Transcriptional analysis of the grape defence response against the root rot agent Armillaria mellea

Armillaria mellea is the main causal agent of grape root rot in some important viticulture areas. A. mellea attacks roots causing a decline in vigour and the death of the plant. Up to now, no resistant Vitis rootstocks have been identified and the existing pesticides are ineffective in controlling this disease. Because young grapes did not show A. mellea symptoms during the first three to four years, the activation of defence mechanisms in young roots has been hypothesised. In order to study this defence response at the molecular level in the widely-used rootstock (‘Kober 5BB’), the suppression subtractive hybridization approach has been used. Specific defence genes induced 24 h after A. mellea inoculation have been identified and validated by real-time RT-PCR experiments. Furthermore, the protein extracts of infected roots showed a direct antifungal activity to A. mellea mycelia growth in vitro, suggesting that young grape roots can activate a defence reaction to A. mellea infection.