Dr Curt Brubaker (CSIRO Plant Industry/ Cotton CRC) discusses how the Molecular Biology is allowing a greater insight into the dilemma of Fusarium in Australian Cotton soils.

Dr Curt Brubaker is a geneticist from CSIRO Plant Industry. He and Dr Bo Wang (CSIRO Plant Industry) have been investigating the origins and diversity of fusarium wilt in the Australian cotton industry. Can you give me a bit of a summary of the work you have been doing.

What we have basically trying to understand is how the Fusarium oxysporum vasinfectum (Fov) that is infecting cotton plants in Australia arise. Was it an introduction from overseas or did it arise from a native form of Fusarium and if the later is the case, what sort of diversity of Fusarium exists in natural soils in Australia and in the cultivated cotton fields and how is that diversity actually changing over time?

How have you done this sampling? Have you looked at cotton around Australia?

Basically we have gone to native cotton populations, sampled the soils and the plants there for Fusarium isolates. We have gone into cotton fields and done exactly the same thing. Bo Wang then isolates all of those Fusarium genotypes out of these samples and we type them using molecular markers like Amplified fragment-length polymorphism (AFLP’s) or gene sequences.

From that work, what sort of Fusarium species have you found in Australian cotton fields?

What we have found is that there is a greater level of diversity than we anticipated within the two Vegetative Compatability Groups (VCG’s). There appear to be a number of small genetic changes that are occurring that have lead to the recognition now of 28 different haplotypes. These aren’t really a change in the pathogens themselves, its just that there is a little bit of diversity within both groups.

The two VCG’s you mentioned, that’s what we commonly refer to as the ‘Boggabilla strain’ and the ‘Darling Downs strain’. Is that right?

Exactly.

You looked at comparisons in native vegetation next to adjacent cotton fields. What sort of difference did you find in that?

What Bo Wang did was sample native remnant vegetation soils right next to a couple of cotton field soils and then the cotton field soils themselves. What he discovered was that there is rather a dramatic shift in the profile of Fusarium species in the two different soil types suggesting that agricultural conditions have affected a change in the biodiversity within the cotton field soils themselves. This in itself is not all that surprising but it does highlight the fact that agricultural conditions have a strong impact on soil biodiversity.

Could that be a change on the crop you are growing or could it be a change from things being introduced through farm hygiene for instance?

It’s very difficult to say at this point. Possibly all things combine to varying levels and until future research can begin to pull those things apart we can’t really say what is the predominant factor in making that change.

You would have looked at some places that have had Fusarium for a long period of time and some that have only just been discovered.  What’s the comparisons in Fusarium diversity in the recent discoveries and the long term sites?

What we have discovered is the number of haplotypes that we find within a field. That diversity within VCG 11 and VCG 12 (the Darling Downs and Boggabilla strains), is actually highest in the areas where the disease has been present the longest. Again, that’s not an unexpected correlation.

We are seeing the dynamics of the Fusarium in the soil changing with farming practice over time. Will that change continue and what sort of implications could that have?

Of course it is going to continue over time because we are dealing with the interactions between living organisms and evolution continues to take place even on small scales. At this point, I can’t see that it has any huge implications for the cotton industry but it is something we do want to continue to monitor. Its because just as the original strains appeared at one point in time there is the remote possibility that a third strain could emerge and we just want to monitor and find that before it actually becomes a problem.

Where to now for your work?

We’re continuing to monitor cotton fields over the long term to keep track of the diversity that’s emerging and what it actually means for farm management systems.

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