23 
Dr. Berns called the vote on the motion to change the language of item (iv). 
By a vote of eighteen in favor, none opposed, and one abstention, the RAC 
noted to amend Section III B-4-c-(3). Dr. Brill abstained. 
IX. REQUEST TO RELEASE STRAINS OF PSEUDOMONAS SYRINGAE AND ERWINIA HERBICOLA 
Dr. Berns called upon Dr. Vidaver to review the proposal (tabs 1103, 1101/VI) 
to field test genetically modified strains of Pseudomonas syringae and 
Erwinia herbicola . Hie proposal, submitted by Drs. Nickolas Panopolous and 
Steven Lindcw of the University of California, Berkeley, requests permission 
to field test these organisms to control, biologically, frost damage in 
plants. Hie strains would be carrying deletions of all or part of the 
genes involved in ice nucleation. 
When freezing occurs on plant tissues, the tissues are damaged on thawing. 
Bacteria then enter through the damaged tissue and destroy the plant or at 
least destroy the tissue. Certain bacteria, such as Pseudomonas syringae 
(various pathovars under the current taxonomic classification), Erwinia 
herbicola , and, occasionally, isolates of Pseudomonas fluorescens , serve 
as nuclei for ice crystal formation in supercooled water at temperatures 
slightly below 0°C (threshold nucleation temperature about -1.8°C). These 
bacteria are common plant epiphytes found in substantial numbers on above- 
ground plant surfaces (leaves, twigs, buds, flowers) with seasonal 
fluctuations from undetectable levels up to 10^ cells/gram tissue fresh 
weight. A causal relationship between frost damage on frost sensitive 
crop plants at relatively warm subzero temperatures (down to -5°C) and 
these organisms has been established. For instance, the degree of damage 
after exposure to lew temperatures either in the field or in controlled 
environments (growth chambers) is directly related to the populations of 
ice nucleation active (INA + ) bacteria present in or on the surfaces of 
abeve ground parts. Plants grown aseptically can tolerate temperatures of 
several (ca. 6) degrees Celsius belcw zero without apparent damage. They 
are rendered sensitive to such temperatures by spraying with suspensions 
of INA + bacteria prior to low temperature exposure. Frost damage to 
plants can be decreased by reducing the natural epiphytic population of 
INA + bacteria; significant protection against frost damage has been obtained 
by application of various bactericides. The use of antagonistic bacterial 
strains which compete with the natural epiphytic flora has also been shown 
to be effective under field conditions. lift - mutants of the naturally 
occurring INA + strains should be especially suitable antagonists. These 
mutants, being basically adapted for epiphytic growth and survival, presum- 
ably displace their wild-type counterparts by occupying the same physical 
spaces and utilizing the same nutrients. 
Dr. Vidaver noted this request had been previously reviewed by the RAC at 
its October 25, 1982, meeting. She said RAC had reccmmended approval of 
the proposal by a narrow margin (seven in favor, five opposed, and two 
[ 108 ] 
