The control of Crown Gall by another organism is a great IPM story, and an Australian discovery now used worldwide.
Crown Gall Disease is caused by the organism Agrobacterium tumefaciens (updated scientific name: Rhizobium radiobacter). It causes tumours and cancer-like growths on lower stems and roots.
It was a particularly devastating disease of the fruit industry.
The bacteria can enter the plant only through wounds. Digging trees from a nursery and re-planting them in an orchard is a major root disturbance. Many wounds on these roots from digging, transport and pruning, all give entry sites for the disease. Mechanical injuries of crown and roots by cultivation equipment, animals, and insects are also important entry points
Galls vary considerably in size from 5 mm to 30 cm or more in diameter, with the majority being around 5 cm cross.
Young galls are soft on the surface and have a light, tan-coloured, frosty appearance.
As the galls become older they grow darker, turning almost black, and are usually hard and woody.
Crown Gall affects productivity
Crown Gall is often underestimated as a cause in lowering tree productivity.
Affects range from poor yields and fruit size, to declining tree production, and early dying or die-back of trees (secondary diseases invade the weaker Crown Gall affected trees).
There often is no visible effect on the plant other than the galls. However, the tumours do compete with the tree and fruits for nutrients.
Crown Gall affected trees are less productive and more prone to other diseases than unaffected trees. When galls are numerous or a large gall has girdled the stem, the plant may become stunted, with small, red or yellow leaves.
The NOGALL story
In 1969 a student at the Waite Agricultural Research Institute in Adelaide isolated a strain of the Agrobacterium that infected plants but didn’t cause the cancer-like growth.
In fact, this benign strain somehow protected young fruit trees against the virulent form of the same bacterium.
Professor Allen Kerr and his team dubbed the strain K84.
K84 produces an antibiotic that is deadly to the disease–causing strain but it is unaffected because it possesses a resistance gene that makes it immune to its own antibiotic (and found to be harmless to most other bacteria).
Unfortunately the close relationship between K84 and the disease Agrobacterium strain also meant that eventually there was gene swapping and the pathogenic strain also developed resistance.
Undeterred, the team then worked with overseas scientists and identified the region of DNA that allowed the transfer to other bacteria. They deleted this region. The bacterium retained its ability to synthesise the antibiotic, but could not pass the resistance gene to other bacteria.
This genetically modified bacterium was called K1026.
In 1988 the NSW Department of Agriculture approved K1026 for commercial use as a pesticide. It was subsequently given the name NOGALL™ and this product is now used all over Australia.
When susceptible plant material is dipped in a suspension of NOGALL prior to planting, the NOGALL K1026 bacteria act by colonizing the wounds and producing antibiotics, which inhibit the Crown Gall causing stain of Agrobacterium.
In 1990 Professor Allen Kerr, Professor Eugene Nestor (USA), and Professor Jeff Schell (Germany) were awarded the Prime Minister’s Australia Prize for Science for this work.
A fascinating IPM story, with some genetic engineering.
Quick points on NOGALL
- NOGALL is a live organism and needs to be treated as such.
- NOGALL containing K1026 is ineffective against strains causing Crown Gall disease in grapes, apples, pears and some ornamentals.
- NOGALL is a preventative treatment. It is not a curative treatment for plants that are already infected.
- NOGALL is suitable to use on stone fruit trees (apricots, cherries, nectarines, peaches, plums and prunes), nut trees (almonds, pecans and walnuts), cane berries (boysenberries and raspberries), clematis, hops, kiwifruit, persimmons, roses and many ornamental annuals, trees and shrubs.
For information and contact details, see the July 2012 Tree Fruit.
