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1.
Stages of oat–vetch cover crop decomposition were characterized over time in terms of carbon and nitrogen cycling, microbial activity and damping-off pathogen dynamics in organically and conventionally managed soils in a field and a controlled incubation experiment. A measurement of relative growth consisting of radial growth of a fungal colony over non-sterilized soil divided by that over sterilized soil was used as an assay of suppressiveness. No differences in relative growth of Pythium aphanidermatum and Rhizoctonia solani were detected between organic and conventionally managed soils amended with cover crop residue. Significant effects of cover crop decomposition stage on the relative growth of both pathogens were obtained. Relative growth of P. aphanidermatum was highest just after incorporation and decreased 3 weeks after incorporation. Relative growth of R. solani was highest about 20 days after incorporation, and decreased 2 weeks later in the organic system, but continued to increase in the conventional system. In both experiments, the N or C content, C:N ratio or dry weight of retrieved debris were significantly correlated with relative growth of P. aphanidermatum. Relative growth of R. solani was significantly correlated with the C:N ratio of soil or the C or N content of debris. Microbial activity was not consistently associated with relative growth of either pathogen.  相似文献   

2.
Stages of oat–vetch cover crop decomposition were characterized over time in terms of carbon and nitrogen cycling, microbial activity and community dynamics in organically and conventionally managed soils in a field experiment and a laboratory incubation experiment. We subsequently determined which variables describing soil microbial community dynamics, C and N cycling could be used as predictors of Pythium aphanidermatum damping-off incidence and relative growth. Disease incidence and relative growth of P. aphanidermatum were measured in growth chamber assays and in vitro growth tests. No significant differences were detected between the conventional and organic farming system with respect to either relative growth or disease incidence. Stepwise discriminant analysis on three classes of disease incidence or relative growth led to selection of qualitatively similar variables. Only one soil microbial variable, total biomass of actinomycetes, was selected. Total C and N content of debris extracted from soil as well as NH4-N content of soil were selected most consistently and show promise for assessment of potential damping-off incidence by P. aphanidermatum for young seedlings.  相似文献   

3.
Transitioning farmland to certified organic vegetable production can take many paths, each varying in their costs and benefits. Here, the effects of four organic transition strategies (i.e., tilled fallowing, mixed-species hay, low-intensity vegetables, and intensive vegetable production under high tunnels), each with and without annual compost applications for 3 years prior to assessment, were characterized. Although transition cropping strategies differed in soil chemistry (P < 0.05), the magnitude of the changes typically were marginal and pairwise comparisons were rarely significant. In contrast, the compost amendment had a much greater impact on soil chemistry regardless of cropping strategy. For example, percent C and total P increased by 2- to 5-fold and K increased from 6- to 12-fold. Under controlled conditions, damping-off of both edamame soybean (cv. Sayamusume) and tomato (cv. Tiny Tim) was reduced from 2 to 30% in soils from the mixed-hay transition. In the field, damping-off of both crops was also significantly lower in plots previously cropped to hay (P < 0.05). Although not always significant (P < 0.05), this pattern of suppression was observed in all four of the soybean experiments and three of the four tomato experiments independent of compost application. The compost amendments alone did not consistently suppress damping-off. However, plant height, fresh weight, and leaf area index of the surviving seedlings of both crops were greater in the compost-amended soils regardless of the transitional cropping treatment used (P < 0.05 for most comparisons). These data indicate that mixed-hay cropping during the transition periods can enhance soil suppressiveness to damping-off. In addition, although compost amendments applied during transition can improve crop vigor by significantly enhancing soil fertility, their effects on soilborne diseases are not yet predictable when transitioning to certified organic production.  相似文献   

4.
Based on the observation that the root disease caused by P. cinnamomi on Q. ilex has a low incidence and severity in soils with medium-high Ca2+ content, we studied the ability of Ca2+ fertilizers to induce soil suppressiveness to the pathogen. Studies on cultures of P. cinnamomi exposed to different Ca2+ fertilizers in vitro showed significant inhibition of sporangial, chlamydospore and zoospore production at millimolar concentrations while mycelial growth was mainly unaffected. Experiments performed with artificially infested soil showed that some Ca2+ fertilizers induce a significant decrease on chlamydospore viability. Additionally, greenhouse experiments using artificially infested soils showed a significant reduction of foliar and root symptom severities in Holm oak seedlings growing in soils amended with Ca2+ fertilizers. We suggest that limestone amendments in oak rangelands could enhance the suppressiveness of soils to P. cinnamomi, and it is likely that the inhibition of sporangial production was the main mechanism involved.  相似文献   

5.
Kasuya M  Olivier AR  Ota Y  Tojo M  Honjo H  Fukui R 《Phytopathology》2006,96(12):1372-1379
ABSTRACT Suppressive effects of soil amendment with residues of 12 cultivars of Brassica rapa on damping-off of sugar beet were evaluated in soils infested with Rhizoctonia solani. Residues of clover and peanut were tested as noncruciferous controls. The incidence of damping-off was significantly and consistently suppressed in the soils amended with residues of clover, peanut, and B. rapa subsp. rapifera 'Saori', but only the volatile substance produced from water-imbibed residue of cv. Saori exhibited a distinct inhibitory effect on mycelial growth of R. solani. Nonetheless, disease suppression in such residue-amended soils was diminished or nullified when antibacterial antibiotics were applied to the soils, suggesting that proliferation of antagonistic bacteria resident to the soils were responsible for disease suppression. When the seed (pericarps) colonized by R. solani in the infested soil without residues were replanted into the soils amended with such residues, damping-off was suppressed in all cases. In contrast, when seed that had been colonized by microorganisms in the soils containing the residues were replanted into the infested soil, damping-off was not suppressed. The evidence indicates that the laimosphere, but not the spermosphere, is the site for the antagonistic microbial interaction, which is the chief principle of soil suppressiveness against Rhizoctonia damping-off.  相似文献   

6.
A study was conducted to investigate the effect of salinity on pythium damping-off and tolerance to salinity among Pythium aphanidermatum isolates from different geographical origins, genetic backgrounds and saline/non-saline soils. Increasing irrigation-water salinity from 0·01 to 5 dS m−1 significantly increased mortality in cucumber seedlings inoculated with P. aphanidermatum and reduced dry weight of non-inoculated seedlings. In vitro tests in culture media amended with different concentrations of NaCl showed that growth of P. aphanidermatum, P. spinosum and P. splendens isolates was stimulated or unaffected at salinity levels stressful for cucumber (electrical conductivity = 5 dS m−1). Significant differences were found in tolerance to salinity among 47 P. aphanidermatum isolates obtained from different greenhouses. The concentration of NaCl required to reduce growth of P. aphanidermatum isolates by 50% varied from 23 to 62 dS m−1, with an average of 46 dS m−1, however, oospore production was more sensitive to salinity and no oospores were produced above 20 dS m−1. Analysis of tolerance of P. aphanidermatum isolates to salinity showed no relationship between tolerance to salinity and geographical origins or genetic data. Isolates of P. aphanidermatum from greenhouses with no salinity problems were as tolerant to salinity as isolates obtained from salinity-affected greenhouses, suggesting lack of evidence for ecological adaptation within P. aphanidermatum in Oman. Increased mortality in cucumber seedlings at higher salinity levels may imply a synergistic interaction between salinity stress and salinity-tolerant Pythium species on cucumber seedlings, resulting in greater seedling losses.  相似文献   

7.
A series of laboratory experiments were conducted to investigate the capacity of Bradysia impatiens (Johannsen) larvae to ingest propagules from two strains each of Pythium aphanidermatum (Edson) Fitzp. and P. ultimum Trow and transmit the pathogens to healthy geranium seedlings on a filter-paper substrate in petri dishes. The capacity of fungus gnat larvae to transmit P. aphanidermatum to seedlings rooted in a commercial peat-based potting mix and germination of Pythium oospores and hyphal swellings before and after passage through the guts of larval fungus gnats were also examined. Assays revealed that Pythium spp. transmission by larval fungus gnats varied greatly with the assay substrate and also with the number and nature of ingested propagules. Transmission was highest (65%) in the petri dish assays testing larvae fed P. aphanidermatum K-13, a strain that produced abundant oospores. Transmission of strain K-13 was much lower (<6%) in plug cells with potting mix. Larvae were less efficient at vectoring P. ultimum strain PSN-1, which produced few oospores, and no transmission was observed with two non-oospore-producing strains: P. aphanidermatum Pa58 and P. ultimum P4. Passage of P. aphanidermatum K-13 through larval guts significantly increased oospore germination. However, decreased germination of hyphal swellings was observed following larval gut passage for strains of P. ultimum. These results expand previous studies suggesting that larval fungus gnats may vector Pythium spp.  相似文献   

8.
Pythium spp. that cause damping-off of seedlings also can cause root rot of older plants and lead to yield reductions. This can be especially severe in soilless cultures where the fungus can spread easily with the nutrient solution. 39Pythium isolates obtained from discolored roots were assayed for their ability to cause damping-off on cucumber seedlings in sand-peat and for their pathogenicity in soilless culture of cucumber in rockwool or hydroponic solution. Isolates ofPythium aphanidermatum, P. irregulare, P. sylvaticum andP. ultimum were highly pathogenic in sand-peat, but onlyP. aphanidermatum strains were pathogenic in soilless conditions and led to root decay, plant death in rockwool culture and growth reduction in hydroponic culture. One strain ofP. aphanidermatum significantly reduced the yield of cucumber grown in rockwool under conditions similar to those of commercial cultures.  相似文献   

9.
ABSTRACT The associations of Pythium oligandrum with the root cortex, rhizoplane, and rhizosphere were measured with 11 crop species. This work was expedited by the use of a semiselective technique for isolation of P. oligandrum from soil and plant material. Cortical colonization of roots by P. oligandrum was not detected, and the rhizoplanes of the roots of most crops were free of the fungus. However, P. oligandrum was detected in large quantities with every crop tested when roots with adhering soil (rhizosphere soil) were assayed. Different crop species and cultivars of cantaloupe, cauliflower, and tomato varied in rhizosphere densities of P. oligandrum, but rhizosphere population densities of the fungus were consistently higher than in nonrhizosphere soils with plants grown in P. oligandrum-infested sterilized potting mix or an unsterilized mineral soil. After transplanting tomatoes into potting mix infested with P. oligandrum, increases in CFU occurred over time in the rhizosphere but not in the nonrhizosphere soil. In trials on delivery methods of inoculum of P. oligandrum, the rhizosphere populations of tomato plants grown in potting mix were about sixfold higher compared to seed-coat treatments when ground, alginate pelleted oospores were applied to seedlings growing in plug containers prior to transplanting or to pots containing potting mix before direct seeding.  相似文献   

10.
This study was conducted in the Mediterranean environment of Central Italy from 2011 to 2013 with the aim of evaluating the effects of winter cover crops and their residues on weed composition in a cover crop‐tomato sequence. Treatments consisted of five soil managements (three cover crop species ‐ hairy vetch, phacelia, white mustard, winter fallow mulched with barley straw before tomato transplanting and conventionally tilled soil), two nitrogen fertilisation levels (0 and 100 kg N ha?1) and two weed management levels (weed free and weedy) on tomato. Cover crop residues were arranged in strips on the soil surface and then used as beds for transplanting the tomato seedlings in paired rows. Rotary hoeing was performed in the bare strips between paired tomato rows. At tomato harvesting, the weed aboveground biomass and density was higher in nitrogen‐fertilised tomato than unfertilised tomato, except in hairy vetch and barley straw that showed similar values. Hairy vetch used as a cover crop and dead mulch was the most suppressive species with the highest production of residues, while phacelia and mustard were not suitable for controlling weeds. The tomato yield was high in nitrogen fertilised and weed‐free treatments, except in barley straw mulch, which showed similar values among the weed management treatments. The mulch strips caused variations in weed species composition that was mainly composed of perennial ruderal weeds, while in tilled soil, the weed flora was dominated by annual photoblastic weeds.  相似文献   

11.
Howell CR 《Phytopathology》2002,92(2):177-180
ABSTRACT Planting the cotton cv. Sure-Grow 747 in cotton seedling disease plots during the 2001 growing season resulted in high levels of preemergence damping-off among the seedlings. Four cotton pathogens, Pythium aphanidermatum, P. ultimum, an unidentified Pythium sp., and Rhizopus oryzae, were isolated from diseased seed embryos and seedlings. Disease incited by the Pythium spp. could be controlled by seed treatment with Metalaxyl, but disease incited by R. oryzae could not. Seed treatment with Metalaxyl in naturally infested field soil was only partially effective; therefore, symptoms in 47% of the diseased seedlings could be attributed to R. oryzae. Susceptibility to disease appeared to be related to release in the spermosphere, by the germinating seeds, of compounds that stimulate pathogen propagule germination, because exudates from seed of the suscept Sure-Grow 747 and extracts from wheat bran induced pathogen germination and growth, whereas exudates from resistant cv. Stoneville 213 did not. However, even Stoneville 213 became susceptible when infested soil was amended with wheat bran. Seed treatment with preparations of Trichoderma virens parent, mutant, and hybrid strains gave effective biological control of preemergence damping-off. Disease control was attributable to metabolism by the biocontrol agent of pathogen germination stimulants released by the seed, because amendment of pathogen-infested soil with the propagule germination stimulants in wheat bran negated the protective effect of the seed treatment.  相似文献   

12.
ABSTRACT Factor(s) involved in soil suppressiveness to Thielaviopsis basicola when hairy vetch was used as a green manure were studied in a cotton production system. Soil suppressiveness was assessed in vitro at hairy vetch amendment levels of 0, 0.25, and 0.75% (wt/wt) by observing chlamydospores, using a nylon fabric technique. Chlamydospore germination in all soils was below 5%, and microscopic examination showed no germ tube lysis or visible propagule destruction. Viability (chlamydospore germination on T. basicola-carrot-etridiazol-nystatin [TB-CEN] medium) was reduced by 29% within 48 h after hairy vetch amendment. Viability also was reduced in atmospheres of amended soils, suggesting that the suppressiveness was due to a volatile factor. In a field study, chlamydospore viability in amended soils was reduced by 16%. T. basicola hyphal growth was more sensitive to ammonia than Rhizoctonia solani or Pythium ultimum, and chlamydospore mortality of T. basicola was 100% in petri dish atmospheres with 0.4 ppm of ammonia (50% lethal dose = 0.15 ppm). Soil atmospheric ammonia was 0.08 and 0.10 ppm for 0.25 and 0.75% amendment levels, respectively, both at 3 and 7 days after incorporation. In the field, 0.11 and 0.14 ppm of ammonia were detected in soil atmospheres 3 and 7 days after incorporation, respectively. The levels of ammonia detected were sufficient to account for the loss in T. basicola chlamydospore viability, indicating that ammonia is responsible for the suppressiveness observed.  相似文献   

13.
Choiromyces aboriginum Mü1w1c6是一株分离自芦苇的拮抗内生真菌。通过离体平板对峙培养检测和光学、电子显微镜观察,以及测定在活体植物上的拮抗活性,研究芦苇内生真菌Choiromyces aboriginum Mü1w1c6与病原菌及其寄主植物黄瓜之间的相互作用。对峙培养显示出较强的营养和空间竞争能力,对病原菌菌丝生长抑制率多高于60％,对立枯丝核菌Rhizoctonia solani的抑制率达到100%。显微观察证明它与多种病原菌有缠绕等重寄生现象。在互作研究中,C.aboriginum Mü1w1c6可成功定殖于黄瓜苗的根部,预先接种能有效抑制瓜果腐霉Pythium aphanidermatum在黄瓜根部组织细胞内的扩展和定殖,对P.aphanidermatum引起的黄瓜苗期猝倒病有良好的防效,接种一次内生菌防治效果为44.29%,接种两次生防效果高达88.49%。结果表明,C.aboriginum Mü1w1c6对多种植物病原真菌具有广谱的拮抗活性,对黄瓜苗期猝倒病具有较好的生防潜力。  相似文献   

14.
播前施用氟乐灵对棉花苗期病害及蕾期枯萎病的影响   总被引：2，自引：0，他引：2  
田间试验在棉花苗病和枯萎病常年发病田进行。以１７５ｍｌ４８％氟乐灵乳油／６６６．７ｍ＾２的剂量处理苗床地表土，播种棉籽后以含氟乐灵（１．０－１．５ｍｇ有效成分／ｋｇ土）的土壤覆盖。以清水处理为对照，。结果表明Ｌ氟乐灵处理组的出苗率高于对照，苗前残废对比照降低，５２．９１％－７９．８０％。处理组苗床期立枯病和侄蛱贩发病率及死苗率显著降低，分别下降３０％和４２％左右；棉苗枯萎病的发病率及病情指明显低于  相似文献   

15.
Trichoderma harzianum was applied to cucumber and pepper seedlings as a peat-bran preparation incorporated into the propagative mixture in a commercial production nursery. On marketing day (after 18 and 30 days for cucumber and pepper, respectively), significant increases of 23.8% and 17.2% in seedling height, 96.1% and 50% in leaf area, and 24.7% and 28.6% in plant dry weight were observed in cucumber and pepper seedlings, respectively, as compared to their non-treated counterparts.Trichoderma-treated seedlings were much more developed and vigorous and had higher chlorophyll contents. No significant differences were found in N, P or K content between treatments. Cucumber seedlings were then transplanted to a commercial greenhouse and analyzed over two successive growth cycles following soil fumigation with methyl bromide (500 kg/ha). Results revealed theTrichoderma-treated plants to be more resistant to damping-off disease. During the first cycle, immediately after soil fumigation, no damping-off was observed with either treatment, except in border beds where 4% of the non-treated plants died, as compared to no damping-off in theTrichoderma-treated plants. During the second growing cycle however, significant reductions in damping-off of 67% and 52% were obtained in middle and border beds, respectively, as compared to the non-treated controls.  相似文献   

16.
A preemergence damping-off of tobacco (Nicotiana tabacum L.) was found in Fukuoka, Japan, in 2009. A fungus repeatedly isolated from the black-rotted seeds reproduced the symptoms in tobacco seeds, and the preemergence damping-off developed after flower and soil inoculation with the fungus. Brown spots and blight developed on leaves of tobacco seedlings after inoculation with the isolate. The fungus was reisolated from the rotted seeds and blighted leaves. The causal fungus was identified as Stemphylium lycopersici based on morphology and phylogenetic analysis. This is the first report to confirm the pathogenicity of S. lycopersici in tobacco in the world.  相似文献   

17.
宁夏腐霉的初步研究   总被引：5，自引：0，他引：5  
 于1987-1989年分别自宁夏银川、永宁、固原、彭阳、肖铜峡等地采集腐霉标样201个,分离纯化到38个分离物,鉴定了其中的32个,得到Pythium aphanidermaturn、P.disso-tocum、P.spinosum、P.Kunmingense和P.ultimum 5种腐霉。致病性测定表明:5种腐霉对供试几种蔬菜出苗、幼苗生长及离体植物组织均有危害,其中以P.aphanidermatum的危害最大,其次是P.spinosum和P.ultimum。这是宁夏腐霉及其致病性的首次报道。  相似文献   

18.
生防菌枯草芽孢杆菌G3^str。菌株与营养添加剂混配使用，在经有机硫土壤熏蒸剂“大扫灭”熏蒸过的土中有一定的增殖，增殖量大于不熏蒸的自然土。同时，在加入菌剂的前6d，灭菌土中脂肽和伊枯草菌素检测量高于自然土。抑制水稻纹枯病菌菌核形成试验表明，G3^str菌增殖过的灭菌土比不增殖的对照有更强的抑菌作用。盆栽试验结果表明，土壤中添加G3^str。菌显著减轻由腐霉引起的茄子猝倒病，土壤熏蒸加强防病效果。  相似文献   

19.
ABSTRACT The capacity of the microflora in rockwool to suppress Pythium aphanidermatum, the causative agent of root and crown rot in cucumber, was assessed. Disease development of cucumber (Cucumis sativus) grown on rockwool was evaluated in an "ebb-and-flood" system with a recirculating nutrient solution after inoculation with P. aphanidermatum. In five independent experiments from 1995 to 1998, 11 batches of used rockwool were tested. All batches without P. aphanidermatum problems in the preceding cucumber crop had significantly lower numbers of diseased plants in nonautoclaved than in autoclaved used rockwool; the disease incidence was reduced by 52 to 100%. Suppressiveness also was present in rockwool previously used to grow other vegetable crops. Rockwool originating from a cucumber crop that was severely attacked by Pythium resulted in a high disease incidence. Previously unused (new) rockwool had higher or similar percentages of diseased plants than did nonsterilized used rockwool. Disease suppression in used rockwool could also be measured in a smaller test system. In both systems, autoclaved rockwool became suppressive to Pythium after recolonization with the indigenous microflora. Population sizes of total culturable aerobic bacteria as well as of fluorescent pseudomonads did not correlate with disease suppressiveness, as numbers of bacteria and pseudomonads were similar or lower in nonautoclaved (suppressive) than in autoclaved (nonsuppressive) rockwool. Differences in the structure of the bacterial populations could be visualized by using eubacterial polymerase chain reaction (PCR) followed by denaturing gradient gel electrophoresis (DGGE). Interestingly, the nonautoclaved and the recolonized used rockwool, which were both suppressive, showed different dominating bacterial groups as compared with the autoclaved rockwool. PCR-DGGE patterns obtained at different sampling times showed that the composition of the bacterial populations changed during plant growth. Fungal populations were present in the treatments that yielded suppressive rockwool, i.e., the nonautoclaved and the recolonized rockwool, but they were absent or present in low numbers in the autoclaved rockwool, which permitted a high disease incidence. Suppressiveness of rockwool to Pythium root and crown rot is a hitherto undescribed phenomenon, and knowledge of the mechanism and microorganisms involved will stimulate the development of microbially balanced soilless growing systems.  相似文献   

20.
An isolate of Trichoderma viride from the surface of an apparently healthy tomato root was found to be pathogenic to seedlings of cucumber, pepper and tomato in laboratory and greenhouse experiments. In laboratory experiments, when seeds of each host species were inoculated with conidia of the pathogen, the subsequent growth of seedlings was decreased and they developed light-brown water-soaked lesions on their roots and crowns. The pathogen could be re-isolated from lesions on the seedlings, and microscopic examination of inoculated seedlings demonstrated that the fungus invaded the vascular tissues of the young seedlings. Culture filtrates of T. viride were found to contain a heat-stable factor that caused a decrease in the growth of the roots of young cucumber, pepper and tomato seedlings. In greenhouse experiments, the fungus did not affect germination or seedling fresh weight of young cucumber seedlings in soil- peat- or rockwool-based germinating media, but 10% of seedlings germinated in rockwool showed signs of infection. This is the first report of T. viride being pathogenic on pepper and tomato.  相似文献   

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