Nutrient Uptake and Organic Acid Anion Metabolism in Lupins and Peas Supplied with Nitrate

Unlike many plants reported in the literature, lupins do notexcrete OH^- in amounts equivalent to the net excess of inorganicanion uptake over inorganic cation uptake. To investigate themechanisms involved in the maintenance of charge balance, nutrientuptake and organic anion accumulation of lupins and peas suppliedwith a range of NO^-₃ concentrations, were compared. Lupins absorbed less NO^-₃ than peas on a dry weight basis, whichlargely accounted for the smaller excess of anion uptake overcation uptake in lupins than in peas at the same NO^-₃ supply.When anion uptake exceeded cation uptake, peas excreted an equivalentcharge of OH^-, whereas lupins excreted much smaller amountsof OH^- than the excess of anion over cation uptake. It was calculatedthat lupins excreted significant amounts of organic anions whenanion uptake exceeded cation uptake, whereas organic anion excretionfrom peas was negligible, regardless of their NO^-₃ supply andcation-anion balance. In this study, organic anion excretion was measured from lupinroots grown in near-sterile conditions while supplied with NO^-₃at 0, 500 and 2000 µM. Although complete sterility wasnot achieved, there was close agreement between the organicanion excreted and the excess anion over cation uptake.Copyright1994, 1999 Academic Press Lupinus angustifolius L., Pisum sativum L., organic acid, nutrient uptake     

The Nature of the Resistance of Oats to the Take-all Fungus

The two varieties of the take-all fungus, Ophiobolus graminisand 0. graminis var. Avenae, show a differential reaction tosap extracted from oats; the type variety, which is incapableof causing a lasting infection of oats in vivo, is inhibitedby the sap in vitro, whereas var. Avenae, pathogenic to oats,can grow in the sap. The inhibitory action of the sap is notdue to a lack of food material required by the fungus, but toa specific substance or toxin. The method used for assayingtoxicity is described. The toxin is thermostable, moderately stable on storage, virtuallyinsoluble in non-polar solvents, and soluble in acetone, water,and methanol. Methanol extraction of the ether-washed residueof the filtrate from boiled sap from oat leaves results in asemi-purified substance which, when added to 2 per cent. Yeastrelsolution, reduces growth of 0. graminis to half that of thecontrol at a concentration of to 10 p.p.m. The inhibitor is produced in considerable quantity in the leavesand stems of oats and in smaller quantity in the roots. It appearsto accumulate mainly during the period of active growth andto be less active, or present in smaller concentration, in adultplants. It can be detected in the seminal roots throughout theirexistence, although during the first 3 weeks of growth 0. graminiscan invade the cells of the cortex. It is present in greaterquantity in the crown roots, which are never penetrated. A similar inhibitor of 0. graminis can be extracted from Arrhenatherumelatius, but not from other grasses which, both in the fieldand in pot experiments, appear to be equally resistant.     

The Nature of the Resistance of Oats to the Take-all Fungus: III. DISTRIBUTION OF THE INHIBITOR IN OAT SEEDLINGS

The distribution in oat seedlings of an inhibitor of fungalgrowth and respiration is described. The inhibitors from rootsand leaves differ in that that from roots has a bright bluefluorescence under ultra-violet light, while in other respectsthey behave similarly; it is suggested that they differ in structureof a part of the molecule not concerned in the biological activity.The inhibitor is present in high concentration in the meristemsof roots and leaves, one root tip extracted in 2 ml. water beingsufficient to reduce growth of O. graminis to 50 per cent. ofthe control; yield from other parts of the seedling is muchless. A quick assay technique based on growth-rate of myceliumis described, also a method for direct identification of inhibitoryzones on chromatograms which avoids the necessity for elution.     

Chlorine Dioxide for Reduction of Postharvest Pathogen Inoculum during Handling of Tree Fruits

Alternatives to hypochlorous acid and fungicides are needed for treatment of fruit and fruit-handling facilities. Chlorine dioxide was evaluated and found effective against common postharvest decay fungi and against filamentous fungi occurring on fruit packinghouse surfaces. In vitro tests with conidial or sporangiospore suspensions of Botrytis cinerea, Penicillium expansum, Mucor piriformis, and Cryptosporiopsis perennans demonstrated >99% spore mortality within 1 min when the fungi were exposed to aqueous chlorine dioxide at 3 or 5 μg · ml^-1. Longer exposure times were necessary to achieve similar spore mortalities with 1 μg · ml^-1. Of the fungi tested, B. cinerea and P. expansum were the least sensitive to ClO₂. In comparison with the number recovered from untreated control areas, the number of filamentous fungi recovered was significantly lower in swipe tests from hard surfaces such as belts and pads in a commercial apple and pear packinghouse after treatment of surfaces with a 14.0- to 18.0-μg · ml^-1 ClO₂ foam formulation. Chlorine dioxide has desirable properties as a sanitizing agent for postharvest decay management when residues of postharvest fungicides are not desired or allowed.     

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.     

Interaction of Rhizosphere Bacteria, Fertilizer, and Vesicular-Arbuscular Mycorrhizal Fungi with Sea Oats

Plants must be established quickly on replenished beaches in order to stabilize the sand and begin the dune-building process. The objective of this research was to determine whether inoculation of sea oats (Uniola paniculata L.) with bacteria (indigenous rhizosphere bacteria and N₂ fixers) alone or in combination with vesicular-arbuscular mycorrhizal fungi would enhance plant growth in beach sand. At two fertilizer-N levels, Klebsiella pneumoniae and two Azospirillum spp. did not provide the plants with fixed atmospheric N; however, K. pneumoniae increased root and shoot growth. When a sparingly soluble P source (CaHPO₄) was added to two sands, K. pneumoniae increased plant growth in sand with a high P content. The phosphorus content of shoots was not affected by bacterial inoculation, indicating that a mechanism other than bacterially enhanced P availability to plants was responsible for the growth increases. When sea oats were inoculated with either K. pneumoniae or Acaligenes denitrificans and a mixed Glomus inoculum, there was no consistent evidence of a synergistic effect on plant growth. Nonetheless, bacterial inoculation increased root colonization by vesicular-arbuscular mycorrhizal fungi when the fungal inoculum consisted of colonized roots but had no effect on colonization when the inoculum consisted of spores alone. K. pneumoniae was found to increase spore germination and hyphal growth of Glomus deserticola compared with the control. The use of bacterial inoculants to enhance establishment of pioneer dune plants warrants further study.     

小麦,玉米轮作田蜘蛛群落结构及多样性研究

一、研究方法本项工作于1988—1990年在青州市南郊农田进行。位于东经118°17′,北纬36°27′,年平均气温9℃,年降雨量860mm以上,无霜期180天左右。调查了不同作物类型的地块,包括玉米间作(大豆)田、净玉米田、有水浇条件的麦田、旱麦田和田埂杂草五种生境。其中小麦、玉米轮作田各3块,每块面积0.2ha以     

Features of Resistance to Take-all Disease in Cereal Species Evaluated by Laboratory Assays

Development of take-all disease, caused by Gaeumannomyces graminis var. tritici, on wheat, barley and rye, respectively, susceptible, moderately susceptible and resistant under field conditions, was evaluated by laboratory assays. The root system, which grew either in vermiculite in plastic tubes or polyethylene sleeves, or in a sand mix in plastic pots, was inculated, and lesion frequency and extension, both considered as resistance factors, were monitored. In assays in tubes and pots, both enabling multiple infection points, the infection scores of wheat, barley and rye on a scale of 0–5 were in decreasing order. In assays in sleeves, with a single point inoculation, lesion length on barley and rye was similar and less than thaton, wheat, but percentage of infected roots was markedly lower on rye than on barley. For large-scale screening programs we suggest to employ both the Tube Assay, which is reliable and easy to perform and the Slanted Sleeve Assay, which is more sensitive allowing detection of even a small degree of resistance. Selected accessions could be subsequently evaluated by the Pot Assay, under more natural conditions, and the resistance to take-all must eventually be verified under field conditions.     

Susceptibility Screening of Hyphae-Forming Fungi with a New, Easy, and Fast Inoculum Preparation Method

In vitro susceptibility testing of clinically important fungi becomes more and more essential due to the rising number of fungal infections in patients with impaired immune system. Existing standardized microbroth dilution methods for in vitro testing of molds (CLSI, EUCAST) are not intended for routine testing. These methods are very time-consuming and dependent on sporulating of hyphomycetes. In this multicentre study, a new (independent of sporulation) inoculum preparation method (containing a mixture of vegetative cells, hyphae, and conidia) was evaluated. Minimal inhibitory concentrations (MIC) of amphotericin B, posaconazole, and voriconazole of 180 molds were determined with two different culture media (YST and RPMI 1640) according to the DIN (Deutsches Institut für Normung) microdilution assay. 24 and 48?h MIC of quality control strains, tested per each test run, prepared with the new inoculum method were in the range of DIN. YST and RPMI 1640 media showed similar MIC distributions for all molds tested. MIC readings at 48 versus 24?h yield 1 log₂ higher MIC values and more than 90?% of the MICs read at 24 and 48?h were within ±2 log₂ dilution. MIC end point reading (log_{2 MIC-RPMI 1640}?log_{2 MIC-YST}) of both media demonstrated a tendency to slightly lower MICs with RPMI 1640 medium. This study reports the results of a new, time–saving, and easy-to-perform method for inoculum preparation for routine susceptibility testing that can be applied for all types of spore-/non-spore and hyphae-forming fungi.     

Uptake of Nitrate by Mutants of Arabidopsis thaliana, Disturbed in Uptake or Reduction of Nitrate

The uptake of nitrate by wildtype plants and chlorate-resistant mutants of Arabidopsis thaliana (L.) Heynh. was studied by intermittent or continuous measurement of the nitrate concentration of the ambient solution. The uptake rate in the wildtype and the nitrate reductase-less mutant B 25 showed a dual-phase relation ship with concentration. Each phase showed Michaelis-Menten kinetics although multiphasic patterns within each phase could not be excluded. A dual-phase relationship was also found in the uptake mutant B I. Here, however, phase II did not follow Michaelis-Menten kinetics and uptake rate of nitrate in the phase II concentration range was considerably lower in the B 1 mutant than in the wildtype. It is concluded that the mutation in B I has disturbed phase II of the nitrate uptake, without affecting phase I, which leads to the suggestion that uptake of nitrate in Arabidopsis is mediated by at least two independent uptake mechanisms. The nitrate uptake rate showed an optimum at pH 8, and it was not stimulated by the presence of calcium. Ammonium had different effects on nitrate uptake: a direct effect, when it was present during the uptake of nitrate, resulting in a release of nitrate and a reduced rate of uptake, and an indirect inhibitory effect, possibly caused by assimilation products of ammonium, which is most pronounced after growth on ammonium as the sole nitrogen source or in long-lasting uptake experiments in the presence of ammonium. Chlorate also showed a multiple effect, an inhibiting one which proved to be competitive and, at very low concentrations of chlorate, a stimulating one. Evidence was obtained that chlorate and nitrate arc taken up by the same carrier.     

Inoculum dynamics ofGliocladium virens associated with roots of cotton seedlings

A system was developed to evaluate the effects of root growth of cotton seedlings on the inoculum dynamics ofGliocladium virens in nonsterile soil. In soil infested withG. virens, inoculum densities of the fungus increased when plants remained alive. After 30 days, shoots were excised and the roots allowed to deteriorate. During this portion of the experiment (30–60 days) soil inoculum densities ofG. virens declined. In infested soil without a seedling, inoculum densities remained constant throughout the duration of the experiments. Colonization of roots byG. virens was found to increase throughout the duration of the experiments. At 60 daysG. virens was recovered from approximately 60% of the root pieces (1-cm) sampled. The percentage of primary, secondary, or tertiary roots colonized was different (P = 0.01), but the total colonization of roots at three depths (0–10, 10–20, and 20–30 cm) was not different (P = 0.64). In noninfested soil, colonization of roots by indigenous propagules ofG. virens was never greater than 3%. Offprint requests to: C. M. Kenerley.     

Inoculum Density-Dependent Mortality and Colonization of the Phyllosphere by Pseudomonas syringae

Pseudomonas syringae inocula containing cell concentrations ranging from 10⁵ to 10⁹ cells per ml were applied to the primary leaves of bean plants. The plants were incubated under conditions of high temperature and illumination and low relative humidity. Bacterial mortality rates and the proportional population decline of the inoculum were lowest at the highest inoculum concentrations. Addition of a high concentration of heat-killed cells to the inoculum containing a low concentration of viable cells significantly reduced both the mortality rate and the proportional population decline of the viable cells. The mechanisms underlying this density-dependent mortality may include cooperative protective effects of extracellular factors, such as bacterial extracellular polysaccharides, and physical protection by neighboring cells. Although epiphytic populations derived from inoculum concentrations of 10⁸ or 10⁹ cells per ml tended toward 10⁶ CFU/g, the presumed carrying capacity of the leaf, populations derived from lower inoculum concentrations never achieved this carrying capacity. Assuming that epiphytic populations of P. syringae reside in discrete protected sites, our results suggest that at low inoculum concentrations, following a period of environmental stress, the number of viable cells may have dropped to zero in some sites; hence, the carrying capacity of the leaf could not be achieved.     

Rapid Detection of Ceratocystis platani Inoculum by Quantitative Real-Time PCR Assay

Ceratocystis platani is the causal agent of canker stain of plane trees, a lethal disease able to kill mature trees in one or two successive growing seasons. The pathogen is a quarantine organism and has a negative impact on anthropogenic and natural populations of plane trees. Contaminated sawdust produced during pruning and sanitation fellings can contribute to disease spread. The goal of this study was to design a rapid, real-time quantitative PCR assay to detect a C. platani airborne inoculum. Airborne inoculum traps (AITs) were placed in an urban setting in the city of Florence, Italy, where the disease was present. Primers and TaqMan minor groove binder (MGB) probes were designed to target cerato-platanin (CP) and internal transcribed spacer 2 (ITS2) genes. The detection limits of the assay were 0.05 pg/μl and 2 fg/μl of fungal DNA for CP and ITS, respectively. Pathogen detection directly from AITs demonstrated specificity and high sensitivity for C. platani, detecting DNA concentrations as low as 1.2 × 10⁻² to 1.4 × 10⁻² pg/μl, corresponding to ∼10 conidia per ml. Airborne inoculum traps were able to detect the C. platani inoculum within 200 m of the closest symptomatic infected plane tree. The combination of airborne trapping and real-time quantitative PCR assay provides a rapid and sensitive method for the specific detection of a C. platani inoculum. This technique may be used to identify the period of highest risk of pathogen spread in a site, thus helping disease management.     

Effect of Inoculum Size on In Vitro Susceptibility Testing with Lincomycin

There is disagreement in the literature as to whether lincomycin is primarily a bacteriostatic or a bactericidal agent against gram-positive cocci and also regarding the levels of activity of this agent against susceptible microorganisms. These questions were examined in a study of the effect of inoculum size on the results of tube dilution susceptibility determinations with lincomycin against 49 clinical isolates of Staphylococcus aureus and 25 strains of streptococci and pneumococci. Lincomycin was both highly active and bactericidal when tested against 40 strains of S. aureus with inocula containing a maximum of 10(4) cells per ml [median minimal inhibitory concentration (MIC), 0.78 mug/ml; median minimal bactericidal concentration (MBC), 1.56 mug/ml]. With inocula of 10(5) cells per ml, lincomycin was primarily bacteriostatic (median MIC, 1.56 mug/ml; median MBC, 12.5 mug/ml). There were further decreases in inhibitory levels and significant losses of bactericidal activity when inocula containing more than 10(7) cells were tested (median MIC, 3.13 mug/ml; median MBC > 100 mug/ml). Similar measurements with streptococci and pneumococci revealed a lesser effect of inoculum size. The mean MBC value for alpha-hemolytic streptococci increased from 0.40 to 1.05 mug/ml with an increase in inocula from 10(4) to 10(6) cells per ml, but without a marked increase in MIC values. Similar results were obtained for beta-hemolytic streptococci and pneumococci.