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Disease Progress Curve (disease + progress_curve)
Selected AbstractsVariety-specific Epidemiology of Cercospora beticola Sacc. and Consequences for Threshold-based Timing of Fungicide Application in Sugar BeetJOURNAL OF PHYTOPATHOLOGY, Issue 4 2010Ulrike Kaiser Abstract In Central Europe, fungicides to control leaf spot disease in sugar beet caused by Cercospora beticola are applied based on thresholds of disease incidence (DI, per cent of infected plants). As variety-specific fungicide application was not analyzed to date, the epidemiology of C. beticola and its effect on white sugar yield (WSY) in varieties with different susceptibility were investigated at seven sites in Germany and Austria in 2004 and 2005. All varieties reached the summary thresholds 5 / 15 / 45% DI in all environments. Fitting a logistic growth curve to DI revealed significant differences among varieties. At high disease pressure, susceptible varieties reached a considerably higher disease severity (DS, per cent of infected leaf area) at harvest and a larger area under disease progress curve (AUDPC) than resistant varieties. Fitting a logistic growth curve to DS showed an increasing differentiation among varieties with time. The growth rate estimated based on the logistic growth curve was the only variable that performed equally well in differentiating varieties under low and high disease pressure. With increasing disease pressure, varieties differed considerably in WSY, but differences between susceptible and resistant varieties were significant only in some environments. The disease-loss relation between AUDPC and relative WSY was variety-specific. Resistant varieties had an approximately identical WSY with and without infection and compensated for negative infection effects even at higher AUDPC. Therefore, at high disease pressure, resistant varieties had a higher relative yield compared to susceptible ones. However, our results indicate that there is no need to develop variety-specific thresholds, but resistant varieties reach the established thresholds later than susceptible ones. Consequently, the time of fungicide application can be delayed in resistant varieties. This will help to reduce the use of fungicides to the bare essentials as requested for the integrated crop protection management. [source] Identification of Critical Stage for Disease Development and Biocontrol of Alternaria Blight of Indian Mustard (Brassica juncea)JOURNAL OF PHYTOPATHOLOGY, Issue 4 2004P. D. Meena Abstract Fungicides mancozeb and carbendazim caused 100% reduction in mycelial growth of Alternaria brassicae over control in vitro while 1% (w/v) aqueous bulb extract of Allium sativum and leaf extract of Acacia nilotica caused significant reductions. In dual culture, GR isolate of Trichoderma viride performed the best among the test isolates of Trichoderma, causing 81%, 82% reduction in mycelial growth of A. brassicae over control. Performance of isolates SI-2, P and SI-1 of T. viride were at par (P < 0.01) with that of GR isolate. Spraying of A. brassicae at different ages of the mustard host plant identified 75 days after sowing (d.a.s.) as the most critical age of the mustard plant for development of Alternaria blight severity on the crop with 45 d.a.s. being the next most important one. Mancozeb was the best among all the treatments, resulting in the lowest disease severity on leaves of mustard at both Sewar and Ludhavai as also the lowest A-value (area under disease progress curve). Performance of bulb extract of A. sativum in checking the disease severity on leaves and pods was at par (P,<,0.05) with mancozeb. The GR isolate of T. viride was at par with mancozeb in checking blight severity on mustard leaves at Sewar while performance of the bioagent was significantly (P,<,0.05) inferior to the chemical fungicide at Ludhavai. Performance of the bioagent isolate GR of T. viride in checking the disease severity on pods was at par (P < 0.05) with mancozeb at both Sewar and Ludhavai, the treatment recording the lowest A-value on pods. While application of bulb extract of A. sativum resulted in highest seed yield at Sewar in 2001,2002, the bioagent isolate GR of T. viride did so at Ludhavai, both the treatments being at par (P < 0.05) with mancozeb and significantly higher than control. Application of bulb extract of A. sativum at 45 and 75 d.a.s. resulted in lowest blight severity on leaves and pods as also in highest seed yield among the different single and combination of treatments. Although disease severity in the treatment was at par (P < 0.05) with that in mancozeb, application of the plant extract at the two stages of crop growth resulted in significantly higher seed yield compared with the two applications of the chemical fungicide. However, application of the treatments singly only at 75 d.a.s., GR isolate of T. viride at 45 and 75 d.a.s., A. sativum 45 d.a.s. + T. viride 75 d.a.s., and T. viride 45 d.a.s. + A. sativum 75 d.a.s. resulted in seed yield at par (P < 0.05) with application of bulb extract of A. sativum at 45 and 75 d.a.s. [source] Linkage and quantitative trait locus mapping of foliage late blight resistance in the wild species Solanum verneiPLANT BREEDING, Issue 3 2006K. K. Sørensen Abstract The global cultivation of potato (Solanum tuberosum) is threatened by epidemics caused by new variants of the late blight pathogen, Phytophthora infestans. New sources of durable late blight resistance are urgently needed and these may be found in wild Solanum species. The diploid wild species, S. vernei, has not previously been subjected to mapping of quantitative trait loci (QTLs) for late blight resistance. Two populations designated HGIHJS and HGG, originating from a cross between a clone of S. vernei and two different S. tuberosum clones were evaluated in field trials for late blight infestation. The relative area under the disease progress curve (RAUDPC) was estimated and used for QTL mapping. A linkage map of S. vernei, comprising 11 linkage groups, nine of which could be assigned to chromosomes, was constructed. Results indicated that the resistance in S. vernei was quantitatively inherited. Significant QTLs for late blight resistance were identified on chromosomes VIII (HGG), VI and IX (HGIHJS). In addition, potential QTLs were detected on chromosomes VII (HGIHJS) and IX (HGG). A putative and a significant QTL for tuber yield were found on chromosomes VI and VII in HGG, but no linkage between yield and resistance was indicated. The QTL for late blight resistance, which mapped to chromosome IX, could be useful for late blight resistance breeding as it was located close to the microsatellite marker STM1051 in both populations. [source] QTL analysis of resistance to Fusarium head blight in wheat using a ,Wangshuibai'-derived populationPLANT BREEDING, Issue 4 2005M. Mardi Abstract Fusarium head blight (FHB) is a devastating disease that reduces the yield, quality and economic value of wheat. For quantitative trait loci (QTL) analysis of resistance to FHB, F3 plants and F3:5 lines, derived from a ,Wangshuibai' (resistant)/,Seri82'(susceptible) cross, were spray inoculated during 2001 and 2002, respectively. Artificial inoculation was carried out under field conditions. Of 420 markers, 258 amplified fragment length polymorphism and 39 simple sequence repeat (SSR) markers were mapped and yielded 44 linkage groups covering a total genetic distance of 2554 cM. QTL analysis was based on the constructed linkage map and area under the disease progress curve. The analyses revealed a QTL in the map interval Xgwm533-Xs18/m12 on chromosome 3BS accounting for up to 17% of the phenotypic variation. In addition, a QTL was detected in the map interval Xgwm539-Xs15/m24 on chromosome 2DL explaining up to 11% of the phenotypic variation. The QTL alleles originated from ,Wangshuibai' and were tagged with SSR markers. Using these SSR markers would facilitate marker-assisted selection to improve FHB resistance in wheat. [source] Late blight resistance in a diploid full-sib potato familyPLANT BREEDING, Issue 4 2004S. Costanzo Abstract Late blight, caused by Phytophthora infestans (Mont.) de Bary, is the most destructive disease of potato worldwide. As this pathogen can rapidly overcome major race-specific resistance genes, identifying the basis for enhanced quantitative resistance has become a crucial element for implementing advanced breeding strategies. A population of 230 full-sib progeny derived from a cross between two diploid hybrid Solanum phureja × S. stenotomum clones was evaluated for foliage resistance against late blight in replicated trials at multiple locations in Pennsylvania between 1999 and 2002. In field experiments, plants were evaluated visually for per cent defoliation, and area under the disease progress curve (AUDPC) was determined. The two parents and three control cultivars (,Atlantic', ,Kennebec' and ,Katahdin') were included in all trials. In all three experiments, the presence of a significant number of clones exhibiting transgressive segregation were observed. There were significant differences among environments as well as among clones, and the clone × environment interaction was also significant. Stability analysis revealed that 37 clones made a significant contribution to the overall environment × clone interaction. Broad-sense heritability for resistance, measured as AUDPC, was estimated as 0.67. The overall results indicate the presence in this potato family of a high level of field resistance against late blight. This segregating diploid family appears to be a good candidate for quantitative trait loci mapping to identify and characterize the genetic components of partial late blight resistance. [source] Resistance in water yam (Dioscorea alata) cultivars in the French West Indies to anthracnose disease based on tissue culture-derived whole-plant assayPLANT PATHOLOGY, Issue 5 2006T. J. Onyeka Reactions of 60 water yam (Dioscorea alata) cultivars to three isolates of the yam anthracnose fungal pathogen (Colletotrichum gloeosporioides) were evaluated using tissue culture-derived whole-plant assay. Three disease parameters: single score on a scale of 0,6 at the seventh day after inoculation (SD7); area under the disease progress curve (AUDPC); and disease progress rate (Rd) were compared, and cultivars were classified into disease-response groups using a rank-sum method based on AUDPC scores for the two most virulent isolates. A wide range of variation in resistance of the D. alata cultivars, and significant effects of pathogen isolate and isolate,cultivar interactions, were observed for all disease parameters. The three disease parameters were positively correlated; however, four cultivars showed great dispersions from the regression lines for comparisons of SD7 with the multiple assessments based AUDPC and Rd. The 60 cultivars were separated into resistant (n = 12), moderately resistant (n = 19), moderately susceptible (n = 18) and susceptible (n = 11) groups. The potential of the tissue culture-derived whole-plant assay to resistance breeding programmes and further understanding of the yam anthracnose pathosystem is discussed. [source] Relationship between leaf emergence and optimum spray timing for leaf blotch (Rhynchosporium secalis) control on winter barleyPLANT PATHOLOGY, Issue 3 2006C. S. Young For wheat, the optimum time to apply fungicide to control disease on a given leaf layer is usually at, or shortly after, full leaf emergence. Data from field experiments on barley were used to investigate whether the same relationship was applicable to control of leaf blotch on barley. Replicated plots of winter barley were sown in the autumns of 1991, 1992 and 1993 at sites in southwest England with high risk of Rhynchosporium secalis infection. Single fungicide treatments at four doses (0·25, 0·5, 0·75 or 1·0 times the label rate) were applied at one of eight different spray times, starting in mid-March in each year, with intervals of 10,11 days between spray timings. Disease was assessed every 10,11 days and area under the disease progress curve (AUDPC) values were used to construct fungicide dose by spray time response surfaces for each of the upper four leaves, for each year. Spray timings shortly before leaf emergence were found to minimize the AUDPC for each year and leaf layer, and also the effective dose (the dose required to achieve a specified level of control), similar to wheat. Fungicide treatments on barley were effective for a longer period before leaf emergence than afterwards, probably because treatments before emergence of the target leaf reduced inoculum production on leaves below. This partly explains why fungicides tend to be applied earlier in the growth of barley compared with wheat. [source] Evaluation of foliar resistance in potato to Phytophthora infestans based on an international field trial networkPLANT PATHOLOGY, Issue 2 2005J. G. Hansen During the period 2000,03, local potato cultivars in Estonia, Latvia, Lithuania, Poland and Denmark were tested for foliar resistance to Phytophthora infestans (late blight) in an international field trial network. Four standard cultivars were included in the trials: Sava, Oleva, Danva and Kuras. Primary disease-assessment data were entered into a common database, and parameters from the disease progress curves were calculated and made available on interactive web pages. A regression model, using relative area under disease progress curve (RAUDPC) values for cv. Oleva as a reference, was developed for the estimation of 1,9 scale values, where 1 = most susceptible. Standard deviations for the estimated 1,9 scale values and a nonparametric rank stability analysis of RAUDPC were used to evaluate the stability of resistance of the cultivars. Overall, the results showed stability of resistance for cvs Sava, Oleva and Danva, but not for Kuras. Use of the Internet-based Web-Blight service in this study facilitated comparison of results among countries for the level and stability of resistance. The estimated 1,9 scale values were similar to, or slightly lower than, those from official cultivar lists or from the European Cultivated Potato Database, especially for the more resistant cultivars. Possible reasons for discrepancies from different sources and locations are discussed. It is concluded that RAUPDC and the derived 1,9 scale values are useful for ranking cultivars for resistance to P. infestans, but this information is not detailed enough for use in a decision support system for late blight control. [source] Predicting effective fungicide doses through observation of leaf emergencePLANT PATHOLOGY, Issue 6 2000N. D. Paveley Experimental data were used to test the hypothesis that the effective fungicide dose (ED) , the dose required to achieve a given level of disease suppression , varies in a predictable manner according to the pattern of development of the wheat canopy. Replicated and randomized field plots received a single systemic fungicide spray at either zero (control), 0·25, 0·5, 0·75 or 1·0 dose (the recommended dose), at one of eight timings from April to June. Wheat cultivars and locations for experiments were selected to promote epidemics of septoria tritici spot and yellow rust caused by Septoria tritici (anamorph of Mycosphaerella graminicola) and Puccinia striiformis, respectively. Logistic or exponential disease progress curves were fitted to disease severity data and used to estimate the date of disease onset (t0) and relative epidemic growth rate (r) on each leaf layer for each treatment. Area under the disease progress curve (AUDPC) values were used to construct fungicide dose by spray timing response surfaces for each of the upper four leaves. A parsimonious function, with an exponential form in the dose,response dimension and a normal distribution in the timing dimension described a high proportion of the variation in AUDPC (R2 values ranging from 0·73 to 0·97). Consistent patterns of treatment effect were noted across pathogen species, leaf layers, sites and seasons. Fungicide applications that coincided with full leaf emergence delayed t0 on that leaf layer. Treatments applied after full leaf emergence did not delay t0, but reduced r. Progressively earlier or later treatments, or lower doses, had decreasing effects. AUDPC was affected more by t0 than r. AUDPC response surface parameter estimates showed that curvature of the dose,response was not affected by spray timing, but appeared to be a characteristic of the fungicide,pathogen combination. However, the lower asymptote of the dose,response curve, and hence the ED, varied substantially with spray timing. The pattern of change in ED with spray timing was consistent across a range of leaf layers, pathosystems and seasons, and the spray timing at which the ED was minimized varied only within a small range, around the time of leaf emergence. In contrast, variation in untreated disease severity, resulting from variation in initial inoculum and weather, was large. It was concluded that the main value of disease forecasting schemes may be in their capacity to predict the level of untreated disease, to which the economic optimum, or ,appropriate', dose relates. Spray timing determines the part of the canopy where disease will be efficiently controlled and hence the green leaf area saved. Timing decisions should relate to observations of emergence of those leaf layers important to yield. [source] Effects of stem canker (Leptosphaeria maculans) and light leaf spot (Pyrenopeziza brassicae) on yield of winter oilseed rape (Brassica napus) in southern EnglandPLANT PATHOLOGY, Issue 4 2000Y. Zhou The relationships between yield loss and incidence or severity of stem canker and light leaf spot in winter oilseed rape were analysed by correlation and regression analyses, using data from experiments at Rothamsted, England in 1992/93, 1994/95 and 1995/96. Growth stages (GS) 6,3/6,4 and 4,0/4,5 were identified as the critical points for relating percentage yield loss to stem canker and light leaf spot (on stems), respectively. Critical point (CP) and area under disease progress curve (AUDPC) models relating percentage yield loss to combined incidence or severity of stem canker and light leaf spot (stems) in each experiment were constructed by linear regression. There were no differences in the CP models for incidence between 1992/93, 1994/95 and 1995/96 experiments, or in the AUDPC models for incidence between 1992/93 and 1994/95 experiments. Therefore, a general CP model relating percentage yield loss (,Y) to combined incidence of stem canker (Si) at GS 6,3/6,4 and light leaf spot (stems) (Li) at GS 4,0/4,5 was constructed using data from the three experiments: ,Y = 0·85 + 0·079Si + 0·065Li (R2 = 43·7%, P < 0·001, 92 df). A general AUDPC model relating ,Y to the AUDPC of combined incidence of stem canker (Sia) from GS 5·7 to GS 6·5 and light leaf spot (stems) (Lia) from GS 4·0 to GS 6·3 was constructed using data from the 1992/93 and 1994/95 experiments: ,Y = 0·07 + 0·00096Sia + 0·0026Lia (R2 = 43·6%, P < 0·001, 68 df). These two general yield-loss models were tested with data from Rothamsted in 1993/94 and Boxworth in 1992/93. The predictive accuracy of the CP model based on combined incidence of stem canker and light leaf spot (stems) was better than that of the AUDPC model. Yield losses predicted by summing the estimates from individual models for incidence of stem canker alone (GS 6,3/6,4) and light leaf spot alone (on leaves at GS 3,3) were greater than observed yield losses in experiments at Rothamsted in 1992/93, 1993/94, 1994/95 and 1995/96 and at Boxworth in 1992/93. [source] Modulation of primary and secondary infections in epidemics of carrot cavity spot through agronomic management practicesPLANT PATHOLOGY, Issue 1 2008F. Suffert The relative importance of primary and secondary infections (auto- and alloinfections) in the development of a carrot cavity spot (CCS) epidemic caused by Pythium spp. were investigated. Three cropping factors: fungicide application, soil moisture and planting density, were selected as the key variables affecting the disease tetrahedron. Their effects on: (i) disease measurements at a specific time, (ii) the areas under the disease progress curves (AUDPCs) and (iii) a time-dependent parameter in a pathometric incidence-severity relationship, were studied. Mefenoxam applications 5 and 9 weeks after sowing reduced the intensity of a field CCS epidemic that involved both primary and secondary infections. In microcosm experiments, mefenoxam reduced secondary infections by Pythium violae obtained by transplanting infected carrot roots and slowed disease progress (1·6 lesions per root in treated versus 5·8 lesions in non-treated microcosms). A deficit of soil moisture limited the movement of Pythium propagules to host tissue, and thus reduced primary infections in the field; it also promoted the healing of lesions, limiting lesion expansion and the potential for alloinfections (6·8,7·5 lesions per root in irrigated plots compared with 2·4 lesions in non-irrigated plots). A negative relationship between the mean root-to-root distance and the rate of alloinfections was established in microcosms; a reduction in mean planting density was also effective in limiting CCS development (0·5, 1·6 and 2·0 lesions per root in microcosms containing 8, 16 and 31 roots, respectively). An integrated disease management system based on a combination of cultural methods, such as optimized fungicide application, date of harvest versus soil moisture content, and host density versus planting pattern, may make a useful contribute to the control of CCS. [source] Evaluation of foliar resistance in potato to Phytophthora infestans based on an international field trial networkPLANT PATHOLOGY, Issue 2 2005J. G. Hansen During the period 2000,03, local potato cultivars in Estonia, Latvia, Lithuania, Poland and Denmark were tested for foliar resistance to Phytophthora infestans (late blight) in an international field trial network. Four standard cultivars were included in the trials: Sava, Oleva, Danva and Kuras. Primary disease-assessment data were entered into a common database, and parameters from the disease progress curves were calculated and made available on interactive web pages. A regression model, using relative area under disease progress curve (RAUDPC) values for cv. Oleva as a reference, was developed for the estimation of 1,9 scale values, where 1 = most susceptible. Standard deviations for the estimated 1,9 scale values and a nonparametric rank stability analysis of RAUDPC were used to evaluate the stability of resistance of the cultivars. Overall, the results showed stability of resistance for cvs Sava, Oleva and Danva, but not for Kuras. Use of the Internet-based Web-Blight service in this study facilitated comparison of results among countries for the level and stability of resistance. The estimated 1,9 scale values were similar to, or slightly lower than, those from official cultivar lists or from the European Cultivated Potato Database, especially for the more resistant cultivars. Possible reasons for discrepancies from different sources and locations are discussed. It is concluded that RAUPDC and the derived 1,9 scale values are useful for ranking cultivars for resistance to P. infestans, but this information is not detailed enough for use in a decision support system for late blight control. [source] Resistance to Leveillula taurica in the genus CapsicumPLANT PATHOLOGY, Issue 5 2003V. L. De Souza One hundred and sixty-two Capsicum genotypes were evaluated for powdery mildew (Leveillula taurica) resistance, following inoculations with a suspension of 5 × 104 conidia mL,1 on 10-leaved to 12-leaved plants. Genotypes were graded into five resistance classes, based on the areas under the disease progress curves calculated from disease incidence (percentage infected leaves per plant) and severity (total number of colonies per plant). Results revealed a continuum from resistance to susceptibility, with the majority (70%) of C. annuum materials being classified as moderately to highly susceptible to L. taurica. Conversely, C. baccatum, C. chinense and C. frutescens were most often resistant, indicating that resistance to L. taurica among Capsicum species is found mainly outside the C. annuum taxon. Nevertheless, some resistant C. annuum material was identified that may be useful for resistance breeding. Eight genotypes were identified as immune to the pathogen: H-V-12 and 4638 (previously reported), and CNPH 36, 38, 50, 52, 279 and 288. Only H-V-12 and 4638 are C. annuum, while all others belong to the C. baccatum taxon. Latent period of disease on a set of commercial sweet pepper genotypes varied, indicating diverse levels of polygenic resistance. The latent period progressively reduced with plant maturity, from 14·3 days in plants at the mid-vegetative stage to 8·6 days in plants at the fruiting stage. Young plants of all commercial genotypes tested at the early vegetative stage were immune, irrespective of the reaction of the genotype at later stages, demonstrating widespread juvenile resistance to L. taurica in the Capsicum germplasm. Inoculation of plants of different botanical taxa with a local isolate indicated a wide host range. Some hosts, including tomato (Lycopersicon esculentum), artichoke (Cynara scolymus) and poinsettia (Euphorbia pulcherrima), produced large amounts of secondary inoculum. Other hosts included okra (Abelmoschus esculentus), eggplant (Solanum melongena), cucumber (Cucumis sativus), Solanum gilo, Chenopodium ambrosioides and Nicandra physaloides. [source] Predicting effective fungicide doses through observation of leaf emergencePLANT PATHOLOGY, Issue 6 2000N. D. Paveley Experimental data were used to test the hypothesis that the effective fungicide dose (ED) , the dose required to achieve a given level of disease suppression , varies in a predictable manner according to the pattern of development of the wheat canopy. Replicated and randomized field plots received a single systemic fungicide spray at either zero (control), 0·25, 0·5, 0·75 or 1·0 dose (the recommended dose), at one of eight timings from April to June. Wheat cultivars and locations for experiments were selected to promote epidemics of septoria tritici spot and yellow rust caused by Septoria tritici (anamorph of Mycosphaerella graminicola) and Puccinia striiformis, respectively. Logistic or exponential disease progress curves were fitted to disease severity data and used to estimate the date of disease onset (t0) and relative epidemic growth rate (r) on each leaf layer for each treatment. Area under the disease progress curve (AUDPC) values were used to construct fungicide dose by spray timing response surfaces for each of the upper four leaves. A parsimonious function, with an exponential form in the dose,response dimension and a normal distribution in the timing dimension described a high proportion of the variation in AUDPC (R2 values ranging from 0·73 to 0·97). Consistent patterns of treatment effect were noted across pathogen species, leaf layers, sites and seasons. Fungicide applications that coincided with full leaf emergence delayed t0 on that leaf layer. Treatments applied after full leaf emergence did not delay t0, but reduced r. Progressively earlier or later treatments, or lower doses, had decreasing effects. AUDPC was affected more by t0 than r. AUDPC response surface parameter estimates showed that curvature of the dose,response was not affected by spray timing, but appeared to be a characteristic of the fungicide,pathogen combination. However, the lower asymptote of the dose,response curve, and hence the ED, varied substantially with spray timing. The pattern of change in ED with spray timing was consistent across a range of leaf layers, pathosystems and seasons, and the spray timing at which the ED was minimized varied only within a small range, around the time of leaf emergence. In contrast, variation in untreated disease severity, resulting from variation in initial inoculum and weather, was large. It was concluded that the main value of disease forecasting schemes may be in their capacity to predict the level of untreated disease, to which the economic optimum, or ,appropriate', dose relates. Spray timing determines the part of the canopy where disease will be efficiently controlled and hence the green leaf area saved. Timing decisions should relate to observations of emergence of those leaf layers important to yield. [source] | ||||||||||