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1.
Extract of soil under colonies of Hypnum plumaeforme inhibited the growth of roots and shoots of cress, lettuce, lucerne, ryegrass, timothy, Digitaria sanguinalis and Echinochloa crus-galli . Increasing the extract concentration increased the inhibition, which suggest that the soil may contain growth inhibitory substances and possess allelopathic potential. The extract of the soil under H. plumaeforme was purified and two main inhibitory substances were isolated and determined by MS and 1H- and 13C-NMR spectral data as momilactone A and B. Momilactone A and B inhibited hypocotyls and roots of cress seedlings at concentrations >10 and 1 μ m respectively. The endogenous concentration of momilactone A and B in H. plumaeforme was 58.7 and 23.4 μg g−1 dry weight respectively and the concentration of momilactone A and B in MS growth medium of H. plumaeforme was 4.3 and 6.4 μg g−1 dry weight of H. plumaeforme , respectively. These results suggest that momilactone A and B were probably secreted into the medium during the incubation and momilactone A and B found in the soil under H. plumaeforme may have been released by the moss. Therefore, growth inhibitory activity of the soil under H. plumaeforme may be caused by momilactone A and B, which may act as allelopathic agents of H. plumaeforme .  相似文献   

2.
Genetic variation of the barley powdery mildew fungus ( Erysiphe graminis f.sp. hordei ) was estimated in three Danish local populations. Genetic variation was estimated from the variation amongst clones of Egh , and was therefore an estimate of the maximum genetic variation in the local populations. The average gene diversity, Ĥ , was estimated as 0.84. The effective population size was estimated as: log10 ( N^ e ) = 0.64 − log10(μ), or 4.4 × 109, assuming a nucleotide mutation rate ( μ) of 10−9 per base per generation. There was no significant genetic differentiation between locations.  相似文献   

3.
Application of Pythium oligandrum to a soil-based compost as a mycelial suspension (5 × 102 CFU g−1 of dry compost) and oospore alginate pellets (105 oospores/g of dry compost) controlled pre- and postemergence damping-off of sugar beet caused by Pythium ultimum to a level similar to metalaxyl seed treatment. Oospore seed treatments and aqueous suspensions of oospores applied to compost failed to control disease. Problems in the use of P. oligandrum oospore inocula for the control of damping-off were highlighted. It was shown that treatment of oospores with cellulase (20 g L−1) increased germination approximately three-fold in comparison to untreated spores. Untreated and cellulase pretreated oospores were subsequently evaluated as seed treatments for their ability to control damping-off of sugar beet. The highest rate of pretreated oospores (104 oospores/seed) gave levels of emergence and establishment in infested compost that were not significantly different from the uninfested controls, whereas seed treatment with untreated oospores gave no significant reduction in disease. In a trial carried out in a controlled environment to assess the effect of pH (4.5–8.0), P. oligandrum (104 cellulase pretreated oospores/seed) was shown to control pre- and postemergence damping-off of sugar beet at pH 7.0 and 7.5 only.  相似文献   

4.
The population of Phytophthora infestans in Brazil consists of two clonal lineages, US-1 associated with tomatoes and BR-1 associated with potatoes. To assess whether host specificity in these lineages resulted from differences in aggressiveness to potato and tomato, six aggressiveness-related epidemiological components – infection frequency (IF), incubation period (IP), latent period (LP), lesion area (LA), lesion expansion rate (LER) and sporulation at several lesion ages (SSLA) – were measured on detached leaflets of late blight-susceptible potato and tomato plants. Infection frequency of US-1 was similar on potato and tomato leaflets, but IF of BR-1 was somewhat reduced on tomato. Incubation period was longer on both hosts with US-1, although this apparent lineage affect was not significant. Overall there was no host effect on IP. On potato, BR-1 had a shorter LP (110·3 h) and a larger LA (6·5 cm2) than US-1 (LP = 162·0 h; LA = 2·8 cm2). The highest LER resulted when isolates of BR-1 (0·121 cm2 h−1) and US-1 (0·053 cm2 h−1) were inoculated on potato and tomato leaflets, respectively. The highest values of the area under the sporulation capacity curve (AUSC) were obtained for isolates of US-1 inoculated on tomato leaflets (6146) and for isolates of BR-1 on potato leaflets (3775). In general, higher values of LA, LER, SSLA and AUSC, and shorter values of LP were measured when isolates of a clonal lineage were inoculated on their original host than with the opposite combinations. There is evidence that there are quantitative differences in aggressiveness components between isolates of US-1 and BR-1 clonal lineages that probably contribute to host specificity of P. infestans populations in Brazil.  相似文献   

5.
The bioherbicidal fungus, Colletotrichum truncatum (Schwein.) Andrus & Moore, was tested at different inoculum concentrations alone and in combination with, prior to or following treatment with different rates of glyphosate ( N -[phosphonomethyl]glycine) (Roundup Ultra) for the control of hemp sesbania ( Sesbania exaltata [Raf.] Rydb. ex A.W. Hill) in Roundup Ready soybean field plots. Colletotrichum truncatum and glyphosate were applied in all pair-wise combinations of 0, 1.25, 2.5, 5.0, and 10.0 × 106 spores mL−1 (i.e. 3.125, 6.25, 12.5, and 25 × 1011 spores ha−1), and 0.15, 0.30, 0.60, and 1.2 kg ha−1, respectively. Weed control and disease incidence were enhanced at the two lowest fungal and herbicidal rates when the fungal spores were applied after glyphosate treatment. The application of the fungus in combination with or prior to glyphosate application at 0.30 kg ha−1 resulted in reduced disease incidence and weed control regardless of the inoculum's concentration. At the highest glyphosate rates, the weeds were controlled by the herbicide alone. These results suggest that it might be possible to utilize additive or synergistic herbicide and pathogen interactions to enhance hemp sesbania control.  相似文献   

6.
In late 2003, nine populations of Sclerotinia homoeocarpa in Ontario Canada (seven of which had been previously sampled in early 1994, prior to the registration of sterol demethylation-inhibiting (DMI) fungicides for turf disease control in Canada) were sampled and tested for sensitivity to propiconazole. Four of the nine populations had not been treated with DMI fungicides during the intervening years, and isolates from these locations were sensitive to propiconazole (geometric mean EC50 values of 0·005–0·012 µ g mL−1, compared with 0·005–0·008 µ g mL−1 for the original 1994 populations). Among the five populations from 2003 that had been exposed to DMI fungicides, mean EC50 values were significantly greater, ranging from 0·020 to 0·048 µ g mL−1. A significant correlation of determination was found between estimated number of fungicide applications and log EC50 ( R 2 = 0·832, P  = 0·0001), and the equation predicted that 42·3 applications of propiconazole would be needed to bring a sensitive population (EC50 < 0·01  µ g mL−1) to a resistant level (EC50 > 0·10  µ g mL−1). Fungicide sensitivity vs. duration of fungicide efficacy was also tested, and it was found that isolates with decreased sensitivity were able to more quickly overcome the inhibitory effects of fungicide application, reducing the duration of control from 3 weeks to 2 weeks.  相似文献   

7.
DONALD 《Weed Research》1998,38(6):425-431
The research goal was to determine whether crop damage from herbicides measured early in the growing season soon after treatment could be used to estimate relative crop yield loss. Percentage stunting was rated visually and percentage crop ground cover (i.e. percentage of the ground surface covered by vegetation) was determined from video photographs taken 2–4 weeks after sethoxydim-susceptible maize ( Zea mays L.) was sprayed with sethoxydim at various rates plus crop oil concentrate. Averaged over 3 years, relative percentage maize yield was a negative sigmoidal function of relative sethoxydim rates from 0.065× to 0.5×, where the 1× rate was 420 g a.i. ha−1 ( r 2 = 0.80). Relative maize yield was positively linearly related to percentage crop ground cover and negatively linearly related to rated percentage stunting averaged over 3 years. Linear regression models of relative maize yield vs. percentage maize ground cover explained only slightly more data variability ( r 2 = 0.86) than did rated stunting ( r 2 = 0.82) over 3 years. The advantages and disadvantages of rated stunting and crop ground cover as scientific measurements are discussed.  相似文献   

8.
Factors affecting the production of conidia of Peronosclerospora sorghi , causing sorghum downy mildew (SDM), were investigated during 1993 and 1994 in Zimbabwe. In the field conidia were detected on nights when the minimum temperature was in the range 10–19°C. On 73% of nights when conidia were detected rain had fallen within the previous 72 h and on 64% of nights wind speed was < 2.0 m s−1. The time period over which conidia were detected was 2–9 h. Using incubated leaf material, conidia were produced in the temperature range 10–26°C. Local lesions and systemically infected leaf material produced 2.4–5.7 × 103 conidia per cm2. Under controlled conditions conidia were released from conidiophores for 2.5 h after maturation and were shown to be well adapted to wind dispersal, having a settling velocity of 1.5 × 10−4 m s−1. Conditions that are suitable for conidia production occur in Zimbabwe and other semi-arid regions of southern Africa during the cropping season.  相似文献   

9.
A qualitative seed-based method useful for the detection of resistance to the herbicide tribenuron-methyl in Papaver rhoeas L. is described. Seeds were germinated on 35 mL of a 1.3% agar medium containing 2 g KNO3 L–1 in 8.5 cm Petri dishes in a growth chamber under 20 μmol s–1 m–2 of fluorescent light. When 0.24 μM tribenuron-methyl or more was added, growth in susceptible plants stopped after the cotyledon stage and they turned chlorotic. The resistant plants continued developing new leaves. The same effect was achieved when 0.2 g gibberellin (GA3) L–1 and 7.68 μM tribenuron-methyl or 0.5 g GA3 L–1 and 61.44 μM tribenuron-methyl were added. Germination percentage rose with gibberellin in the presence or absence of the herbicide. Plants developed rapidly, with only about 14 d needed to finish the test but sometimes root growth was reduced because of the addition of gibberellin. In the absence of gibberellin but in the presence of the herbicide, plants grew more slowly and developed smaller leaves with a 17-d evaluation period requirement. The test was validated with pot experiments in a greenhouse and also with field trials. The best combination was found to be 0.2 g GA3 L–1 and 7.68 μM tribenuron-methyl, assuring homogenous germination and testing of dormant seeds but avoiding root inhibition associated with too much gibberellin.  相似文献   

10.
Elemental sulphur levels, sulphur localization in stems, and levels of sulphate, glutathione and cysteine were studied in pepper ( Capsicum annuum ) cvs Yolo Wonder (higher resistance) and Luesia (lower resistance) after inoculation with Verticillium dahliae , the cause of vascular wilt. Accumulation of elemental sulphur (S0) was first detected 10 days after inoculation in Yolo Wonder (mean S0 level 7·3  µ g g−1 DW), and 15 days after inoculation in Luesia (mean S0 level 3·3  µ g g−1 DW). The maximum level was reached 21 days after inoculation in Yolo Wonder (14·1  µ g g−1 DW). In control plants, elemental sulphur was not detected. SEM-EDX (scanning electron microscopy-energy dispersive X-ray microanalysis) indicated that the sulphur was not restricted to a specific location, but was dispersed throughout the vascular tissue. Sulphate levels showed a decline at the end of the experiment in inoculated plants, possibly related to the increase in sulphur levels seen in the two cultivars. The differences in sulphate levels between the two cultivars may be due to faster sulphate breakdown in cv. Yolo Wonder.  相似文献   

11.
Thirty-nine isolates of Fusarium verticillioides from maize seeds from three regions of Costa Rica were classified on fertility, fumonisin production, vegetative compatibility and pathogenicity. The identity of the isolates was verified by sexual crosses with standard tester strains and by isozyme analysis. Twenty-three isolates (59%) were mating type A− and 16 (41%) were A+; 29 (74%) were female fertile. The isolates produced high amounts of fumonisin B1 when grown on sterilized maize grits, 32 isolates producing more than 1000 μg g−1, as determined by TLC, and 7 less than 1000 μg g−1. Vegetative compatibility tests by pairing nit mutants identified 34 vegetative compatibility groups (VCGs), of which 29 had one member and 5 had two members. Isolates belonging to the same VCG were obtained from the same seed sample. Two pathogenicity tests with different inoculation methods were performed: on toothpick inoculation of 7-week-old maize stalks, 71% of the isolates were pathogenic according to the length of the necrosis formed in the stalk, and on sand inoculation of maize seedlings all the isolates were pathogenic, according to shoot length and dry weight production. Differences in aggressiveness between some of the isolates were recorded. It is concluded that natural populations of F. verticillioides in Costa Rica consist of genetically diverse, highly fertile and pathogenic isolates that represent a potential risk for disease development and fumonisin accumulation in maize crops.  相似文献   

12.
To improve the breeding of chickpea varieties with resistance to Fusarium wilt, an attempt was made to analyse the biochemical basis of disease resistance by measuring levels of chitinase, β-1,3-glucanase, protease and proteinase inhibitor activities in dry and soaked seeds and in root and shoot tissues of wilt-resistant and wilt-susceptible cultivars. Marginal variation was observed in the levels of the candidate proteins in dry or soaked seeds. Chitinase activity was higher in roots than in shoots or cotyledons. No proteinase inhibitor activity was detected in root and shoot tissue of any of the cultivars. When the levels of these proteins were analysed in resistant (Vijay) and susceptible (JG-62) cultivars during development of wilt by growing plants in soil infested with F. oxysporum f.sp. ciceri , race 1, both cultivars showed induction of chitinase activity in the roots. However, the induced activity in JG-62 (3.82 U g−1) was equivalent to the constitutive level in Vijay (3.90 U g−1) and much lower than that induced in Vijay (5.18 U g−1). Induction of protease activity was observed only in root extracts of Vijay when challenged by the pathogen. The root extract of Vijay showed in vitro antifungal activity in a plate assay. Simultaneous induction of proteolytic and chitinolytic activities specifically in the resistant cultivar was correlated with antifungal properties of root extracts effective in conferring resistance.  相似文献   

13.
Ten barnyard grass ( Echinochloa crus-galli var. crus-galli ) ecotypes collected from several locations in Malaysian and Indonesian granaries were tested for variation in their susceptibility to the leaf blight pathogen ( Exserohilum longirostratum ). Four phenological growth stages of the ecotypes were sprayed with E. longirostratum at the rate of 1 × 107 conidia mL−1 under glasshouse conditions. The results of the study showed that plants inoculated with 1 × 107 conidia mL−1 and exposed for 24 h dew periods were severely infected and the percentage dry weight reduction of all ecotypes significantly increased. The 1–2 and 2–3-leaf stage plants were completely killed within 6 days after inoculation. However, susceptibility reactions among the ecotypes were observed at the 4–5-leaf stage, while the 6–7-leaf stage was resistant. The ecotypes, K-02, PK-04, KN-02, CJ-01, and L-01, were the most susceptible ecotypes as indicated by a higher area under disease progress curve value. The apparent disease progress rates for these ecotypes were significantly faster compared to the other ecotypes. The dry weight reduction among the four growth stages was variable. These findings show that the 1–2 and 2–3-leaf stages are the most susceptible, while the 6–7-leaf stage was resistant. This study has confirmed that a variable response to the fungal pathogen occurred within an intraspecific barnyard grass collection.  相似文献   

14.
The effect of wind on the dispersal of oospores of Peronosclerospora sorghi , cause of sorghum downy mildew (SDM) is described. The oospores are produced within the leaves of aging, systemically infected sorghum plants. These leaves typically undergo shredding, releasing oospores into the air. Oospores are produced in large numbers (6.1 × 103 cm−2 of systemically infected leaf) and an estimate of the settling velocity of single oospores (0.0437 m s−1) of P. sorghi indicated their suitability for wind dispersal. In wind tunnel studies wind speeds as low as 2 m s−1 dispersed up to 665 oospores per m3 air from a group of leaves previously exposed to wind and displaying symptoms of leaf shredding. The number of oospores dispersed increased exponentially with increasing wind speed. At 6 m s−1, up to 12 890 oospores per m3 air were dispersed. Gusts increased oospore dispersal. A constant wind speed of 3 m s−1 dispersed a mean of 416 oospores per m3. When gusts were applied the mean was 15 592 oospores per m3. In field experiments in Zimbabwe, oospores were sampled downwind from infected plants in the field and at a height of 3.8 m above ground level immediately downwind of an infected crop. These data indicate that wind could play a major role in the dispersal of oospores from infected plants in areas where SDM infects sorghum, perhaps dispersing oospores over long distances.  相似文献   

15.
Control of Penicillium expansum by plant volatile compounds   总被引：1，自引：0，他引：1  
Nine plant volatiles were tested for their activity in vitro and in vivo against Penicillium expansum , the cause of blue mould of pear. In vitro spore germination and mycelial growth assay showed a consistent fungicidal activity by trans -2-hexenal, carvacrol, trans -cinnamaldehyde and citral, while hexanal (-)- carvone, p -anisaldehyde, eugenol and 2-nonanone exhibited a progressively lower inhibition. trans -2-Hexenal was the best inhibitor of conidial germination [MIC (minimum inhibitory concentration) = 24·6  µ L L−1; ED50 = 10·2  µ L L−1], while carvacrol was the best inhibitor of mycelial growth (MIC = 24·6  µ L L−1; ED50 = 9  µ L L−1). The four most active compounds in in vitro studies were tested in vivo as fumigants against blue mould on pear cv. Conference. Best control was achieved by trans -2-hexenal vapour treatments (12·5  µ L L−1) when applied over a 24-h period, beginning 24 h after inoculation. In contrast, carvacrol (12·5–200  µ L L−1), and trans -cinnamaldehyde (50–400  µ L L−1) were ineffective and citral (200  µ L L−1) showed only slight effect.  相似文献   

16.
Conditioned seeds of Striga asiatica (L.) Kuntze release ethylene, which elicits germination. We investigated the activity of 1-aminocyclopropane-1-carboxylate (ACC) oxidase and respiration during conditioning. Seeds incubated in vivo with ACC, the substrate for ACC oxidase, produced negligible ethylene at the beginning of conditioning or if they were dormant (i.e. would not germinate after conditioning and treatment with stimulant). Non-dormant seeds produced 3000 ηL of ethylene/600 seeds/24 h after 12 days of conditioning. In vitro ACC oxidase activity at day 0 of conditioning produced 500 ηL of ethylene/μg protein/h and 8000 ηL of ethylene/μg protein/h after 12 days of conditioning. Incubation of seeds in strigol before protein extraction did not enhance enzyme activity. Seeds released 4000 μL/L CO2 in the first 24 h of conditioning, with the rate increasing to 15 000 μL/L/24 h on day 4 and then remaining roughly unchanged. Maximum in vitro activity of ACC oxidase required ACC, catalase, O2, Fe2+, ascorbate and CO2. In vivo activity of ACC oxidase required ACC and/or germination stimulant(s), suggesting that stimulants may be involved in providing substrates for the ACC oxidase. No difference was observed in the separation of extracted proteins, which suggests that ACC oxidase is activated during conditioning, perhaps as a result of changes in co-factor concentration. Application of these findings to Striga control is discussed.  相似文献   

17.
Current status of biological control of paddy weeds in Vietnam   总被引：1，自引：0，他引：1  
Rice is a staple food in Vietnam and accounts for > 7.7 × 106 cultivated ha, which provide 35.5 × 106 t of rice, of which 4.2 × 106 t were exported in 2004. The enlargement of the cropping area and the enhancement of rice yield have rapidly increased the amount of agrochemicals, including herbicides, in crop production in Vietnam. From 1990–2003, the percentage of herbicides in total pesticides has increased ≈ 10-fold to 30.2%. In addition, the improper use of herbicides caused environmental hazards, unsafe agricultural products, and human health problems. Biological management integrated with traditional weed control techniques might help to reduce the dependence on synthetic herbicides and build eco-friendly, sustainable agricultural production in Vietnam. This paper reviews the efforts in establishing a strategy for biological management of weeds that was conducted in recent years by Vietnamese weed scientists. This has included cropping system management, water and soil management, integrated pest management, and utilization of plant allelopathy as major components of the strategy. Many plants with strong allelopathic potential can be a source for biological weed suppression and soil fertility improvement. The utilization of allelopathic properties in rice might also help to provide new rice cultivars with weed-suppressing characteristics.  相似文献   

18.
The effects of different levels of inoculum of Aspergillus carbonarius and time of inoculation on berry infection and the development of aspergillus bunch rot on grapevines (cv. Sultana) were studied under field conditions. Inflorescences at full bloom were inoculated with aqueous spore suspensions of A. carbonarius containing 0 or 1 × 106 spores mL−1 in 2004/05 and 0, 1 × 102 or 1 × 105 spores mL−1 in 2005/06. In both years, the incidence of infection in inoculated berries was significantly higher than in uninoculated berries. Incidence of infection in berries from veraison until harvest was higher than at earlier stages of bunch development (berry set to berries that were still hard and green). Inoculation of bunches at veraison did not significantly increase A. carbonarius infection prior to harvest, at harvest, 6 days after harvest or when berries were over-ripe. Bunches inoculated at harvest did not significantly increase infection 6 days after harvest or when berries were over-ripe. Aspergillus carbonarius was isolated more frequently from the pedicel end (53·1%) than from the middle section (37·5%) and distal end (35·0%) of berries that were inoculated with 105 spores mL−1.  相似文献   

19.
Methods to assess light leaf spot ( Pyrenopeziza brassicae ) on winter oilseed rape cultivars were compared in laboratory, controlled-environment and field experiments. In controlled-environment experiments with seedling leaves inoculated at GS 1,4, the greatest differences in percentage area affected by P. brassicae sporulation were observed with inoculum concentrations of 4 × 103 or 4 × 104 spores mL−1, rather than 4 × 102 or 4 × 105 spores mL−1, but older leaves had begun to senesce before assessment, particularly where they were severely affected by P. brassicae . In winter oilseed rape field experiments, a severe light leaf spot epidemic developed in 2002/03 (inoculated, September/October rainfall 127·2 mm) but not in 2003/04 (uninoculated, September/October rainfall 40·7 mm). In-plot assessments discriminated between cultivars best in February/March in 2003 and June in 2004, but sometimes failed to detect plots with many infected plants (e.g. March/April 2004). Ranking of cultivar resistance differed between seedling experiments done under controlled-environment conditions and field experiments. The sensitivity of detection of P. brassicae DNA extracted from culture was greater using the PCR primer pair PbITSF/PbITSR than using primers Pb1/Pb2. P. brassicae was detected by PCR (PbITS primers) in leaves from controlled-environment experiments immediately and up to 14 days after inoculation, and in leaves sampled from field experiments 2 months before detection by visual assessment.  相似文献   

20.
Antifungal activity of bergenin, a constituent of Flueggea microcarpa   总被引：1，自引：0，他引：1  
The antifungal activity of bergenin against some plant pathogenic fungi, namely, Alternaria alternata , A. brassicae , A. carthami , Fusarium udum , F. oxysporum f.sp. ciceri , Curvularia lunata and Erysiphe pisi , was studied. Bergenin as its monosodium salt was effective against all the fungi and the effective dose for complete inhibition of spore germination varied from 15 μg mL−1 for F. udum to 125 μg mL−1 for E. pisi . Experiments on the effect of bergenin on powdery mildew development under glasshouse conditions revealed that it can control powdery mildew of pea at 2000 μg mL−1 by postinoculation treatment, the results being comparable with those of carbendazim (1000 μg mL−1) and wettable sulfur (2000 μg mL−1). It affected hyphal elongation and the number of primary and secondary branches.  相似文献   

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