Breeding wheat for a changing climate

Australian cropping systems are facing increasingly variable growing seasons and it was a strong theme at the Wagga Wagga grains research update event. The literature, but also the evidence suggests that our climate is changing. Increasing CO2 is linked to warming and models are showing both in terms of the Indian Ocean dipole and also the ENSO atmospheric disruptions are such that the future for southern New South Wales and more widely southern Australia we’re going to be seeing or experiencing more frequent droughts. So do we need to change the way we think about our farming systems? Australian grain scientists, like Greg Rebetzke, are using climate modelling to target their pre-breeding efforts – to give growers access to new crop varieties with improved performance suited to future climate conditions. For Greg and his pre-breeding team at the CSIRO – it’s all about understanding and sourcing wheat genetics from across the globe that complements Australia’s existing breeding program.

01:32 - Australian breeding programs are among the best in the world for yield under drought, for grain quality and for disease. And breeders have done an amazing job of accumulating and aggregating those genetics and to lose those genetics with a very wild and woolly breeding program I guess would deliver varieties that are unacceptable. Our focus has been more about identifying targeted traits from already commercial wheats either in Australia or overseas and focusing on these, and putting them in a way that they are readily picked up and used in a commercial breeding program. This pre-breeding work in identifying key genetic traits has been supported by numerous GRDC investments over the past 20 years. One such trait they’ve focused on is coleoptile length.

02:21 - Coleoptile is a modified leaf it basically guides a leaf from the embryo to the soil surface. If, for example, we have good rain through summer but the break for sowing doesn’t arrive we’re limited with our current varieties and how deep they can be sown so they can access the moisture. A long coleoptile allows us to sow up to six inches, up to fifteen centimetres, thereby making use of that deep moisture and so allowing us to sow and establish a crop at the right time. The main driver of coleoptile length is the dwarfing genes, the genes that reduce plant height. It makes the cells in the plant very small, so stems are shorter the leaves and coleoptile are smaller.

03:07 - We’ve identified other dwarfing genes that also reduce plant height and give us high yields. But they don’t affect the coleoptile, they don’t affect leaf size. And so we brought these genes in from Europe, Russia, Italy, the Mediterranean and have been exploring and establishing which of those genes are most likely to be useful for Australian growers. We looked at coleoptile length associated with this new Rht18 dwarfing gene under control conditions and what we basically showed was in comparing the original donor, here Espada with the Rht2 green revolution dwarfing gene, with Espada where we replaced the Rht2 with the Rht18. Gregory, Mace, Magenta, Scout and Yitpi that indeed removing the handbrake with Rht1 or Rht2 allowed us to develop long coleoptile wheats while retaining that dwarf stature associated with Rht18.

04:04 - On average we increased coleoptile length simply by removing and replacing the green revolution dwarfing gene with this Italian dwarfing gene. Early vigour is another key genetic trait that is showing big potential for Australian wheats. Early vigour represents early growth and we’ve always valued barley as a very adaptable crop and under drought. Barley, a large part of what barley does is it shades the soil surface and if most of the water that the crop uses comes as rainfall, then if you’re not shading the soil surface the sun and the wind evaporate a large part of that moisture away. In fact, estimates suggest as much as 60 per cent of the rain that falls is evaporated away from our wheat crops because our crops aren’t vigorous enough to protect it.

04:54 - Learning from barley, we’ve established that we can develop a greater leaf area, greater early vigour, and by doing so we improve the capacity of our crops to shade the soil surface. They’re more drought tolerant because they’re more water is sufficient, they’re basically protecting that water. Early vigour is also an important trait in the battle of weed competitiveness, particularly around minimising herbicide losses from resistance. The CSIRO has been researching the impact of early vigour genes on a crops ability to out compete weeds. The final area we see incredible value with vigour and we’re talking about doubling the leaf area and doubling the biomass at flowering, is with late sowing.

05:38 - And we’re seeing with climate change that there is the risk of increasingly later breaks. What that means is the rainfall or the water needed for sowing may come later. So one idea might be to - can we can we develop wheats, which form part of that opportunistic response that rather than be sown in early April or main season May, can be sown as late as early to mid-July, but have the capacity to build biomass very quickly. The value there is that we ensure a good initial good establishment with late sowing. We avoid frost, which is an issue, but the other value is too in late sowing is we can use other herbicide options to control weeds, often less expensive, less damaging, so double knock solutions.

06:30 - Typically wheats that are well adapted to drought in terms of high rates of grain filling also perform well under irrigated conditions so it appears to be a repeatable trait and there appears to be lots of genetic diversity there. The team at CSIRO has also been researching traits to give growers the upper hand in an unkind season – as Greg terms it – such as heat stress at grain filling or a frost event. One avenue showing promise is planting awnless wheat varieties - to give growers the capacity to use the crops in other ways. Many years ago, growers would either graze damaged crops with on-farm animals or cut the hay, bale it and sell it. And there is still there is still option opportunity for that with current wheats.

07:16 - But but the value of our current wheats is less because our current wheats contain awns. These are these the beards on wheats and unfortunately when crops are dried, those awns become like needles and they they can stick into the lips and the jowls of the animals. And so the market favours awned varieties less. And yet they’re the mainstay of Australian grains industry. And so introducing the awnless trait back into breeding programs and just back of the envelope calculations from Nick Falkner.

07:51 - In 2019 on the Eyre Peninsular hay was returning $2100 per hectare compared with $740 for grain so there is a real opportunity for growers, if we can establish an end-point royalty system, to look at other options for our crops particularly if they are damaged by frost, heat or drought. So we’ve actually been developing main season wheat using main season varieties and removing the awns and they’ve been delivered to the breeding programs. And I guess it’s excited the breeding programs in thinking about other ways in which they can commercialise varieties of value to growers. The take-away messages on this topic are far from simple – but the work being done in this pre-breeding space should give every wheat grower optimism for the future. The hardest thing I find with any GRDC update is is actually developing a set of key messages because I think in the case of breeding, the key message is that Australian science is very mindful of the future.

08:55 - I guess my key message is that yeah thinking around adaptability, both in terms of how we manage our farming system and how we grow crops, but also adaptable around the varieties we choose and how we use those varieties around the system, around the timing and amount of water, around risk of frost. I think that will be a real change for us. And so, yeah, I look forward to the day when I can drive past a paddock of wheat and I know that that wheat there was developed in GRDC/CSIRO funding work coming out of my lab. Dr Greg Rebetzke, chief scientist at the CSIRO. And this video is one in a series of update videos recorded at the 2020 grains research updates. .