• of nitrogen nutrition,
  
• of elevated CO2,
  
• and of arbuscular mycorrhiza.
  

• Soluble phenolic compounds are related to resistance against scab.
• They are synthesised only in young leaves.
• Infection of leaves by V. inaequalis induces biosynthesis of phenolics.
• Accumulation of phenolics depends on carbon availability.
• Young leaves depend on import of carbohydrates.

• Does the sink strength of the apex of vigorously growing trees interfere with the carbon availability in young leaves?
• Are sink-source-relationships between leaves responsible for effective defense mechanisms?

• Characterisation of transition of leaves from sink to source by sorbitol-dehydrogenase and aldose-6-P-reductase, respectively.
• Quantification of C-allocation and partitioning in growing shoots (B11)

• Do apple trees with mycorrhizal roots grow better than trees with non-mycorrhizal roots?
• What is the effect of mycorrhiza on sink-source-relationships, on C-partitioning, and resistance?
  

• Inoculation with V. inaequalis and P. cactorum and quantification of response
• C-Partitioning and allocation towards the roots (B11)
• Quantification of phenolic compounds in the relevant organs
  

Based on our results since 1998, it is postulated that apple trees favour shoot growth at the cost of secondary metabolism and defense, contradicting the central hypothesis, which postulates that the plant's defense may reduce its growth.
C-partitioning is proposed to be triggered by sink-source-relationships and will be examined by monitoring sorbitol transport and metabolism.
Cost and benefit of mycorrhiza with respect to C-partitioning, sink-source-relatonships and resistance mechanisms will be elucidated.

Description: Phase III

The resistance of apple trees against Venturia inaequalis

•  of the scab resistant cultivar Rewena and the susceptible cultivar Golden Delicious,

•  under the influence of N-nutrition,

•  within a time-frame of 25 days.

Questions:

•  What is the effect of different N-supply levels on the resistance mechanisms of two different apple cultivars?

•  Which defense genes play a role in the concerned plant-pathogen interaction?

•  What kind of kinetic changes occur within the V. inaequalis infection process concerning secondary metabolites and gene expression?

Experimental approach:

•  Quantification of secondary metabolites by HPLC-analyses.

•  Identification of V. inaequalis induced genes by subtracted cDNA libraries.

•  Quantification of V. inaequalis induced gene expression by quantitative RT-PCR and macroarray analyses.

•  Quantification of flavonoid enzyme activities by measuring the conversion of labelled substrates (Phase II).