New wheat winning war against weeds

Transcript

Glen Paul: G'day, and welcome to CSIROpod. I'm Glen Paul. In an effort to improve water efficiency in bread wheat CSIRO has developed new wheat lines capable of competing against weeds for precious water and nutrients, effectively suppressing weed growth. Pivotal to the CSIRO trait are increases in wheat growth and leaf size that make the seedlings roots and shoot system more vigorous.

Joining me on the line to discuss it is Dr Greg Rebetzke from CSIRO Plant Industry.  Now Greg, considering the speed at which weeds grow, this sounds like quite an achievement – what’s the secret behind the wheat’s ability to wipe out weeds?

Dr Rebetzke: The wheat's secret is that we've identified from looking at other winter crops – crops like barley, triticale, and rye – that wheat is fairly conservative in its growth. It tends to grow quite slowly.

We're not sure why that is, but in indentifying characteristics, or what we call traits, we've learnt we can improve the vigour of wheat by changing its leaf architecture, and also changing some of the characteristics of the seed, so that we're giving the seedling a bit more of a chance to really sort of get up out of the ground more quickly and get ahead of the weeds.

Now it's about the timing of emergence, a timing of when the seeding merges relative to the developing weeds, but also it’s being able to outcompete the weeds below ground – so a larger root system means that our wheats have a better chance of getting at precious water and precious nutrients that the weeds would typically rob of our slower growing wheat plants.

Glen Paul: How many wheat varieties did you have to screen then to find these traits?

Dr Rebetzke: Oh, we're still screening, you know. Currently we screen around 5000 wheats from all around the world, and they've been screened here at CSIRO under very controlled conditions where we can observe very closely both the early growth above the ground, the shoot growth, and leaf growth, and the root growth.

So from our screening of around 5000 wheats – and these are wheats that have been collected for us, and by ourselves, from places far away as China, India, Israel, Canada, South America. We've sort of brought it down to around 20 or 30 wheats that are unrelated, they're genetically unrelated, and because they're genetically unrelated we believe that the early vigour, the wheat competitiveness characteristic that we're targeting, we believe that the genes controlling the vigour across these different wheats may be separate, may be different, and this is where the excitement begins.

If we have different genes controlling characteristics that are important, we can then embark on a breeding program to bring together all these different genes into a few very elite, very vigorous varieties.

Glen Paul: But how do you ensure that the genes from one variety that offer the trait you're looking for, don't then impact on the breeding of the new plant – sort of interact in the wrong way so to speak?

Dr Rebetzke: Yeah, that’s a good question. It's a bit of a juggling act. In some cases people tend to think of breeding as one step forward and two steps back, but we're very, very careful in working with commercial breeding partners, and working with agencies overseas, to ensure that as we select for these underlying or underpinning genes for improved vigour, that we're not impacting negatively on other important traits.

And so as we develop these new strains, new varieties, we are very careful to assess this material – these elite materials – in the hands of commercial breeders, to look at what other traits may be impacted upon. And we know we are having some negative impacts, so we’ve learnt that in improving early vigour we've had to change the plant architecture in other ways.

A good example is the genes that control plant height, so these are the green revolution genes that were, I guess essential to the improved productivity of wheat and rice back in the '60s and '70s, and which resulted in Norman Borlaug receiving the Nobel Peace Prize.

What Norman Borlaug did was he identified that we could improve the productivity of our cereal crops – our wheats for example – by reducing their height, so that they wouldn't fall over. By making them shorter we could put on more fertilizer, put on more water, which meant the crop could yield more without lodging(?) or falling over.

In the work that we're doing on early vigour and wheat competitiveness, we've identified that the current suite of dwarfing genes actually put a bit of a handbrake on early growth, so these genes which are currently used all around the world – these height reducing, or dwarfing genes – not only make the plant shorter in height, but they also make the cells in the leaves smaller.

So in trying to make our new vigorous wheats more vigorous, and to make them big and leafy, and juicy, we've had to change the dwarfing genes that underpin height.  And so we've been undertaking a separate research activity which complements the early vigour work, to identify new sources of reduced height, and we’ve stumbled upon some pretty amazing dwarfing genes which we believe will allow us to develop very vigorous wheats which are short in height.

Glen Paul: Right. And what method are you using then to transfer these genes into the new varieties?

Dr Rebetzke: We're using conventional breeding that has pretty much followed from when the farmers were domesticating wheat 10 000 years ago, identifying the very best looking types, assuming that the best ones have the important genes, and then keeping these.

We've been fast tracking a little bit over the last 10 000 years and using modern genetic techniques – these are statistical in(?) genetic techniques – to identify those genes much earlier, and then using traditional or standard hybridisation to bring together genes from those plants which we like, and infer have the right combination alleles, so traditional breeding with good use of statistics, and also use of molecular markers for some of the traits that we're targeting.

Glen Paul: OK. Getting back then to the trait of the large broad leaves, now I'd imagine they'd be soaking up a lot more sunshine being a larger leaf, which would then kind of negate the whole water saving process because there'd be the chewing up of the moisture in the soil with photosynthesis?

Dr Rebetzke: Yes, you're right – in growing faster you’re using more water.  But if you think that our typical Australian wheat crops in the southern part of Australia grow when rain is provided – so they grow on current rainfall – as much 50 per cent of the rain that falls on the crop evaporates away.

What we believe is if we can capture that water by shading the soil surface, or by robbing the weeds of the water, we believe that water will be going through the plants for photosynthesis and building up of growth, that’s a better way of using water, or losing water, than losing it simply through evaporation from the soil surface.

So the amount of water that's used is the same, it's just that we're putting it through the plants and through the stomata for use in photosynthesis, than just losing it through evaporation into the air.

Glen Paul: OK. How about with sowing the wheat though, would a wheat like this, with its more vigorous root system and broader leaves, require more space in the field, meaning less plants say?

Dr Rebetzke: No. Growers sowing the new types will be sowing under the same conditions in which they grow – they'll still sow the same amount of seed – they'll just be getting double to triple the growth rates of commercial varieties.  But we believe that there's a greater capacity with the new types to be used in going to wider rows, or with later sowing.

See, current varieties have really been developed for traditional farming systems – sort of narrow rows – and we see the highest yields when growers sow at the right time. So depending on where you are in the Australian wheat belt – anywhere from early May to mid June. 

But with the more vigorous wheats we believe you can go to much wider row spacings, which are being used more and more to help control stubble, to control weeds, and also to slow water use, and also with late sowing.

I mean I really feel that these more vigorous wheats will provide a little more insurance. Farming is a risk adverse industry, and growers have the capacity to sow multiple varieties, and with more vigorous wheats you’ve got a little more flexibility to be able to sow a little later, and we don’t have the current varieties to allow that.

The reason I think this is important is with climate change the models tend to predict that there could be greater climate variability, and therefore there is the capacity for later breaks, which means growers may have to sow later into the season, and with our current slow growing varieties sowing later isn't going to be a good thing. 

But if you have a variety which grows faster, can intercept more light, bigger leaves, bigger solar panels, and grow faster, there is the capacity for growers to allocate part of their farm to later sowing of more vigorous varieties. That's what they’re doing now with barley – we want to do the same thing with wheat.

Glen Paul: So you can see a future for this wheat in other parts of the world, drier parts of the world such as Africa?

Dr Rebetzke: Absolutely. I mean I don’t feel this is a one stop shop for varieties. I think there are going to be places where these wheats are going to do better than existing varieties, but they’re not going to displace all the varieties being grown – another string in the bow – and so places like Africa, where we have droughts, where we have low nutrient soils, or where we have weeds, more vigorous wheats give the capacity to improve differing uptake, improve productivity in a drought, and also reduce the reliance on herbicide use, or at least give a little more insurance where herbicides are being used. So in Australia, in Africa and other parts of the world, I see real opportunities with more vigorous wheats.

Glen Paul: Well, the less herbicides the better, and food security to boot sounds promising. Thank you very much for discussing the research, Greg.

Dr Rebetzke: No worries. And thank you.

Glen Paul: Dr Greg Rebetzke. For more information find us online at csiro.au. You can like us on Facebook, or follow us on Twitter at CSIROnews.