The effect of nitrogen on disease development and gene expression in bacterial and fungal plant pathogens

Successful colonisation of plants by pathogens requires efficient utilisati on of nutrient resources available in host tissues. Several bacterial and f ungal genes are specifically induced during pathogenesis and under nitrogen -limiting conditions in vitro. This suggests that a nitrogen-limiting envir onment may be one of the cues for disease symptom development during growth of the pathogens in planta. Here we review recent literature on the effect of nitrogen and nitrogen-regulated genes on disease development, caused by phytopathogenic bacteria and fungi. Furthermore, the potential influence o f nitrogen-limitation or general nutrient limitation on several in planta-i nduced bacterial and fungal pathogenicity, virulence and avirulence genes w ill be discussed.