CROWN GALL Flashcards
Also know as
Kroongal
Where does it occur? and which cultivars are affected
Orange river region. Sultanina & Muscat d’Alexandrie
Causitive organism
Agrobacterium tumefaciens
Which cultivar is resitant
Semillon
Moderately resistant?
Pinot noir
Susceptible?
Cabernet Sauvignon
Very susceptible
Merlot noir
How is it spread?
The bacteria survive in the soil for long periods, whereafter they can be distributed successfully by drift actions, implements, vehicles and animals.
Host plants can aid as an accumulation point for members of the bacterial population
How does it penetrate?
wounds via weeding actions, frost and insects
the bacteria then spread systematically through the grapevine
Establishment of the young infected vine
poor initial vigour
followed by early dieback (2-3y)
Older infected vines
production decline insufficient lignification (damage by frost)
What happens after penetration?
tissue is stimulated by bacteria and multiplies abnormally rapidly
this tissue is then protruded outwards in the form of galls or tumours = galls on the trunk near soil surface
Characteristics of the gall
creamy white to pale green, round soft and smooth appearance but change to
dark-coloured, hard wart-like structures with parts that fall off and become rotten
Where do the galls develop?
close to the soil surface
higher up on trunks, canes and on susceptible rootstocks below the graft union
What will happen when galls are on trunks?
cause dieback of the grapevine
