Effect of soil cultivation and anaerobiosis on cavity spot of carrots

Cultivating between rows and narrow beds of carrots reduced the severity of cavity spot in one year and reduced the incidence and severity in single rows in a second year on land where the disorder was endemic. Growing carrots on ridges initially reduced symptoms more than inter-row cultivation. Soluble carbohydrates leached from carrot roots in vitro and the quantities increased when anaerobic conditions were imposed. Untreated and cell-free extracts of soil suspensions amended with 1% glucose and incubated anaerobically applied to carrots in the laboratory caused the outer layers of the secondary phloem to collapse resembling a cavity spot lesion. Unamended and fresh soil solutions had no effect.     

Application of actinomycetes to soil to ameliorate water repellency

AIMS: The aim of this study was to develop a novel isolation technique using a mixture of Bacillus and Streptomyces phages to selectively isolate wax-utilizing non-streptomycete actinomycetes effective in ameliorating water repellency in a problem soil. METHODS AND RESULTS: Phages added to a soil suspension reduced the dominance of Bacillus and Streptomyces isolates and significantly increased the number of non-streptomycete actinomycetes on isolation plates. Promising isolates, grown on a medium containing beeswax as sole carbon source, were selected for application to water repellent soil. Their addition significantly reduced water repellency. CONCLUSIONS: Phage application significantly increased the isolation of non-streptomycete actinomycetes. Wax-utilizing isolates were found to significantly reduce water repellency in a problem soil. SIGNIFICANCE AND IMPACT OF THE STUDY: The phage technique can be used for the routine isolation of non-streptomycete actinomycetes. Beeswax medium can be used to selectively isolate wax-utilizing micro-organisms with the potential to ameliorate water repellency in soil.     

Detection of Pythium violae and Pythium sulcatum in carrots with cavity spot using competition ELISA

Conventional methods indicated that Pythium violae was most commonly isolated from carrot cavity spot samples from 14 UK sites. For one site the most frequently isolated species was Pythium sulcatum. Results of similar isolation work were compared with the assay of cavity spot lesions using polyclonal antibodies, raised to P. violae or P. sulcatum, in competition ELISA. Where lesions were artificially induced the test confirmed which pathogen was causal. With cavities developed on the field-grown carrots P. violae again predominated and the ELISA confirmed this. In one sample P. sulcatum was also isolated from a small number of lesions and was not detected in ELISA. The competition ELISA did not indicate presence of either Pythium in a range of non-cavity spot lesions from which attempts at isolation were negative.     

Growth and nutrient concentrations of alfalfa and common bean as influenced by soil acidity

Growth and nutrient utilization of alfalfa (Medicago sativa L. cv. Arc) and common bean (Phaseolus vulgaris L. cv. Carioca) were studied in an acid soil adjusted to eight levels of soil acidity by lime addition. Application of lime significantly (P<0.05) increased shoot and root growth for both species. However, common bean was far less sensitive to soil acidity than alfalfa. Maximum alfalfa growth was obtained at a soil pH of 5.8 and maximum bean growth was achieved at pH 5.0. Root and shoot growth of both legumes was positively correlated (P<0.01) with soil pH, exchangeable Ca and exchangeable Mg and negatively correlated (P<0.01) with soil exchangeable Al. Common bean had a lower internal P requirement for maximum growth and was more efficient than alfalfa in taking up Ca and Mg. These characteristics would contribute to the favorable growth of common bean in acid-infertile soils.     

Role of magnesium in combination with liming in alleviating acid-soil stress with the aluminium-sensitive sorghum genotype CV323

An experiment to study the effects of Mg nutrition on root and shoot development of the Al-sensitive sorghum (Sorghum bicolor (L.) Moench) genotype CV323 grown in pots of sandy loam under different acid soil stress is reported. This experiment had a factorial design: four rates of liming were combined with four rates of Mg fertilization. When no Mg was added, the pH of the soil solutions (collected in ceramic cups) increased from 4.0 (unlimed) to 4.2, 4.7 and 5.9 at the increasing rates of liming. After 30 days of growth dry matter yields of the limed treatments were 40%, 115% and 199% higher than that of the unlimed treatment. Without liming and at the highest liming rate, adding Mg did not affect plant biomass significantly. At the two intermediate levels of liming, however, 11.3 mg extra Mg per kg soil increased dry matter yield to the same levels as found at the highest liming rate. Concentrations of Mg in the soil solution rose after Mg was added and fell when lime was added, but adding both Mg and lime increased Mg concentrations in the plant shoots. In plants of the limed treatments, dry matter yield was correlated closely with the Mg concentration in the shoot. This was not so in the unlimed treatment. Furthermore, in the unlimed treatments root development was inhibited, but reduced Mg uptake by the plants resulted mainly from the direct effect of Al- (or H-) ions in the soil solution rather than from impaired root development. It is concluded that Mg fertilization counteracted the interfering effects of Al- and H ions on Mg uptake.     

Biochemical characterisation of Pythium spp. involved in cavity spot of carrots in France

The pathogenicity and growth rate in vivo were assessed on 27 isolates of Pythium spp. recovered from cavity spot lesions on carrots grown in various parts of northwest France. Polyacrylamide gel electrophoresis of isoesterases was used to identify the Pythium spp. involved. Slow-growing isolates were more aggressive than fast-growing ones when inoculated on carrot tap roots. Isoesterase patterns identified the slow-growing isolates as P. violae and P. sulcatum; P. ultimum and P. intermedium were identified among the less aggressive fast-growing isolate group, in which some isolates were also classed as P. sylvaticum or P. irregulare, which have similar electrophoretic profiles. The incidence of Pythium spp. associated with the disease in France is discussed in regard to cavity spot in other countries.     

Influence of iron and pH on the yield and iron,manganese, zinc,and sulfur concentrations of carrots grown on sphagnum peat soil

Summary In two greenhouse experiments, sphagnum peat, adjusted to various pH levels, was used to study the effect of various levels of Fe on the growth of carrots (Daucus carota L., var. sativa D.C.). The Fe was added to the medium as sequesterine 330 chelate. Maximum carrot root and top tissue yields were obtained at soil pH 6.6 and 7.1. At soil pH 5.2 and 7.8 the yields were in the intermediate range. The yields were low at pH 4.3, 4.5 and 8.1 and at pH 8.4 the carrots did not grow. The chlorotic symptoms on carrot leaves, accom-panied by reduced yields, were associated with 39 to 82 ppm Fe and > 332 ppm Mn in the leaf and were likely due to Mn toxicity. Toxic levels of Mn in tissue were found even at soil pH 8.1 and were associated with reduced carrot yields. The leaf tissue concentrations of Fe and Mn decreased as the pH of soil increased; however, at pH 5.2, 7.8, and 8.1 the tissue Mn concentration increased. The added Fe had no effect on the Fe concentration but decreased the Mn and Zn concentration of leaf tissue and increased carrot root yields. There was a significant interaction between added lime and Fe, whereby the decrease in leaf tissue Mn concentration and increases in root yields with added Fe were much greater at pH 4.5 and 5.2 than at pH values of 6.6 and 7.8. The S concentration in the leaf tissue decreased with added Fe and lime. The leaf tissue Zn concentrations of 184 to 490 ppm and S concentrations of 0.32 to 0.63%, as found here, are considered to be high but not in the toxic range.Contribution No. 321, Research Station, Charlottetown, P.E.I. and No. 1534, Research Station, Kentville, N.S.Contribution No. 321, Research Station, Charlottetown, P.E.I. and No. 1534, Research Station, Kentville, N.S.     

Cavity spot of carrot (Daucus carota)

Cavity spot disease of carrot (Daucus carota) has been one of the intractable problems for both growers and scientists. Carrots are rejected at grading with one or two visible lesions, and when disease incidence passes a relatively low threshold it becomes uneconomic to harvest crops. For the scientist, there has been considerable pressure to produce both information on the cause of the disease and a cure. Many putative causes have been advanced over the years, but these were almost always contradicted by subsequent work. The first solid indication of involvement of a pathogen was when three different fungicides with activity against Oomycete fungi all reduced disease. Very quickly the causal agents Pythium violae and Pythium sulcatum were isolated from cavity spot lesions and Koch's postulates satisfied. The species are not typical of the more common pythia, having slow growth at normal temperatures, which means that in the context of isolation work, plates may be overgrown by other species before they are seen. Metalaxyl fungicide was identified as the most effective in controlling cavity spot caused by P. violae, but P. sulcatum is naturally tolerant of the fungicide. Recently, metalaxyl has been shown to be subject to enhanced microbial degradation. This phenomenon has been associated with failure to control cavity spot. No other fungicide has been shown to be consistently effective in the field, and none has been registered for disease control. For the future, this means that control of cavity spot can not be based solely on fungicidal control. Other, complementary strategies are necessary for reducing disease. Calcium carbonate is known to have significant effects on cavity spot, probably by inducing a soil microflora inhibitory to filamentous fungi. Management of agronomic aspects such as irrigation, soil cultivation and the length of time for which crops are grown may all be used, while carrot cultivars with some field resistance may be beneficial. However, one of the most significant factors is disease avoidance by not selecting fields with high inoculum levels. One serology‐based risk assessment test has been produced and commercialised, and molecular probes which could be the basis of more sensitive tests are available for both pathogens. The potential for disease reduction via a management strategy combining several key components is discussed.     

Bacterial endophytes in processing carrots (Daucus carota L. var. sativus): their localization, population density, biodiversity and their effects on plant growth

A survey of endophytic bacteria colonizing roots of processing carrots (Daucus carota) was performed with two high-yielding cultivars (Carochoice, Red Core Chantenay) grown at two locations (Canning, Great Village) in Nova Scotia. Most bacterial endophyte colony-forming units (CFU) were recovered from the carrot crown tissues (96%) compared to the periderm and metaxylem tissues of carrot storage tissues irrespective of the cultivars and field locations. Greater population densities of endophytic bacteria were recovered from the crowns of Red Core Chantenay (5.75 × 10⁵ CFU/g FW in Great Village; 3.0 × 10⁵ CFU/g FW in Canning) cultivar, which accounted for 78% of all of CFU recovered compared to cv. Carochoice. Independent of the cultivars, more endophytes were recovered from the carrots produced in Great Village compared to the ones grown in Canning (62 vs. 38%, respectively). Of 360 isolates examined, 28 bacterial genera were identified, of which, Pseudomonas, Staphylococcus, and Agrobacterium were the most common (31, 7 and 7%, respectively). Diversity indices showed no significant differences between the two locations. A bioassay using selected strains of bacteria was performed on 4 week-old carrot (cv. Bergen) and potato (Solanum tuberosum cv. Atlantic) plantlets. In carrots, 83% of the bacterial strains tested were found to be plant growth promoting, 10% remained plant growth neutral and 7% inhibited plant growth. In contrast, in the potato bioassay 38% remained growth neutral, 33% promoted and 29% inhibited plant growth.     

河北省冬枣黑斑病病原菌的分离鉴定及生物防治初探

冬枣黑斑病是冬枣重要病害之一,目前多以化学农药进行防治,给自然环境和人类健康带来了严重的威胁。河北省是冬枣种植大省,进行冬枣黑斑病病原菌的分离鉴定对冬枣黑斑病的有效防治具有重要意义。2014年8月至10月从河北省沧州、衡水、邯郸、邢台等地采集冬枣黑斑病病果,采用PDA培养基进行病原菌分离,从病样中共分离出2株分离频率较高的真菌,经过回接和再分离实验筛选出河北省冬枣黑斑病的致病菌株,经形态学和ITS序列分析初步确定该菌为细交链格孢(Alternaria alternata)。以枯草芽胞杆菌J18进行冬枣采后黑斑病的防治,浓度为1×108cfu/m L的菌液对病害的防效为80.67%。     

Influence of soil pH on the soybean-endomycorrhiza symbiosis

Summary Soybean (Glycine max {L.} Merr.) cultivars were inoculated withGigaspora gigantea andGlomus mosseae to determine mycorrhizal: cultivar relationships as affected by soil pH. The specific cultivarfungal response was dependent on soil pH. Overall cultivar responses in unlimed soil (pH 5.1) were greater forG. gigantea thanG. mosseae. The Bossier —G. gigantea combination was particularly responsive in unlimed soil and showed an increase of 10% in shoot length, 35% in shoot dry weight. 75% in root dry weight, and 397% in nodule dry weight over uninoculated controls. Little cultivar response was observed withG. mosseae inoculation in unlimed soil. In limed soil (pH 6.2), the larger responses were obtained withG. mosseae inoculated plants, although inoculation with eitherG. mosseae orG. gigantea appeared effective. In general, nodulation was greater on mycorrhizal roots than on control roots.     

Carbon flow in an upland grassland: effect of liming on the flux of recently photosynthesized carbon to rhizosphere soil

The effect of liming on the flow of recently photosynthesized carbon to rhizosphere soil was studied using ¹³CO₂ pulse labelling, in an upland grassland ecosystem in Scotland. The use of ¹³C enabled detection, in the field, of the effect of a 4‐year liming period of selected soil plots on C allocation from plant biomass to soil, in comparison with unlimed plots. Photosynthetic rates and carbon turnover were higher in plants grown in limed soils than in those from unlimed plots. Higher δ¹³C‰ values were detected in shoots from limed plants than in those from unlimed plants in samples clipped within 15 days of the end of pulse labelling. Analysis of the aboveground plant production corresponding to the 4‐year period of liming indicated that the standing biomass was higher in plots that received lime. Lower δ¹³C‰ values in limed roots compared with unlimed roots were found, whereas no significant difference was detected between soil samples. Extrapolation of our results indicated that more C has been lost through the soil than has been gained via photosynthetic assimilation because of pasture liming in Scotland during the period 1990–1998. However, the uncertainty associated with such extrapolation based on this single study is high and these estimates are provided only to set our findings in the broader context of national soil carbon emissions.     

Cavity spot of carrots: II. Cell-wall-degrading enzymes secreted by Pythium and pathogen-related proteins produced by the root cells

This study investigates the biochemical relationships between carrot roots and Pythium violae, the pathogen responsible for cavity spot (CS) disease. P. violae isolates obtained from CS lesions, cultured in Petri dishes on agar were used for inoculation of uninfected mature carrots. The fungus secreted a wide spectrum of enzymes that degraded the cellulose and pectic substances of the carrot cell walls. Cellulase and polygalacuronase (pg) showed the highest activity during the first day post-inoculation, subsequently declining. Pectin lyase (PnL), pectate lyase (PeL) and pectin methylesterase (PME) gradually increased to their highest levels of activity 14 to 30 days post-inoculation. This pattern of activity enables the penetration of the fungus through the walls of the host cells and the establishment of the hyphae. Several plant pathogen-related substances such as peroxidase, chitinase, glucanase and polyphenol oxidase were produced in the infected tissue. Peroxidase activity rose in the inoculated roots from day 1 post-inoculation. Chitinase, glucanase and polyphenol oxidase activities first appeared 3–4 days post-inoculation. At this time, two bands corresponding to chitinase at about 26 and 33 KDa and one band corresponding to glucanase at about 24 KDa could be resolved by SDS-PAGE.     

Rare genera of actinomycetes as potential producers of new antibiotics

A literature survey covering more than twenty-three thousand bioactive microbial products including eight thousand antiinfectives demonstrated the increasing relevance of the so called 'rare' actinomycetes as a source of new antibiotics. Past and present efforts in the isolation of rare actinomycetes have enriched the Biosearch Italia Strain Collection with more than twenty thousand strains, showing that, when selective isolation methods are developed and extensively applied, some genera, such as Actinomadura, Actinoplanes, Micromonospora, Microtetraspora, are not rare at all and can be recovered from many soil samples. The current focus is on the isolation of members of Streptosporangiaceae family, given their promising chemical diversity.     

Inhibitory efficacy of different essential oils against storage carrot rot with antifungal and resistance‐inducing potential

The inhibitory effects of essential oils (EOs) derived from coriander, lavender, geranium, thyme, savoury and eucalyptus were assessed against Sclerotinia sclerotiorum, the causal agent of carrot white mould. All EOs showed antifungal activity against the pathogen in vitro and in vivo. In addition, all EOs markedly increased 6‐methoxymellein in the treated carrots. The EOs of thyme and savoury were found to be more effective than other tested EOs. The enzymatic tests showed that thyme and savoury EOs were more able than lavender EO to significantly increase the level of chitinases, peroxidases, β‐1,3‐glucanases, polyphenol oxidase, peroxidase and phenylalanine ammonia‐lyase in the treated carrots, indicating that the EOs of thyme and savoury have potential to be considered as effective inducers of resistance against carrot white mould. In this study, all EOs inhibited myceliogenic and carpogenic germination of sclerotia at concentrations 1 and 10 µl/ml sterile distilled water, respectively. After gas chromatography/mass spectrometry, major component in the thyme EO was found to be thymol (39.15%) followed by p‐cymene (13.85%) and carvacrol (10.36%), while in savoury EO were carvacrol (41.9%), γ‐terpinene (17.38) and p‐cymene (11.25%).     

The selective isolation ofMicromonospora from soil by cesium chloride density gradient ultracentrifugation

Summary A novel method is described for the selective isolation ofMicromonospora from mixed microbial populations in soil. Microorganisms were released from soil by sonication, and the bulk of the soil debris was discarded by low-speed centrifugation. The supernatant microbial suspension was concentrated and applied to a continuous, linear (1.1–1.6 g/ml) gradient of CsCl which was then centrifuged at high speed. The gradient was fractionated, and each fraction was diluted and plated on a medium devoid of antimicrobial agents.Micromonospora were found in the 1.35–1.42 g/ml density band. Occasionally,Bacillus species were also obtained in this density range, but other nonfilamentous bacteria or actinomycetes were usually not observed. This technique allowed the isolation of portions of the soilMicromonospora population which were suppressed by conventional isolation techniques employing heat and antibiotics.     

Yield,root morphology and chemical composition of two pasture legumes as affected by lime and phosphorus applications to an acid soil

Summary Effects of increasing rates of lime (0, 900, 1725, and 3000 kg Ca(OH)₂/ha producing soil pH of 4.0, 4.7, 5.1 and 5.6) and P (50, 150, 250 and 350 kg P/ha) on top and root yield, root morphology and chemical composition of lotus (Lotus pedunculatus Cav.) and white clover (Trifolium repens L.), were studied, using an acid soil in a greenhouse experiment. Increasing rates of applied lime and phosphate resulted in substantial increases in top yields of both species but concomitant increases in root yield were small. In the unlimed soil, lotus out-yielded (tops and roots) white clover at all P levels. However, in the three limed treatments, white clover clearly out-yielded lotus. Yield response curves to applied P levelled off at the two highest lime rates for lotus but not for white clover. Nodulation and N content of white clover increased significantly with increasing lime applications, but for lotus there was a significant decrease in nodulation at the highest lime rate. Increased P rates had a small stimulatory effect on nodulation in both species. Of the total root weight, the percentage contribution of the tap and primary lateral root fractions was smaller and that of the secondary plus tertiary lateral roots was greater for lotus than for white clover although root length per unit weight tended to be larger for white clover at the two highest lime rates. Furthermore, lotus possessed longer and more numerous root hairs than white clover. Lime applications significantly decreased the percentage contribution of the tap and primary lateral roots to the total root weight and increased the percentage contribution of the secondary plus tertiary lateral roots. Al and Mn contents of tops and roots of both species decreased with increasing lime rates. There was a highly significant negative correlation between relative yield and Al content of lotus and white clover tops. In comparison with the limed treatments, in the unlimed treatments a greater percentage of total P, Al, Mn and N content accumulated in the roots of both species. In addition, lotus accumulated a much greater percentage Al in its roots than white clover.     

Selecting iodine-enriched vegetables and the residual effect of iodate application to soil

A greenhouse pot experiment was conducted to select vegetables for iodine uptake. The residual effect of iodate fertilization on the growth of and iodine uptake by spinach plants were also investigated. Six vegetables, including leafy vegetables (pakchoi [Brassica chinensis L.], spinach [Spinacia oleracea L.]), tuber vegetables (onion [Allium cepa L.]), shoot vegetables (water spinach [Ipomoea aquatica Forsk.], celery [Apium graveolens L.]), and root vegetables (carrot [Daucus carota var. sativa DC.]) were examined. Results showed that the concentrations of iodate in soil had significant effect on the biomass of edible parts of pakchoi and spinach (p<0.01), whereas the concentrations of iodate in soil had no significant effect on that of carrots, water spinach, celery, and onion. Iodine concentrations in edible parts of vegetables and the transfer factors (TF_{edible parts}) of soil-to-edible parts of vegetables significantly increased with increasing iodine concentrations in soil (p<0.001), and iodine concentrations in edible parts and TF_{edible parts} of spinach were much higher than those of other vegetables at any treatment. Both transfer coefficients for edible parts (TC_{edible parts}) and for aerial parts (TC_{aerial parts}) of vegetables changed differently with increasing iodine concentrations in the soil, and TC_{edible parts} and TC_{aerial parts} of spinach were higher than those of other vegetables. Therefore, spinach (leafy vegetable) was considered as an efficient vegetable for iodine biofortification. Further experiment showed that there is considerable residual effect of soil fertilization with iodate.     

Increased calcium in carrots by expression of an Arabidopsis H+/Ca2+ transporter

We demonstrate that carrots expressing the Arabidopsis H⁺/Ca²⁺ transporter CAX1 (Cation Exchanger 1) contained up to 50% more calcium (Ca) than plants transformed with control vectors. The CAX1-expressing carrots were fertile, and robust plant growth was seen in the majority of the transgenic plants. CAX1-expressing carrots were crossed to a commercial carrot variety to confirm that the increased Ca accumulation was mediated by CAX1-expression, and the increased Ca content was clearly correlated with the transgene. This study suggests that modulation of ion transporters could be an important means of increasing the Ca content of agriculturally important crops. To our knowledge, this study represents the first attempts to use biotechnology to increase the Ca content of an agriculturally important crop.     

Studies on the etiology of black rot, Stemphylium radicinum (Meier, Drechsl. & Eddy) Neerg., and leaf blight, Alternaria dauci (Kühn) Groves & Skolko, on carrot crops; and on fungicide control of their seed-borne infection phases

Of nineteen commercial samples of carrot seed in use at Wellesbourne in 1963, eight were found to be infected with both Stemphylium radicinum and Alternaria dauci and five with S. radicinum alone. Both fungi caused damping-off of seedlings and when carrots were grown at high densities A. dauci caused severe foliar infection. Neither fungus gave rise to marked infection of ware crops at normal spacings but, when seed infected with S. radicinum was sown in the autumn, the resulting seed crop was heavily infected by the succeeding autumn. Spring-sown carrots grown in soil that had borne infected crops or contained debris infected with either fungus showed little or no infection in the autumn or after storage for 3 1/2 months; autumn-sown or spring-planted (steckling) carrots put into ground infected with S. radicinum showed severe infection in the following autumn. This suggested that ware-crop carrots were resistant to infection from the soil whereas the seed crop was not. Both fungi were eradicated from seed by a 24 hr. soak at 30d? C. in a 0.2% thiram suspension, but were not completely eliminated by seed dust treatments with a range of fungicides.