Changes in the genetic structure of the lettuce crop ( Lactuca sativa ) and populations of the lettuce downy mildew pathogen ( Bremia lactucae ) in Germany from 1974 to 1997 were studied and the genetic and population genetic results of race surveys of B. lactucae were reinterpreted. Data on 176 B. lactucae isolates collected from L. sativa cultivars at 48 sites in 11 German federal states were analysed. The host population contained 12 well-defined race-specific resistance genes ( Dm 1, Dm 2, Dm 3, Dm 4, Dm 5/8, Dm 6, Dm 7, Dm 11, R12, Dm 13, Dm 16 and R18). However, only some of these genes (e.g. Dm 3, Dm 7, Dm 11, Dm 16 and R18) played an important role in management of resistance in the host crop. Substantial changes in the frequencies of these R-genes were recorded over the period as a reaction to the occurrence of new virulent phenotypes in the pathogen population. Generally, the durability of resistance was very short. However, distinct regional patterns were observed for the frequencies of different virulence (v) factors. The data on changes in the virulence of B. lactucae population exemplified well the process of host-pathogen coevolution. During the period studied, there was a considerable increase in the frequency of some v-factors (v2, v3, v5/8, v6, v7, v11 and v16) and in the complexity of v-phenotypes, while the diversity in the pathogen population in general decreased. In 1996/97, 12 of the 14 v-factors evaluated reached frequencies higher than 0·90 in the pathogen population. Relatively low frequencies were observed only for factors v14 (0·17) and v18 (0·24). The presence of 23 v-factors was studied in six German isolates virulent on lettuce cultivar Titan, possessing the resistance gene R36 derived from Lactuca saligna and introduced in German lettuce crops during the mid-1990s. Isolate DEG2 showed the highest complexity of v-phenotype; it overcame the resistance in cv. Mariska (R18) and line CS-RL (R18+?), but some sporulation occurred also on cv. Titan ( Dm 6 + R36). Conversely, the isolates SR2 and SAW1 overcame resistance based on R36, but were avirulent to R18. Future utilization of R-genes in commercial lettuce cultivars is proposed; R-genes R18 and R36 could be considered most efficient for this purpose. However, they may be effective only in certain regions.

Four German isolates (FS1, SR2, SAW1 and DEG2) of Bremia lactucae originating from lettuce cultivars with R‐factors R18 and Dm6 + R36 were used for detailed characterization of virulence factors (v‐factors) and for the study of the resistance efficiency in wild Lactuca spp. germplasm. The highest complexity of v‐phenotype was recognized in isolate DEG2, which overcomes resistance in cv. Mariska (R18) and line CS‐RL (L. serriola × L. sativa, R18 + ?), until now known as resistant to all known races of B. lactucae in Europe. However, some sparse sporulation also occurred on cv. Titan (Dm6 + R36). The isolates SR2 and SAW1 overcome the resistance based on the gene R36, but are avirulent to R18. The v‐phenotype of SR2 is highly complex with the most important v‐factors being present except for v14 and v18. The isolate FS1 is the first in Germany originating from a cultivar with R18 (cv. Samourai). The search for efficient sources of resistance in 64 accessions of 11 wild Lactuca spp. and primitive forms of L. sativa showed broad variation in accession–isolate interactions. Expression of race‐specific resistance in wild Lactuca spp. (L. serriola, L. viminea, L. virosa) was recorded frequently. Lactuca indica and L. saligna could be considered as the most efficient sources of resistance against isolates FS1, SR2 and SAW1. The isolate DEG2 showed the highest level of virulence. On seedlings of L. saligna, which is considered as a most important source of resistance against B. lactucae, there was frequently recorded limited sporulation, however this response cannot be considered as a susceptible. Except for some L. saligna accessions (CGN 05310 and CGN 05315), the resistance to all studied isolates was only observed in one accession of L. serriola (PI 253467).

For organic potato producers, the two main challenges are disease and nutrient management. Both are limited by regulations that on the one hand prohibit the use of chemical fertilizers, especially nitrogen, and on the other hand prohibit most synthetic pesticides. Late blight caused by Phytophthora infestans is commonly thought to be the most yield-reducing factor. However, because there is no really effective fungicide available to control late blight, there are virtually no yield loss data available for organic farming conditions. In this paper, the state of the art of organic potato tuber growth under on-farm conditions with respect to disease and nutrient management is summarized by field trials and on-farm surveys on commercial organic crops carried out in the years 1995-1998. Soil nitrogen (N) levels, plant N uptake, disease development of P. infestans and potato yield were measured. Results indicated that N availability was most important in limiting yields in organic potato crops. From on-farm data, a model including disease development, growth duration of the crops until foliage decay and different parameters related to N status of the crop could explain 73% of the observed variation in yield. Only 25% of this variation in yield could be attributed to the influence of late blight. Differences in N availability explained 48%. In conclusion, several points emerged from the results. In organic farming, yields are mainly limited by nutrient availability in spring and early summer. The effects of late blight on yields may often be overestimated and cannot be deduced from results in conventional farming because of the strong interaction with nutrient status. Depending on N availability, tubers stop growing between mid-July (70-90 kg N ha −1 uptake), the end of July (110-140 kg N ha −1 uptake) and mid-August (140-180 kg N ha −1 uptake) due to N limitations. The higher the N status of a potato crop, the longer the growing period needed to achieve the attainable yield and the higher the probability that late blight stops further tuber growth and becomes the key tuber-yield-limiting factor. In the second part of this paper, the interactive effects of soil N availability and the impact of P. infestans on yield in the presence and absence of fungicides from 1996 to 1998 for mid-early main crops are reported. An empirical schematic model of disease impact depending on N availability was developed.

The aim of our study was to evaluate clinical diagnoses in symptomatic persons exposed to aerosols from humidifiers or air conditioners. In addition, we tried to identify the causative antigens. Results of clinical investigations, including inhalation challenge tests, demonstrated a typical hypersensitivity pneumonitis (humidifier lung) in 9 persons and isolated systemic symptoms without significant changes in lung function and chest x-rays (humidifier fever) in 3 persons. Microbiological studies revealed a variety of fungi and bacteria in the water supplies of humidifiers and air conditioners at patients' workplaces. The detection of 4 members of the order Sphaeropsidales (Deuteromycotina), not previously associated with humidifier-induced diseases, is of special interest. By means of an improved polystyrene tube-immunoradiometric assay, high concentrations of IgG antibodies against extracts prepared from water of patients' humidifier systems were found in all cases. In addition, patients demonstrated low concentrations of IgG antibodies against thermophilic Actinomycetes, and usually also against various fungi, such as Alternaria tenuis, Aureobasidium pullulans, Penicillium notatum, Aspergilli, and fungi of the order Sphaeropsidales, which were isolated and cultured from humidifier water supplies. The much higher concentrations of antibodies against humidifier/air conditioner water extracts seem to result from sensitization to a variety of antigens from different fungi and bacteria. For in vivo and in vitro diagnostic tests in humidifier-induced lung diseases, we especially recommend using extracts from water systems installed at the corresponding workplaces.

The nematode species Longidorus attenuatus, L. elongatus, L. macrosoma and Paralongidorus maximus are economically important pests to the viticulture industry due to their ability to vector two nepoviruses (Raspberry Ringspot Virus and Tomato Black Ring Virus) to grapevines. In Germany, these species occur in vineyard soil with other non-vector but morphologically similar longidorid species, L. helveticus, L. profundorum and L. sturhani.Species-specific primers were designed from ribosomal DNA for all seven species to facilitate taxonomic identification for non-specialists. Primers were assessed for their reliability by screening, where possible, a number of populations of each species. Furthermore, their selectivity and sensitivity were determined when challenged with closely related longidorid species and general nematode communities typical of vineyard soil. A multiplex approach using a common forward primer combined with species-specific reverse primers enabled three target nematode species to be detected in the same PCR reaction. All primers were highly specific, detecting all nematode developmental forms from disparate populations and were sufficiently sensitive to detect a single target nematode within a whole nematode community typical of a vineyard soil comprising of a range of non-target species.Given their specificity, sensitivity and reliability, these diagnostic primers should be of great benefit to both phytosanitary/quarantine services related to the viticulture industry and also as a decision management tool for growers.

Xiphinema diversicaudatum and X. index are vector nematode species of economic importance in viticulture regions as they can transmit Arabis Mosaic, Grapevine Fanleaf and Strawberry Latent Ringspot viruses to grapevine. Wang et al. (2003) designed species-specific diagnostic primers from ribosomal genes for both these vector species as well as a vector and a non-vector species X. italiae and X. vuittenezi, respectively. Our study aimed to confirm the specificity and determine the sensitivity and reliability of the primers for the two vector species, X. diversicaudatum and X. index when challenged with closely related longidorid species and general nematode communities typical of vineyard soil. With one exception, no PCR product was observed when the primers were tested against six Longidorus, one Paralongidorus and one Xiphinema non-target species. Occasionally (three out of eight replicate PCR reactions) a weak PCR product was noted when primers for X. index were tested with L. elongatus. Furthermore, when challenged with a range of nontarget nematode species comprising the nematode community typical of viticulture soil, no PCR product was amplified. An experimental dilution series of extracted DNA rigorously demonstrated that DNA from an equivalent single specimen of the target virus-vector species, X. diversicaudatum and/or X. index, could be detected amongst 1000 equivalent non-target X. vuittenezi. Also, extracted DNA from an equivalent single target specimen was detected when added to DNA extracted from the overall soil nematode community. The primers were assessed further by using serial mixtures of actual nematodes rather than extracted DNA to simulate field soil. Using this method, a single target nematode could be detected amongst 200 non-target specimens. Given their specificity, sensitivity and reliability, it appears that these diagnostic primers will be of great benefit to phytosanitary/quarantine services related to the viticulture industry.

Approximately 150 seed lots of Allium cepa and more than 30 different Allium species were tested in the greenhouse under strictly controlled conditions against Sclerotium cepivorum, the causal fungus of Allium white rot disease. The quantity and quality of the inoculum was determined using a simple and rapid test to achieve a high degree of standardization. Only the A. cepa cultivar “Sweet Sandwich’ and A. porrum, A. rotundum, A. sphaerocephalon and two further unidentified Allium species showed significantly lower disease incidence than the cultivar ‘Golden Bear’. The stimulatory effect of the root exudates on sclerotial germination was compared with that of diallyl sulphide. With the exception of A. species‘PI 249549′, extracts of all species that showed low levels of disease incidence in the greenhouse test stimulated sclerotial germination only weakly.

Glasshouse experiments to test the activity of commercial fungicides against Septoria tritici were carried out under controlled conditions. In addition to the parameter, % necrotic leaf area (NEC), used to estimate the pathogen-induced leaf damage, the number of pycnidia per leaf (PYC) was determined to quantify the pathogen itself. Curative fungicide treatments were applied 100-210 day degrees after inoculation. A high curative activity was achieved up to 170 day degrees after inoculation, whereas the treatments at 200-205 day degrees were less effective. The best curative activity was observed for epoxiconazole-based treatments, followed by slightly less active azoles in the ranking tebuconazole, cyproconazole, prochloraz and flusilazole. Greater differences between the fungicides were observed for the protectant fungicide properties, which were tested 50-350 day degrees prior to inoculation. The best persistency was observed for epoxiconazole, whereas tebuconazole, cyprocoazole, prochloraz and flusilazole showed declining activity with this ranking. Combinations of triazoles with the active ingredients kresoxim-methyl and chlorothalonil, which are known to inhibit spore germination, significantly improved the longevity of the remaining green leaf area in comparison with disease-free treatments with triazoles alone. The results obtained under glasshous conditions were compared with field studies on S. tritici development after treatments with tebuconazole to place the results in context. The comparison of the assessment parameter PYC and NEC between glasshouse and field trial showed that curative and protectant fungicide properties based on microscopic assessments of PYC in the glasshouse correlated well with results from field trials.