Use of multispectral radiometry in wheat yellow rust experiments1

Winter-wheat field fungicide experiments were monitored by multispectral radiometry to determine yellow rust impact on crop growth and to predict yield loss caused by disease. Spectral reflectance data were highly correlated with yellow rust severity. Linear regression models with spectral ratios as independent variables explained 90–93% of the variation in yield between plots with different treatments of fungicide. The area under the NIR/Red curve, calculated from heading to soft-dough growth stages, was a good predictor of yield loss determined at harvest.     

Heritability of dollar spot resistance in creeping bentgrass

ABSTRACT The dollar spot disease incited by Sclerotinia homoeocarpa is an important disease of creeping bentgrass (Agrostis stolonifera). Genetic resistance is an important control strategy and could reduce fungicide use. Despite recent research, the genetic mechanism of dollar spot resistance in turfgrasses is still not fully understood. The objectives of this study were to (i) determine narrow-sense heritability and predicted gain from selection for dollar spot resistance in creeping bentgrass and (ii) evaluate inheritance characteristics of dollar spot disease resistance. Inheritance characteristics such as the detection of major genes, heterosis, maternal effects, and combining ability were determined by evaluating the disease severity of progeny from crosses between resistant and susceptible bent-grass clones. Parental clones and progenies from crosses were established in a field trial in a randomized complete block design and inoculated with one isolate of S. homoeocarpa applied at a rate of 0.25 g m(-2) of prepared inoculum. Differences in progeny means between crosses were observed over both years. Progeny from resistant x resistant crosses had significantly less disease severity than resistant x susceptible and susceptible x susceptible crosses. High narrow-sense heritability estimates (0.79 [2002], 0.79 [2003]) and large mean squares for general combining ability support the idea that additive gene action plays a significant role in disease resistance and support previous research that dollar spot resistance is most likely quantitatively inherited.     

Spatial and temporal dynamics of Meloidogyne minor on creeping bentgrass in golf greens

Meloidogyne minor, first reported on potatoes in the Netherlands in 2004, is an emerging nematode pest in Europe. It damages turfgrass, particularly creeping bentgrass (Agrostis stolonifera) grown on sandy soils such as those of golf greens. However, little is known of the nematode's life history and pathology. In this study, the spatial and temporal distribution of M. minor on a creeping bentgrass green in Ireland was determined over a 15 month period. Cores were taken on transects across yellowing patches of grass caused by nematode damage. Second‐stage juveniles (J2) were absent from the soil from November to February, when soil temperatures were below 10°C. Both galls and egg masses were present throughout the year but were more abundant in late summer and early autumn. More J2, galls and egg masses were present in the top 10 cm of soil than at a depth of 11–20 cm. The nematode population tended to decrease as distance from the centre of the yellow patches increased. The diameter of visual symptoms (yellow patches) was also recorded over the 15 months. The mean diameter of five sampled patches increased from 23·7 cm in June 2003 to 45·2 cm in August 2004. There were 158–193 galls per 100 cm³ soil at the margin of the visible infested area, indicating that this could be the threshold level for visible symptoms.     

Acibenzolar-S-methyl efficacy against bacterial brown stripe caused by Acidovorax avenae subsp. avenae in creeping bentgrass

Journal of General Plant Pathology - Bacterial brown stripe caused by Acidovorax avenae subsp. avenae (Aaa) causes serious damage on creeping bentgrass on golf course greens. However, there are few...     

Use of geographic information systems in warning services for late blight*

One of the important aims of the German Crop Protection Services (GCPS) is to reduce spraying intensity as part of an environmentally friendly crop protection strategy. ZEPP is the central institution in Germany responsible for the development of methods with the goal of improving the control of plant diseases and, to this end, more than 20 meteorological data‐based models have been developed and introduced into practice. This study shows that it is possible to improve the accuracy of the results given by the models by using Geographic Information Systems (GIS). The influence of elevation, slope and aspect on meteorological data was interpolated with GIS and the results were used as input for forecasting models. The results will be presented as spatial risk maps on which areas of maximum disease risk are displayed. The modern presentation methods of GIS enable the results to be displayed in a more user‐friendly way.     

Resistance to Rhizoctonia solani AG‐2‐2 (IIIB) in creeping bentgrass plants transformed with pepper esterase gene PepEST

A pepper esterase (PepEST) gene was introduced into creeping bentgrass (Agrostis stolonifera) by Agrobacterium‐mediated transformation. Purified recombinant PepEST proteins were sufficient to inhibit the growth of the fungal pathogens Rhizoctonia solani AG2‐2 (IIIB) (causing brown patch) and Sclerotinia homoeocarpa (dollar spot), but not the oomycete responsible for pythium blight, Pythium aphanidermatum. PepEST proteins were most effective against R. solani. After genetic transformation of creeping bentgrass with PepEST, the genomic integration of transgenes bar and PepEST was confirmed by Southern blot analysis, and their expression was also validated by northern blot and western blot analyses. Disease severity on R. solani‐inoculated leaves of transgenic plants was <10% compared to ca. 50% in non‐transgenic plants. Microscopic observation of infected leaves indicated that PepEST inhibited the growth of hyphae upon fungal infection.     

Use of survival analysis to assess management options for ray blight in Australian pyrethrum fields

The effects of fungicide, cultivar and plant density on the time‐to‐death of pyrethrum flowers affected by ray blight (caused by Phoma ligulicola var. inoxydablis) in Australia were analysed using nonparametric Kaplan–Meier (KM) estimates and accelerated failure time (AFT) models with a Weibull probability distribution. Analyses using KM estimates and AFT models yielded similar results. The median survival time (T) for all flowers in the fungicide trial was estimated at 53 days [95% confidence interval (CI) = 43–53] in 2000 and 60 days (CI = 51–60) in 2001. In both years, all fungicides tested except copper oxychloride significantly (P ≤ 0·0495) increased the duration of flower survival compared with nontreated plots. Significant variation (P < 0·0001) was noted between years and among four cultivars in terms of flower survival, with T values for different cultivars ranging from 41 to 81 days, and averaging 69 days (CI = 60–69) in 2005 and 64 days (CI = 56–64) in 2006 for all cultivars. Planting at a quarter the density currently recommended increased flower survival by 41·8% (χ² = 29·19; P < 0·0001), but did not increase yield. Linear regression indicated that defoliation severity accounted for at least 94% of variation in median survival time. Improved management may be achieved via an integrated strategy incorporating these factors.     

Methods of reducing rhizoctonia patch of cereals in Western Australia

Cultivation reduced rhizoctonia patch of cereals. In a continuous cropping experiment where zero-tillage and cultivation were compared over three seasons, cultivation reduced patch score in all seasons by an average of 83%. In the fourth season, when the treatments were reversed, the incidence of rhizoctonia patch was also reversed. Nitrogen (ammonium sulphate, sodium nitrate or urea) also reduced patch score under zero-tillage, but sources of nitrogen did not differ significantly in their effects. In another experiment it was demonstrated that a contact herbicide used in the zero-tillage system was unlikely to be responsible for the high incidence of patch in that system. One cultivation reduced total patch score by an average of 46% compared to zero-tillage, but these scores were not reduced further by a second cultivation.     

Methods of measuring rhizoctonia patch of cereals in Western Australia

Methods of measuring rhizoctonia patch in cereals are compared. Included are mapping and determination of area with a leaf area planimeter, aerial photography and determination of area by a grid overlay, a patch scoring technique, sampling and assessing for rhizoctonia root rot, and determination of yield. Mapping, aerial photography, and patch scoring were all highly correlated. Of these methods, the patch scoring technique was the quickest and most convenient. Yield within a patch was about 8% of yield immediately outside the patch.     

马铃薯晚疫病CARAH预警模型在我国的应用及评价

CARAH预警模型引入我国后,在马铃薯晚疫病监测预警中发挥了重要作用。本文对目前各地CARAH模型的应用情况进行了综合分析,总结了模型在马铃薯晚疫病中心病株出现时间预测、发生程度风险评估、防治效果等方面的作用,分析了品种抗性、区域气候特征等因素对模型应用的影响,提出了进一步研究和完善建议。     

Responses of annual bluegrass (Poa annua L.) and creeping bentgrass (Agrostis palustris Huds.) seedlings to nitrogen,phosphorus and potassium†

The growth response to fertilizer under different soil texture (light clayey soil and composite soil consisting of the light clayey soil and sand), and the timing of N fertilization (early summer and fall fertilization) were determined for annual bluegrass (Poa annua L.) and creeping bentgrass (Agrostis palustris Huds., var. Penncross) in glasshouse experiments. At the three‐leaf stage, both plant species were treated with 30, 100, 300, 1,000, 3000 or 10 000 p.p.m. (w/v) of N, P₂O₅ and K₂O equivalent to ammonium sulfate (N), calcium superphosphate (P) and potassium chloride (K). Three weeks after fertilization, the dry weight of shoots or roots was measured. Both plant species were more sensitive to N than to P or K; however, creeping bentgrass required a higher rate of N (1000 p.p.m.) for maximum shoot and root growth than did the weed (300 p.p.m., N). Shoot growth of both plant species was strongly affected by the timing of N fertilization and soil texture; their shoot responses to N increased in the order: composite soil > light clayey soil, and early summer N fertilization > fall N fertilization, and this tendency was especially marked for creeping bentgrass. These results suggest that the response of annual bluegrass to fertilizer is similar to that of creeping bentgrass; however, the two plants are different in regard to the N requirement or their relationship between response to N and application timing and/or soil texture.     

Use of airborne multispectral imagery to discriminate and map weed infestations in a citrus orchard

Reliable information on weed abundance and distribution within fields is essential for weed management in agricultural systems. Such information is necessary to adopt localized and variable rates of herbicide spraying, thus reducing chemical waste, crop damage, and environmental pollution. This paper examined the potential of airborne multispectral imagery to discriminate and map weed infestations in an experimental citrus orchard in Japan. Using an airborne digital sensor, multispectral imagery was acquired over the study site on 10 April 2003. The obtained reflectance imagery was analyzed using an image object-based approach in eCognition. After creating image objects on the image, the spectral information for weeds and citrus, represented by corresponding selected sample image objects, was extracted. Significant differences in the spectral characteristics between weeds and citrus were observed in each of the red, green, and blue wavebands. The simple average values of these wavebands were used to classify image objects with the nearest neighbor algorithm. Maps were generated with different classes or levels of class groups. A subsequent accuracy assessment demonstrated that the weeds were successfully discriminated from other image objects with a classification accuracy of 99.07%. Therefore, maps generated based on the classification result could provide valuable information for developing a site-specific weed management program for the study orchard.     

Risk assessment models for wheat fusarium head blight epidemics based on within-season weather data

ABSTRACT Logistic regression models for wheat Fusarium head blight were developed using information collected at 50 location-years, including four states, representing three different U.S. wheat-production regions. Non-parametric correlation analysis and stepwise logistic regression analysis identified combinations of temperature, relative humidity, and rainfall or durations of specified weather conditions, for 7 days prior to anthesis, and 10 days beginning at crop anthesis, as potential predictor variables. Prediction accuracy of developed logistic regression models ranged from 62 to 85%. Models suitable for application as a disease warning system were identified based on model prediction accuracy, sensitivity, specificity, and availability of weather variables at crop anthesis. Four of the identified models correctly classified 84% of the 50 location-years. A fifth model that used only pre-anthesis weather conditions correctly classified 70% of the location-years. The most useful predictor variables were the duration (h) of precipitation 7 days prior to anthesis, duration (h) that temperature was between 15 and 30 degrees C 7 days prior to anthesis, and the duration (h) that temperature was between 15 and 30 degrees C and relative humidity was greater than or equal to 90%. When model performance was evaluated with an independent validation set (n = 9), prediction accuracy was only 6% lower than the accuracy for the original data sets. These results indicate that narrow time periods around crop anthesis can be used to predict Fusarium head blight epidemics.     

茭白纹枯病发生规律及产量损失测定

茭白纹枯病发生规律与产量损失的研究结果表明:高温高湿、种植过密、偏施氮肥、缺乏钾素是病害加重的主要原因;田间发病盛期在7月中旬至8月中旬;单茭重减低率与病级之间呈极显著线性相关;始病期越早,危害越重,产量损失也越大;病害危害程度与有效分蘖数(孕茭数)减少率、单茭重减低率、产量损失率之间呈高度正相关。在产量损失构成中,有效分蘖数的减少为主要因素。     

Use of bayesian methods to improve prediction of panicle and shoot blight severity of pistachio in california

ABSTRACT Panicle and shoot blight, caused by a Fusicoccum sp., is one of the major aboveground diseases of pistachio in California. The effects of temperature, number of continuous rainy days in April and May, irrigation system, and incidence of latent infection of the Fusicoccum sp. on severity of panicle and shoot blight of pistachio leaves and fruit have been quantified previously, using data collected from 1999 through 2001. A predictive model for leaves and another model for fruit with good explanatory power were generated. In 2003 and 2004, newly collected data were used to evaluate the two models with non-Bayesian and Bayesian methods. The 95% credible (i.e., confidence) intervals of initial (before modification with non-Bayesian and Bayesian methods) and updated parameter estimates were used to investigate their prognostic validity. In 2003, the non-Bayesian analysis resulted in all parameter estimates, with the exception of cumulative daily mean temperature from 1 June until harvest, having different 95% confidence intervals than the parameter estimates of the original models. In addition, the parameter estimates for drip irrigation for the leaf infection and the parameter estimates for drip irrigation and number of continuous rainy days in April and May for fruit infection were not statistically significant. With Bayesian methods, the reestimated model parameters had overlapping 95% credible intervals with the initial estimated parameters, except for the number of continuous rainy days in April and May. When the two sets of modified parameter estimates were used to predict disease severity, statistically significant (alpha = 0.05) differences between observed and predicted disease severities were found with non-Bayesian analysis for leaf infection in three locations and with Bayesian analysis for fruit infection in one orchard. The parameter estimates were modified again at the end of the 2004 season and were all statistically significant with both non-Bayesian and Bayesian methods. Both sets of parameter estimates gave predictions that were not significantly different from observed disease severity on leaves and fruit in all monitored orchards in 2004. In summary, Bayesian methods gave more consistent results when used to update parameter estimates with new information and yielded predictions not statistically different from observed disease severity in more cases than the non-Bayesian analysis.     

Evaluation of kasugamycin for fire blight management, effect on nontarget bacteria, and assessment of kasugamycin resistance potential in Erwinia amylovora

The emergence and spread of streptomycin-resistant strains of Erwinia amylovora in Michigan has necessitated the evaluation of new compounds effective for fire blight control. The aminoglycoside antibiotic kasugamycin (Ks) targets the bacterial ribosome and is particularly active against E. amylovora. The efficacy of Ks formulated as Kasumin 2L for control of fire blight was evaluated in six experiments conducted over four field seasons in our experimental orchards in East Lansing, MI. Blossom blight control was statistically equivalent to the industry standard streptomycin in all experiments. E. amylovora populations remained constant on apple flower stigmas pretreated with Kasumin and were ≈100-fold lower than on stigmas treated with water. Kasumin applied to apple trees in the field also resulted in a 100-fold reduced total culturable bacterial population compared with trees treated with water. We performed a prospective analysis of the potential for kasugamycin resistance (Ks(R)) development in E. amylovora which focused on spontaneous resistance development and acquisition of a transferrable Ks(R) gene. In replicated lab experiments, the development of spontaneous resistance in E. amylovora to Ks at 250 or 500 ppm was not observed when cells were directly plated on medium containing high concentrations of the antibiotic. However, exposure to increasing concentrations of Ks in media (initial concentration 25 μg ml(-1)) resulted in the selection of Ks resistance (at 150 μg ml(-1)) in the E. amylovora strains Ea110, Ea273, and Ea1189. Analysis of mutants indicated that they harbored mutations in the kasugamycin target ksgA gene and that all mutants were impacted in relative fitness observable through a reduced growth rate in vitro and decreased virulence in immature pear fruit. The possible occurrence of a reservoir of Ks(R) genes in orchard environments was also examined. Culturable gram-negative bacteria were surveyed from six experimental apple orchards that had received at least one Kasumin application. In total, 401 Ks(R) isolates (42 different species) were recovered from apple flowers and leaves and orchard soil samples. Although we have not established the presence of a transferrable Ks(R) gene in orchard bacteria, the frequency, number of species, and presence of Ks(R) enterobacterial species in orchard samples suggests the possible role of nontarget bacteria in the future transfer of a Ks(R) gene to E. amylovora. Our data confirm the importance of kasugamycin as an alternate antibiotic for fire blight management and lay the groundwork for the development and incorporation of resistance management strategies.     

Brachypodium distachyon is a pathosystem model for the study of the wheat disease rhizoctonia root rot

Brachypodium distachyon (Bd) is increasingly being used as a model for cereal diseases and to study cereal root architecture. Rhizoctonia solani AG 8 is a necrotrophic root pathogen that infects wheat soon after germination resulting in reduced plant growth and yield loss. Genetic resistance to R. solani AG 8 is not available in commercial wheat cultivars, although some quantitative levels of resistance have previously been found in mutant lines and grass relatives. Resistance mechanisms in cereals remain unknown. The ability to use Bd as a model to study the wheat–R. solani AG 8 pathosystem was investigated. The results presented show that Bd is susceptible to R. solani AG 8 and that the pathogen infects both species to a similar degree, producing comparable disease symptoms. Root length reduction was the primary indicator of disease, with shoots also affected. The second objective was to develop a repeatable phenotyping method to screen Bd populations for resistance to R. solani AG 8. Results of a preliminary experiment provide evidence for variation in resistance between Bd inbred lines. This is the first report showing the potential of Bd as a model plant for discovery of quantitative genetic variation in resistance to a necrotrophic cereal root pathogen.     

Identification of new resistant sources for bacterial blight in pomegranate

Bacterial blight is a highly devastating disease caused by Xanthomonas axonopodis pv. punicae, recording 60 to 80 percent yield-loss of pomegranate in India. In the present investigation, a total of 209 genotypes including 105 exotic types from USDA, 66 wild types and 38 cultivated types from India were screened and categorized into fifteen clusters using cluster and principal component analysis. Genotypes of cluster 15, viz. 108 B and 99 A from USDA and 318734, Daru-18 and IIHR-30 from India, were found to be resistant to bacterial blight while genotypes of cluster 9 were highly susceptible. Two genotypes, each from cluster 15 (318734) and 9 (Ruby), were compared for biochemical and histological parameters to understand the defense mechanism. Significantly, higher accumulation of defense related metabolites, viz. total phenol, flavonoid and antioxidant contents, were observed in resistant genotype (318734). Fewer numbers of stomatal pores that served as portals of entry for plant pathogens were recorded in this genotype. Resistance observed in genotype 318734 might be due to an incompatible interaction between host and pathogen compared to other genotypes. This is the first report of putative resistance sources in pomegranate against Xanthomonas axonopodis pv. punicae.     

Fire blight risk assessment during bloom in an experimental orchard using BIS (Billing's Integrated System)

The value of BIS for blossom blight risk assessment was studied from data collected in an experimental orchard in south-west France. Trees observed included mature commercial pear and apple trees and some young trees in experimental plots. There was a weather station in the orchard and beehives were present. Field records included flowering times of the pear and apple cultivars studied (mostly Passe-Crassane and Beurré Hardy, Royal Gala and Golden Delicious) and dates when blossom blight was first seen on each cultivar. Between 1980 and 1991, records of blight were available for 25 cases. In most cases, one or more infection risk (IR) days, as defined for BIS, could be found during bloom. DD13 mean sums (sums of degree days above a mean temperature of 13 °C) gave good guidance on times when early signs of blossom blight were present in 14 cases. There was only a slight divergence from BIS guides in a further five cases. Possible reasons for divergence and for non-fit in the remaining six cases are discussed. It is concluded from this study that BIS should give useful guidance on optimal times for protective spray applications and for timing of searches for signs of early blossom blight in south-west of France. Graphical presentations of data provide additional information.