The metabolism of secondary compounds in plants is strongly involved in the interaction between the host and the parasite. The resistance of apple against Venturia inaequalis is based on a rapid and localised accumulation of phenylpropanoids which is induced by the infection. However, the biosynthesis and accumulation of secondary compounds is dependent on environmental and growth conditions. A prerequisite for the formation of phenolic compounds is the availability of C-skeletons. High nitrogen fertilisation of apple trees results in an increased shoot growth and in a lower C/N-ratio in all organs. In addition, the constitutive level of phenolic compounds in leaves and shoots is reduced and the susceptibility to Venturia inaequalis increased. The limitation in the biosynthesis of phenylpropanoids is caused by a lack of necessary C-components. Thus, there is a carbon trade off in apple trees between carbon required for growth and carbon required for the synthesis of resistance-related secondary metabolites. The price for growth is a higher susceptibility to apple scab. Therefore, a restriction of shoot growth by a moderate N-nutrition would support the defence against pathogens.     «

The metabolism of secondary compounds in plants is strongly involved in the interaction between the host and the parasite. The resistance of apple against Venturia inaequalis is based on a rapid and localised accumulation of phenylpropanoids which is induced by the infection. However, the biosynthesis and accumulation of secondary compounds is dependent on environmental and growth conditions. A prerequisite for the formation of phenolic compounds is the availability of C-skeletons. High nitrogen...     »