首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 46 毫秒
1.
Standard area diagrams (SADs) to assess the severity of potato early blight (Alternaria grandis) on leaves of potato (Solanum tuberosum L.) were developed and validated. The proposed SADs include images of leaves with 10 distinct disease severities (0.1, 1, 3, 5, 10, 20, 40, 60, 80 and 100 %). The SADs were validated by 12 raters who had no previous experience in evaluating plant disease. Lin’s concordance correlation analysis of estimated vs. actual disease severity (based on image analysis) showed that precision and accuracy improved for most raters using the SADs, compared to assessments made without the SADs. The SADs improved accuracy (coefficient of bias, C b ?=?0.97 and 0.99, without and with SADs, respectively) and agreement (Lin’s concordance correlation coefficient, ρ c ?=?0.91 and 0.98 without and with SADs, respectively) of the estimates of severity. Severity estimates were more reliable when using SADs (coefficient of determination, R 2 ?=?0.80 unaided and R 2 ?=?0.95 with SADs, and the intra-class correlation ρ?=?0.86 without SADs and ρ?=?0.97 using the SADs). The SADs improved raters’ ability to accurately, precisely and reliably estimate potato early blight severity, and as such can be used to assess severity for several purposes, including breeding for resistance, fungicide screening, and pathotype characterization.  相似文献   

2.
The aim of this study was to develop and validate a standard area diagram set (SADs) to assess the severity of peach rust, caused by Tranzschelia discolor. The proposed SADs includes ten images of leaves with a range of severity (0.1, 0.5, 1.0, 2.0, 5.0, 10, 15, 20, 25 and 30%). The SADs was validated by 14 raters who had no experience in plant disease severity estimation. In the first step of the validation, the raters made severity estimates of 50 leaves with a range of rust severity without using SADs. In the second step, the same raters estimated severity of rust on the same 50 leaves using the SADs to aid estimation. Lin’s concordance correlation analysis showed that both precision and accuracy improved when the raters used the SADs compared to the assessments made without SADs. Accuracy, as measured by the coefficient of bias (C b ) improved from 0.70 to 0.98, without and with SADs, respectively, and precision measured by the correlation coefficient (r) improved from 0.85 to 0.90, without and with SADs, respectively. Overall agreement, measured by Lin’s concordance correlation coefficient (ρ c ), improved from 0.59 to 0.88 without and with SADs, respectively. Furthermore, estimates were more reliable when using SADs: the coefficient of determination (R2) was 0.60 without and 0.73 with SADs; and the intra-class correlation coefficient (ρ) was 0.72 without, and 0.86 with SADs. Thus, the use of SADs improved the precision, accuracy and reliability of visual estimates of severity of peach rust.  相似文献   

3.
A standard area diagram set (SAD) to aid visual assessment of loquat scab (caused by Fusicladium eriobotryae) severity on fruit was developed and evaluated for improving accuracy, precision and reliability of visual estimates. The SAD set contains eight black and white diagrams of diseased fruit with severity values from 2 % to 98 %. To evaluate the SADs, a group of 20 raters (comprising 10 ‘experienced’ and 10 ‘inexperienced’ raters) assessed the same set of 50 images three times, the first without SADs and the second and third using the SADs as an aid. Only for the group of inexperienced raters did SADs significantly improve accuracy (bias correction factor, C b?=?0.93 without SADs and 0.98 with SADs), precision (correlation coefficient, r?=?0.88 without SADs and r?=?0.96 with SADs) and overall agreement (Lin’s concordance correlation coefficient, ρ c?=?0.82 without SADs and ρc with SADs = 0.95) of the estimates. Accuracy and precision of the estimates by inexperienced raters were significantly higher than those obtained by the experienced raters, especially for the second assessment with SADs. Inter-rater reliability was improved when SADs were used by inexperienced raters, whereas a high degree of intra-rater reliability was obtained by both experienced and inexperienced raters when using SADs. The SADs developed in this study were useful for obtaining more accurate, precise and reliable assessments of loquat scab for inexperienced raters, and should be used as an aid for assessing scab in epidemiological studies or monitoring for decision-making purposes.  相似文献   

4.
A standard area diagram set (SADs) with eight severity values ranging from 0.5 to 32% was evaluated as a tool to improve the accuracy of the estimates of Phomopsis leaf blight severity on eggplant by ten inexperienced raters. A first assessment in a 50-leaf dataset of digital images was performed unaided (UN, no SAD). Two further aided (A) assessments, conducted two (A1) and four weeks after the first (A2) unaided one were performed. The precision of the estimates, as indicated by the Pearson’s correlation coefficient (r), improved significantly when using the aid (A1: r = 0.96 and A2: r = 0.96) compared to unaided (UN: r = 0.79). However, the generalized bias (C b) was not significantly affected because the unaided estimates were already quite accurate (C b = 0.93). The overall concordance (ρ c) was significantly improved due to the large gains in precision when using the SADs. The raters’ estimates were more uniform (ρ c > 0.9) when using the aid, with progressive gains in the reliability of the estimates among them, indicated by the concordance correlation coefficient statistics. The SADs proposed in this study will be useful in severity estimation during field work involving multiple raters, especially as use of the SADs results in less variable estimates, improving accuracy and reliability among raters.  相似文献   

5.
This study aimed to develop and validate a standard area diagram (SAD) set to quantify the severity of spot blotch, caused by Bipolaris sorokiniana, on wheat leaves. The proposed SAD set includes images of leaves with 11 distinct disease severities (0·1, 1, 5, 10, 20, 30, 40, 50, 60, 70 and 83%). The SAD set was validated by 12 raters without experience in evaluating plant disease. Lin's concordance correlation analysis of estimated versus actual disease severity (based on image analysis) showed that precision and accuracy improved for all raters using the SAD set in contrast to assessments made without it. The SAD set improved accuracy (coefficient of bias, Cb = 0·88 and 0·99, without and with the SAD set, respectively) and agreement (Lin's concordance correlation coefficient, ρc = 0·81 and 0·96 without and with the SAD set, respectively) of the estimates of severity. The severity estimates were also more reliable when using the SAD set (coefficient of determination, R2 = 0·76 unaided and R2 = 0·92 with the SAD set, and intra‐class correlation ρ = 0·79 without the SAD set and ρ = 0·95 using the SAD set). The SAD set proposed in this study will improve the accuracy and reliability of estimates of spot blotch severity on wheat leaves.  相似文献   

6.
Pecan scab (Fusicladium effusum) causes losses of pecan nutmeat yield and quality in the southeastern United States. Disease assessment relies on visual rating, which can be inaccurate and imprecise, with poor inter‐rater reliability. A standard area diagram (SAD) set for pecan scab on fruit valves was developed. A set of 40 images of diseased fruit valves with known severity was assessed twice by 23 raters. The first assessment was conducted without SADs, and the second assessment was made using the SADs as an aid. SADs improved rater accuracy (correction factor, Cb = 0·86 and 0·97, without and with SADs, respectively) and agreement (Lin’s concordance correlation coefficient, ρc = 0·79 and 0·89 without and with SADs, respectively) with true values. SADs improved inter‐rater reliability (intra‐class correlation coefficient, ρ = 0·77 and 0·96 without and with SADs, respectively). The least accurate and precise raters without SADs improved more using SADs compared to the most accurate and precise raters. Experienced raters had significantly higher accuracy and precision compared to inexperienced raters, but only when unaided by the SAD set. There was no significant difference in time to assess images without SADs, but experienced raters using SADs were faster compared to inexperienced raters. There was a slight tendency for faster raters to assess more slowly, and slower raters to assess faster when using SADs. SADs improve rater estimates of pecan scab severity on fruit, and this SAD set should be useful for assessment where greater precision, accuracy and inter‐rater reliability are required.  相似文献   

7.

Apple blotch (Marssonina coronaria) is a foliar disease of increasing importance globally. Methods to quantify the disease and knowledge about epidemiology are required for new studies on the disease. The objectives of this study were to develop a standard area diagram set (SADs) to assess apple blotch severity and to describe the temporal progress of the disease under field conditions on older and younger leaves of two apple cultivars. For the development of SADs, symptomatic leaves were collected and scanned to obtain the actual severity. Based on the pattern of the disease, a SADs was elaborated and validated. Leaf severities were estimated without and with SADs by 12 raters to validate the tool. After validation, the SADs was used to assess apple blotch in older and younger leaves of selected shoots during the vegetative cycle of cvs. Eva and Gala. SADs severities ranged from 0.2 to 96%. Accuracy, precision, and reliability of the estimates were significantly improved when the SADs was used. In the field, the onset of apple blotch was in late spring and greater increases in severity occurred during summer. Rates of disease progress ranged from 0.09 to 0.13. Epidemics were different in older and younger leaves at the end of the apple vegetative cycle for both cultivars tested. Our work provided a tool for apple blotch quantification and described the disease progress curve under subtropical conditions, which can contribute as basis for future studies.

  相似文献   

8.
The objective of this study was to assess the effect of severity of stripe rust (Puccinia striiformis) on the hyperspectral reflectance of wheat. A total of 110 leaf samples with a range of disease severity were collected at the heading stage (Stage ?, 29 April) and grain filling stage (Stage II, 21 May). The spectra of the adaxial and abaxial surfaces of the leaf samples were taken using an ASD Leaf Clip, and the spectral characteristics were analysed. The photochemical reflectance index (PRI) was used to build two linear regression functions from the two growth stages using 70 leaves, and the remaining 40 leaves were used to validate their effectiveness. The results indicated that P. striiformis caused changes in foliar water and chlorophyll, and those changes made it feasible to assess disease severity using in situ hyperspectral measurements. In general, the reflectance values from the adaxial surfaces of the leaf samples were smaller than the abaxial surfaces. In comparison to Stage ?, the spectral contrast of four different disease severities was greater at Stage II. By comparing the regression functions, the coefficient of determination using the set of leaves for validation for Stage ? (R 2?=?0.74) was smaller than that for Stage II (R 2?=?0.83). However, the coefficient of determination for validation for Stage ? (R 2?=?0.91) was slightly larger than that of Stage II (R 2?=?0.90). The results suggest that the ASD Leaf Clip is an ideal tool to collect in situ hyperspectral measurements of wheat leaves showing symptoms of stripe rust, and Stage II is more appropriate to assess severity compared to Stage ?.  相似文献   

9.
Error in estimates of plant disease severity occur and standard area diagrams (SADs) help improve accuracy and reliability. The effects of diagram number in SADs are unknown. The objective of this study was to compare estimates of pecan scab severity made without SADs, and using three‐, five‐, seven‐ or 10‐diagram SADs. Disease severity was estimated to the nearest percent (NPE), or classified to the closest reference diagram value using a scale. Twelve raters assessed 20 images of scabbed pecan valves with and without the SADs using NPEs and the scale method (values were converted to midpoints prior to analysis). Increases in diagram number using NPEs did not necessarily result in more accurate or reliable estimates. Inter‐rater reliability was positively correlated with number of diagrams using NPEs (r = 0·3288 (P < 0·0001)) or a scale (r = 0·2803 (P < 0·0001)). The least accurate estimates improved the most using SADs with NPEs, but the gain did not relate to number of diagrams; as few as three diagrams reduced error of inaccurate estimates as much as five, seven or 10 diagrams. When used as a scale, only estimates made with 10‐diagram SADs had similar accuracy and inter‐rater reliability to estimates made using SADs with NPEs. Maximum disease severity and the disease severity range for the pathosystem and the SADs are important factors and will probably influence resulting accuracy and reliability. The ramifications of diagram numbers in SADs and assessment methods on accuracy and reliability of disease estimates are discussed.  相似文献   

10.
Methods to estimate disease severity vary in accuracy, reliability, ease of use and cost. Severity of septoria leaf blotch (SLB, caused by Zymoseptoria tritici) was estimated by four raters and by image analysis (assumed actual values) on individual leaves of winter wheat in order to explore accuracy and reliability of estimates, and to ascertain whether there were any general characteristics of error. Specifically, the study determined: (i) the accuracy and reliability of visual assessments of SLB over the full range of severity from 0 to 100%; (ii) whether certain 10% ranges in actual disease severity between 0 and 100% were more prone to estimation error compared with others; and (iii) whether leaf position affected accuracy within those ranges. Lin's concordance correlation analysis of all severities (0–100%) demonstrated that all raters had estimates close to the actual values (agreement: ρc = 0·92–0·99). However, agreement between actual SLB severities and estimates by raters was less good when compared over short 10% subdivisions within the 0–100% range (ρc = ?0·12 to 0·99). Despite common rater imprecision at estimating low and high SLB severities, individual raters differed considerably in their accuracy over the short 10% subdivisions. There was no effect of leaf position on accuracy or precision of severity estimate on separate leaves (L1–L3). Pursuing efforts in understanding error in disease estimation should aid in improving the accuracy of assessments, making visual estimates of disease severity more useful for research and applied purposes.  相似文献   

11.
The objectives of this study were to assess the reliability and accuracy of visual methods used to quantify the severity of bacterial spot (Xanthomonas arboricola pv. pruni) symptoms and evaluate the effects of rater experience on the quality of disease estimates. Three cohorts of raters differing in experience with disease assessment rated three sets of peach or nectarine leaves (n ≥ 103; disease severity levels from 0% to 100%) by direct estimation of percentage leaf area with symptoms. Four of the experienced raters also rated the leaves using a 1–7 interval scale. Actual disease severity on the leaves was obtained with the APS assess image analysis software. Equivalence tests based on a bootstrap analysis were used to compare the rating scale and direct estimation methods, and to evaluate the effects of rater experience, computer training and human instruction on accuracy and reliability of disease estimates. In concordance analysis of continuous variables, with data from scale converted to percentage, the direct estimation method resulted in more accurate and reliable estimates than the interval scale. Analysing the scale data without conversion to percentage improved the concordance statistics for the scale but not sufficiently to match the direct estimation method. Accuracy was affected more by rater experience and intrinsic ability than reliability. Instruction on disease symptoms resulted in the largest improvement in estimates from inexperienced raters. Accurate and reliable direct estimation of bacterial spot severity on peach and nectarine can be made by raters with varying levels of experience provided they receive sufficient instruction.  相似文献   

12.
Field trials conducted on a yellow-red latossol (pH 6.0), replicated in 2010 and 2011, sought to examine the effect of silicon, phosphite minerals, synthetic fungicides and genetic resistance for wheat blast management (Magnaporthe grisea) in Central Brazil. Disease intensity was measured on cvs. BRS 264 and BR18 subjected to the following Si treatments: pre-plant furrow application of Ca & Mg silicate (300 kg ha-1); post-plant scattered application of Ca & Mg silicate on top of the soil (1 ton ha-1); multiple foliar SiO2 applications (30 g l -1); and non-treated control. Blast incidence and severity were scored. Further experiments were conducted on cv. BR-264, for examination of the effect of potassium phosphite and synthetic fungicides on wheat blast intensity, with the following treatments: K2HPO3 (1ml l -1); epoxinazole + pyraclostrobin (700 ml ha-1); tebuconazole (600 ml ha-1); tebuconazole + trifloxystrobin (750 ml ha-1); and non-treated control. In 2010, disease intensity was lower than in 2011. In the silicate experiments, disease was significantly lower when plants were treated with foliar or furrow silicate. Si applications significantly reduced disease in BRS-264. While BR-18 consistently demonstrated lower disease levels, cv. BRS-264 generally responded more markedly to silicon applications. In the phosphite/fungicide experiment of 2010, all treatments reduced disease when compared with the control, and in 2011 phosphite efficiency was not significantly different from some fungicide treatments. Synthetic fungicides demonstrated an average blast control of 55% by severity values. Yields were increased in the phosphite-treated plots (by 9–80%), in the Si treatments (by 26–92%), and more so, and more consistently, with synthetic fungicides (by 90–121%). Combined results of all field studies, carried out under environmental conditions highly conducive to disease, indicated that control of wheat blast necessitates the joint integration of several alternatives for efficient disease management.  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.
Black leaf mold (BLM), caused by Pseudocercospora fuligena is a serious threat to tomato production in the humid tropics. Accurate information about the incubation (IP) and latent period (LP) under various host susceptibility and weather favourability circumstances will help to formulate holistic approaches to manage this disease. In this study, effects of temperature, wetness duration, and leaf age on the monocyclic components (IP and LP) of BLM were studied from growth chamber (GC) and greenhouse (GH) experiments as well as detached leaf assays in growth cabins. Linear interpolation and inflection point (of logistic regression model) methods were used to determine IP and LP. These two methods were highly correlated in GC (r 2?=?0.89; P?<?0.0001) and GH experiments (r 2?=?0.90; P?<?0.0001) except when the epidemics were not asymptotic. Thus, IP and LP were estimated according to inflection point method. There was a delay of at least 5 days of IP and LP when plants were left in non-humid open environment than when exposed to wetness durations of 1, 2 or 3 days after inoculation. In general, IP and LP became shorter as the temperature increased from 20–24 and then to 28 °C. In growth chambers, there was more disease and consequently shorter IP and LP on young and unfolded tomato leaves that were 1-, 3-, or 5-week old at the time of inoculation than 7-week old leaves. In the greenhouse, there was about 50 % more disease incidence and sporulation on 1-week than 3-week old leaves. The shortest IP (8–11 days) and LP (12–13 days) were recorded from two out of three GH experiments on 1-week old leaves at an ambient mean temperature of 28.5 °C. This study implicated that fresh market tomatoes planted during warm temperatures in 50-mesh greenhouses and exposed to extended periods of wetness are highly prone to BLM infection at their young stages of growth.  相似文献   

15.
With the aim of unravelling the role of airborne Fusarium graminearum inoculum in the epidemic of Fusarium head blight (FHB) caused by this species in wheat spikes, a network of Burkard air samplers was set up in five wheat fields distributed in Belgium from 2011 to 2013. Each year from April to July, the daily amounts of F. graminearum inoculum above the wheat canopy were quantified using a newly developed TaqMan qPCR assay. The pattern of spore trapping observed was drastically different per year and per location with a frequency of detection between 9 and 66% and a mean daily concentration between 0.8 and 10.2 conidia-equivalent/m3. In one location, air was sampled for a whole year. Inoculum was frequently detected from the wheat stem elongation stage until the end of the harvesting period, but high inoculum levels were also observed during the fall. Using a window-pane analysis, different periods of time around wheat flowering (varying in length and starting date) were investigated for their importance in the relation between airborne inoculum and FHB parameters (FHB severity, frequency of F. graminearum infection and DON). For almost all the combinations of variables, strong and significant correlations were found for multiple window lengths and starting times. Inoculum quantities trapped around flowering were highly correlated with F. graminearum infection (up to R?=?0.84) and DON (up to R?=?0.9). Frequencies of detection were also well correlated with both of these parameters. DON concentrations at harvest could even be significantly associated with the F. graminearum inoculum trapped during periods finishing before the beginning of the anthesis (R?=?0.77). Overall, these results highlight the key role of the airborne inoculum in F. graminearum epidemics and underline the importance of monitoring it for the development of disease forecasting tools.  相似文献   

16.
Preliminary studies were undertaken to establish the occurrence of Turnip mosaic virus (TuMV) resistance phenotypes in 99 Brassica napus and 32 B. carinata accessions, breeding lines and cultivars mostly from Africa, Australia, the Indian sub-continent or China. An isolate of TuMV pathotype 8 (WA-Ap1) was used in most inoculations. The influence of temperature on expression of resistance phenotypes was determined. Those identified were O (extreme resistance), RN (localised hypersensitivity), R (resistance to systemic movement without necrosis), +N (systemic infection with some necrosis), + (susceptibility), and RN/+ (systemic infection with necrosis limited to inoculated leaves). In the initial glasshouse evaluations with B. napus, 18 lines developed phenotype O, 42 RN, two + (both from Australia), and 30 segregated for O and RN, two for R and RN, one for O and R, two for O, R and RN, one for O, RN and +N, and one for RN and +N. Phenotype +N only occurred in two lines from India. In the initial glasshouse evaluations with B. carinata, 14 lines developed O, two RN or R, and one +; the 13 remaining lines segregated for phenotypes O and R (12), or RN and R (1). In B. carinata, phenotype RN only occurred in African lines, and phenotype + only in a line from Pakistan. The 18 B. napus and 14 B. carinata lines that developed phenotype O uniformly were re-evaluated at low (16 and/or 18 °C) and high (25 °C) temperatures in the glasshouse three or two times, respectively, and again under controlled environment room conditions at 16 and at 28 °C. While in most lines phenotype O was replaced by other phenotypes or segregated with other phenotypes at the higher temperatures, it occurred uniformly regardless of temperature in Chinese B. napus line (06-6-3777) and three African B. carinata lines (IP 117, ST 18 and ST 50). Graft inoculations confirmed extreme resistance in these four lines. Other promising lines which displayed phenotype O in >75 % of inoculated plants included for B. napus Chinese lines 06-p71-1 and 06-p74-4 and French line Cresor, and for B. carinata African lines Mbeya Green, ML-EM-1, ML-EM-7 and ML-EM-8, and Australian lines P 195923.3 and 30200533. Five promising lines segregated for phenotype RN, B. napus Ding 110, Hyola 42, Fan 028, ZY 007 and Qu 1104. Chinese B. napus line Ding 110 developed phenotype RN uniformly at high (25 and 28 °C) temperatures. Thus, in plants developing phenotypes RN, R and +, low temperature retarded virus multiplication in inoculated leaves to below the level at which it can be identified using ELISA. No clear phenotypic differences attributable to TuMV pathotype were found in tests in which isolates from pathotypes 1, 7 and 8 were used. This highlights the need for future evaluations for TuMV resistance in Brassica germplasm to be done at higher temperatures. This study also highlights the need to identify additional genes responsible for the different resistance and susceptibility reactions found, especially in B. carinata. The four lines that developed phenotype O uniformly at all temperatures and also withstood graft-inoculation will be particularly valuable for developing new TuMV-resistant cultivars of oilseed and forage Brassicas.  相似文献   

17.
The effect ofPyricularia oryzae, the causal organism of leaf blast in rice, on photosynthesis characteristics of rice leaves was measured in two greenhouse experiments. Leaf blast reduced photosynthesis not only through a reduction in green leaf area, but also through an effect on photosynthesis of green leaf tissue surrounding the lesions. The assimilation rate at light saturation (P max ) was more affected than the initial light use efficiency (). Dark respiration (R d ) increased as a result of infection. The experimental data were used to derive relations between leaf blast severity andP max , andR d .  相似文献   

18.
The green peach aphid, Myzus persicae (Sulzer) (Hemiptera: Aphididae), is a major pest of pepper. In this study, we collected data on the development, survival, fecundity, and proportion of apterous and alate forms of green peach aphid reared on five commercial pepper cultivars (Amiral, Erciyes, Mert, Mertcan, and Naz) at 25?±?1°C, 60?±?5% RH, and a photoperiod of 16:8 (L:D) h. We analyzed the life history raw data by using the age-stage, two-sex life table. The shortest development time (6.66 days) and highest fecundity (62.68 individuals) occurred on the Erciyes cultivar. The highest intrinsic rate of increase (r?=?0.332 d?1), finite rate of increase (λ?=?1.394 d?1), net reproductive rate (R0?=?62.7 offspring) and shortest mean generation time (T?=?12.45 d) also occurred on the Erciyes cultivar; while the lower fitness occurred on the Amiral, Mertcan and Naz cultivars. Our results compared differences in the population growth rate of M. persicae on different pepper cultivars. This information will be useful to individuals working in pest management programs particularly those involving M. persicae.  相似文献   

19.
Citrus canker (Xanthomonas citri subsp. citri, Xcc) is one of the most serious diseases citrus in Florida, and elsewhere in the world. The disease causes yield loss and some fresh fruit trade restrictions may apply. Cultural management techniques such as windbreaks may work by not only reducing wind speed, but also reducing the period of exposure of susceptible foliage or fruit to those wind speeds that support infection from incoming inoculum. To investigate the effect of exposure period to inoculum of Xcc, seedlings of canker-susceptible Swingle citrumelo were exposed to sprayed inoculum for increasing periods at different wind speeds. The incidence and severity of citrus canker was assessed. In three experiments the incidence and severity of citrus canker most often increased with longer periods of exposure to inoculum, especially so at wind speeds of ≥16 m/s compared to wind speeds of ≤5 m/s (wind speed also increased disease incidence and severity). Regression analysis demonstrated relationships between period of exposure to inoculum and the percent infected leaves per plant, the number of lesions per plant, the number of lesions per infected leaf, and for the percent of infected leaves with lesions on the petioles at wind speeds of ≥16 m/s (R2?=?0.16–0.72). Due to the effect of inoculum exposure period and wind speed, attempts should be made to minimize exposure of canker-susceptible citrus when wind speed is highest and inoculum is available. Windbreaks should help minimize periods of exposure to splashed inoculum in high winds.  相似文献   

20.
The herbicide diclofop-methyl caused an early and pronounced inhibition of the incorporation of [14C]acetate into leaf lipids of the sensitive plant species maize (Zea may L.), wild oat (Avena fatua L.), and barnyardgrass (Echinochloa crus-galli L.). With an EC50 value of approximately 10?7M inhibition was already apparent 0.5–4 hr after herbicide application. The fatty acid biosynthesis of tolerant bean (Phaseolus vulgaris L.), sugar beet (Beta vulgaris L.), and soybean (Glycine max L.) was not affected, with one exception [wheat (Triticum aestivum L.) belongs to the more tolerant species]; the inhibition of fatty acid biosynthesis, however, was in the same order of magnitude as in sensitive plants. More detailed studies showed that in wheat a recovery from inhibition of fatty acid biosynthesis occurred. Four days after herbicide application (0.18 kg diclofop-methyl/ha) in wheat normal fatty acid biosynthesis was restored, whereas in sensitive maize a 60% inhibition was maintained over the whole experimental period (8 days). The results support the view that tolerance of wheat to diclofop-methyl is based on its inactivation in leaves, whereas the tolerance of dicotyledonous species may probably lie at the level of the site of action of diclofop-methyl. In experiments with intact leaves, the inhibition of fatty acid biosynthesis resulted in an enhanced flow of [14C]acetate into organic acids and amino acids. This effect, however, was not always reproducible in experiments with leaf pieces or isolated root tips.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号