2-Plants: More difficulties arise for Australian Bt cotton resistence management plans

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TITLE:  Kits put the acid on Bt varieties
SOURCE: cottonworld.com, Australia, by Donald Turner
        http://www.cottonworld.com.au/cworld/index.php3?type=2000_12_30_5&
        directory=archives&rst=lk&title=Story6
DATE:   December 30 , 2002

------------------ archive: http://www.gene.ch/genet.html ------------------


Kits put the acid on Bt varieties

RESEARCH confirming large variations in the level of toxin expressed by Bt 
cotton varieties could speed up adoption of test kits by growers seeking 
improved insect control. Research entomologist John Adamczyk (USDA-ARS, 
Stoneville, MS) explained the findings and implications of these 
differences to researchers at the Australian Cotton Research Institute, 
Narrabri last week.

US study reveals resistance challenge:
- Managing resistance to pests such as bollworm could be complicated by 
differences in expression - not only between varieties, but also between 
plant parts and different times of the season, he said.
- Resistance management could be complicated further as low-dose 
insecticide strategies are employed against "intrinsically tolerant 
Lepidoptera, such as armyworms and bollworms".

"Our study shows that the level of endotoxin decreases throughout the 
season, and that the trend in endotoxin levels between varieties was not 
geographically isolated," Dr Adamczyk said.

There were big differences between 17 varieties in the Bt expression trial. 
Two related varieties in the trial also showed far higher expression 
throughout the season, suggesting a parental link between high-expressing 
varieties.

Dr Adamczyk said more work needs to be done to confirm factors such as 
parental link, and whether the findings are similar in Australia. The trial 
was run by Dr Adamczyk and colleagues at the US Department of Agriculture's 
Stoneville, Mississippi research station. A quantification assay (ELISA) 
was used to quantify the levels of toxin in two varieties throughout the 
season. The trials were planted in May 1999. Differences in the amount of 
toxin present in various plant parts and leaves of these varieties were 
correlated with larval survival and development.

US cotton growers, who have more than 25 transgenic varieties to choose 
from, are expected to lead the uptake of commercialised CryIA(c) endotoxin 
quantification systems. "These systems will allow more routine evaluations 
of Bt varieties," Dr Adamczyk said. "As with any foliar insecticide and 
herbicide research, research must be performed to determine the efficacy of 
every variety to ensure the best recommendation to growers."


The kit in Australia

The Cotton Research and Development Corporation has introduced the 
technology to Australia and it will be available in kit form from Cotton 
Growers Services. CRDC research manager Bruce Pyke says most growers and 
consultants will be familiar with the technology. "The CRDC hopes to 
calibrate this kit to give an indicator of efficacy in the field," he says.

CGS business development manager Phil Armytage says variations in efficacy 
have been noted in the Australian Bt crop. "This season we are calibrating 
test results against bioassay work -- we need to be able to compare plant 
data with what happens to insects in the field," he says.

The main limit on the test is how long samples may be kept in transit -- 
another factor being tested this season. Test kits are available for 
Australian growers this season.

"Without having the calibration we are still able to test levels of Bt 
toxin in the plant, which will be useful in monitoring the effect of 
management practices or weather events," Phil Armytage says. In-field tests 
will initially involve collection and analysis of leaves from head and tail 
ditches in each field.


Two genes, more punch

Adding an encouraging note, Dr Adamczyk told researchers at the ACRI work 
on two-gene cotton had shown dual protein action worked well throughout the 
season. "We have done extensive efficacy testing with Bollgard II and it 
looks very superior to anything else we have. We hope the research will 
continue and we will have this cotton shortly." Results of the Bt 
expression trial will be published soon in the United States. Look for more 
detailed coverage to come.



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