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See detailDisease severity assessment in epidemiological studies: accuracy and reliability of visual estimates of Septoria leaf blotch (SLB) in winter wheat.
El Jarroudi, Moussa ULg; Kouadio, Louis; Mackels, Christophe et al

in Phytopathology (2014), 104(11), 37

The accuracy and reliability of visual assessments of SLB severity by raters (i.e. one plant pathologist with extensive experience and three other raters trained prior to field observations using standard ... [more ▼]

The accuracy and reliability of visual assessments of SLB severity by raters (i.e. one plant pathologist with extensive experience and three other raters trained prior to field observations using standard area diagrams and DISTRAIN) was determined by comparison with assumed actual values obtained by digital image analysis. Initially analyses were performed using SLB severity over the full 0-100% range; then, to explore error over short ranges of the 0-100% scale, the scale was divided into sequential 10%-increments based on the actual values. Lin’s concordance correlation (LCC) analysis demonstrated that all raters were accurate when compared over the whole severity range (LCC coefficient (ρc)= 0.92-0.99). However, agreement between actual and visual SLB severities was less good when compared over the short intervals of the 10×10% classes (ρc= -0.12-0.99), demonstrating that agreement will vary depending on the actual disease range over which it is compared. Inter-rater reliability between each pair of raters over the full 0-100% range (correlation analysis r= 0.970-0.992, P<0.0001), and inter-class correlation coefficient (ρ≥ 0.927) were very high. This study provides new insight into using a full range of actual disease severity vs limited ranges to ensure a realistic measure of rater accuracy and reliability, in addition to contributing to the ongoing debate on the use of visual disease estimates based on the 0-100% ratio scale for epidemiological research. [less ▲]

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See detailThe effects of rater bias on hypothesis testing when using different assessment methods for estimating disease severity.
CHIANG, KUO-SZU; Bock, Clive; El Jarroudi, Moussa ULg et al

in Phytopathology (2014), 104(11), 26

Bias (over and underestimates) in estimates of disease severity, and the impact of that inaccuracy on hypothesis testing using different disease scales was explored. Nearest percent estimates (NPE), the ... [more ▼]

Bias (over and underestimates) in estimates of disease severity, and the impact of that inaccuracy on hypothesis testing using different disease scales was explored. Nearest percent estimates (NPE), the Horsfall-Barratt (H-B) scale and four different linear category scales (5% and 10% increments, with and without additional grades at low severity) were compared. Actual values and estimates by 4 different raters of the severity (0 to 100%) of Septoria leaf blotch on leaves of winter wheat were used to develop distributions for a simulation model. The simulations were based on i) all the 4 raters data combined, ii) only the most accurate rater estimates, and iii) only the most biased rater. Regardless of the effect of rater ability, we found that, there were lower type II error rates with NPEs as compared with the other category scales at severities of 80 to 100%. On the other hand, with lower severities (0 to 20%), the 5% and 10% scales with additional grades had type II error rates comparable to those for the NPEs. Raters who overestimated severity and used the H-B scale had the highest risk of a type II error when the mean disease severity was low. Knowledge of how rater ability and scale type can affect hypothesis testing can be used to improve disease assessment as well as to provide a logical framework for developing standard area diagrams. [less ▲]

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See detailA comparison of raters and disease assessment methods for estimating disease severity for purposes of hypothesis testing.
Bock, Clive; El Jarroudi, Moussa ULg; Kouadio, Louis et al

in Phytopathology (2014), 104(11), 26

Assessment of disease severity is most often made visually, and estimates can be inaccurate. Nearest percent estimates (NPEs) of Septoria leaf blotch on leaves of winter wheat by four raters (R1-R4 ... [more ▼]

Assessment of disease severity is most often made visually, and estimates can be inaccurate. Nearest percent estimates (NPEs) of Septoria leaf blotch on leaves of winter wheat by four raters (R1-R4) assessing non-treated (NT) and fungicide-treated (FT) plots were compared to true values using Lin’s concordance correlation coefficient (ρc) on two dates in 2006 and 2007. Estimates were converted to Horsfall-Barratt (HB) mid-points and again compared for accuracy and precision. Estimates of severity from FT and NT plots were analyzed to ascertain effects of rater using both the NPE and HB values. Regardless of method, all raters showed a range of agreement with true values on FT and NT plots (ρc = 0 to 1). Use of the HB scale most often reduced agreement (84.4% of the time), and did not improve rater-associated bias of treatment mean severity estimates. Consequently, estimates of mean severity differed significantly among raters and from true values (F=126 to 1260, P=0.002 to<0.0001). However, a comparison of treatment effects showed that the true values and R1 to R4 all demonstrated significant effects of fungicide (F=101 to 1952, P=0.002 to <0.00001). Ranking of raters differed on one occasion when HB values were used. These results demonstrate the effect of the HB scale, and the need for accurate disease assessment to minimize over or underestimates compared to true severity so as to minimize the potential for type II errors. [less ▲]

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See detailOperational warning for Septoria leaf blotch and leaf rust in winter wheat: Importance of fungicide dosage, formulation, and spray time
El Jarroudi, Moussa ULg; Kouadio, Louis; Beyer, Marco et al

in Phytopathology (2013), 103

Field experiments were conducted in 2010 to investigate the effect of fungicide commercial formulation, timing and dosages on the severity of these two diseases in winter wheat in Luxembourg. Different ... [more ▼]

Field experiments were conducted in 2010 to investigate the effect of fungicide commercial formulation, timing and dosages on the severity of these two diseases in winter wheat in Luxembourg. Different types of fungicides and fungicide combinations containing active ingredients such as triazoles and strobilurins were used in field trials including susceptible cultivars to Septoria leaf blotch (SLB, caused by Septoria tritici) and wheat leaf rust (WLR, caused by Puccinia triticina). The three formulations of fungicides tested were: (i) a mix of triazole and amine (Prothioconazole 250 g/l + Spiroxamine 500 g/l) associated with chlorothalonil 500 g/l, (ii) sole strobilurin (Azoxystrobine 250 g/l), and (iii) a mix of strobilurin and triazole (Epoxiconazole 125 g/l; Azoxystrobine 250 g/l). The optimum time of fungicide spray was assessed through the mechanistic model PROCULTURE and a stochastic model based on night favourable weather conditions conducive to WLR development. The results showed that for plots treated with fungicide formulation containing either a triazole or a strobilurin, the grain yield earned was not significantly different from the untreated plots (P > 0.05). Whereas single fungicide treatment involving a mixture of triazole and strobilurin at the optimum time gave an earning (on average 7 dt ha-1) compare to the control and a yield similar to that obtained with the double or triple fungicide treatments. [less ▲]

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See detailProfitability of using warning system for foliar disease of wheat in the Grand-Duchy of Luxembourg
El Jarroudi, Moussa ULg; Kouadio, Louis; Beyer, Marco et al

in Phytopathology (2013), 103

Although small grain cereals (i.e. winter wheat) are routinely protected with two or three foliar treatments in the Grand-Duchy of Luxembourg (GDL), environmental concerns and changes in the cost-benefit ... [more ▼]

Although small grain cereals (i.e. winter wheat) are routinely protected with two or three foliar treatments in the Grand-Duchy of Luxembourg (GDL), environmental concerns and changes in the cost-benefit ratio are likely to increase the demand for more accurate identification of spraying needs. A Vol. 103 (Supplement 2), No. 6, 2013 S2.39 warning system assessing in real time the risk of progression of fungal diseases on winter wheat (Triticum aestivum L.) was tested in the GDL over the 2009-2012 period in four-replicated field experiments located in three representative villages of the different agro-climatological zones. The fungicide treatments recommended by the warning system during this period have ensured economic profitability equivalent to or even better than double and triple treatments. In 2010 and 2011, weather conditions impeded fungal infections of wheat and no warning was issued, reducing fungicide use. The study also highlighted that multiple fungicide applications were not better than a single application. In 2009 and 2012, although the weather conditions were very favourable for fungal wheat diseases, the single recommended fungicide application resulted in an additional yield of 30% compared to untreated plots. This study shows the importance of the positioning of fungicide treatment in such a warning system and in strategies aiming at reducing the spread fungicide molecules in the environment. [less ▲]

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See detailNew method for establishing a network of operational warning of Septoria leaf blotch disease in winter wheat
El Jarroudi, Moussa ULg; Giraud, Frédéric; Delfosse, Philippe et al

in Phytopathology (2011), 101

A mechanistic model, PROCULTURE, based on commonly available meteorological data and assessing in real time the risk of progression of septoria leaf blotch disease on winter wheat has been developed in ... [more ▼]

A mechanistic model, PROCULTURE, based on commonly available meteorological data and assessing in real time the risk of progression of septoria leaf blotch disease on winter wheat has been developed in Belgium and the Grand-Duchy of Luxemburg (GDL) to limit fungicide use. However, the reliability of meteorological stations used for the warning system varies according to the distance to the fields. A weather analysis based on the Fourier transform highlighted a great difference in the intraday variation between two sites in the GDL (Everlange and Reuland). The correlation between these two sites is very high for the hourly temperature (R = 0.96), and for the hourly relative humidity (RH) (R = 0.86), (P < 0.05). However, the intraday variation (<11 hours) highlights contrasts for a given meteorological parameter. Hence, the correlation between temperature or RH decreased respectively from 0.96 to 0.43 and from 0.86 to 0.30. The comparison between infection conditions given by PROCULTURE using the Fourier transform, shows: (i) a positive but weak correlation between temperature at Reuland and Everlange (R = 0.64), (ii) a good correlation between RH for these two sites (R = 0.86), and (iii) a contrasted difference for rain (R = 0.27), (P < 0.05). This Fourier transform based method enables to take into account the RH and temperature variation related to topography levels in the warning system and to understand and explain the variation in disease expression between a plateau and a valley bottom or between North and South slopes. [less ▲]

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See detailRegional-based typology of the main fungal diseases affecting winter wheat in the Grand-Duchy of Luxembourg
El Jarroudi, Moussa ULg; Giraud, Frédéric; Delfosse, Philippe et al

in Phytopathology (2011), 101

Despite its small territory size, the Grand-Duchy of Luxembourg (GDL) has several microclimates that result in a variability of disease severity between the South (Gutland) and the North (Oesling ... [more ▼]

Despite its small territory size, the Grand-Duchy of Luxembourg (GDL) has several microclimates that result in a variability of disease severity between the South (Gutland) and the North (Oesling). Septoria leaf blotch disease of wheat is an important disease in the GDL. Over 2003–2009, the severity was strong in Gutland (51% on average over the last two upper leaves at the late milk growth stage) and low in the Oesling (16% for the same leaves). For the years 2006, 2008 and 2009, the disease severity was less than 6% in the Oesling while it exceeded 40% in the Gutland. The second fungal disease that has become economically important is the wheat leaf rust. Over the same period, the Gutland and the Oesling showed consistently the highest and lowest disease severity respectively. In 2003 and 2007, the Gutland showed the highest disease severity with 66% and 57% respectively, whereas the lowest severity (<1%) was observed in the Oesling. Another important disease is wheat powdery mildew. The 2003 and 2009 cropping seasons showed the highest disease severity with 15% and 40%, respectively, in the Oesling whereas less than 1% severity was registered in the Gutland. Fusarium head blight was also present in the eastern part of the Gutland showing the highest prevalence and severity in 2007 and 2008 (8.5% and 8.3% respectively). These prevalence and severity percentages were significantly higher compared to the Oesling (% prevalence % severity, p = 0.049 and p = 0.012, respectively, Tukey’s test). [less ▲]

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See detailBiological control of Rhizoctonia root rot on bean by phenazine and cyclic lipopeptide producing Pseudomonas CMR12a
D’aes, J.; Hoang Hua, G. K.; De Maeyer, K. et al

in Phytopathology (2011), 101

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See detailSpatial heterogeneity of leaf wetness duration in winter wheat canopy and its influence on plant disease epidemiology
Mahtour, Abdeslam ULg; El Jarroudi, Moussa ULg; Giraud et al

in Phytopathology (2010)

Leaf wetness duration (LWD) is an important factor influencing the occurrence of plant disease <br />epidemiology. Despite considerable efforts to determine LWD, little attention has been given to <br ... [more ▼]

Leaf wetness duration (LWD) is an important factor influencing the occurrence of plant disease <br />epidemiology. Despite considerable efforts to determine LWD, little attention has been given to <br />study its variability within the canopy. The objective of this study was to evaluate its <br />spatiotemporal variability in wheat fields in a heterogeneous landscape. The spatiotemporal <br />variability of LWD was evaluated in a site close to Arlon (Belgium) during the period May to July <br />2006 and 2007. LWD measurements were made using a set of flat plate sensors deployed at <br />five different distances from a 18 m high hedge (5, 10, 20, 50, 100 m). Each set of two <br />sensors was placed horizontally close the flag leaf. In addition, we collected the amount of <br />dew water that deposited on rigid epoxy plates placed next to each sensors. Experimental <br />results showed that LWD measurements revealed substantial heterogeneity among sensor <br />positions. LWD is longer for sensors closer to the hedge mainly because of its shadowing <br />effect. 3 to 4 hours of difference was observed between sensors located at 5 m and those <br />located at 100 m, and besides, a significant quantitative difference (p < 0.0001) of dew <br />deposit was observed between area beside hedge and those placed at 100 m. In summary, this <br />study provides new information on how wetness is distributed on wheat leaves according to <br />the distance from a hedge. This leads to local microclimate conditions that will contribute to <br />the disease spatial heterogeneity. [less ▲]

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See detailTime spray strategies for Septoria leaf blotch disease progress on winter wheat: The use of forecasting model
El Jarroudi, Moussa ULg; Giraud, Frédéric; Delfosse, Philippe et al

in Phytopathology (2010), 100

A mechanistic model, PROCULTURE, for assessing in real time the risk of progression of Septoria tritici (teleomorph Mycosphaerella graminicola) on winter wheat (Triticum aestivum L.) was used in Grand ... [more ▼]

A mechanistic model, PROCULTURE, for assessing in real time the risk of progression of Septoria tritici (teleomorph Mycosphaerella graminicola) on winter wheat (Triticum aestivum L.) was used in Grand-Duchy of Luxemburg over 2003 to 2009 to simulate disease progression in the canopy at four-replicated field experiments located in three villages (Diekirch district: Reuler; Grevenmacher district: Burmerange and Christnach), representative of the different agroclimatological zones of Luxembourg. This model has been developed in order to guide field observations on the different leaf layers and to find the optimum time of fungicide spray in fields. The model provides information which explains disease progression on the upper leaves. The relationship between disease control by fungicides and yield loss varies from site-to-site and from season-to-season. A weekly PROCULTURE recalibration is routinely done using actual disease levels observed on site. On average, no spray of fungicides or only one application is required to control efficiently the septoria leaf blotch disease. The PROCULTURE forecasts have been validated to be correct in about 85% of all cases. The treatment defined with the simulation model over 2003 to 2009 gave an earning grain yield (80%) more than the other treatments tested and as important as the double treatment for Everlange, Christnach and Burmerange. At Reuler, over 2003 to 2009, treatments based on the Septoria risk simulation model were recommended only in 2007. The climatic conditions of this site tend to favour organic farming in this region where the evolution of the foliar disease is very weak. [less ▲]

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See detailAssessment Of The Night Weather Parameters And Their Use In Forecasting Model Of Wheat Leaf Rust.
El Jarroudi, Moussa ULg; Giraud, Frédéric; Delfosse, Philippe et al

in Phytopathology (2010), (100), 32

A stochastic model was developed to predict the wheat leaf rust (Puccinia triticina Eriks.) severity (percentage of leaf area with symptoms showing uredinia) in four-replicated field experiments located ... [more ▼]

A stochastic model was developed to predict the wheat leaf rust (Puccinia triticina Eriks.) severity (percentage of leaf area with symptoms showing uredinia) in four-replicated field experiments located in three villages (Diekirch district: Reuler; Grevenmacher district: Burmerange and Christnach), representative of the different agroclimatological zones of Luxembourg. The model was elaborated by the analysis of the night weather and leaf rust incidence. Statistical validation using regression analysis reports a strong correlation between the number of hours with specific meteorological conditions and the percentage leaf area covered by brown rust lesions for the two upper and youngest leaves, which are mostly responsible for photosynthesis activity and assimilates production filling the grains. The development of the brown rust requires a period of at least twelve consecutive hours with temperatures between 8 and 16°C and a relative humidity (RH) greater than 60%, with optimal values lying between 12 and 16°C and RH greater than 80%. <br />During the 2004 to 2009 period, at four sites, the linear regression between simulated and observed values for Puccinia triticina was highly significant (P < 0.01) and R2 (coefficient of determination) explained 80 to 85% of the variability. Efforts are now being developed to better define thresholds for fungicide applications and to spatialize the outputs of the model over the entire Luxembourg territory. [less ▲]

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See detailDifferential roles of lipopeptides in plant host defenses and pathogen suppression.
Ongena, Marc ULg; Henry, G.; Jourdan, Emmanuel ULg et al

in Phytopathology (2010), 100

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See detailPre-and post-harvest application of antagonistic yeasts for the control of gray and blue mold: efficacy and monitoring
De Clercq, D.; Dickburt, C.; Lepoivre, Philippe ULg et al

in Phytopathology (2001), 91(6), 21

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See detailUse of molecular tools to enhance antagonistics activity of yeasts against postharvest diseases of apples
Jijakli, Haissam ULg; De Clercq, Deborah; Cognet, Stéphane et al

in Phytopathology (2001), 91(6 (supplément)), 154

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See detailIdentification Of Distinct Potyviruses In Mixedly-Infected Sweet-Potato By The Polymerase Chain-Reaction With Degenerate Primers
Colinet, D.; Kummert, J.; Lepoivre, Philippe ULg et al

in Phytopathology (1994), 84(1),

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