Disease progress of downy mildew on cucumber leaves, caused by the obligate biotrophic pathogen Pseudoperonospora cubensis, was shown to be associated with various changes in transpiration depending on the stage of pathogenesis. Spatial and temporal changes in the transpiration rate of infected and noninfected cucumber leaves were visualized by digital infrared thermography in combination with measurements of gas exchange as well as microscopic observations of pathogen growth within plant tissue and stomatal aperture during pathogenesis. Transpiration of cucumber leaf tissue was correlated to leaf temperature in a negative linear manner (r = -0.762, P < 0.001, n = 18). Leaf areas colonized by Pseudoperonospora cubensis exhibited a presymptomatic decrease in leaf tem perature up to 0.8 degrees C lower than noninfected tissue due to abnormal stomata opening. The appearance of chlorosis was associated with a cooling effect caused by the loss of integrity of cell membranes leading to a larger amount of apoplastic water in infected tissue. Increased water loss from damaged cells and the inability of infected plant tissue to regulate stomatal opening promoted cell death and desiccation of dying tissue. Ultimately, the lack of natural cooling from necrotic tissue was associated with an increase in leaf temperature. These changes in leaf temperature during downy mildew development resulted in a considerable heterogeneity in temperature distribution of infected leaves. The maximum temperature difference within a thermogram of cucumber leaves allowed the discrimination between healthy and infected leaves before visible symptoms appeared.

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The spatial pattern of Fusarium‐infected kernels and their mycotoxin contamination was studied in four wheat fields in Germany using geo‐referenced sampling grids (12–15 × 20–30 m, 28–30 samples per field) at harvest. For each sample, frequency of Fusarium‐infected kernels and spectrum of species were assessed microbiologically; mycotoxin contents were determined by HPLC‐MS/MS analysis. Spatial variability of pathogens and mycotoxins was analysed using various parameters including Spatial Analysis by Distance IndicEs (sadie®). Microdochium majus, the most frequent head blight pathogen in 1998, was less frequent in 1999 and could not be detected in kernels from two fields in 2004. Fusarium avenaceum, F. graminearum and F. poae were the most frequent Fusarium species, with 7–8 species per field. The frequency of Fusarium‐infected kernels was 3–15% and the incidence of species showed considerable within‐field variability. Spatial patterns varied among Fusarium species as well as from field to field. Although pathogens and mycotoxin were often distributed randomly in the field, F. avenaceum, F. graminearum, F. poae, F. sporotrichioides, F. tricinctum and the mycotoxin moniliformin had an aggregated pattern in at least one field. Patterns are discussed in relation to spread of Fusarium species depending on inoculum sources, spore type, kind of dispersal, availability of susceptible host tissue and micro‐climate. Sampling of wheat fields for representative assessment of mycotoxins is complicated by random patterns of Fusarium‐infected kernels, especially where the frequency of infection is small.

Arbuscular mycorrhizal (AM) fungi and non-pathogenic strains of soil-borne pathogens have been shown to control plant parasitic nematodes. As AM fungi and non-pathogenic fungi improve plant health by different mechanisms, combination of two such partners with complementary mechanisms might increase overall control efficacy and, therefore, provide an environmentally safe alternative to nematicide application. Experiments were conducted to study possible interactions between the AM fungus Glomus coronatum and the non-pathogenic Fusarium oxysporum strain Fo162 in the control of Meloidogyne incognita on tomato. Pre-inoculation of tomato plants with G. coronatum or Fo162 stimulated plant growth and reduced M. incognita infestation. Combined application of the AM fungus and Fo162 enhanced mycorrhization of tomato roots but did not increase overall nematode control or plant growth. A higher number of nematodes per gall was found for mycorrhizal than non-mycorrhizal plants. In synergisms between biocontrol agents, differences in their antagonistic mechanisms seem to be less important than their effects on different growth stages of the pathogen.