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1.
The Epidemiology of Purple Leaf Blotch on Leeks in Victoria, Australia   总被引：1，自引：0，他引：1  
The incidence of purple leaf blotch disease was investigated on seven successive commercial leek crops grown at Cranbourne, Victoria between 1996 and 1997. First symptoms occurred on older leaves, 54–69 days after transplanting. Lesions with typical symptoms were colonised by either Alternaria porri (6%), Stemphylium vesicarium (42%) or mixtures of both pathogens (52%). Purple leaf blotch was caused by a disease complex and was endemic at nobreak Cranbourne due to the continuous cropping of leeks. Disease incidence in all monitored crops increased as plants matured (123–158 days after transplanting) until harvest but never exceeded 11% due to fortnightly applications of mancozeb. Disease levels showed no significant correlation with weekly temperature, precipitation, relative humidity or leaf wetness duration. Disease levels were significantly (P < 0.05) higher on autumn/winter (May/June) 1997 crops when 38 periods of leaf wetness 8 h because of dew and low temperatures (10–13 °C). The weekly rate of increase of disease incidence was significantly (P < 0.01) correlated with days after transplantation. nobreak Concentrations of airborne A. porri and S. vesicarium conidia within leek crops showed a diurnal periodicity and maximum numbers were trapped between 11:00 and 15:00 h. The concentration of airborne S. vesicarium conidia was three to six times the concentration of airborne A. porri conidia. Conidia were more abundant during spring/summer (September–February). Ascospores of Pleospora allii were found during May–September. The greater concentrations of airborne S. vesicarium conidia suggest that it may be the dominant pathogen in the purple leaf blight complex. Fungicide sprays were unnecessary until 8–10 weeks after transplanting, and regular protectant sprays curtailed but did not eradicate purple leaf blight. The results indicated that predictive models, based on temperature and the frequency of leaf wetness periods 8 h, will assist in reducing fungicide inputs as plants mature and, in southern Victoria, fungicide applications on leeks should be timed for autumn/winter when infection periods occur.  相似文献   

2.
Samenvatting Van een aantal voor de plantengroei schadelijke bodemorganismen werd het verloop van de afsterving bij verschillende temperaturen nagegaan (zie grafieken 1–5).Het verband tussen de duur van verhitting (x) en de afstervingstemperatuur (y) wordt goed weergegeven door een curve van de algemene gedaante (y–a)x=b.Bij een grondontsmetting door stomen is het gewenst de grond ook na de behandeling ongeveer 3 uur afgedekt te houden.Bij de volgende temperaturen wordt een afdoende doding verkregen: Fusarium 70°C;Sclerotinia enVerticillium (komkommerstam) 60°C;Heterodera marioni 55° C;Verticillium (tomatenstam) enAgriotes (ritnaalden) 50°C.Tomatenzaad kan ontsmet worden tegenVerticillium door het een half uur onder te dompelen in water van 45–50°C. De kiemkracht van het zaad wordt hierdoor niet in het minst geschaad.Summary For a number of soil-organisms, injurious to plant-growth, the process of dying-off was examined at different temperatures (see curves 1–5).The relation between the period of heating (x) and the death-temperature (y) is expressed reasonably well in a curve of the general form: (y–a)x=b.In sterilizing the soil by steaming it is desirable to keep the ground covered, also after the treatment, for about three hours.At the following temperatures a thorough killing-off is obtained: Fusarium 70°C;Sclerotinia andVerticillium (from cucumber) 60°C;Heterodera 55°C;Verticillium (from tomato) andAgriotes (wireworms) 50°C.Tomatoseed may be rendered sterile against Verticillium by submerging it it water of 45–50°C for half an hour. By this treatment the germinative power is not harmed in the least.  相似文献   

3.
The effects of age of ascospores (0–18 days after discharge), photon flux density (0–494 mol m–2 s–1 PAR), temperature (4–30 °C), frost (–15 °C for 30 min), relative humidity (RH; 0–100%), pH (2.5–6.5) and dryness (0 and 53% RH for up to 40 min) on the germination of the ascospores of the mycotoxin-producing fungus Gibberella zeae (anamorph Fusarium graminearum) were studied. Freshly discharged ascospores germinated within 4 h at 20 °C and 100% RH. The rate of germination and the percentage of viable ascospores decreased over time after the spores were discharged from perithecia. The time course of ascospore germination was not significantly affected by photon flux density. The period of time required to obtain 50% germinated ascospores at 100% RH was 26.90 h at 4 °C, 10.40 h at 14 °C, 3.44 h at 20 °C and 3.31 h at 30 °C. There was no significant effect of frost on the percentage of viable ascospores. A small percentage (6.6 ± 3.8%) of the ascospores germinated at 53% RH. At RH 84% and 20 °C almost 100% of the freshly discharged ascospores germinated. The time course of ascospore germination was affected by pH. The maximum rate of ascospore germination was estimated to be at pH 3.76. Ascospores lost their ability to germinate following exposure to 0% RH almost instantaneously. No germinating spores were detected after an incubation period of 1 min at 0% RH. Incubating the ascospores at 53% RH decreased the percentage of viable spores from 93 to 6% within 10 min. The data demonstrate that age of spores, relative humidity, temperature and pH, but not photon flux density, are key factors in germination of G. zeae ascospores.  相似文献   

4.
Inoculum density, temperature, leaf age, and wetness duration were evaluated for their effects on the development of black streak (Itersonilia perplexans) on edible burdock (Arctium lappa L.) in a controlled environment. The effect of relative humidity (RH) on ballistospores production by I. perplexans was also evaluated. Symptoms of black streak on leaves increased in a linear fashion as the inoculum density of I. perplexans increased from 102 to 106 ballistospores/ml. Rugose symptoms on young leaves were observed at densities of ≥104 ballistospores/ml. Disease severity of I. perplexans in relation to leaf age followed a degradation curve when the leaves were inoculated with ballistospores. Disease severity was high in newly emerged leaves up to 5 days old, declined as leaf age increased to 29 days, and was zero when leaf age increased from 30 to 33 days. Disease development of edible burdock plants exposed to ballistospores of I. perplexans was evaluated at various combinations of temperature (10°, 15°, 20°, 25°C) and duration of leaf wetness (12, 24, 36, 48, and 72 h). Disease was most severe when plants were in contact with the ballistospore sources at 15° or 20°C. The least amount of disease occurred at 25°C regardless of wetness duration. Ballistospores required 24–36 h of continuous leaf wetness to cause visible symptoms by infection on edible burdock. Ballistospores production in infected lesions required at least 95.5% RH.  相似文献   

5.
The pupal duration of the red palm weevil, Rhynchophorus ferrugineus (Oliv.) at two different temperatures revealed that the thermal threshold is –2.3°C, while the thermal constant is 423 degree days. Around 20.7 cycles of weevil emergence per year have been predicted in Egypt. A temperature between 44–45°C was found to be the higher threshold at which the pupae are killed. The heat units required for the pupal development were utilized to predict the dates of adult emergence throughout the year.  相似文献   

6.
Asparagus replant-bound early decline (ARED) was characterized and its etiology was elucidated in experiments under greenhouse and field conditions. Selective soil treatments were used to differentiate between autotoxic compounds and soil-borne pathogens as causal agents. In greenhouse experiments, there were symptoms of ARED within 12—15 weeks. Asparagus plants grown in soil formerly used for asparagus (asparagus soil) showed brown lesions on primary and secondary roots, and many secondary roots had rotted. Root weights of plants grown in asparagus soil were lower than those of plants grown in fresh soil.Fusarium oxysporum f. sp.asparagi (Foa) was by far the most common species among the fungi isolated from roots with lesions. Under greenhouse and field conditions, there were similar symptoms, which indicates that the results obtained under greenhouse conditions are similar to those in the field. The vertical distribution of the ARED-causing factor(s) was studied in a greenhouse experiment in which plants were grown in soil from three layers: 0–30, 30–60, and 60–90 cm. For all four asparagus soils tested, there were ARED symptoms and similar disease severity in samples from all three depths. The causal factor persisted at least 11 years after soil was no longer used for asparagus. When asparagus soil was diluted with fresh soil to give mixtures with 100%, 80%, 50%, 20% and 0% asparagus soil, disease severity did not decrease with increasing dilution of the asparagus soil from 100% to 20%. Disease severity of all mixtures with asparagus soil was significantly higher than that for fresh soil. The results imply that ARED is caused by a pathogen colonizing the soil rather than inhibition by autotoxins released from residues of the preceding asparagus crop. This conclusion is supported by the results of greenhouse and outdoor experiments with heat and fungicide treatments of soil. ARED was nullified by heat treatments of 30 min at 55 or 60 °C but not 45 and 50 °C, eliminating autotoxins as an important cause of ARED because they are heat-stable. Foa is eliminated by a 30-min soil treatment at 55–60 °C but not 50 °C. Prochloraz, known for its toxicity toF. oxysporum, also nullified ARED. Disease severity level was related to the density of Foa in soil. The results provide conclusive evidence thatF. oxysporum f. sp.asparagi is the main cause of ARED in the Netherlands, which largely removes the need to discriminate between early decline and replant-bound early decline, because Foa is the main cause of both diseases.  相似文献   

7.
The effect of vapour pressure deficit, temperature and radiation on the postharvest susceptibility of gerbera flowers toB. cinerea, on the water relations of gerbera flowers and on the lesion formation after conidial infection ofB. cinerea was studied. The temperature range in whichB. cinerea could germinate and growin vitro is 5–30 °C. In climate chamber experiments flowers had more lesions ofB. cinerea at temperatures of 20 and 25 °C than at 10 and 15°C. At 15, 20 and 25°C the infectivity ofB. cinerea conidia was negatively affected during a storage-period of 7 days. At a vapour pressure deficit (VPD) of 200 Pa significantly more conidia ofB. cinerea were infective than at 800 Pa. At a VPD of 800 Pa the susceptibility of gerbera flowers forB. cinerea was not significantly different than at 200 Pa. High radiation levels in glasshouses in spring and summer negatively influenced the infectivity of conidia ofB. cinerea on the flower surface, but did not affect the susceptibility of gerbera flowers forB. cinerea. In spring and early summer conidia lost their infectivity at high radiation levels, high temperatures and high levels of VPD. In summer gerbera flowers could be more susceptible toB. cinerea because of high temperatures in glasshouses, but the negative effect of radiation on the conidia ofB. cinerea seemed to overrule the temperature effect. Thus, the numbers of lesions in spring and summer can be low compared with the numbers in other seasons, although the numbers ofB. cinerea colonies on spore traps can be high. The effect of temperature on the susceptibility of gerbera flowers can probably be explained by changes of water status in the petals. At higher temperatures the number of lesions and the turgor (=water potential—osmotic potential) in the petals increased. Temperatures <10°C during lesion formation (RH>95% and VPD<50 Pa) had a temporary negative effect on the number of lesions. After 3 days of incubation the numbers of lesions were about equal (30 lesions/cm2) from 5 to 20°C. At 30°C no lesion formation was observed even after 3 days.  相似文献   

8.
The effectiveness ofTrichoderma harzianum in suppression of tomato stem rot caused byBotrytis cinerea was examined on tomato stem pieces and on whole plants. Ten days after simultanous inoculation withB. cinerea andT. harzianum, the incidence of infected stem pieces was reduced by 62–84%, the severity of infection by 68–71% and the intensity of sporulation by 87%. Seventeen days after inoculation of wounds on whole plants, the incidence of stem rot was reduced by 50 and 33% at 15 and 26 °C, respectively, and the incidence of rot at leaf scar sites on the main stem was reduced by 60 and 50%, respectively. Simultanous inoculation and pre-inoculation withT. harzianum gave good control ofB. cinerea (50 and 90% disease reduction, 10 days after inoculation). The rate of rotting was not reduced by the biocontrol agent once infection was established. However, sporulation byB. cinerea was specifically reduced on these rotting stem pieces. Temperature had a greater effect than vapour pressure deficit (VPD) on the efficacy of biocontrol. Suppression ofB. cinerea incidence byT. harzianum on stem pieces was significant at 10 °C and higher temperatures up to 26 °C. Control of infection was significantly lower at a VPD of 1.3 kPa (60% reduction), than at VPD<1.06 kPa (90–100% control). Reductions in the severity of stem rotting and the sporulation intensity of grey mould were generally not affected by VPD in the range 0.59–1.06 kPa. Survival ofT. harzianum on stems was affected by both temperature and VPD and was greatest at 10 °C at a low VPD and at 26 ° C at a high VPD.  相似文献   

9.
Abstract The biology of two important lepidopterous pests, Prays oleae Bernard and Palpita unionalis Hübner, was studied. The target pests were reared on olive plants, Oleae europaea L. (Oleaceae) under laboratory conditions for two successive generations, from March to June 2002. For P. oleae, the duration of larval stage development in the first generation was 21.4 ± 0.18 days at 19.3–20.9 °C, 65–68 % R.H, while in the second generation it was 14.8 ± 0.10 days at 20.8–24.2 °C, 65–69 % R.H. The number of eggs laid per female ranged from 58 to 109 eggs in the first generation, and from 47 to 113 in the second. The larval stage duration of P. unionalis was 16.3 ± 0.12 days at 16.8–22.9 °C, 65–69 % R.H. and 15.5 ± 0.12 days at 21.6–25.5 °C, 66–69 % R.H. for the first and second generations, respectively. Also, the number of eggs laid per female ranged from 630 to 653 eggs, and from 425 to 493 eggs in the second generation under the same previous laboratory conditions. P. oleae laid eggs at night mostly singly on flower-buds, more on the calyx. than on the petals. The larvae mined on leaves and damaged groups of flowers. P. unionalis adults were active at night, laid eggs singly at twilight usually on the lower surface of foliage. Larvae fed on leaves spinning several leaves together to form shelter for the pupa.  相似文献   

10.
Coniothyrium minitans grew on all ten solid-substrates (barley, barley-rye-sunflower, bran-vermiculite, bran-sand, maizemed-perlite, millet, oats, peat-bran, rice and wheat) tested, producing high numbers of germinable pycnidiospores (1.9–9.3×108 g–1 air dry inocula). All solid substrate inocula survived better in the laboratory at 5 and 15 °C than at 30 °C for at least 64 weeks.In pot bioassays carried out in the glasshouse and field, soil incorporations of each inoculum almost completely inhibited carpogenic germination ofS. sclerotiorum. In the field bioassay, no sclerotia were recovered after 38 weeks fromC. minitans-treated pots compared to 56% from control pots. In the glasshouse bioassay, 9–30% of sclerotia were recovered after 20 weeks fromC. minitans-treated pots, but 88–100% of these were infected by the antagonist. The antagonist also spread to infect sclerotia in control pots.In larger scale glasshouse trials, single preplanting soil-incorporations of five inocula (barley-ryesunflower, maizemeal-perlite, peat-bran, rice and wheat) controlled Sclerotinia disease in a sequence of lettuce crops, with only small differences between the types of inocula tested. At harvest,C. minitans reduced sclerotial populations on the soil surface and over 74% of sclerotia recovered fromC. minitans-treated plots were infected by the antagonist.C. minitans survived in soil in all solid-substrate inocula-treated plots for at least 39 weeks at levels of 104–105 colony forming units cm–3 soil and spread to infect over 36% of sclerotia recovered from control plots.  相似文献   

11.
Experiments to investigate the factors affecting the incubation period of dark leaf and pod spot (Alternaria brassicae) on leaves and pods of oilseed rape (Brassica napus) were done in controlled environment (constant temperatures) and glasshouse conditions (fluctuating temperatures). The length of the incubation period of dark leaf and pod spot decreased as infection and incubation temperatures increased from 6 to 20 °C. The incubation period decreased as wetness period increased from 2 to 12 h, as inoculum concentration increased from 80 to 2 × 103 spores ml–1 and as leaf age increased from 4 to 10 days. Asymptotes of leaf age and inoculum concentration, above which the length of the incubation period did not decrease, were 10 days and 2 × 103 spores ml–1, respectively. The shortest and longest incubation periods were 1 and 11 days. The mechanism by which the infection conditions influenced the incubation period of dark leaf and pod spot on oilseed rape seemed to be linked to lesion density. Usually, the length of the incubation period decreased greatly with increasing lesion density.  相似文献   

12.
White tip disease of leek (Allium porrum), caused byPhytophthora porri, was studied in field experiments. On fields infested by soil-borne inoculum (oospores), relatively short periods of explosive disease increase alternated with periods in which apparently no new infections occurred. The analysis of rain data and disease data, using a degree-day model for incubation periods at constant temperatures, confirmed the hypothesis that disease increase ofP. porri is significantly correlated with rain; R adj 2 was 0.91, 0.41 and 0.51 in 1992, 1993 and 1994, respectively. Correlations were highest early in the season. Lack of correlation later in the season may be ascribed to the effect of lesion death, which may be caused by total or partial leaf death, by desiccation or by other fungi overgrowingP. porri, and to the effect of secondary infection by zoosporangia, which appears to be not so strongly rain-driven as primary infection. Zoosporangia were observed in fields on water-logged light-green lesions. High lesion densities of leaf tips and leaf units at 10–20 cm above the leaf axils indicated that most infections depend on free water, either in puddles or in a water basin near the leaf axils. Although disease correlates well with rain data, disease forecasts will be unreliable as long as rain forecasts are unreliable.  相似文献   

13.
Distribution of the cherry bark tortrix, Enarmonia formosana (Scopoli) (=CBT) was determined by detecting the presence of their frass tubes on the trunk of rosaceous shrubs and trees throughout the Czech Republic. Tree disjunctive areas of CBT were indicated in the country. The overall distribution of CBT approximates the annual isothermes 8–9°C and 10–11°C, but a number of zonal exceptions were also determined. The occurrence of CBT on sweet cherry, Prunus avium (L.) was the key target association, but P. armeniaca L., P. cerasus L., P. divaricata Ledeb., P.domestica L., P. persica L., and P. serrulata Lindley were also identified on the distributional map.  相似文献   

14.
Distribution of the cherry bark tortrix, Enarmonia formosana (Scopoli) (=CBT) was determined by detecting the presence of their frass tubes on the trunk of rosaceous shrubs and trees throughout the Czech Republic. Tree disjunctive areas of CBT were indicated in the country. The overall distribution of CBT approximates the annual isothermes 8–9°C and 10–11°C, but a number of zonal exceptions were also determined. The occurrence of CBT on sweet cherry, Prunus avium (L.) was the key target association, but P. armeniaca L., P. cerasus L., P. divaricata Ledeb., P.domestica L., P. persica L., and P. serrulata Lindley were also identified on the distributional map.  相似文献   

15.
Survival of a heat-tolerant pathogen Macrophomina phaseolina, causing dry root rot of clusterbean, was studied by incorporation and retrieval of infected residue samples at various stages of the composting process of pearl millet (Pennisetum glaucum) and clusterbean (Cyamopsis tetragonoloba) residues. During the heating phase, temperatures varied from 48–51°C at 30cm and 60–62°C at 60cm depth in compost pits. Reduction in survival of M. phaseolina propagules (13–23%) was significantly higher in the residues enriched with 4% urea-N and kept at 60cm compared to 2% urea-N and at 30cm. However, a heat phase (48–62°C) was not enough to completely eradicate M. phaseolina propagules from infected residues. Further reductions (54–61%) in survived propagules were achieved by sub-lethal temperatures (48–53°C) when moistened compost materials were exposed to heat during summer days. Beneficial effects of composts were ascertained on dry root rot intensity, seed yield of clusterbean and densities of M. phaseolina, Nitrosomonas and antagonists in soil. In a two-year field study, all the composts significantly reduced plant mortality due to dry root rot and increased the yield of clusterbean. The highest disease suppression and yield promotion were recorded in soil amended with pearl millet compost and cauliflower leaf residue compost, respectively. Soil amendment with compost also lead to a significant reduced density of M. phaseolina and an increased density of antagonistic actinomycetes, lytic bacteria and Nitrosomonas. Among composts, greater potential of cauliflower compost in enhancing population of antagonists in soil was discernible.  相似文献   

16.
Signs on strawberry leaves with latent infection by Glomerella cingulata became visible by a simple diagnostic method using ethanol immersion treatment (SDEI). Leaves treated with SDEI changed to dark brown or nearly black, and salmon-pink conidial masses were subsequently produced in the acervuli 5–10 days after incubation in moist petri dishes. The formation rate of conidial masses through SDEI was higher as the position of the leaves became lower. Conidial masses were produced more readily and abundantly when SDEI was performed at 28°C than at 22°, 25°, or 31°C. Latent infection was found to last 1–180 days. There was no difference in the time required for conidial production or in the rate of conidial formation regardless of isolate, cultivar, or leaf position. The varietal difference in resistance to strawberry anthracnose did not influence the rate of conidial mass formation after SDEI. SDEI is thus useful for detecting latent infections during the process of selecting disease-free plants.  相似文献   

17.
Abstract The biology of two important lepidopterous pests, Prays oleae Bernard and Palpita unionalis Hübner, was studied. The target pests were reared on olive plants, Oleae europaea L. (Oleaceae) under laboratory conditions for two successive generations, from March to June 2002. For P. oleae, the duration of larval stage development in the first generation was 21.4 ± 0.18 days at 19.3–20.9 °C, 65–68 % R.H, while in the second generation it was 14.8 ± 0.10 days at 20.8–24.2 °C, 65–69 % R.H. The number of eggs laid per female ranged from 58 to 109 eggs in the first generation, and from 47 to 113 in the second. The larval stage duration of P. unionalis was 16.3 ± 0.12 days at 16.8–22.9 °C, 65–69 % R.H. and 15.5 ± 0.12 days at 21.6–25.5 °C, 66–69 % R.H. for the first and second generations, respectively. Also, the number of eggs laid per female ranged from 630 to 653 eggs, and from 425 to 493 eggs in the second generation under the same previous laboratory conditions. P. oleae laid eggs at night mostly singly on flower-buds, more on the calyx. than on the petals. The larvae mined on leaves and damaged groups of flowers. P. unionalis adults were active at night, laid eggs singly at twilight usually on the lower surface of foliage. Larvae fed on leaves spinning several leaves together to form shelter for the pupa.  相似文献   

18.
Three conifer species (European larch, Norway spruce, Scots pine) were investigated for their resistance to five damping-off pathogens (Rhizoctonia solani, Fusarium solani, F. oxysporum, F. culmorum, F. avenaceum). Inoculation of the primary roots of seedlings with these pathogens caused host cell death which did not prevent the invasive growth of these fungi; seedlings that had formed secondary and tertiary roots could overcome the infection to a significant degree. Infections with R. solani caused significant mortality to all the conifer species. In contrast, the tree species expressed different levels of resistance when challenged with the Fusarium isolates, with Norway spruce being the most resistant compared to uninoculated controls. Some of the Fusarium isolates were more pathogenic to certain hosts than others; F. oxysporum for European larch, F. avenaceum for Scots pine, F. solani for European larch; only F. culmorum was significantly pathogenic to Norway spruce. No significant differences in disease severity were observed at different soil pH (4.3–7.5). Disease progression was delayed at lower (10–15°C) rather than higher temperatures (20–25°C).  相似文献   

19.
Pestalotiopsis isolates obtained from the foliage, stem-base and roots of hardy ornamentals grown on commercial nurseries in the UK were identified and characterised according to pathogenicity and colony morphology. All 18 isolates were identified as Pestalotiopsis sydowiana on the basis of conidia morphology, and confirmation of identification was made by experts at CABI Bioscience. Isolates were pathogenic on the host from which originally isolated. Typical symptoms included foliar browning of foliage and stems, and the presence of black or greenish-black acervuli on diseased tissue. Isolates were not host specific and infected other species of hardy ornamentals. Three colony types on potato dextrose agar were distinguished according to colour and production of acervuli by individual isolates.Three selected isolates of P. sydowiana were characterised by examining the effects of growth media, temperature, pH, and water potential on hyphal extension. Isolates grew well on commonly used growth media, including PDA, Sabouraud dextrose agar (SDA), V8 juice agar (V8), malt extract agar (MEA) and Czapek Dox agar (CDA). The optimum temperature for growth on PDA was in the range 20–25°C, with little or no growth occurring below 5°C or above 30°C. Hyphal extension occurred over a pH range between 2.6–8.6, with optimum values occurring at pH 5.5. In general, decreases in osmotic and matric potential caused a reduction in growth. Hyphal extension on media adjusted osmotically as NaCl ceased between –9.9 and –10.5MPa. Isolates were more tolerant of osmotic than matric potential, with no growth occurring at –6.5MPa on media adjusted with polyethylene glycol.  相似文献   

20.
The effects of various storage temperatures on germination of sclerotia ofSclerotium cepivorum Berk. were investigated. Sclerotia buried in soil for 10 weeks at temperatures of 5 and 10 °C were conditioned to a fast germination. When germination was performed at 15 °C and induced byAllium extracts, 50% of these sclerotia germinated within 10 days and the total of germination was over 90%. Sclerotia buried at temperatures of 15, 20 and 25 °C were conditioned to a slow germination. About 50% of these sclerotia could be induced to germinate at 15 °C byAllium extracts. The conditioning by high or low temperatures proved to be reversible.The optimum temperature for germination of the cold (5°C) conditioned sclerotia was 10–20 °C. The optimum temperature for germination of sclerotia conditioned at 20 °C was about 10 °C. WithoutAllium extracts 90%, 80%, 50% and 40% of the sclerotia stored at 5 °C, germinated at temperatures of 10, 5, 15 and 20 °C respectively. Sclerotia stored at 20 °C did not germinate withoutAllium extracts at any temperature.Samenvatting Sclerotiën vanSclerotium cepivorum Berk. werden onder niet steriele omstandigheden bewaard bij verschillende temperaturen. Het effect van de bewaring bij verschillende temperaturen op de kieming werd onderzocht. Het bleek dat sclerotiën, die 70 dagen bewaard werden in zakjes met zand in niet steriele grond bij een temperatuur van 5 °C of 10 °C, geconditioneerd werden tot een snelle, vrijwel volledige kieming. Onder invloed van vluchtige stoffen uit gesnipperde ui en knoflook kiemden meer dan 90% van deze sclerotiën bij een temperatuur van 15 °C. Sclerotiën die bij een hogete temperatuur bewaard werden, namelijk bij 15, 20 of 25 °C, kiemden na de bewaarperiode langzaam bij 15 °C. Ongeveer 50% van deze sclerotiën konden tot kieming gebracht worden onder invloed van ui- en knoflookextract. Sclerotiën die door een koude bewaarperiode geconditioneerd waren, namelijk bij 5 of bij 10 °C, kiemden ook zonder ui-en knoflookextract; 78% en 90% van deze sclerotiën kiemden bij temperaturen van respectievelijk 5 en 10 °C. De sclerotiën die een warme bewaarperiode ondergaan hadden, namelijk bij 15, 20 of 25 °C, kiemden niet zonder ui en knoflook. De optimum temperatuur voor de kieming was 15–20 °C voor sclerotiën die bij 5 °C bewaard waren. De optimum temperatuur voor de kieming van sclerotiën die bij 20 °C bewaard waren was lager, en wel ca. 10 °C.De conditionering door een hoge of door een lage bewaartemperatuur bleek reversibel te zijn. Sclerotiën die eerst bij 5 °C bewaard werden en daarna bij 20 °C onderscheidden zich niet van sclerotiën die continu bij 20 °C bewaard werden. Sclerotiën die eerst bij 20 °C bewaard werden en vervolgens bij 5 °C, kiemden als sclerotiën die continu bij 5 °C bewaard waren.  相似文献   

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