Prof. Rick Roush - University of California, Davis Campus - Outlines the implications of Bt resistance and its effect on GM cotton

Rick you gave a presentation at the ACGRA cotton conference on managing biotech resistance. Could you just give us the key points of that presentation as far as what we need to be aware of in Australia now with our change over to Bollgard® II cotton?

Sure. Resistance can evolve to Bt. crops but Bollgard II will be less sensitive to that than INGARD® was. People have needed to make a conversion quite quickly to Bollgard II because we didn’t want selection to continue to occur from the Cry1ac genes that are unprotected in Bollgard but still we know that there is a potential for resistance evolve to Bollgard II and it’s going to be important for people to continue to observe the resistance management recommendations that have been made, including maintaining an adequate refuge and continuing to refine pupae busting as a management strategy. Very recently it has turned out that there is fairly high frequency of resistance to the second gene in Bollgard, the Cry2ab gene. This has come as quite a surprise to us because it wasn’t found in the United States it was quite a surprise but if anything what that means is that we have to be ever more vigilant to make sure that resistance doesn’t evolve to this clearly very useful technology.

So the key to preventing resistance build up and obviously with resistance already out there the size of refuges, the maintenance of those refuges to keep them attractive is going to be a key area?

That’s absolutely right; we need to make sure that the refuges are attractive to susceptible boll worms so they continue to generate susceptible boll worms that will dilute resistance coming off the Bt. plants. Part of the reason this works so much better is any insect that can survive on the Bt. plants might be carrying two resistance genes but when they mate with another insect the tendency will be for those insects to split among the offspring. So we have to make sure that there is still a lot of mating going on so there actually is this dilution effect splitting the resistance genes out so that they are less likely to build up on the crop.

As far as resistance levels to the Cry1ac gene, is that high in the field at the moment amongst the heterozygote or more so to the Cry2 gene?

We believe that resistance to Cry1ac is still low. There have been from time to time some reports that resistance was starting to creep up but they’ve been unsubstantiated we’ve looked at that pretty hard and to my knowledge there’s still no real evidence that the frequency of Cry1ac has increased to any significant frequency, and that’s all the more reason why it was such a surprise to find out that there was, actually it’s easier at this point it seems to find resistance to Cry2ab even though it’s never been used in a wide spread way, then it was to Cry1ac. I mean for those of us that are researches this is a huge disappointment and it’s quite a big surprise. It’s not what we anticipated at all. It’s a real tribute to Rod Mann and the rest of his group that they are actually looking into this to make sure we had a better forewarning about it.

You mentioned in your presentation that with traditional chemistry normally your life cycle before resistance builds up of about 7 years. How do you see that correlating with Bt. resistance if something did go wrong?

We’ve already beat the 7 year average in the United States. Resistance evolved to pyrethroids in Mississippi in 7 years time. The adoption of Bt. cotton in Mississippi and especially Alabama has been very high and low areas so the selection areas pressure has been about as intense and yet there is no evidence of resistance evolving to Bt. yet, so by using the refuge strategy we believe we have beaten the historical average for chemical insecticides and I think we will continue to stretch that out for quite some time and it really is driven because we have an effective resistance management strategy with a reasonably high dose and really defined refuge system to try to delay resistance.

Those populations that are in labs at the moment as far as the resistant groups of armigera and probably punctigera, they’re going to play an important role in research. Is that going to continue, there’ll always be a need for some resistant grubs or worms or to keep that ongoing research?

Absolutely, in fact we do have populations that have been selected from field collected material selected in the lab to try and anticipate resistance problems and in Australia in Canberra with CSIRO we have populations resistant to the Cry1ac gene and now the resistance to the Cry2ab gene. Similarly in the United States we are looking at strains that are resistant to our Boll worms and these are very useful tools because when somebody else comes to the market with a new product we can at least test to find out if there is resistance across resistance problems to the strains that we know about.

That’s one of the things that will probably be done with the new Widestrike cotton. So just find out what’s the extent, how effective is the Cry1f protein in the Widestrike at managing the kinds of resistance we already know about. Now it’s still possible that there will be resistance genes lurking in the field that we haven’t found yet but at the very least if we found resistance to some of the ones we already know about that’s a real warning about how we can try to use these things.

Resistance management is like freedom, it requires eternal vigilance to make sure that you can actually stay on top of it, so just as has been in the case in Australia quite properly for many years about pyrethroids. You know resistance management is an important part of product stewardship to make sure these things work in the future and part of that is resistance monitoring and doing some of this futuristic things just checking to make sure that things work the way they are supposed to work.

And that will relate through to field checking no doubt with consultants out in the field collecting eggs, sending those eggs in for sampling just to get field monitoring levels of any base resistance building up in the field?

Absolutely, continued egg collection just to check on this sort of thing. I mean in the grand scheme of things these projects cost some money but in the grand scheme of things they are much less costly to control failures in the field, so it’s a small investment in the future. So they’ll be checking for eggs and those will go back and be tested but in addition I’m sure we’ll be encouraging people that find any enlarged grubs in Bollgard II fields to try to collect those too and report them in because those are the kinds of ways we can find some early warnings of the potential for resistance.

Further Information:
Robert Eveleigh, John Marshall,  Craig McDonald, David Kelly or James Quinn