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1.
Colonization of Vibrio pelagius and Aeromonas caviae in early developing turbot (Scophthalmus maximus L.) larvae 总被引:2,自引:1,他引:1
Polyclonal antisera made in rabbits against whole washed cells of Vibrio pelagius and Aeromonas caviae were used for detection of these bacterial species in the rearing water and gastrointestinal tract of healthy turbot ( Scophthalmus maximus ) larvae exposed to V. pelagius and/or Aer. caviae . The results demonstrated that this method is suitable for detection of V. pelagius and Aer. caviae in water samples and larvae at population levels higher than 103 ml−1 and 103 larva−1 . Populations of aerobic heterotrophic bacteria present in the gastrointestinal tract of turbot larvae, estimated using the dilution plate technique, increased from approximately 4 × 102 bacteria larva−1 on day 3 post-hatching to approximately 105 bacteria fish−1 16 days post-hatching. Sixteen days after hatching, Vibrio spp. accounted for approximately 3 × 104 cfu larva−1 exposed to V. pelagius on days 2, 5 and 8 post-hatching. However, only 103 of the Vibrio spp. belonged to V. pelagius . When larvae were exposed to Aer. caviae on day 2 post-hatching, the gut microbiota of 5-day old larvae was mainly colonized by Aeromonas spp. (104 larva−1 ), of which 9 × 103 belonged to Aer. caviae . Later in the experiment, at the time when high mortality occurred, 9 × 105 Aer. caviae were detected. Introduction of V. pelagius to the rearing water seemed to improve larval survival compared with fish exposed to Aer. caviae and with the control group. It was therefore concluded that it is beneficial with regard to larval survival to introduce bacteria ( V. pelagius ) to the rearing water. 相似文献
2.
Abstract There was a progressive increase in the size of the aerobic heterotrophic bacterial populations along the gastro-intestinal tract of farmed Dover sole. Moreover, higher counts were recorded in juvenile than in adult animals. Thus, in juvenile fish, 5.2 × 105 , 8.0 × 105 and 9.8 × 106 aerobic heterotrophs/g were recovered from the stomach/foregut, midgut and hindgut/rectum, respectively. In adult fish, comparative samples revealed the presence of only 3.0 × 104 , 7.0 × 104 and 2.3 × 105 bacteria/g, respectively. There bacteria were equated with Acinetobacter, Alcaligenes , Enterobacteriaceae representatives, Flavobacterium, Micrococcus, Photobacterium, Staphylococcus and Vibrio . Of the compounds tested, many isolates, particularly those recovered from the hindgut/rectum, degraded p -nitrophenyl- β - N -acetylglucosaminide, chitin and collagen. Consequently, it is likely that such organisms may contribute to nutritional processes within Dover sole. 相似文献
3.
Abstract: The feeding of the marine ciliate Euplotes mutabilis was studied using bacteria ( Vibrio natriegens ) doubly labelled with 3 H-thymidine and 14 C-leucine. In the presence of abundant bacteria (30 × 106 bacteria ml−1 ), an average Euplotes cell (initially without food vacuoles) with a protein content of 12 ng consumed 16 × 103 bacteria in the first hour and 27 × 103 bacteria over four hours, accumulating about 60% of the bacterial protein into ciliate macromolecules. Euplotes which had been starved or under-fed to reduce cell protein biomass to 7 or 9 ng consumed significantly fewer bacteria, but the gross growth efficiency for protein did not change. The rate of consumption of bacteria by large Euplotes of protein content 15 ng was initially less than that of 12 ng cells, and it decreased markedly before the end of a 4-hour experiment. Recently divided cells ingested bacteria rapidly, but showed a reduced gross growth efficiency of about 40%. At low bacterial concentrations (6 × 106 bacteria ml−1 ) the rates of ingestion were markedly reduced to between and of maximal levels; the smallest cells could not sustain feeding activity at the low prey concentration and gross growth efficiency fell from 43 to 20% during a 4-hour experiment. The strategy adopted by Euplotes in response to local fluctuations in food supply involves rapid consumption with high growth efficiency in times of plenty, but slow shrinkage without cell division to survive in times of shortage. 相似文献
4.
OBSERVATIONS ON THE MICROFLORA OF MINCED CHICKEN MEAT IRRADIATED WITH 4 MeV CATHODE RAYS 总被引:4,自引:3,他引:1
MARGARET J. THORNLEY 《Journal of applied microbiology》1957,20(2):286-298
SUMMARY: Experiments are described in which minced chicken meat, packed anaerobically, was irradiated at room temperature and in the frozen state with a wide range of doses of 4 MeV cathode rays. Sterility was achieved in 14 out of 15 samples which had received 2 × 106 rads or more. Doses of 0·5 and 1·0 × 106 rads allowed survival of a few bacteria/g, usually spore formers. Bacterial counts indicated an approximately logarithmic decrease in numbers at lower doses, while freezing reduced the bactericidal effect.
The storage life at 5° was prolonged only slightly by doses of 5 × 104 and 10 × 104 rads, and highly variable results were obtained with 17·5 × 104 rads. A dose of 25 × 104 rads, however, increased the storage life very considerably. The types of bacteria present initially, and after irradiation with low doses and storage at 5°, were studied. After storage for 12 days or more various types of nonsporing Gram-positive rods were predominant in almost all samples, both control and irradiated. Streptococci were also important where irradiation with 17·5 × 104 and 25 × 104 rads was followed by long storage. 相似文献
The storage life at 5° was prolonged only slightly by doses of 5 × 10
5.
SUMMARY 1. Temporary ponds are inhabited by a variety of invertebrates, of which anostracans are an important group. We studied the lifetables of male and female anostracan Streptocephalus mackini at 3 algal concentrations (0.5 × 106 , 1.0 × 106 and 1.5 × 106 cells mL−1 ).
2. Regardless of sex, S. mackini showed better survivorship at lower food levels. The longest average lifespan observed was 85 ± 2 days for males fed Chlorella at 0.5 × 106 cells mL−1 .
3. Both net reproductive rate and generation time decreased with increasing food level. The highest net reproductive rate was about 120 cysts per female. The longest generation time of about 40 days, observed at 0.5 × 106 cells mL−1 , was more than three times that at 1.5 × 106 cells mL−1 .
4. The rate of population increase ( r ) was nearly the same (0.31 ± 0.06) at high (1.5 × 106 cells mL−1 ) and intermediate (1.0 × 106 cells mL−1 ) food levels. The r -value at low food level (0.5 × 106 cells mL−1 of Chlorella ) was 0.20 ± 0.01 per day. 相似文献
2. Regardless of sex, S. mackini showed better survivorship at lower food levels. The longest average lifespan observed was 85 ± 2 days for males fed Chlorella at 0.5 × 10
3. Both net reproductive rate and generation time decreased with increasing food level. The highest net reproductive rate was about 120 cysts per female. The longest generation time of about 40 days, observed at 0.5 × 10
4. The rate of population increase ( r ) was nearly the same (0.31 ± 0.06) at high (1.5 × 10
6.
ABSTRACT. Various doses of a microsporan parasite, Nosema sp., were fed to third and fourth instar larvae of Lesioderma sericorne that infested different types of stored grains. A spore dose of 3 × 103 spores/individual resulted in a 39% infection rate, reduction in larval and adult weights, and mean spore concentrations of 1.28 ± 0.2 × 108 spores/larva and 1.1 ± 0.2 × 108 spores/adult. At the above dose, mortality was not well marked (about 35% in larvae and 25% in adults). At 3 × 104 spores/individual, the rate of mortality increases to 80% in larvae and 60% in adults. However, more of the pest population (88% of larvae and 73% of adults) died at a dose of 3 × 105 spores/individual. This dose produced mean spore concentrations of 3.91 ± 0.2 × 108 spores/larva and 2.89 ± 0.2 × 108 spores/adult. Insect death was caused by heavy damage to gut epithelia and fat bodies. 相似文献
7.
DIRECT DETECTION OF ESCHERICHIA COLI 0157:H7 IN UNPASTEURIZED APPLE JUICE WITH AN EVANESCENT WAVE BIOSENSOR 总被引:1,自引:1,他引:0
DANIEL R. DeMARCO DANIEL V. LIM 《Journal of Rapid Methods and Automation in Microbiology》2001,9(4):241-257
An evanescent wave biosensor was used to detect Escherichia coli O157:H7 in unpasteurized apple juice. Light is launched from a 635 nm laser diode into silica or polystyrene optical waveguides, generating an evanescent field which extends from the waveguide surface. Fluorescent molecules within the evanescent field are excited resulting in an emission signal that the biosensor then detects and quantifies. A sandwich immunoassay was performed on the waveguides using cyanine 5 dye-labeled anti-E. coli O157:H7 antibodies for generation of the specific fluorescent signal. The lower limit of detection was between 6.0 × 102 and 6.0 × 104 CFU/mL with silica waveguides and between 3.2 × 104 and 3.2 × 104 CFU/mL using polystyrene waveguides. One-hundred percent correct identification of true positive samples occurred at 6.0 × 104 and 3.2 × 104 CFU/mL for silica and polystyrene waveguides, respectively. Signals from a variety of non-E. coli O157 bacteria, including closely related enterotoxigenic strains of E. coli at concentrations of ˜ 106 CFU/mL, were below the limits of detection. Assays were conducted in near real-time with results obtained within 15 min of sample processing. 相似文献
8.
Gari was examined for its post-processing microbial content. Aerobic mesophilic bacteria and fungi were isolated from all samples. The total viable bacterial counts ranged from 2.0 × 102 to 8.0 × 104 cfu/g. Fungal counts ranged from 1.0 × 102 to 1.5 × 104 cfu/g. The total viable counts of fresh samples were much lower than those of market and packaged samples. Bacillus, Micrococcus and Proteus spp. were the bacteria isolated, Aspergillus niger, Aspergillus flavus and Penicillium spp. the fungi. Food borne parasites and pathogens such as Staph. aureus and Clostridium perfringens were not found. The gari samples were quite stable, having a shelf life of 3–6 months. The water activities of the samples ranged from 0.52 to 0.68. Based on the microbial counts of the samples, the critical upper limit for the safety of gari was set at 104 cfu/g dry sample. 相似文献
9.
Random mutagenesis of Legionella pneumophila with mini-Tn10 总被引:5,自引:0,他引:5
Abstract The degradation of sheets of poly(3-hydroxybutyrate- co -3-hydroxyvalerate) (BIOPOL® ) by aerobic sewage sludge was analyzed. Degradation of the polymer was highly dependent on the pH of the culture medium and was maximal between pH 7 and pH 8.5. Below pH 6 and above pH 9 the degradation rate was very low. Agitation of the culture fluid had relatively little influence on the rates of degradation. 1.2×105 aerobic polymer-degrading bacteria per ml sewage sludge were identified by halo formation on solid poly(3-hydroxybutyrate) (PHB)-containing media. The number of PHB-degrading bacteria in other ecosystems amounted to 3.8×103 per ml sludge of a fresh-water lake, 9.2×105 per g garden-soil, 1.3×106 per g field-soil and 4.3×106 per g compost. 相似文献
10.
SYNOPSIS. Euplotes vannus , a hypotrich ciliate. grows well over broad ranges of temperature and salinity. It requires higher densities of food (> 1 × 104 cells/ml) for rapid reproduction than do the other herbivores, the foraminiferan Al-logromia laticollaris (> 1 × 102 cells/ml), and the nematode Chromadorina germanica (∼ 1 × 103 cells/ml), to which it was compared. If food levels were initially very high (∼ 1 × 108 cells/ml) the ciliates reproduced rapidly and consumed the algae faster than it could reproduce. Some balance between the algae and the ciliates was achieved at initial algal concentrations of ∼ 1 × 105 cells/ml. In microcosm experiments at 25 C with equal numbers of C. germanica and A. laticollaris. E. vannus proved to be a very poor competitor; reaching only 20% of control levels when grow with C. germanica and only 13% when cultured with A. laticollaris . It was a better competitor in 2-species microcosms, at lower temperatures, and when its ratio to the other species was initially higher.
The experimental evidence suggests that E. vannus is best adapted to being a migrating initial colonizer of fresh algal blooms. 相似文献
The experimental evidence suggests that E. vannus is best adapted to being a migrating initial colonizer of fresh algal blooms. 相似文献
11.
Peat from three sources was dried, milled and packed separately in polyethylene bags and sterilized by irradiation. The carrier was impregnated with broth cultures of either Rhizobium leguminosarum bv. trifolii strain WU95, Bradyrhizobium japonicum strain CB1809 or B. lupini strain WU425 and sterile water to provide five moisture potentials in the range > - 1 × 104 - 1 × 106 Pa. The packets were stored at 26°C under conditions which restricted moisture loss. Numbers of root nodule bacteria were counted at intervals up to 12 weeks. No single moisture potential was optimum for all strains in all carriers because of a significant ( P < 0.05) interaction between moisture potential × strain × carrier × time. Where direct comparisons could be made, all strains survived best at - 1 × 104 and/or −3.2 × 104 Pa. Seeds of Trifolium subterraneum and polypropylene beads (used to avoid seed coat toxicity), were inoculated with WU95 prepared in two sources of peat and at each of the above moisture potentials and stored at 15°C. Seed coat toxicity significantly effected the log death rate ( k ) of WU95 on subterraneum clover seed for the period 0–0.25 d ( k 1.796) compared with k - 0.399 for polypropylene beads. In the first 24 h moisture did not affect survival but by 28 d rhizobia grown in Badenoch peat survived best at −3.2 × 104 Pa. In Millicent peat, survival was equally as good at −3.2 × 104 and −1 × 104 Pa. 相似文献
12.
Katrin Wendt-Potthoff Horst Backhaus Kornelia Smalla 《FEMS microbiology ecology》1994,15(3-4):279-290
Abstract The fate of a Bacillus amyloliquefaciens with the recombinant plasmid pSB20 sprayed on the phyllosphere of grass, and of a Tn 5 marked Pseudomonas syringae sprayed on the phyllosphere of bush beans was studied in planted soil microcosms. B. amyloliquefaciens showed a decline from 1.5×108 to 3.1×102 cfu g−1 on the phylloplane of grass in the course of the experiment. B. amyloliquefaciens was easy to follow by selective cultivation due to the complete absence of bacterial background growth. Southern blot hybridization of Hin dIII digested genomic DNA showed plasmid restriction patterns identical with pSB20 indicating high plasmid stability. In total DNA extracts from phyllosphere bacteria the recombinant plasmid was detectable by Southern blot hybridization up to 6×104 cfu g−1 (wet weight). Counts of hybridizing colonies showed that P. syringae established on the phyllosphere of bush beans at between 5×103 and 4×106 cfu g−1 fresh weight. During senescence of the bean plants the strain was no longer detectable by selective cultivation and subsequent colony hybridization. In contrast, Tn5 marked DNA was detected after PCR amplification over the whole period of the experiment. 相似文献
13.
Impact of biological activity on detritus transported in the lower river Rhine: an exercise in ecosystem analysis 总被引:4,自引:0,他引:4
SUMMARY. 1. Published data are used to construct a tentative carbon budget for the ecosystem of the lower river Rhine and its sedimentation areas in The Netherlands.
2. It is estimated that 287 × 106 kg Cy−1 of particulate organic material is transported by the river Rhine, and 100 × 106 kgCy−1 of this material is deposited in the delta.
3. Phytoplankton and nitrifying bacteria seem to contribute significantly to the carbon budget, by producing c. 78 × 106 kgCy−l .
4. The mineralization in the water (estimated from routine determinations of biological oxygen demand and from in situ diurnal fluctuations of oxygen) and in the bottom (estimated from the denitrification rates in the delta, from the production rate of methane and from overall oxygen consumption) is shown to degrade c. 50% of the carbon input plus autochthonous production.
5. The carbon budget and oxygen regime in the lower Rhine suggest that after decades of severe organic pollution the river has more or less resumed the normal, slightly heterotrophic state of a large lowland river. 相似文献
2. It is estimated that 287 × 10
3. Phytoplankton and nitrifying bacteria seem to contribute significantly to the carbon budget, by producing c. 78 × 10
4. The mineralization in the water (estimated from routine determinations of biological oxygen demand and from in situ diurnal fluctuations of oxygen) and in the bottom (estimated from the denitrification rates in the delta, from the production rate of methane and from overall oxygen consumption) is shown to degrade c. 50% of the carbon input plus autochthonous production.
5. The carbon budget and oxygen regime in the lower Rhine suggest that after decades of severe organic pollution the river has more or less resumed the normal, slightly heterotrophic state of a large lowland river. 相似文献
14.
Abstract The distribution of heterotrophic bacteria in polluted coastal and unpolluted pelagic seawaters was studied using a 14 C-MPN method with either five of seven kinds of 14 C-organic compounds as substrates. The total number of heterotrophic bacteria in pelagic waters ranged from 9.2 × 103 to 5.4. ¢ 104 cell/ml and more than 85% of the heterotrophic bacteria were represented by obligate oligotrophs. In coastal waters, the number of heterotrophs was one order of magnitude higher (av. 3.5 ¢ 105 cells/ml), and eutrophic and facultatively oligotrophic bacteria were predominant. Oligotrophs in pelagic waters had a high specificity for the utilization of amino acids, especially glycine, and acetate-utilizing bacteria were scarce. The in situ maximum uptake rates of glutamate and glycine were much higher than those of glycolate and acetate. Acetate uptake rates were extremely low or not detectable in pelagic waters. The specificity of uptake kinetics is assumed to depend on the existence of obligate oligotrophs as dominant bacteria in pelagic seawater. 相似文献
15.
The distribution of some freshwater planktonic bacteria in two stratified eutrophic lakes 总被引:6,自引:0,他引:6
J. G. JONES 《Freshwater Biology》1978,8(2):127-140
SUMMARY. Changes in bacterial populations and certain physical and chemical variables in Esthwaite Water between June and September 1975 were studied and compared with results obtained from 1972 to 1974 in the hypolimnia of Blelham Tarn and the Lund tubes. The counts of total bacteria ranged between 1 and 7 × 106 ml−1 and were highest in the anoxic hypolimnion. The bacterial genera examined in more detail constituted only a small percentage of this count and included Ochrobium (104 ml−1 ), Naumanniella (103 ml−1 ), Leptothrix (102 ml−1 ), Planctomyces (103 ml−1 ), and Metallogenium (102 ml−1 ). The iron bacteria appear to grow best in the oxycline where there was not only sufficient oxygen for aerobic growth but also a plentiful supply of reduced iron. Planctomyces numbers increased as the thermocline became depressed in September. The results from Blelham Tarn might be interpreted as further evidence of growth by iron bacteria in the absence of dissolved oxygen, but other explanations are possible. Examination of the results by multiple regression analysis showed that it was possible to explain a significant proportion of the bacterial variation (with the notable exception of the Planctomyces counts) in spite of considerable intercorrelation of the regressor variables. 相似文献
16.
Quantification of pathogenic micro-organisms in the sludge from treated hospital wastewater 总被引:1,自引:1,他引:0
The sludge from hospital waste treatment facilities is a potential source of infectious organisms. The average numbers of micro-organisms in the sludge of hospital wastewater in Taiwan were as follows: total count 8·1 × 107 cfu g−1 (dry weight of sludge), and 1·4 × 106 , 3·6 × 105 , 1·6 × 105 , 2·2 × 105 and 5·5 × 104 cfu g−1 (dry weight of sludge) for total coliforms, faecal coliforms, faecal streptococci, Pseudomonas aeruginosa and Salmonella spp., respectively . Salmonella spp. were detected in 37% (10 of 27) of the sludges from hospital wastewaters. Therefore, the treatment of such sludge to reduce pathogenic micro-organisms should be considered. 相似文献
17.
Abstract The sulfur cycle in a microbial mat was studied by determining viable counts of sulfate-reducing bacteria, chemolithoautotrophic sulfur bacteria and anoxygenic phototrophic bacteria. All three functional groups of sulfur bacteria revealed a maximum population density in the uppermost 5 mm of the mat: 1.1 × 108 cells of sulfate reducers cm−3 sediment, 2.0 × 109 cells of chemolithoautotrophs cm−3 sediment, and 4.0 × 107 cells of anoxygenic phototrophs cm−3 sediment. Bacterial dynamics were studied by sulfate reduction rate measurements, both under anoxic conditions (dark incubation) and oxic conditions (incubation in the light), and determination of the vertical distribution of the potential rate of thiosulfate consumption under oxic conditions. Sulfate reduction rates in the top 5 mm of the sediment were 566 nmol cm−3 d−1 in the absence of oxygen, and 123 nmol cm−3 d−1 in the presence of oxygen. In the latter case, the maximum rate was found in the 5–10-mm depth horizon (361 nmol cm−3 d−1 ). Biological consumption of amended thiosulfate was rapid and decreased with depth, while in the presence of molybdate, thiosulfate consumption decreased to 10–30% of the original rate. 相似文献
18.
Kamtin Leung Michael B. Cassidy Steve B. Holmes Hung Lee Jack T. Trevors 《FEMS microbiology ecology》1995,16(1):71-82
Abstract A method was developed for direct extraction, purification and amplification of DNA from forest soil. Eighty-two % of the DNA in Pseudomonas aeruginosa UG2Lr introduced into soil was recovered. The detection limit for the strain was approximately 800 cfu g−1 of dry soil based on the polymerase chain reaction (PCR). Survival of κ-carrageenan-encapsulated and unencapsulated UG2Lr was monitored by antibiotic selective and bioluminescence-based nonselective plating and PCR-amplification of a tnsA fragment. After freeze-thaw treatment of soil samples, the unencapsulated UG2Lr declined from an initial population density of 1 × 109 cfu g−1 of dry soil to below the detection threshold of both selective (14 cfu g−1 of dry soil) and nonselective (1 × 103 cfu g−1 of dry soil) plating. However, presence of nonculturable UG2Lr cells in the soil was revealed by PCR and resuscitation of the bacteria. Population density of the encapsulated UG2Lr increased from 2.7 × 106 to 2.9 × 108 cfu g−1 of dry soil after a 3-week incubation at 22°C and declined to 6.3 × 106 cfu g−1 of dry soil after the freeze-thaw treatment. 相似文献
19.
Abstract: The rates of ingestion of bacteria and of accumulation of bacterial biomass by hungry Pteridomonas danica and Paraphysomonas imperforata were measured using dual radioactive-labelled bacteria in experiments lasting 4–8 h. Pteridomonas continuously consumed 4–5 bacteria h−1 throughout experiments lasting 8 h, irrespective of bacterial concentration above a threshold of about 5 × 105 bacteria ml−1 , and continued to catch bacteria even below this density. The clearance rate of about 1 nl cell−1 h−1 at higher bacterial concentrations increased three or four times as bacterial numbers fell. Paraphysomonas cells, with only half the biomass of Pteridomonas , ingested up to 10 bacteria h−1 at high bacterial concentrations, and gradually reduced the feeding rate, effectively ceasing to feed at 106 bacteria ml−1 ; their initial clearance rate of 1–2.5 nl cell−1 h−1 subsequently fell as low as 0.1 nl cell−1 h−1 . Estimation of feeding rate by extrapolation from short-term experiments on such flagellates requires extreme caution. These flagellates, starved to levels typical of the natural environment, accumulated ingested bacterial biomass at an efficiency of between 16 and 21%, indicating that in nature they would recycle 80% or more of the nutrients contained in their food. 相似文献
20.
Yuan Li Daniela Minerdi Angelo Garibaldi Maria Lodovica Gullino 《Journal of Phytopathology》2009,157(7-8):438-445
In this work, a protocol for zoospores production of Phytophthora cryptogea , an economically important plant pathogen was optimized. Five different concentrations of zoospores (5 × 105 , 5 × 104 , 5 × 103 , 5 × 102 , 5 × 101 zoospores/ml) from four different isolates of P. cryptogea (Maria 1, Maria 2, S3 1-A, Amazzone) were used as inoculum on pot marigold ( Calendula officinalis ) and gerbera ( Gerbera jamesonii ) plants. Maria 1 was the most virulent isolate both on pot marigold and gerbera plants according to disease severity. A rapid and sensitive pathogen DNA extraction protocol suitable for large quantities of plant samples was adopted. Conventional polymerase chain reaction (PCR) was able to detect the pathogen in artificially inoculated symptomless pot marigold (collected day 12) and gerbera plants (day 8) after pathogen inoculation, with the suspension of 5 × 105 , 5 × 104 , 5 × 103 P. cryptogea zoospores/ml. Real-time PCR showed the possibility to detect the pathogen in artificially inoculated symptomless pot marigold (collected day 8) and gerbera plants (day 4) after pathogen inoculation, with the suspension of 5 × 105 , 5 × 104 P. cryptogea zoospores/ml. The first symptoms appeared on pot marigold plants 14 days after pathogen inoculation and on gerbera plants 10 days after inoculation. Real-time PCR showed the possibility to detect the pathogen 4 days before conventional PCR and 6 days before the appearance of disease symptoms both on pot marigold and gerbera plants. 相似文献