Nemafric-BL phytonematicide induces egg hatch inhibition in Meloidogyne incognita

Contribution of egg hatch inhibition in the overall reduction of Meloidogyne incognita numbers by Nemafric-BL phytonematicide was determined in vitro using a series of water-diluted phytonematicide solutions. Hatched juveniles were assessed at four different incubation periods. Thereafter, each phytonematicide solution was water-diluted 5 times and incubated for 5 days to evaluate the reversibility of egg hatch inhibition. At all exposure periods, except the shortest (24?h), concentration effects on egg hatch were highly significant with juvenile numbers versus increasing concentrations exhibiting quadratic relations. The models for the three consecutive exposure periods explain the quadratic relations by 95%, 94% and 98%, respectively. Results suggested that egg hatch inhibition was one of the mechanisms involved in reducing M. incognita population densities by Nemafric-BL phytonematicide.     

Suitable organ(s) in wild Cucumis africanus for the production of nemafric-BL phytonematicide

Cucurbitacin B in fruit of wild watermelon (Cucumis africanus) is an active ingredient in products that range from pesticides to various medicines. Reports suggested that cucurbitacins occur in all parts of C. africanus, without specifying whether they are equally distributed or not. Should the active ingredient not be equally distributed in all organs, it would not be prudent to combine the organs for those products that are produced from raw organs of C. africanus plants, like the phytonematicides. A study was, therefore, conducted to determine whether cucurbitacin B was equally distributed in all organs of C. africanus plants. Cucurbitacin B was quantified from oven-dried organs (52°C for 72?h) using isocratic elution Shimadzu HPLC Prominence. Concentration of cucurbitacin B was higher in fruit than in other organs, where the concentrations were not different. Relative to cucurbitacin B concentration in fruit, leaves, roots and vines had 94%, 70% and 67% less cucurbitacin B concentrations, respectively. In conclusion, leaves, roots and vines would introduce the dilution effect when combined with fruits in product development and should therefore not be included.     

Influence of cucurbitacin-containing phytonematicides on selected nutrient elements in leaf tissues of green bean under greenhouse conditions

Cucurbitacin-containing phytonematicides consistently reduce nematode population densities in various crops. However, there is no information on how these products affect the accumulation of essential nutrient elements in crops. The objective of this study was to determine the influence of Nemafric-BL and Nemarioc-AL phytonematicides on accumulation of essential nutrient elements in leaf tissues of green bean (Phaseolus vulgaris L.) under greenhouse conditions. Weekly application of phytonematicides each at 0%, 2%, 4%, 8%, 16% and 32%, were assessed on plant growth variables, nematode suppression and nutrient elements (Ca, K, Na, Fe, Zn) in leaf tissues of green bean at 56 days after initiating the treatments. Phytonematicide concentrations significantly (P?≤?0.05) affected nematode numbers and nutrient elements, without affecting plant growth. Calcium (R²?=?0.97), K (R²?=?0.93), Na (R²?=?0.94) and Fe (R²?=?0.91) each with increasing Nemafric-BL phytonematicide concentration exhibited positive quadratic relations. In contrast, K (R²?=?0.97) and Fe (R²?=?0.98) each with increasing Nemarioc-AL phytonematicide concentration exhibited positive quadratic relations, whereas Na (R²?=?0.92) and Zn (R²?=?0.72) each with increasing phytonematicide concentration exhibited negative quadratic relations. In conclusion, accumulation of essential nutrient elements in green bean leaf tissues and increasing phytonematicide concentrations exhibited density-dependent growth patterns prior to the eventual expression of plant growth responses.     

Isolation and characterization of multi-potential Rhizobium strain ND2 and its plant growth-promoting activities under Cr(VI) stress

Soil contaminated by chromium (Cr) is a major concern for sustainable agriculture. Considering this as a basis, the present study was designed to isolate Cr(VI)-reducing and plant growth-promoting bacterial strain from contaminated sampling sources. In this study, Rhizobium strain ND2 was isolated from the root nodules of Phaseolus vulgaris grown in leather industrial effluent contaminated soil. The strain ND2 exhibited strong resistance to different heavy metals and reduced 30 and 50 µg ml^?1 concentrations of Cr(VI) completely after 80 and 120 h of incubation, respectively, as well as chromium adsorption and immobilization were confirmed by scanning electron microscopic equipped with energy X-ray spectroscopy. In addition, the strain produced 21.73 and 36.86 µg ml^?1 of indole-3-acetic acid at 50 and 100 µg ml^?1 of L-tryptophan supplimentations, respectively. Strain ND2 positively affected the exo-polysaccharide, ammonia, protease and catalase production and stimulated root length of various test crops under Cr(VI) stress. Moreover, Rhizobium strain ND2 has the potential to colonize the diverse agricultural crops. Thus, the present findings strongly suggested that the multipotential properties of ND2 could be exploited for bioremediation of contaminated sites with Cr(VI) as well as potential bio fertilizer for enhancing the agricultural productivity.     

Role of effective microorganisms in efficacy of Nemarioc-AG phytonematicide on suppression of Meloidogyne incognita and growth of tomato plants

The release of active ingredient chemicals in conventional organic amendments is primarily through microbial degradation, whereas in granular phytonematicides, leaching through irrigation water had been implied as a probable mechanism. The objective of this study was to determine the role of effective microorganisms (EM) on the efficacy of Nemarioc-AG (NAG; G?=?granular formulation) phytonematicide on suppression of root-knot (Meloidogyne species) nematodes and growth of tomato (Solanum lycopersicum) plants. A 5?×?6 factorial experiment, with EM at 0%, 0.14%, 0.17%, 0.20% and 0.25% and phytonematicide at 0, 3, 6, 9, 12 and 15?g per plant, was conducted under microplot conditions. Each plant was inoculated with 11,000 eggs and second-stage juveniles (J2) of Meloidogyne incognita. Seventy days after initiating the treatments, the interactions were not significant (P?≥?.05) on all variables, but the main factors were highly significant. Regression of nematode population densities, root gall and dry shoot mass over increasing phytonematicide concentration exhibited quadratic relations, which were explained by 93%, 97% and 99%, respectively. In contrast, stem diameter and phytonematicide concentration had a positive linear relation, which was explained by 98%. Nematode numbers over increasing EM concentration exhibited quadratic relation, which was explained by 97%. All plant variables and EM had no significant relations. In conclusion, the efficacy of NAG phytonematicide on nematode suppression and plant growth was independent of EM activities, suggesting that irrigation water played a major role in the efficacy of the product in granular formulation.     

Effects of nitrogen dioxide on selected soil processes

Nitrogen dioxide gas was rapidly absorbed by soil. After a 15 min incubation at 25°C, soil at a moisture content of 16% absorbed 99% of the NO₂ introduced into the gas-phase volume of a closed system. The presence of microorganisms hatl no influence on the rate of absorption of the gas by soil. The absorption of NO₂ by sandy clay loam soil was not an oxygen- or temperature-dependent process nor did it depend upon the moisture content of the soil. These physical factors acquired significance only in determining the initial rate of absorption of the gas and the rate at which NO₂ diffused through the soil. Exposure of soil to NO₂ resulted in substantial increases in the levels of NO _inf2 ^sup? N in the soil. Chemical oxidation of the NO _inf2 ^sup? N resulted in an increase in NO _inf3 ^sup? N levels. During a 14-day incubation, NO _inf2 ^sup? N concentrations in sterile soil exposed to an atmosphere containing 100 μg ml^?1 of NO₂ decreased from 190 μg g^?1 of soil to 105 μg g^?1 with an accompanying increase in NO _inf3 ^sup? N from 2 μg g^? ₁ to 63 μg g^?1 of soil. Nitrogen dioxide severely inhibited the growth of both aerobic and anaerobic asymbiotic N₂-fixing bacteria in soil. After a 48 h incubation at 25°C, soil aggregates exposed to an atmosphere containing 100 μg ml^?1 of NO₂ contained 88% and 98% fewer aerobic and anaerobic N₂-fixing bacteria, respectively. C₂H₂-reduction measurements showed that nitrogenase synthesis and activity in artificial soil aggregates amended with 2% glucose were inhibited by 20% and 48%, respectively, when exposed to atmospheric concentrations of 35 and 3.5 μg ml^?1 of NO₂, respectively.     

Broad-spectrum antifungal metabolites produced by the soil bacterium Serratia plymuthica A 153

Chlorinated macrolides, haterumalide NA, B and NE, and a new haterumalide X, were produced by the soil bacterium Serratia plymuthica. Haterumalides NA, B and NE caused complete suppression of apothecial formation in sclerotia of Sclerotinia sclerotiorum at a concentration of 0.5 μg ml⁻¹. Ascospore germination of this fungus was inhibited in the concentration range 0.8-3.0 μg ml⁻¹. Haterumalides NA, B and NE prevented spore germination of several other filamentous fungi as well as Oomycetes at concentrations ranging from 0.4 to 40 μg ml⁻¹, but did not show any effect against the yeast Candida albicans. Inhibition data could not be collected for haterumalide X due to its rapid conversion to haterumalide NA. The bacterium also produced two other antifungal metabolites: pyrrolnitrin and 1-acetyl-7-chloro-1-H-indole, which in contrast to the haterumalides, did not inhibit the apothecial formation on sclerotia. Pyrrolnitrin, and haterumalide NA, B and NE effectively inhibited spore germination of tested filamentous fungi at concentrations ranging from 0.06 to 50 μg ml⁻¹, whereas 1-acetyl-7-chloro-1-H-indole inhibited spore germination only at concentrations above 50 μg ml⁻¹. The minimal inhibitory concentrations of the respective compounds needed for total inhibition of spore germination varied for the fungal species tested.     

Comparison of N Mineralization Rate and Pattern in Different Manure- and Sewage Sludge-Amended Calcareous Soil

A 12-week incubation experiment was conducted to determine the pattern and rate of N mineralized from organic materials. Treatments consisted of sheep manure (SM), cattle manure (CM), poultry manure (PM), sewage sludge (SS) at 1% (W/W) level, and unfertilized treatment with three replications. The concentrations of nitrate (NO₃)- nitrogen (N) and ammonium (NH₄)-N were determined in day 1 and 1, 2, 4, 8, and 12 weeks after the beginning of incubation. Results indicated that the magnitude of N mineralized during the incubation time periods was in the order of CM (134 mg kg^?1) > PM (83 mg kg^?1) > SS (56 mg kg^?1) > SM (55 mg kg^?1), and different management is required for obtaining optimum N-use efficiency. In conclusion, improving N-uptake efficiency in manure- and SS-amended soils depends on the pattern and rate of N mineralization to synchronize N released with crop N demand periods.     

Disruption of soil aggregates by varied amounts of ultrasonic energy in fractionation of organic matter of a clay Latosol: carbon,nitrogen and δ13C distribution in particle‐size fractions

Ultrasonic energy has been widely used to disrupt soil aggregates before fractionating soil physically when studying soil organic matter (SOM). Nevertheless, there is no consensus about the optimum energy desirable to disrupt the soil. We therefore aimed (i) to quantify the effect of varied ultrasonic energies on the recovery of each particle‐size fraction and their C, N and δ¹³C distribution, and (ii) to determine an ideal energy to fractionate SOM of a specific soil. Our results show that the 2000–100 μm particle‐size fraction was composed mainly of unstable aggregates and the 100–2 μm fraction of stable aggregates. Energies of 260–275 J ml^?1 were sufficient to disrupt most of the unstable aggregates and leave stable aggregates. The use of this threshold energy combined with particle‐size fractionation was not satisfactory for all purposes, since litter‐like material and relatively recalcitrant organic carbon present in stable aggregates > 100 μm were recovered in the same pool. An ultrasonic energy of 825 J ml^?1 was not sufficient to stabilize the redistribution of soil mass and organic matter among particle‐size fractions, but at energies exceeding 260–275 J ml^?1 relatively stable aggregates would fall apart and cause a mixture of carbon with varied nature in the clay fraction.     

Changes in Soluble Manganese and Iron Concentrations of Tropical Wetland Soils as Influenced by Glyphosate Dosage

Glyphosate is largely used to control weeds in wetland soils of Brazil. We investigated changes in the chemistry of soluble manganese (Mn) and iron (Fe) in these soils as affected by glyphosate dosage. Triplicate samples of the A horizon of wetland soils with different organic-matter contents were incubated with deionized water (1:2) for 1, 3, and 30 days under flooding. Three different glyphosate doses (0, 0.048, and 0.096 g L^?1 m^?2) were spiked on the flooded water at the beginning of the incubation periods. After incubation, pH was measured and samples of the supernatant were collected for determination of Mn/Fe concentrations by atomic absorption. Glyphosate application impacted Mn but had no effect on pH and Fe. Soluble Mn concentrations decreased as glyphosate dosage increased for the high organic-matter soil after 3 days of incubation. It indicated that glyphosate application can change the chemistry of soil metals. The intensity of these changes depends on the glyphosate dosage, evolved metal, incubation time, and soil properties.     

Using time domain reflectometry for monitoring mineralization of nitrogen from soil organic matter

The mineralization of nitrogen from soil organic matter is important when one tries to optimize nitrogen fertilization and assess risks of N losses to the environment, but its measurement is laborious and expensive. We have explored the possibilities for monitoring N mineralization directly using time domain reflectometry (TDR). Net N and S mineralization were monitored over a 101‐day period in two layers (0–30 and 30–60 cm) of a loamy sand soil during aerobic incubation in a laboratory experiment. At the same time electrical conductivity of the bulk soil, σ_a, was measured by TDR. A series of calibration measurements with different amounts of KNO₃ at different soil moisture contents was made with the topsoil to calculate the electrical conductivity, σ_w, of the soil solution from σ_a and θ. The actual σ_w was determined from the conductivity of 1:2 soil:water extracts (σ_1:2) with a mass balance approach using measured NO₃^– concentrations, after correction for ions present prior to the addition of KNO₃. The average N mineralization rate in the topsoil was small (0.12 mg N kg^?1 day^?1), and, as expected, very small in the subsoil (0.023 mg N kg^?1 day^?1). In the top layer NO₃^– concentrations calculated from σ_a determined by TDR slightly underestimated measured concentrations in the first 4 weeks, and in the second half of the incubation there was a significant overestimation of measured NO₃^–. Using the sum of both measured NO₃^– and SO₄^2– reduced the overestimation. In the subsoil calculated NO₃^– concentrations strongly and consistently overestimated measured concentrations, although both followed the same trend. As S mineralization in the subsoil was very small, and initial SO₄^2– concentrations were largely taken into account in the calibration relations, SO₄^2– concentrations could not explain the overestimation. The very small NO₃^– and SO₄^2– concentrations in the B layer, at the lower limit of the concentrations used in the calibrations, are a possible explanation for the discrepancies. A separate calibration for the subsoil could also be required to improve estimates of NO₃^– concentrations.     

RELATIONSHIP OF SOIL EXTRACTABLE AND FERTILIZER BORON TO SOME SOIL PROPERTIES,CROP YIELDS,AND TOTAL BORON IN COTTON AND WHEAT PLANTS ON SELECTED SOILS OF PUNJAB,PAKISTAN

Boron (B) is an essential microelement, which is necessary for reproductive organs including pollen tube formation in wheat (Triticum aestivum L.), and flowering and boll formation in cotton (Gossypium hirsutum L.) The study was associated with wheat-cotton rotation in 80 farm fields, belonging to different soil series, in four districts of cotton belt of Punjab, Pakistan to assess concentrations of extractable B in soils [0.05 M hydrochloric acid (HCl) extractable B], and added fertilizer B and their relationship to some soil physico-chemical properties [pH, organic matter (OM), calcium carbonate (CaCO₃) and clay content], yields and total B concentrations in wheat and cotton plants. All soils had alkaline pH (7.45 to 8.55), high CaCO₃ content (2.14 to 8.65%), less than 1.0% OM (0.33 to 0.99%), low plant available-P (Olsen P less than 8 mg kg^?1 soil) and medium ammonium acetate extractable potassium (K) (< 200 mg K kg^?1 soil). Of the 80 soil samples, 65 samples (81%) were low in available B (<0.45 mg B kg^?1, ranging from 0.11 to 0.43 mg B kg^?1) Of the corresponding 80 plant samples, leaves B concentrations were below critical levels (<10 mg B kg^?1 for wheat; <30 mg B kg^?1 for cotton) for all the tested samples for wheat and cotton. The regression analysis between plant total B concentrations and soil extractable B concentrations showed strong linear positive relationships for both wheat (R² = 0.509***, significant at P <0.001) and cotton (R² = 0.525***, significant at P <0.001). Further regression analysis between extractable soil B and wheat grain yield as well as between wheat leaves total B and wheat grain yield also depicted strong linear relationships (R² = 0.76 and 0.42, respectively). Boron fertilizer demonstration plots laid out at farmers’ fields low in extractable B, in each district not only enhanced grain yields of wheat crop but also contributed a significant increase towards seed cotton yield of succeeding cotton crop through residual B effect. In conclusion, the findings suggest that many soils in the cotton belt of Punjab may be low in extractable B for wheat and cotton, especially when these crops are grown on low OM soils with high CaCO₃ content.     

Effects of Boron Fertilizer on Tomato,Pepper, and Cucumber Yields and Chemical Composition

In many parts of the world, boron (B) levels are insufficient for potential production. Boron deficiency is also widespread in the Anatolia region of Turkey. Boron deficiency could impact production and quality of tomatoes (Lycopersicon esculentum L.), pepper (Capsicum annum L.), and cucumber (Cucumis sativus L.). A two-year greenhouse experiment was conducted to study yield and quality response of three vegetables to B addition (0, 1, 2, 3, and 4 kg B ha^?1). The optimum economic B rates (OEBR) were 2.3, 2.6, 2.4 kg B ha^?1, resulting in soil B concentrations of 0.33, 0.34 and 0.42 mg kg^?1. Independent of plant species, B application decreased tissue nitrogen (N), calcium (Ca), and magnesium (Mg) but increased tissue phosphorus (P), potassium (K), iron (Fe), manganese (Mn), zinc (Zn), and copper (Cu) concentrations. We conclude that a B addition of 2.5 kg ha^?1 is sufficient to elevate soil B levels to nondeficient levels. Similar studies with different soils and initial soil-test B levels are needed to conclude if these critical soil test values and OEBR can be applied across the region.     

Growth Response and Selenium and Boron Distribution in Broccoli Varieties Irrigated with Poor Quality Water

Abstract

Selenium (Se), and boron (B), and salinity contamination of agricultural drainage water is potentially hazardous for water reuse strategies in central California. This greenhouse study assessed tolerance and Se, B, and chloride (Cl^?) accumulation in different varieties (Emerald City, Samurai, Greenbelt, Marathon) of broccoli (Brassica oleracea L.) irrigated with water of the following different qualities: (1) non‐saline [electrical conductivity (EC) of <1 dS m^?1]; (2) Cl^?/sulfate salinity of ～5 dS m^?1, 250 µg Se L^?1, and 5 mg B L^?1; and (3) non‐saline and 250 µg Se L^?1. One hundred and ten days after transplanting, plants were harvested and dry weight (DW) yields and plant accumulation of Se, B, and Cl^? was evaluated in floret, leaf, and stem. Irrespective of treatments floret yields from var. Samurai were the lowest among all varieties, while floret yields from var. Marathon was the only variety to exhibit some sensitivity to treatments. For all varieties, plant Se concentrations were greatest in the floret (up to 51 mg kg^?1 DW) irrespective of treatment, and B and Cl^? concentrations were greatest in the leaves; 110 mg B kg^?1 DW and 5.4% Cl^?, respectively. At post harvest, treatment 2 (with salinity, B, and Se) increased soil salinity to almost 6 dS m^?1, total Se concentrations to a high of 0.64 mg kg^?1 DW soil, and water soluble B concentrations to a high of 2.3 mg B L^?1; soluble Se concentrations were insignificant. The results indicate that var. Emerald City, Greenbelt, and Marathon should be considered as recipients of moderately saline effluent enriched with Se and B under field conditions.     

Characteristics of Nitrous Oxide (N2O) Emissions from Intermittently-Aerated Sequencing Batch Reactors Treating the Separated Liquid Fraction of Anaerobically Digested Pig Manure

In this study, the N₂O emission from an intermittently aerated sequencing batch reactor (IASBR-1) treating the separated liquid fraction of anaerobically digested pig manure (SLAP) was investigated. The wastewater had chemical oxygen demand (COD) concentrations of 11,540?±?860?mg?l^?1, 5-day biochemical oxygen demand (BOD₅) concentrations of 2,900?±?200?mg?l^?1and total nitrogen concentrations of 4,041?±?59?mg?l^?1, with low COD:N ratios (2.9, on average) and BOD₅:N ratios (0.72, on average). Synthetic wastewater, simulating the SLAP with similar COD and nitrogen concentrations but with higher BOD₅ concentrations of up to 11,500?±?100?mg?l^?1, was treated in another identical reactor (IASBR-2) to compare the effects of carbon source on nutrient removals and N₂O emissions. In steady-state, soluble N₂O accumulated in the non-aeration periods, with the highest N₂O concentrations measured at the end of the non-aeration periods. There was a significant reduction in N₂O concentrations during the aeration periods with reductions occurring immediately on commencement of aeration. The mean N₂O emissions in an operational cycle were 253.6 and 205.3?mg for IASBR-1 and IASBR-2, respectively. During the non-aeration periods, only 8.3% and 8.4% of total N₂O emissions occurred in IASBR-1 and IASBR-2, respectively; while during the aeration periods, 91.7% and 91.6% of N₂O emissions took place in IASBR-1 and IASBR-2, respectively. The mean specific N₂O generation rates were 0.010 and 0.005?mg (g VSS·min)^?1 in the aeration periods, 0.024 and 0.021?mg (g VSS·min)^?1 in the non-aeration periods for IASBR-1 and IABSR-2, respectively. Mean nitrogen removal via N₂O emissions was 15.6% and 10.1% for IASBR-1 and IASBR-2, respectively. The IASBR-1 with low influent BOD₅ concentrations emitted and generated more N₂O.     

Host-status and host-sensitivity of wild Cucumis species to Meloidogyne incognita race 4

Abstract

Wild watermelon (Cucumis africanus) and wild cucumber (Cucumis myriocarpus), which are highly resistant to the southern root-knot nematode (Meloidogyne incognita) race 2, have the potential for serving as seedling rootstocks for the highly nematode-susceptible watermelon (Citrullus lanatus) cultivars. In South Africa, due to high labour costs, most cotton farmers are turning to watermelon production. In these regions, there is high incidence of M. incognita race 4. A pot experiment in the greenhouse was, therefore, initiated to investigate the host-status and host-sensitivity of Cucumis africanus and Cucumis myriocarpus to M. incognita race 4, when inoculated with 0, 200, 600, 100, 1400, 1800 and 2200 eggs and second-stage juveniles (J2s). At harvest, 56 days after inoculation, the reproductive factor values at all levels of inoculation were less than one. Penetration indices on both plant species were greater than one, suggesting that the resistance was post-infectional and therefore, introgressible. Sex (male: female) ratios of M. incognita race 4 on the two Cucumis species were greater than one, suggesting that more J2s were converted into males. Infection of Cucumis species by the test nematode had no effect on yield components of the two plant species due to poor feeding sites. The two Cucumis species were, therefore, resistant to M. incognita race 4, with post-infectional resistance, where the sex ratio was skewed towards maleness. Thus, the two Cucumis species have the potential to be used as nematode-resistant rootstocks in watermelon production.     

A proposal for re-evaluating the most probable number procedure for estimating numbers of Bradyrhizobium spp.

The reliability of the most probable number (MPN) method for estimating bradyrhizobial numbers was evaluated by comparison with the plate count procedure. MPN estimates increased with time of nodulation scoring after seedling inoculation through 6 weeks of incubation. Ratios of MPN to plate counts increased as the bradyrhizobial cell suspension concentration increased. The MPN method could not detect Bradyrhizobium japonicum numbers at concentrations of 10³ colony forming units (CFU) ml^-1 and below. A proposal for re-evaluating MPN estimates is discussed.     

Impact of molybdenum on Chinese cabbage response to selenium in solution culture

Molybdenum (Mo) and selenium (Se) are both essential micronutrients for animals and humans. Increasing Mo and Se contents in food crops offers an effective approach to reduce Mo and Se deficiency problems. A hydroponic trial was conducted to investigate the interactions of Mo and Se on uptake, transfer factors (TF _shoot ) as well as distribution coefficients (DC) of Mo and Se on Chinese cabbage (Brassica campestris L. ssp. Pekinensis). In Experiment 1 three concentrations of Mo (0.01, 0.1 and 1?mg?L^?1) and four concentrations of Se (0, 0.01, 0.1 and 1?mg?L^?1) were arranged with a randomized block design. In Experiment 2, there were three treatments, 0.1?mg?L^?1 Mo, 0.1?mg?L^?1 Se and a combination of 0.1?mg?L^?1 Mo?+?0.1?mg?L^?1 Se. Experiment 1 showed that Se decreased Mo concentrations in shoots and roots. The impact of Mo on Chinese cabbage response to uptake of Se varied, depending on whether the root Se concentration was saturated or not; Experiment 2 showed that there is a strong antagonism between Mo and Se on nutrition uptake when Mo and Se deficiencies persist for long periods; Mo and Se were easily translocated from solution to plants and from roots to shoots. The results will also be of help in cultivating Mo-enriched and Se-enriched crops.     

Carbon source and time dependent enhancement of aerobic nitrogenase activity in soil samples and soil cores of cereals by Alachlor,Carbofuran and 4-nitrophenol

Aerobic nitrogenase activity (acetylene reduction test) in rhizosphere from Pearl Millet is enhanced by a factor of 2 during a 36 h incubation period by concentrations of the herbicide Alachlor and also the insecticide Carbofuran as used in the field. Supplementing soil with sucrose increased this enhancement effect to a 2-to 4-fold stimulation. The increase of nitrogenase activity in intact soil cores from Pearl Millet by Alachlor during a 5 h incubation period is about 30 to 40%. Aerobic nitrogenase activity in soil sediments is enhanced by concentrations of between 10^?5 and 10^?6 mol · 1^?1 4-nitrophenol but only within an incubation period of 3 to 4 days. These enhancement effects are discussed in terms of carbon source and incubation period.     

Host-status of 20 sweet potato lines to Meloidogyne species in South Africa

ABSTRACT

Experimental system: Due to serious economic challenges posed by root-knot (Meloidogyne species) nematodes in sweet potato (Ipomoea batatas) production, the Sweet Potato Programme (SPP) of the Agricultural Research Council (ARC) in South Africa has since included screening for nematode host-status in its breeding-selection activities. Procedures: 20 sweet potato lines were screened against M. javanica, M. incognita race 2 and M. incognita race 4 in parallel trials inoculated with 3000 eggs and second-stage juveniles (J2) per established cutting. Results: At 56 days after inoculation, the reproductive potential (RP) of all test Meloidogyne species on sweet potato line 1990-10-2 was zero, whereas RP values on other lines were 19.48–342.7, 31.9–995.1 and 10.3–380.44 ranges for M. javanica, M. incognita race 2 and M. incognita race 4, respectively. Conclusion: Among the test sweet potato lines, line 1990-10-2 was non-host to populations of tropical Meloidogyne species in South Africa and could, therefore, be subjected to nematode resistance tests.