Allen Kerr, Fellow 1995
Many younger plant pathologists will know of Allen Kerr as an APPS Fellow
and via the Allen Kerr prize, which is awarded each year by APPS for the most
outstanding PhD research in plant pathology.
Allen Kerr’s own research career had many significant highlights,
including fundamental observations which led to the discovery of the
tumour-inducing plasmids (Ti plasmids) in Agrobacterium, paving the way
for plant genetic engineering, and the discovery and understanding of the most
successful example of biological control in plant pathology, the use of strain
K84 for control of crown gall disease of stonefruit.
Allen’s career began in
Edinburgh
University
where he enrolled in Science, with an interest in bacteriology.
His interest in botany and an inspiring mycologist as a teacher led Allen
to discover the joy of plant pathology, and his career as a plant pathologist
began. In 1950, he was offered a job
at the Waite Agricultural Research Institute.
He enrolled in a PhD on Rhizoctonia solani, then (as now) an
important pathogen of cereals in southern
Australia
. A sabbatical with Dr SD Garrett at
Cambridge
in 1959 stimulated a lifelong interest in biological control.
After a period in
Ceylon
in the 1960’s studying blister blight of tea (Exobasidium vexans),
Allen returned to
Adelaide
at a time when crown gall disease was causing very significant economic losses
in the South Australian stonefruit industry.
At this time, it was known that, after infection, crown gall tumours
could grow without the causal bacterium, and a hypothetical “tumour- inducing
principle” had been proposed by Braun, but the discovery of the Ti plasmid was
still a decade away.
Allen’s research at the Waite focused on the ecology of Agrobacterium,
and through his use of different selective media, realised that pathogenicity
was being transferred from pathogens to non-pathogens. He soon understood that
this must be the result of plasmid transfer between strains. The demonstration
of pathogenicity transfer led to an international race to locate the
“tumour-inducing principle” and in 1975 Eugene Nestor’s lab in
Seattle
published evidence for the Ti plasmid. This created the basis of the revolution
in plant genetic engineering.
Allen Kerr’s own research re-focused on the biology of Agrobacterium
studies on non-pathogenic and pathogenic
strains led to the important observation that a non-pathogenic strain of Agrobacterium
completely inhibited crown gall formation when mixed with a pathogen.
Work in the lab then demonstrated that control was dependent on the
production of an antibiotic, agrocin 84 by the non-pathogen, strain K84.
As with many effective controls, the seriousness of crown gall disease to
stonefruit production is now largely forgotten.
Stonefruit growers were supplied with strain K84 on agar slopes
from a small incubator in Allen Kerr’s lab for many years.
A report from
Greece
that pathogens could arise which produced agrocin 84 led to a detailed genetic
study of the agrocin 84 plasmid. Using transposon mutants supplied by
Stephen Farrand (
University
of
Illinois
), the genes controlling agrocin synthesis and plasmid transfer were mapped.
Dr. David Jones, working with Allen Kerr, constructed a deletion mutant
of K84, which was unable to transfer the plasmid.
The deletion mutant, K1026, was shown to be as effective as K84 at
controlling crown gall disease and approval was gained to use this genetically
modified strain as a commercial control. It was the first genetically engineered
organism in the world to be released for commercial use.
The highlights of Allen’s research were undoubtedly the discovery of
pathogenicity transfer, the successful biological control of crown gall and the
commercial use of the genetically engineered biological control agent.
However, Allen and his collaborators also made a wide range of
contributions to plant bacteriology with significant impact on the control of
crown gall disease of grapevines, on the understanding of conjugation in Agrobacterium,
and on the role of bacteria and bacteriophage in Annual Ryegrass Toxicity (ARGT).
Allen Kerr’s career and achievements were recognised by the award of the
inaugural Australia Prize (1990), election as a Fellow of the
Australian
Academy
of Science, Fellow of the Royal Society, Foreign Associate of the National
Academy of Sciences, US and Fellow of the
American
Academy
of Microbiology, not to forget the APPS Allen Kerr Prize. The recipients of
this award can hope that some of Allen Kerr’s intellect and insight will be
transferred along with this prize!
-
Kathy Ophel-Keller
- SARDI
- December 2006
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