Experience with new fireblight resistant rootstocks in South Germany

Summary

Fireblight (Erwinia amylovora) was detected on rootstocks in several apple orchards in Baden-Württemberg.
In Germany the mostly used rootstocks on apple ‘M9’ and ‘M26’ are known to be susceptible to fire blight.
Therefore the LVWO Weinsberg participated in the “European Cornell-Geneva rootstocks trial” which is a
common experiment of seven research institutes over whole Europe. Six fire blight resistant or tolerant rootstocks
from the Geneva® breeding program were tested in comparison to ‘M9’ (Type T337 and Pajam 2).
The variety was ‘Golden Delicious’ and the trees were planted in 2001 . An outstanding new rootstock was
‘Geneva® 11’. The tree size was similar to ‘M9’ (above 7% more growth in comparison to ‘T337’). Besides
that the influence on the fruit size is positive (bigger fruits) and the relationship yield to growth (kg/cm2 trunk
diameter) better than on ‘M9’. A further interesting new rootstock is Geneva® 41 which is in tree size similar
to ‘M26’. It’s efficiency was as good as ‘M9’ and the fruit size was better. The Geneva® rootstocks seem to
be better adapted to the hot climate and dry soil conditions of the Neckar region than ‘M9’. Alternate bearing
could not be seen until today, but might be a problem in 2006 because of heavy bearing in 2005. Further
experiments concerning the influence of those rootstocks on the colouring of fruits will follow.