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1.
 Rice reflectance was measured to determine the spectral regions most sensitive to leaf blast infection with a multispectral radiometer. As disease severity increased, reflectance also increased in the 400–500 nm (blue), 570–700 nm (red), and 900–2000 nm regions but decreased in the 500–570 nm and 700–900 nm regions. The increased reflectance in the blue and red regions may be attributed to decreased chlorophyll and carotenoid contents in response to the blast infection. The maximum and minimum reflectance differences occurred at 680 nm and 760 nm for the nondiseased and diseased rice, respectively. The spectral location of maximum sensitivity was 675 nm regardless of disease severity. Rice reflectance ratios were evaluated as indicators of leaf blast severity. Two ratios, R550/R675 (reflectance at 550 nm divided by reflectance at 675 nm), and R570/R675 quantified the significant disease severity. These wavelengths were selected based on the sensitivity minima and maxima. The ratios of nondiseased rice plants varied depending on growth stage. The variation in ratios must be considered when they are used to estimate leaf blast severity. Received: April 2, 2002 / Accepted: August 12, 2002  相似文献   

2.
Temporal dynamics of soybean sudden death syndrome (SDS) root and foliar disease severity were studied in growth chamber experiments on susceptible plants exposed to different inoculum densities (0, 100, 101, 102, and 103 conidia g−1 soil) of Fusarium virguliforme. The monomolecular model provided the best fit to describe the progress of root and foliar disease severity over time. Disease severity and area under disease progress curve (AUDPC) both increased in response to increasing inoculum density (P < 0.01), particularly for foliar symptoms. Rate of disease progress increased as inoculum densities increased for both root and foliar disease severities. The incubation period for root and foliar disease severity ranged from 9 to 18 and 15 to 25 days, respectively. Significant differences in root rot severity were most easily detected during the early stages of infection, whereas root rot and foliar severities were only weakly correlated when both were assessed simultaneously at later stages of disease development. Root rot severity assessments performed 15 to 20 days after inoculation (DAI) were most highly correlated (r > 0.9, P < 0.01) with foliar disease severity assessments performed 30 to 50 DAI. Root biomass was reduced by up to 67% at the three highest inoculum densities, indicating the aggressiveness that F. virguliforme possesses as a root rot pathogen on soybeans.  相似文献   

3.
The aim of the study was to quantify peach scab (Fusicladosporium carpophilum) lesion distribution relative to the point of maximum lesion number on the fruit surface, the relationship between lesion count and distance from the point of maximum lesion density, and establish whether the distribution of lesions was consistent with a splash dispersed pathogen, and to assess the effect of lesion number on fruit size. Fruit of four cultivars, Jerseyqueen, Jefferson, BY07-6428r and Dixiland were collected and the fruit (assumed spherical) sliced taking three horizontal planes across the axis from the point of maximum disease, such that each horizontal zone (Z1-Z4) had the same vertical height, and thus equal surface areas. Lesion counts were analysed using general linear modeling with a Poisson distribution and a log-link function. Zones on the fruit had different numbers of lesions (P < 0.0001), with most lesions found on Z1. Cvs differed in the number of lesions per fruit (P = 0.0042–<0.0001). An analysis of covariance showed that although fruit size varied among most cvs (P = 0.1614–<0.0001), the number of lesions on a fruit did not affect fruit size (P = 0.5654). Measurements of the point of maximum disease relative to the peduncle-flower scar axis of the fruit suggest that fruit are not always held upright when infection occurs, such that up to 40% of fruit showed maximum infection at an angle >90° to the peduncle. This pattern of disease is consistent with observations of the splash-borne nature of conidia, with the most exposed, easily wetted, uppermost portion of fruit developing most disease.  相似文献   

4.
This study evaluated the impact of time between the application of cell suspensions or cell-free filtrates of Bacillus subtilis strains SB01 or SB24 on soybean plants under field conditions and inoculation with Sclerotinia sclerotiorum on their effectiveness for suppression of S. sclerotiorum. The results showed that the cell suspensions of two strains provided greater effectiveness than the cell-free filtrates, but the suppression effectiveness decreased as the time between application in the field and S. sclerotiorum inoculation increased. The B. subtilis cell suspensions applied on soybean leaves for up to 10 days under field conditions were able to provide a significant (P < 0.01) reduction in disease severity by approximately 20–90% at 5 days after the S. sclerotiorum inoculation. When rated 15 days after S. sclerotiorum inoculation, plants treated with bacterial cells for ≤6 days reduced Sclerotinia stem rot severity by 15–70%. Most effectiveness was provided by the cell suspensions present on soybean leaves for <3 days under field conditions, which significantly (P < 0.01) reduced disease severity by 40–70% over 15 days. In comparison, the cell-free filtrates remaining on leaves for <6 days significantly (P < 0.01) reduced disease severity during the first 5 days after the inoculation, while the best cell-free filtrate treatments were those with ≤1-day intervals, which significantly (P < 0.01) reduced disease severity by 10–40% during 15 days after the inoculation. The effectiveness of B. subtilis was reduced when it rained after application.  相似文献   

5.
Fusarium graminearum is a common agent causing Fusarium head blight (FHB) on wheat throughout the world. Aggressiveness is crucial for understanding the interaction between host-pathogen in the FHB-wheat system. In this paper, we modified and validated the Petri-dish test originally described by Mesterhazy (Phytopathologische Zeitschrift 93:12–25, 1978) to quantify the aggressiveness of 25 F. graminearum strains using four durum wheat cultivars with different resistance levels for FHB. The results were highly significant and correlated with those obtained using adult plants in the growth chamber and in the field (r = 0.94, P < 0.001 and r = 0.65, P < 0.001, respectively). The Petri-dish test was further investigated for its repeatability and stability in different durum wheat cultivars and highly significant correlation coefficients were obtained (r = 0.90–0.91 (P < 0.001), 0.89–0.95 (P < 0.001), respectively). In this study, we also demonstrated that germination rate reduction and coleoptile length reduction are parameters involved with aggressiveness of F. graminearum. The mean of three disease parameters from the modified Petri-dish method is introduced in this paper as a new parameter for aggressiveness and named “Petri-dish aggressiveness index”. The results obtained reveal that this modified Petri-dish test is rapid, reliable and stable with different durum wheat cultivars, and yields highly significant correlation coefficients with floret and ear inoculations, thus it is suitable to be used for quantification of aggressiveness of F. graminearum.  相似文献   

6.
Spot blotch, caused by Cochliobolus sativus (Ito & Kuribayashi) Drechs. ex Dastur, is one of the important diseases of wheat worldwide. The main objective of this study was to investigate the phenotypic and genotypic variability among C. sativus isolates from the hills and plains in Nepal. A total of 48 monoconidial isolates of C. sativus from the hills (n = 24 isolates) and plains (n = 24 isolates) in Nepal were analyzed for morphology, aggressiveness and genetic structure. C. sativus isolates were grouped into three categories on the basis of their colony texture and mycelia colour. Thirteen isolates from the hills and plains belonging to three morphological groups were randomly selected and evaluated for aggressiveness on eight wheat cultivars (Chirya 1, Chirya 7, Milan/Shanghai 7, SW 89–5422, PBW 343, BL 1473, BL 3036, and RR 21) at the seedling stage. Nonparametric analysis revealed that the isolates from the plains (median disease rating of 5) were significantly (P = 0.0001) more aggressive than the isolates from the hills (median disease rating of 3). A significant (P = 0.0001) isolate by cultivar interaction was demonstrated and the isolates from the same geographic region and morphological group displayed different degrees of aggressiveness on wheat cultivars tested. Combined IS-PCR and rep-PCR analyses revealed moderate gene diversity (H = 0.24 and 0.25 for the hills and plains, respectively). Low linkage disequilibrium (LD) value and non-significant (P = 0.001) population differentiation (G″ST = 0.05) were detected, indicating that isolates of C. sativus from the hills and plains in Nepal were genetically similar. Analysis of molecular variation (AMOVA) revealed low (7%) levels of genetic variation between the hill and plain populations, whereas >93% of genetic variation was found within populations. Overall, C. sativus isolates from Nepal are pathologically and genetically diverse, and such information will be useful in developing wheat cultivars resistant to C. sativus.  相似文献   

7.
The use of cultivar mixtures is increasingly practical in wheat stripe rust management. Field experiments with wheat cultivar mixtures were conducted to determine their effects on temporal and spatial patterns of stripe rust epidemics in three regions. In the Beijing and Gangu fields, where the epidemics were caused by artificial inoculation, disease incidence and the area under the disease progress curve (AUDPC) of the cultivar mixtures were significantly lower (P < 0.05) than those of the susceptible pure stands. We defined the relative effectiveness of cultivar mixture on disease development related to that in pure stands (REM). The results demonstrated that in many treatments of mixtures of susceptible cultivar with resistant cultivars at various ratios in different locations, their effects on disease reduction were positive (REM < 1). The reduction of epidemic rate in cultivar mixtures expressed in either early season or late season depended on the initial pattern of disease and cultivar mixture treatments. Semivariograms were used to determine the spatiotemporal patterns of disease in the Gangu field. The spatial analysis showed clear spatial patterns of the disease in all four directions of the fields on susceptible pure stands but not on cultivar mixtures. The results implied that the mechanisms of cultivar mixture on disease management might include the interruption of disease spatial expansion and a physical barrier to pathogen inoculum by resistant cultivars.  相似文献   

8.
The effect of a chitosan coating on antifungal activity and rate of respiration, chitinase and β, 1-3 glucanase activities with reference to papaya variety ‘Rathna’ was investigated. One percent chitosan, extracted from locally available prawn waste, was selected as the effective concentration to inhibit spore germination via a series of experiments on potato dextrose agar. Rate of respiration and the concentration of CO2 in the internal cavity of chitosan-treated and untreated papaya were tested via gas chromatography. Chitinase and β,1-3 glucanase activities were tested in peel samples using gel diffusion and spectrophotometric assays, respectively. Complete inhibition of spore germination was observed in-vitro at treatments of 1% chitosan and above. This concentration significantly (P < 0.05) reduced both disease incidence and severity on inoculated fresh papaya. Significant (P < 0.05) decrease was observed in rate of respiration while internal CO2 concentration of the fruit increased (P < 0.05) with the chitosan treatment. Chitinase and β,1-3 glucanase activities of papaya variety Rathna subjected to chitosan treatment were much higher than in the untreated control. Chitosan shows antifungal activity to the anthracnose disease causing fungus and stimulates the defense response on the papaya peel by increasing the chitinase and β,1-3 glucanase activities. The antifungal activity of chitosan could be attributed to the induction of elicitation activity due to these defense enzymes. It also forms a semi-permeable coating around the fruit and extends storage life of papaya by reducing the rate of respiration and delaying ripening.  相似文献   

9.
Apple proliferation (AP), caused by ‘Candidatus Phytoplasma mali’, is an economically important disease affecting many apple-growing areas in Europe. A new TaqMan real-time PCR assay was established for absolute quantification of ‘Ca. P. mali’ by using a single-copy gene of the host plant as a reference, which is amplified with the pathogen DNA in a single-tube reaction. Normalised estimates of phytoplasma concentration are ultimately expressed as the number of phytoplasma cells per host plant cell. The assay was used to monitor the ‘Ca. P. mali’ titre over the course of two growing seasons in roots and branches of symptomatic and asymptomatic but AP-positive apple trees. All 252 root samples from symptomatic and asymptomatic trees tested positive, with an average number of 59.8 ± 5.68 (standard error) and 55.1 ± 9.83 ‘Ca. P. mali’ per host cell, respectively. From the 378 shoot samples analysed, 81% of the symptomatic and only 20% of the asymptomatic samples were AP-positive with an average number of 9.4 ± 1.04 and 0.7 ± 0.13 ‘Ca. P. mali’ per host cell, respectively. This strengthens evidence that not the pathogen occurrence alone but the presence of a certain quantity of ‘Ca. P. mali’ in the aerial tree sections is involved in symptom expression. In addition, pronounced seasonality of the phytoplasma concentration was found, not only in branches, but also for the first time in roots of symptomatic and asymptomatic apple trees. Highest phytoplasma levels in roots were detected from December to May.  相似文献   

10.
Leaf blast suppression in multilines was evaluated based on the number of susceptible lesions observed in a pure stand of susceptible rice cultivar Sasanishiki, and in 1 : 1 and 1 : 3 mixtures of Sasanishiki and a resistant near-isogenic line, Sasanishiki BL4 or BL7, from 1998 to 2001. The number of lesions first observed in fields in the 1 : 1 and 1 : 3 mixtures were close to theoretical numbers calculated using the number of lesions observed in the pure stands and the ratios of the susceptible Sasanishiki in the mixtures. The ratio of the number of lesions in the 1 : 1 and 1 : 3 mixtures to the number in the pure stand was 0.29 and 0.09, respectively. The relationship between these ratios and the ratios of susceptible Sasanishiki in mixtures was defined in an equation to estimate the degree of leaf blast suppression. Validation studies for the ratios of the number of lesions in the 1 : 1 and 1 : 3 mixtures to the number in the pure stand were conducted in two different locations and showed that the ratios are almost acceptable. The calculated autoinfection to alloinfection ratio was 1.3 and 1.4 in the 1 : 1 and 1 : 3 mixtures, respectively, suggesting that the calculated ratio will affect the degree of leaf blast suppression. Thus, predictors were obtained to estimate leaf blast suppression for effective blast control in multilines.  相似文献   

11.
During 2005–2007, under the environmental conditions of Cacak (43°53’N; 20°21’E), western Serbia, the effect of Plum pox virus (PPV) on the phenology of vegetative shoot and fruit growth was investigated in a plum orchard of cv. ‘Cacanska Rodna’ including trees non-infected with PPV and those with infection and clearly visible symptoms, as verified by RT-PCR. The results showed that PPV did not affect the growth phenology of the vegetative shoot (length and thickness) and the fruit growth. However, it caused negative effects on the average length (22.31 ± 0.28 cm in non-infected trees, 18.35 ± 0.07 cm in infected trees) and thickness (4.21 ± 0.03 mm in non-infected trees, 4.01 ± 0.02 mm in infected trees) of vegetative shoots as well as on the average fruit weight (20.43 ± 0.16 g in non-infected fruits, 17.58 ± 0.18 g in infected fruits) and fruit dimensions. The greatest effect of PPV during the trial was the induction of a massive premature fruit drop and, consequently, a 52.94% decrease in total yields per tree (18.0 ± 1.10 kg) and unit area (12.0 ± 0.89 t ha-1) in infected vs non-infected trees.  相似文献   

12.
The greater wax moth Galleria mellonella L. (Lepidoptera: Pyralidae) is occasionally found in beehives and is a major pest of stored wax. Entomopathogenic fungi have recently received attention as possible biocontrol elements for certain insect pests. In this study, 90 isolates of Beauveria bassiana and 15 isolates of Metarhizium anisopliae were screened for proteases and lipases production. The results showed significant variations in the enzymatic action between the isolates. In the bioassay, the selected isolates evinced high virulence against the 4th instar of the G. mellonella larvae. The isolates BbaAUMC3076, BbaAUMC3263 and ManAUMC3085 realized 100% mortality at concentrations of 5.5 × 106 conidia ml−1, 5.86 × 105 conidia ml−1, and 4.8 × 106 conidia ml−1, respectively. Strong enzymatic activities in vitro did not necessarily indicate high virulence against the tested insect pest. The cuticle of the infected larvae became dark and black-spotted, indicating direct attack of fungus on the defense system of the insects. The LC50 values were 1.43 × 103, 1.04 × 105 and 5.06 × 104 for Bba3263AUMC, Bba3076AUMC and Man3085AUMC, respectively, and their slopes were determined by computerized probit analysis program as 0.738 ± 0.008, 0.635 ± 0.007 and 1.120 ± 0.024, respectively.  相似文献   

13.
Citrus canker assessment data were used to investigate effects of using the Horsfall-Barratt (H-B) scale to estimate disease compared to direct estimation to the nearest percent. Twenty-eight raters assessed each of two-hundred infected leaves (0–38% true diseased area). The data were converted to the H-B scale. Correlation (r) showed that direct estimates had higher inter-rater reliability compared to H-B scaled data (r = 0.75 and 0.71 for direct estimates and H-B scaled data, respectively). Lin’s concordance correlation (LCC, ρ c ) analysis showed individual rater estimates by direct estimation had better agreement with true values compared to H-B scaled data. The direct estimates were more precise compared to H-B scaled data (r = 0.80–0.95 and 0.61–0.90, respectively), but measures of generalised bias or accuracy (C b ) were similar for both methods (0.38–1.00). Cumulative mean disease and cumulative variance of the means were calculated for each rater on a leaf-by-leaf basis. Direct estimates were closer to the true severity 59.5% of the time, and to the cumulative true sample mean 53.7% of the time, and to the cumulative true sample mean variance 63.6% of the time. Estimates of mean severity for each leaf based on estimates by 3, 5, 10, 20 and 28 raters were compared to true disease severity. LCC showed that rater-means based on more raters had better agreement with true values compared to individual estimates, but H-B scale data were less precise, although with means based on ≥ 10 raters, agreement was the same for both assessment methods. Magnitude and dispersion of the variance of the means based on H-B scaled data was greater than that by direct estimates. H-B scaling did not improve reliability, accuracy or precision of the estimate of citrus canker severity compared to direct visual estimation.  相似文献   

14.
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15.
To investigate the frequency distribution of purple seed stain of soybean caused by Cercospora kikuchii in two experimental fields in 2004, we set up rows 75 cm apart and sowed two asymptomatic seeds at each of positions 20 cm apart in each row. We sowed purple-stained seeds infected with the pathogen as inocula at four points instead of asymptomatic seeds in each field. We assessed disease incidence in harvested seeds by counting the numbers of purple-stained and asymptomatic seeds. To determine the spatial distribution of the disease, we grouped the field points into analytical units of several sizes. Beta-binomial and binomial distributions described the distribution patterns of purple-stained seeds. The smallest value of α, a beta-binomial parameter, occurred with analytical units that contained three or nine points next to each other within a single row, suggesting that these units showed the most aggregated distribution of the disease, each of the patches of seeds infected with C. kikuchii could be defined approximately by the area covered by three or nine points (75 × 60 or 75 × 180 cm), and the disease tended to infect plants next to each other within rows.  相似文献   

16.
A nonpathogenic strain of Agrobacterium vitis VAR03-1 was tested as a biological control agent against crown gall of grapevine (Vitis vinifera L.). A mixture of the nonpathogenic strain VAR03-1 and a tumorigenic strain G-Ag-27 of A. vitis at cell ratios of 1 : 1, 3 : 1, 9 : 1, and 99 : 1 significantly inhibited gall formation and size on stems of tomato (Lycopersicon esculentum Mill.). Strain VAR03-1 also inhibited gall formation on stems of both tomato and grapevine at a 1 : 1 cell ratio with several tumorigenic A. vitis strains isolated from different fields of grapevine in Japan. In biological control tests, when roots of grapevine and tomato seedlings were soaked in a cell suspension of strain VAR03-1 for 24 h before a 1-h soaking in a cell suspension of the pathogen and subsequent planting in pots of infested soil, strain VAR03-1 significantly reduced the incidence of gall formation on both plants.  相似文献   

17.
The vertical distribution of leaf blast lesions caused by the fungus Pyricularia grisea was studied to estimate the degree of leaf blast suppression in rice multilines in experimental paddy fields for 4 years. Leaf blast in 1 : 1 and 1 : 3 mixtures of susceptible rice cultivar Sasanishiki and its resistant near-isogenic line, Sasanishiki BL7, developed slower than that in pure stands of Sasanishiki. The average distance of lesions on leaves from the ground in the 1 : 3 mixtures was significantly lower than that in the pure stands at the end of leaf blast epidemics (at booting stage). This result shows that the distribution of leaf blast lesions in the upper layer differs between the susceptible pure stands and the 1 : 3 mixtures at the end of leaf blast epidemics.  相似文献   

18.
Resistance to the fungicide boscalid in laboratory mutants of Botryotinia fuckeliana (Botrytis cinerea) was investigated. The baseline sensitivity to boscalid was evaluated in terms of colony growth (EC50 = 0.3–3 μg ml−1; MIC = 10–30 μg ml−1) and conidial germination (EC50 = 0.03–0.1 μg ml−1; MIC = 1–3 μg ml−1) tests. Mutants were selected in vitro from wild-type strains of the fungus on a fungicide-amended medium containing acetate as a carbon source. Mutants showed two different levels of resistance to boscalid, distinguishable through the conidial germination tests: low (EC50 ∼ 0.3 μg ml−1, ranging from 0.03 to 1 μg ml−1; MIC > 100 μg ml−1) and high (EC50 > 100 μg ml−1) resistance. Analysis of meiotic progeny from crosses between resistant mutants and sensitive reference strains showed that resistant phenotypes were due to mutations in single major gene(s) inherited in a Mendelian fashion, and linked with both the Daf1 and Mbc1 genes, responsible for resistance to dicarboximide and benzimidazole fungicides, respectively. Gene sequence analysis of the four sub-units of the boscalid-target protein, the succinate dehydrogenase enzyme, revealed that single or double point mutations in the highly conserved regions of the iron-sulphur protein (Ip) gene were associated with resistance. Mutations resulted in proline to leucine or phenylalanine replacements at position 225 (P225L or P225F) in high resistant mutants, and in a histidine to tyrosine replacement at position 272 (H272Y) in low resistant mutants. Sequences of the flavoprotein and the two transmembrane sub-units of succinate dehydrogenase were never affected.  相似文献   

19.
Two isolates of Streptomyces spp. DAUFPE 11470 and DAUFPE 14632 were evaluated to determine the antagonist–pathogen inoculum concentration relationship under greenhouse conditions. Pathogen and antagonist concentration, significantly (P < 0.05) affected development of Fusarium disease in maize with a significant interaction between pathogen and antagonist concentration. Dose–response relationship also differed significantly (P < 0.05) between the two isolates, but both isolates demonstrated effective control of Fusarium disease, regardless of pathogen concentration. The isolate DAUFPE 11470 provided the most effective control. The lowest value for disease incidence occurred at low pathogen (103 chlamydospore g−1 soil) and high antagonist concentration (106 cfu ml−1) for both isolates. The disease incidence for control plants ranged from 19% to 76%. However, in relation to control the lowest disease reduction occurred at low pathogen (103 chlamydospore g−1 soil) and high antagonist concentrations (106 cfu ml−1). These reductions were 10.6% and 13% for DAUFPE 14632 and DAUFPE 11470, respectively. The highest disease reductions, in relation to control plants, occurred at high pathogen (106 chlamydospore g−1 soil) and antagonist (106 cfu ml−1) concentrations for both isolates. These values were 55% and 62.2% for DAUFPE 14632 and DAUFPE 11470, respectively. The chlamydospore germination of Fusarium moniliforme was affected by glucose addition, antagonist isolates and type of inoculum. The lowest chlamydospore germination was observed with bacterial suspensions of the isolates, for all glucose additions. The results suggested that both Streptomyces spp. isolates were effective at different doses as biocontrol agents against F. moniliforme. Also, there was evidence for at least two mechanisms of biocontrol and that apparently, both isolates showed the same mechanisms of biocontrol action related to production of bioactive compounds and competition for carbon. Further studies will be developed to improve the level and effectiveness of control by these isolates.  相似文献   

20.
Bacterial blight disease of Persian walnut (Juglans regia, L.), caused by Xanthomonas arboricola pv. juglandis (Xaj), leads to significant nut losses in northern, central and western areas of Iran. To identify the natural sources of resistance to disease in the endemic walnut genotypes of Iran, sixteen walnut genotypes, collected from different areas of Hamedan province, were inoculated with Xaj in a randomized complete block design with five replicates for each genotype. Two-year old genotypes were gently sprayed with a suspension of bacteria adjusted to approximately 2 × 109 cfu ml−1 of distilled water in May. Infected leaves were rated for disease 28 and 42 days after inoculation, using a 0 to 5 severity scale, based on the number, size and distribution of lesions on the leaves. Data analyses showed that there were variations among genotypes in response to pathogen. Upon inoculation by bacterial suspension genotype 94 showed the highest resistance to both disease incidence and its progress after 4–6 weeks of infection. Genotype 65 showed high susceptibility to disease and genotype 69 showed high susceptibilities both to disease incidence and its progress after 4–6 weeks of infection.  相似文献   

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