The development of plant diseases is associated with biophysical and biochemical changes in host plants. Various sensor methods have been used and assessed as alternative diagnostic tools under greenhouse conditions. Changes in photosynthetic activity, spectral reflectance and transpiration rate of diseased leaves, inoculated with Cucumber mosaic virus (CMV), Cucumber green mottle mosaic virus (CGMMV), and the powdery mildew fungus Sphaerotheca fuliginea were assessed by the use of non-invasive sensors during disease development. Spatiotemporal changes in leaf temperature related to transpiration were visualized by digital infrared thermography. The maximum temperature difference within a leaf was an appropriate parameter to differentiate between healthy and diseased plants. The photosynthetic activity of healthy and diseased cucumber plants varied as measured by chlorophyll fluorescence and compared to the actual chlorophyll content. Hyperspectral imaging data were analysed using spectral vegetation indices. The results from this study confirm that each pathogen has a characteristic influence on the physiology and vitality of cucumber plants, which can be measured by a combination of non-invasive sensors. Whereas thermography and chlorophyll fluorescence are unspecific indicators for plant diseases, hyperspectral imaging offers the potential for an identification of plant diseases. In a sensor data fusion approach, an early detection of each pathogen was possible by discriminant analysis. Although it still needs to be validated under real conditions, the combination of information from different sensors seems to be a promising tool.

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Near-range and remote sensing techniques are excellent alternatives to destructive methods for measuring beneficial effects of fungicides on plant physiology. Different noninvasive sensors and imaging techniques have been used and compared to measure the effects of three fungicidal compounds (bixafen, fluoxastrobin and prothioconazole) on wheat (Triticum aestivum L.) physiology under disease-free conditions in the greenhouse. Depending on the fungicidal treatment, changes in green leaf area and yield parameters were observed. Chlorophyll fluorescence of leaves was useful for measuring differences in the effective quantum yield of PSII. Reflectance measurements of wheat leaves were highly sensitive to changes in plant vitality. The spectral vegetation indices were useful for determining the differences among treatments in terms of leaf senescence, pigments and water content. The analysis of ear and leaf surface temperature was reliable for detecting effects of fungicides on plant senescence. Using nondestructive sensors, it was possible to assess a delay in senescence of wheat due to fungicide application. Furthermore, it was deduced that sensors and imaging methods are useful tools to estimate the effects of fungicides on wheat physiology. Physiological parameters measured by the sensors were actually more sensitive than yield parameters to assess the effect caused by fungicide application on wheat physiology.

The aim of this study was to investigate interactions between Ditylenchus dipsaci and Rhizoctonia solani. Both pathogens are known to cause problems in the primary sugar beet production areas in Germany. Furthermore, the organisms' ecological niches in the soil and on the beet overlap. Hence, it is probable that these parasites interact and have a deleterious synergistic impact on sugar beet production. The stem and bulb nematode, D. dipsaci, is a migratory endoparasite that penetrates the sugar beet seedling during the spring when temperatures are low. The main symptoms include distorted, bloated petioles and leaves. The fungus causing Rhizoctonia crown and root rot, R. solani, enters the plant at the beet-leaf transition zone. Synergistic damage was obtained when both organisms occurred on the same plant. Hyperspectral leaf reflectance data was used to calculate a vegetation index, the Normalised Difference Vegetation Index (NDVI), which could successfully be used to discriminate between growth reduction caused by R. solani and by dual inoculation (disease complex). High correlations were observed between ratings of disease symptoms and the vegetation index over a time series of seven weeks.

Una de las alternativas más eficientes y ambientalmente seguras para controlar las enfermedades causadas por Rhizoctonia solani en remolacha azucarera es el uso de variedades resistentes o tolerantes. Se probaron dos métodos de inoculación de R. solani: inóculo sólido (mezcla de arena-harina) e inóculo líquido (caldo de papa dextrosa). Se utilizó una variedad susceptible y una moderadamente tolerante a R. solani. Los síntomas en la raíz y en las hojas de remolacha se evaluaron cuatro semanas después de la inoculación individual con uno de los dos grupos de anastomosis de R. solani (GA 2-2IIIB y GA 4). En ambas variedades, la incidencia de la enfermedad fue del 100%, y la severidad en la remolacha y en las hojas fue mayor con el empleo del inóculo líquido, independientemente del grupo de anastomosis usado. La severidad de la enfermedad fue siempre mayor cuando GA 4 se utilizó como inóculo. La mortalidad fue significativamente diferente entre las plantas tratadas con diferentes grupos de anastomosis y entre variedades. Los resultados de este estudio demostraron que el uso de inóculo líquido de R. solani es muy eficaz para producir la infección en las remolachas, y se convierte en una alternativa viable para evaluar la resistencia de variedades de remolacha azucarera en programas de mejoramiento. 176 ABSTRACTThe most efficient and environmentally safe alternative to control Rhizoctonia solani diseases is the use of resistant or tolerant varieties. In order to establish the resistance level of sugar beet varieties several inoculation methods and techniques to produce the inoculum were used. The aim of this study was to compare inoculation techniques useful to estimate genetic resistance in sugar beet varieties. Two already used inoculation techniques were tested; solid inoculum (sand-flour mix) and liquid inoculum (Potato Dextrose Broth). One susceptible and one moderate tolerant variety towards R. solani were used. Beet and leaf symptoms were assessed in plants, four weeks after the inoculation of one of the two R. solani anastomosis groups (AG 2-2IIIB and AG 4). Plants were harvested, evaluated and compared to non-inoculated control. In both varieties, disease incidence was 100% and the average of the disease severity in beets and leaves was higher regardless the anastomosis group when the liquid inoculum was used. In contrast, high number of «escapes» was found when the solid inoculum was used. Disease severity was always higher when AG4 was used as inoculum. The mortality was significantly different among plants treated with different anastomosis groups and between varieties. The results of this study demonstrated that the use of liquid R. solani inoculum is highly effective in order to produce an infection on beets and becomes a viable alternative to evaluate resistance of sugar beet varieties in breeding programs.