increased to 10 mM, there was about an 86% reduction in the rate of photosynthesis but the enzyme activities were reduced by only about 40%. Although Ni²⁺ reduced the photosynthetic rate by 65%, it had little effect on enzyme activities. The reduction in photosynthesis seems to occur indirectly through a decrease in chlorophyll content and stomatal conductance but not due to decreased enzyme activities. Oxygen evolution by leaf discs was inhibited by Cd²⁺ and Ni²⁺ in parallel with a reduction in photosynthesis. These data confirm the earlier reported effects of Cd²⁺ and Ni²⁺ on O₂ evolution in isolated chloroplasts.Abbreviations FBPase Fructose-1,6-bisphosphatase - PCR Photosynthetic carbon reduction - 3-PGA 3-Phospho-glycric acid - RUBP Ribulose, 1,5-bisphosphate     

Enhancement of nickel and lead accumulation and their toxic growth-inhibitory effects on amaranth seedlings in the presence of calcium

The effects of Ni(NO₃)₂ and Pb(NO₃)₂ on Amaranthus sp. L. root growth and the effect of calcium on heavy metal (HM) accumulation in the growing root zone and root growth inhibition were studied. The seeds were germinated in the Pb(NO₃)₂ solutions at concentrations of 50, 100, 200, 500 and 700 μM or Ni(NO₃)₂ solutions at concentrations of 10, 50, 70, 100, and 500 μM in the presence of 100 μM Ca(NO₃)₂ or without it. HM toxicity was assesses in 7 days after seed sowing by the root length. Distribution of HM over the tissues of the growing root part was examined histochemically. Ni was more toxic to root growth than Pb. In the presence of Ca, Ni and Pb accumulation in the amaranth root growing part increased markedly, and this enhanced their growth-inhibitory of action. A comparison of results obtained in this work and available from the literature permitted a conclusion that the routes of HM penetration into the root differ in different plant species, and this determines ambiguity of protective Ca action.