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1.
During the winters of 1977/78 and 1978/79 tubers of cv. Arran Banner naturally contaminated with Phoma exigua var, foveata were kept at either high or low humidity and at 5, 10, 15 or 20 C. During the 1978/79 winter cv. Majestic tubers were stored under similar conditions at 5 and 10°C only. At monthly intervals tubers from each lot were damaged to encourage gangrene development and returned to their storage condition except the Majestic tubers which were switched from high to low humidity or vice versa and returned to the appropriate temperature. No gangrene rots developed in tubers kept at 1 5 or 20°C at either humidity. At 5 and 10°C fewer rots developed at high humidity compared with low humidity including Majestic tubers kept Initially at high humidity. Inoculum levels in soil on tubers were not markedly affected by storage conditions.  相似文献   

2.
The susceptibility of tubers of different potato cultivars to soft rot by Erwinia carotovora subspp. uroseptica and carotovora was assessed in 3 years by two methods. In one method, whole tubers inoculated at wounds with either bacterium were incubated under anaerobic conditions for 5 or o days at 15°C. In the other method, wounds made in tuber slices were allowed to heal or not, before inoculation with different concentrations of each bacterium and were then incubated under aerobic conditions for 3 days at 15°C. Most cultivars gave consistent reactions in repeated experiments using the same method, but there was some seasonal variation. A few cultivars were consistently susceptible (Klondyke and Manna) or resistant (Drayton) in both methods but others gave completely contrasting results (Record). In both methods and with all cultivars more rotting was caused by subsp. atroseptica than by subsp. carotovora because of the temperature of Incubation.  相似文献   

3.
Potato mop-top virus (PMTV) causes disease in both the growing plant and tubers (spraing) of potato and is transmitted by the plasmodiophorid Spongospora subterranea , the cause of powdery scab. The effect of temperature during plant growth on the transmission of PMTV from infected seed tubers and from infested growing media was investigated in a series of glasshouse experiments. Symptoms developed on foliage of plants derived from infected seed tubers but none developed when PMTV was transmitted by S. subterranea in soil. The incidence of foliar symptoms was greatest on plants grown at 12°C, less at 16°C, few at 20°C and absent at 24°C. The transmission of PMTV from infected seed tubers was not significantly affected by temperatures between 12 and 24°C, but when the virus was transmitted by S. subterranea , minimal tuber infection occurred at 24°C and no differences were recorded at temperatures between 12 and 20°C. The incidence of powdery scab on tubers was greatest at 12 and 16°C and very low at 20 and 24°C. However, the incidence and severity of root galling caused by S. subterranea , was greatest at 20 and very low at 24°C. The incidence of powdery scab was greater on tubers of plants derived from infected seed tubers grown in a fluctuating temperature regime of 12 h at 20°C followed by 24 h at 12°C than on those grown at a constant 20°C, whereas the incidence of tuber infection by PMTV and spraing was similar for both regimes. This demonstrates that infection of roots can occur at a higher temperature than that for powdery scab on tubers and that this root infection can enable the transmission of PMTV into the potato plant.  相似文献   

4.
Fusarium species obtained from stored potato tubers affected with dry rot were grown on agar containing thiabendazole. All 40 isolates of F. coeruleum and 60 isolates of F. avenaceum tested were sensitive to the fungicide, but 68% of the 85 isolates of F. sulphureum and one isolate of F. culmorum were classified as resistant. When isolates were made from dry rots on tubers that had been treated with thiabendazole during loading into store, all 81 isolates of F. sulphureum were resistant, whereas all the isolates of F. coeruleum (25), F. avenaceum (4) and Phoma foveata (10) were sensitive. Resistance was not found in five isolates of Cylindrocarpon destructans. All the Fusarium spp. were sensitive to imazalil and were pathogenic when inoculated into potato tubers. Resistant and sensitive isolates of F. sulphureum caused rots of similar size.  相似文献   

5.
Botrytis allii colonies incubated at low temperatures have been reported to produce larger conidia that germinate faster and give rise to longer germ-tubes than those grown at room temperature. The present study compared the effect of conidia produced at 20°C and at 0 and –2°C on their pathogenicity to artificially inoculated white onion bulbs, and the effect of conidial concentration (5×103 and 5×104 conidia/mL) on disease incidence, lesion area, incubation and latent period during storage at 20, 5 and 0°C. At all storage temperatures and periods tested conidia produced at −2°C caused a higher disease incidence and larger areas of rot than those produced at higher temperatures. When the conidial production temperature was raised to 20°C, the duration of incubation on the bulbs inoculated with 5×104 conidia/mL was more than doubled during storage at 0°C, tripled at 5°C, and took 50% longer at 20°C. The incubation period was not significantly affected by conidial concentration at 20°C, and only slightly at 5 and 0°C, but at low temperatures the latent period was longer because of the delay induced in sporulation. These data are consistent with the packers' opinion that cross-infection of spring onions by long-term refrigerated onions in grading lines caused earlier and heavier rotting.  相似文献   

6.
Summary. The effects of all combinations of five desiccation treatments, two temperatures and three durations of desiccation on the survival of Cyperus esculentus tubers and two-node Cynodon dactylon rhizome fragments were examined in laboratory and glasshouse experiments.
Cyperus esculentus tuber survival was greater at 22°C than at 4°C. Duration of desiccation did not influence tuber survival, except at the lower temperature.
Survival of Cynodon dactylon rhizome fragments was greatly influenced by desiccation treatment, duration of desiccation and the interaction of these two factors. No buds survived when rhizomes reached 50% of their original weight, indicating good tolerance of desiccation since the original dry-matter content of rhizomes in this experiment was 41·2%.  相似文献   

7.
To investigate the ability of black dot symptoms to develop on infected potato tubers during storage, the growth of Colletotrichum coccodes was followed in vitro on malt agar at temperatures ranging from 5–27°C, and in vivo on artificially infected potato tubers kept at 5, 10 and 15°C. In vitro , 13 isolates from different geographical origins grew at all temperatures tested; growth started with a delay of 10 days at 5°C and of 4 days at 10°C, and was fastest at 27°C. All isolates had similar growth patterns and produced conidia and sclerotia at all temperatures. Minitubers were successfully infected at 5, 10 and 15°C by depositing either a mycelial plug or a drop of conidial suspension on the tuber surface. Sclerotia were observed after 7 days at the point of inoculation. Symptoms extended in all cases, although more slowly at 5 and 10 than at 15°C. Latent infections were detected in up to 21% of tubers without black dot symptoms at harvest. These results show that latent infections by C. coccodes are probably quite frequent, and that the pathogen is able to develop at low temperatures in controlled conditions. This suggests that black dot symptoms can increase during storage if stores are not adequately managed.  相似文献   

8.
Purple nutsedge ( Cyperus rotundus L.) tubers remain viable for several years and serve as its principal means of survival. The maintenance of high moisture content is essential to tuber survival. Apical dominance influences bud dormancy within a tuber and in a chain of tubers, and dormancy increases with tuber age. Several growth inhibitors were identified in tubers, but their role in tuber dormancy has not been established. Moisture levels in soil must increase to a critical level before sprouting occurs, but excess soil moisture deters sprouting. Oxygen may be a limiting factor for tuber sprouting in waterlogged soils. Although light is not a requirement for sprouting, it has promoted sprouting. Temperature regulates sprouting; no sprouting occured below 10°C and above 45°C. Optimum sprouting occurred between 25 and 35°C when provided with constant temperatures. However, daily alternating temperatures greatly stimulated sprouting. A daily short duration (0.5 h) of high temperature increased sprouting to nearly 100%, whereas less than 50% sprouting occurred without the daily high temperature pulse. Bud break occurred readily for most tubers at 20°C and in nearly 100% of the tubers with a single 0.5 h exposure to a high temperature (35°C) pulse. However, most buds did not elongate if the tuber remained at 20°C. Bud elongation occurred at higher temperatures, and daily alternating temperatures stimulated shoot elongation up to eightfold greater than at the respective mean constant temperatures. Daily soil temperature fluctuation may be a major signal for purple nutsedge emergence, such as when the plant canopy is removed, or when soils are solarized. Future research is needed to determine tuber sprouting for different ecotypes, and on the role of the rhizome chain. Systems to manipulate sprouting may provide new strategies for purple nutsedge management.  相似文献   

9.
In 1999, New Zealand carrots ( Daucus carota ) exported to the Middle East incurred substantial damage due to bacterial soft rot that resulted in major financial loss to farmers. A modified carrot tissue bioassay was developed under standard conditions to provide an economical and rapid means of monitoring export carrots for bacteria able to cause severe bacterial soft rot. Using this bioassay, two bacterial isolates causing severe degradation were detected and subsequently identified as Pseudomonas viridiflava (designated NZCX09) and P. marginalis (NZCX27), using the Biolog system and 16S rRNA phylogenetic analysis. Investigation of disease epidemiology of NZCX09 and NZCX27 at low temperatures showed that tissue degradation occurred at temperatures approaching 0°C. These findings emphasize the importance of postharvest sanitization, and the efficacy of refrigeration methods used in controlling soft rots in carrots stored over time.  相似文献   

10.
A time-saving and cost-effective polymerase chain reaction (PCR)-based method was developed for species-specific detection of the scab pathogens ( Streptomyces scabies and S. turgidiscabies ) prevalent in potato ( Solanum tuberosum ) in northern Scandinavia. Species specificity of primers was verified using a collection of previously characterized Streptomyces strains isolated from potato scab lesions in Finland and Sweden. A total of 1245 scab lesions was tested from potato cvs Matilda and Sabina grown in the field in two geographic regions of Finland in 2000 and 2001. Freshly harvested or stored potato tubers were incubated at room temperature (18–21°C) under humid conditions for a few days. Bacterial growth was collected from scab lesions for DNA isolation and PCR. The two scab pathogens were detected in the same potato fields, tubers and scab lesions. The relative incidence of S. scabies was high in freshly harvested tubers but was much lower than that of S. turgidiscabies following storage. Both pathogens were seed-transmitted in Matilda and Sabina after 24 weeks of storage at 4°C.  相似文献   

11.
Neonectria galligena can cause European canker of apple as well as fruit rot. Healthy unwounded fruits on potted trees of cvs Cox, Bramley and Gala were inoculated with conidia of N. galligena to investigate the effects of wetness duration and fruit maturity on rot development. Overall, the incidence of fruit rot was influenced more by fruit maturity at the time of inoculation than by duration of wetness (6–48 h). Young fruit were most susceptible to infection, with 50% of fruit infected when inoculated up to 4 weeks after full bloom. The susceptibility decreased initially until c. 2 months after full bloom and then increased gradually until harvest. Almost all preharvest symptoms (eye rot) developed only on the fruit inoculated up to 4 weeks after full bloom. All other rots were observed after six‐month postharvest storage under controlled atmospheric conditions. However, the relative proportion of preharvest eye rots and postharvest storage rots varied greatly among three years. The effect of wetness duration was only significant for fruit inoculated in their early stages of development but not for those inoculated near harvest. Regression models were developed to describe the observed effects of fruit maturity and wetness on the incidence of total nectria rots.  相似文献   

12.
Phytophthora infestans is able to produce oospores in leaves of potato and tomato plants after inoculation with a mixture of Al and A2 mating-type isolates. Various conditions for oospore formation were analysed. Under controlled conditions, oospores were produced in potato leaves at temperatures ranging from 5 to 25° C. In leaves of potato cultivar Bintje incubated at 15°C, oogonia and antheridia were observed 6 days after inoculation and thick-walled oospores appeared 3-4 days later. In field experiments oospores were found in leaves and stems of potato cultivars Bintje, Irene and Pimpernel and in leaves, stems and fruits of tomato cultivar Moneymaker within 2 weeks after inoculation. A bioassay was developed to test the survival of oospores in soil under various conditions. To determine whether late-blight infections derived from infectious soil were caused by oospwres, DNA fingerprinting was performed. DNA fingerprint probe RG-57 was suitable for distinguishing asexual progeny from recombinant progeny arising from soil-borne oospores. We demonstrated survival of viable, infectious oospores of P. infestans in soil during the winter of 1992–93. Oospores were not infectious from soil exposed to temperatures of 40°C or higher but in the range 35°C to as low as – 80°C for 48 h, oospores survived.  相似文献   

13.
Botrytis allii was incubated at 20, 10,4, 2,0, – 2 and –4° to investigate effects of temperature on growth, sporulation and germination on potato dextrose agar (PDA), and to estimate incidence and severity of disease on garlic bulbs inoculated with the pathogen during storage. B. allii-was capable of growing to a colony diameter of 17 mm after 20 weeks, sporulating and germinating on PDA at temperature as low as – 4°C. After 12 weeks at –4 and -2°C the mycelial growth was observed only on 45–54% of bulbs wound-inoculated with conidial suspension, and infection was limited to 5 mm in diameter on the surface of inoculation sites without producing any symptoms of the disease. Temperature responses were similar for mycelial growth, conidial germination and infection, but mycelial growth and sporulation was slower and later on garlic bulbs than in culture. Wounds were readily colonized by B. allii. No disease was found on unwounded bulbs that were inoculated with conidial suspensions and with mycelial plugs at various temperatures. Only 16–95% of cloves became infected by contact with other cloves within the same bulb after 12 weeks of storage at temperatures of 4–20 C.  相似文献   

14.
Potato tubers are usually contaminated by more than one species or pathovar of soft rot erwinia and, because blackleg incidence is related to the contamination level of seed tubers, the disease potential of seed stocks may be assessed by determining seed-tuber contamination level. A method is described for identifying and quantifying directly from tubers the three soft rot erwinias commonly associated with potatoes. Replicate lots of 10–15 tubers are peeled by dry abrasion in a commercial potato peeler and the peel weight determined by weighing the tubers before and after peeling. Sap is expressed from the peel, an antioxidant (0.075% dithiothreitol) added, and the sap is dilution-plated on a diagnostic selective medium (crystal violet pectate [CVP]). After incubating for 24 h at 20°C, the plates are velvet-replicated onto fresh plates of CVP with or without 35 μg ml-1 erythromycin and incubated for 48 h at 27°C and 24 h at 33.5 or 37°C. Soft-rot erwinias typically form deep cup-like cavities on CVP and they can be identified and enumerated according to the pattern of cavity formation. Cavities are formed by Erwinia carotovora pv. atroseptica only at 27°C, by E. carotovora pv. carotovora at 27 and 33.5°C but not at 37°C, whereas E. chrysanthemi forms cavities at all temperatures but fails to grow in the presence of erythromycin. Contamination levels can be expressed as the number of different erwinias per tuber or per g peel.  相似文献   

15.
Population dynamics of epiphytic fungi associated with the summer bunch rot complex of five wine grape ( Vitis vinifera ) varieties in commercial vineyards in the San Joaquin Valley of California were monitored every two weeks by berry washings during 1989-1992. Vines in the five replicated experiments were subjected to basal leaf removal or left unaltered. Although numerous genera of fungi were isolated, species of Cladosporium, Aspergillus, Penicillium and Alternaria predominated. Population densities of most fungal taxa increased at or after véraison. Leaf removal in the fruiting zones of bilateral cordon-trained vines generally reduced ( P >0·05) mid to late season numbers of epiphytic mycoflora: species of Penicillium, Botrytis and Aspergillus were most commonly reduced. Populations of Alternaria spp. and yeasts were not consistently affected by leaf removal. Numbers of fungi were no lower on berries when leaves were removed from both sides of vines than when leaves were removed only from the shaded side. Incidence and severity of bunch rots (sour rot, rots caused by Botrytis cinerea, Aspergillus niger , and total rot) at harvest were consistently reduced where leaves had been removed in comparison to vines where no leaves were removed. In one experiment, berries from vines sprayed with the grower's choice of pesticides at 50% or 100% of label rates had similar numbers of epiphytic mycoflora in both cases frequently lower than those from unsprayed controls. There was a significant interaction between chemical rate and leaf removal on the incidence of sour rot at harvest. Timing and extent of leaf removal did not affect population dynamics of epiphytic fungi, or incidence or severity of bunch rots ( P ≤0·05) at harvest in other trials.  相似文献   

16.
Disease incidence was recorded in tubers of various cultivars following inoculation with macerated mycelium of Phoma exigua var. foveata and wounding in various ways. A method which produced predominantly crush wounds gave most rots and the most consistent results. The length of time between inoculation and wounding did not significantly affect the incidence of disease but disease severity did increase with damage infliction time. Inoculated, undamaged tubers produced rots but the incidence was low and discrimination between cultivars was poor when compared with damaged tubers. In some tests the resistance to gangrene could be measured by the proportion of tubers affected, in others all tubers had lesions but the extent of infection was different, The latent period of the disease differed between cultivars. Rate of lesion development was constant over a period of 12 wk within cultivars but differed between them.  相似文献   

17.
In controlled environment experiments, when oilseed rape pods or leaves were inoculated with spore suspensions of Alternaria brassicae, the maximum disease incidence (proportion of pods or leaves diseased) increased as wetness period after inoculation increased from 4 to 24 h and as temperature increased to 20°C. There was a clear relationship between disease incidence on pods and incidence on leaves with the same wetness/temperature conditions. Logistic equations described the effects of wetness period after inoculation on disease incidence (number of pods or leaves infected) or disease severity (number of lesions on pods or leaves) using temperature-dependent and tissue-dependent parameters. The time from inoculation to the appearance of the first lesions was shorter on pods than on leaves at temperatures ≤15°C and wetness periods ≤12 h. Two-dimensional response surface equations or simple interpolations from one-dimensional equations were used to develop contour maps of expected disease incidence and severity, respectively, on leaves or pods to estimate the effects of different combinations of wetness period during infection and temperature on disease development.  相似文献   

18.
The effects of apple fruit maturity, temperature of fruit or dip solution, period of time in fungicidal dip, storage conditions, and spore inoculum concentration, on the efficacy of fungicides for control of blue mould ( Penicillium expansum ) were examined in various experiments.
Iprodione and imazalil were only effective when inoculum concentration was low, whilst prochloraz was highly effective in controlling rot on fruit inoculated with 3 × 106 spores/ml. There was no consistent effect of dip temperature or fruit maturity on the efficacy of the fungicides. Iprodione was more effective on warm fruit (19°C) than cold fruit (6°C) whilst the reverse was true of imazalil. Extended periods of immersion in the fungicides slightly reduced the incidence of rotting but not to any useful degree.
The incidence of rotting in fruit treated with prochloraz and etaconazole was less in fruit stored under controlled-atmosphere cold storage conditions than in fruit stored in air cold-storage. Both fungicides were also effective for short-term storage at 20 C in air. Captan, benomyl, captan plus benomyl or vinclozolin were either ineffective or of poor efficacy under all storage conditions.  相似文献   

19.
The reactions of potato cultivars to inoculation with germinating winter spores of Synchytriuum endobioticum at 10, 15 and 20°C were compared. The classification of wart reactions for cultivars at the Resistant Grade 1/Resistant Grade 2 (RG1/RG2) and RG2/susceptible borderlines was found to depend on the inoculation temperature. For RG2 cultivars, there was a clear increase in the proportion of more resistant reactions with increase in inoculation temperature. The borderline cultivars 'Teena' and 'Alhamra' reacted as RG2 when inoculated at 10°C and as RG1 when inoculated at higher temperatures. However the inoculation temperature is unlikely to influence the outcome of tests on cultivars that produce a higher percentage of RG2 reactions. An inoculation temperature of 10–15°C more readily identified cultivars that are slightly susceptible. The slightly susceptible cultivars 'Apache', 'Morven' and 'Hassia' reacted as susceptible at 10 and 15°C and as RG2 at 20°C. However, cultivars known to produce wart tissue, including the very slightly susceptible 'Altena', were found readily to produce susceptible reactions when inoculated at all the temperatures tested.  相似文献   

20.
In controlled environment experiments, sporulation of Pyrenopeziza brassicae was observed on leaves of oilseed rape inoculated with ascospores or conidia at temperatures from 8 to 20°C at all leaf wetness durations from 6 to 72 h, except after 6 h leaf wetness duration at 8°C. The shortest times from inoculation to first observed sporulation ( l 0), for both ascospore and conidial inoculum, were 11–12 days at 16°C after 48 h wetness duration. For both ascospore and conidial inoculum (48 h wetness duration), the number of conidia produced per cm2 leaf area with sporulation was seven to eight times less at 20°C than at 8, 12 or 16°C. Values of Gompertz parameters c (maximum percentage leaf area with sporulation), r (maximum rate of increase in percentage leaf area with sporulation) and l 37 (days from inoculation to 37% of maximum sporulation), estimated by fitting the equation to the observed data, were linearly related to values predicted by inserting temperature and wetness duration treatment values into existing equations. The observed data were fitted better by logistic equations than by Gompertz equations (which overestimated at low temperatures). For both ascospore and conidial inoculum, the latent period derived from the logistic equation (days from inoculation to 50% of maximum sporulation, l 50) of P. brassicae was generally shortest at 16°C, and increased as temperature increased to 20°C or decreased to 8°C. Minimum numbers of spores needed to produce sporulation on leaves were ≈25 ascospores per leaf and ≈700 conidia per leaf, at 16°C after 48 h leaf wetness duration.  相似文献   

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