Möglichkeiten der Bekämpfung des Falschen Mehltaus an Gurke (Pseudoperonospora cubensis) mit alternativen Präparaten

In organic cucumber production the infection with downy mildew (Pseudoperonospora cubensis) is one of the major problems. Use of biological control agents based on plant extracts and antagonistic micro organisms may be one possibility to control the disease. Plant extracts from Salvia officinalis and a plant belonging to the family Fabaceae (P1), as well as cultures of Brevibacillus brevis showed, in bioassays on potted cucumber plants, high potential to control the disease with efficacies between 55% and 100%. For S. officinalis extract the efficacy was close to 100% even at a concentration of 0.1325%. Initial trials under commercial growing conditions showed that the control of P. cubensis is better in protected than in open field production. In order to optimise the efficacy of the preparations for use in commercial cucumber production, further investigations on the mode of action, the active ingredients etc. are under way

Süßholz (Glycyrrhiza glabra) - Extrakt zur Regulierung von Falschem Mehltau im Öko-Gemüseanbau

A raw extract of licorice (Glycyrrhiza glabra) was tested against downy mildew in vegetables under semi-commercial conditions. In two greenhouse trials in cucumber, efficacies of ca. 70% were achieved (3% extract concentration) in either 7 or 10-11 day application intervals. Under open field conditions, weekly treatments resulted in ca. 2 week retardation of disease. In open field trials in lettuce, efficacies after weekly application of 5% G. glabra extract were variable, depending on disease pressure. In contrast, on lettuce seedlings in climate chambers, the extract reduced disease incidence of Bremia lactucae by 66 to 100%. In onion, applications of the extract at 6% concentration failed to control Peronospora destructor, despite of high efficacies under controlled conditions in the greenhouse. Overall, the G. glabra raw extract was highly effective in protected vegetables. Under field conditions low efficacies were most likely due to reduced rain fastness or UV-stability

Molecular effects of resistance elicitors from biological origin and their potential for crop protection

Plants contain a sophisticated innate immune network to prevent pathogenic microbes from gaining access to nutrients and from colonising internal structures. The first layer of inducible response is governed by the plant following the perception of microbe- or modified plant-derived molecules. As the perception of these molecules results in a plant response that can provide efficient resistance towards non-adapted pathogens they can also be described as ‘defence elicitors’. In compatible plant/microbe interactions, adapted microorganisms have means to avoid or disable this resistance response and promote virulence. However, this requires a detailed spatial and temporal response from the invading pathogens. In agricultural practice, treating plants with isolated defence elicitors in the absence of pathogens can promote plant resistance by uncoupling defence activation from the effects of pathogen virulence determinants. The plant responses to plant, bacterial, oomycete or fungal-derived elicitors are not, in all cases, universal and need elucidating prior to the application in agriculture. This review provides an overview of currently known elicitors of biological rather than synthetic origin and places their activity into a molecular context