Manipulating nitrogen fertilization for the management of diseases in the tomato greenhouse: what perspectives for IPM?

Abstract : Although controlled conditions studies have shown that nitrogen nutrition can affect the susceptibility of tomato to certain pathogens, fertilization schemes for disease management at crop level remain to be designed. With this aim, a study has been conducted in an experimental greenhouse with cultural practices similar to those of commercial soilless production. The heated greenhouse was equipped with drip irrigation networks allowing the comparison of up to three different fertigation solutions (containing 4, 8 or 16mmol of NO3- per litre). In the first two years of the study (2010 and 2011), plants were inoculated with known spore concentrations of either Botrytis cinerea or Oidium neolycopersici and disease incidence and severity were recorded. Although variability was higher than in controlled conditions, these crop-level studies generally confirmed the influence of nitrogen fertilization on both diseases. Low nitrogen levels resulted in higher severity of Botrytis stem lesions while they decreased that of powdery mildew. In contrast, fruit yield from un-inoculated control plants did not differ significantly among the three nitrogen levels. More results should become available from similar studies conducted by other partners of a national collaborative project. For the design of health-enhancing fertilization schemes, further information will be needed on possible effects of nitrogen nutrition on the susceptibility of tomato to other pests and diseases and on the efficacy of various control methods used in IPM.