Dr Nicolas Taylor: Developing salt-tolerant wheat

 

Dr Taylor: Salinity is major constraint to the production of crop plants in Western Australia, Australia and globally. In WA, dryland salinity affects 0.9-1.1 million hectares of farmland and remains a potential threat to 2.8-4.5 million hectares of low lying and valley soils. Farmers in affected areas see crop yields reduced by more than a quarter and the Department of Primary Industries and Regional Development estimated that the value of lost agricultural production for the period of 2013-14 was $519 million.

 

Although large areas of saline land existed prior to large-scale cultivation, land clearing for agriculture has increased water recharge due to the replacement of perennial, deep-rooted native vegetation with the shallower rooted annual crops and pastures. Increased groundwater recharge levels have raised water tables and increased the amount of land affected by salinity. It took decades to centuries for salinity to spread across the Western Australian landscape following land clearing, depending on a range of factors that include the area cleared and the depth of the water table.

 

In the rest of Australia, another one million hectares of agricultural land is impacted by dryland salinity, mainly in South Australia and New South Wales, with smaller impacts in Victoria and Tasmania. Unlike WA, these states suffer from another form of salinity that mainly impacts irrigated land. Irrigated salinity results from the accumulation of salt in the soil from the water used for irrigation or the raising of water tables as a result of irrigation bringing salt to the surface, leading to similar impacts as dryland salinity. In NSW, irrigated salinity is estimated to impact five per cent of current irrigated land and up to 30 per cent of land is under threat. Globally, salinity is viewed as a major threat to food security. It currently affects more than 800 million hectares of agricultural land and results in annual losses of between US$12 to US$27.3 billion ($17-40 billion) due to a reduction in crop productivity. Those losses could increase as 50 per cent of the world’s arable land is expected to be affected by salinity by 2050.

 

 

Dr Taylor: What we have shown is that a couple of key enzymes that are critical in converting the energy harnessed from the sun into growth and yield are especially sensitive to salt. Those enzymes appear to be a weak link that leads to plant death in saline soils. We also found that wheat uses a natural defence system, called the GABA shunt, which can bypass one of the sensitive enzymes and partially protect the plant against salt.

 

Previously we could observe the impacts of salinity on plant growth and survival and we could measure yield losses in plants, but we had not identified specific molecular targets that were damaged by salt. By finding these targets, it provides us with new opportunities to further investigate how we can bypass, select for or change the salt responsiveness of these enzymes with the aim of producing more salt-tolerant wheat.

 

At the same time, we are continuing to examine the molecular responses of wheat plants to salinity, to identify other potential targets. For example, we currently have a project that specifically focusses on the responses of roots to salinity, as this is the first tissue exposed to salinity in the soil. We are also examining if the inhibition of these enzymes occurs in other crop plants. For example, we know that barley is significantly less salt sensitive than wheat, and we want to know how barley overcomes the inhibition that we see in wheat. It could, for instance, have structurally different enzymes that are more salt-tolerant that we could use as follows: as a basis to transfer these into wheat; to design new, better proteins for wheat; or to utilise other bypasses that are not used in wheat. The insights we can gain from barley are likely to inform our next decision on how to proceed in improving the salt tolerance of wheat.

 

Given the impacts that salinity has on agricultural production, both in Australia and globally, now and into the future, the development of more salt-tolerant wheat could ensure that production remains at current levels, despite the increasing amounts of salt affected land. It could even allow the return of wheat planting to areas previously unsuitable for wheat production.

 

 

Dr Taylor: At this stage of the project we have not decided on the best approach to modify current wheat varieties to be more salt-tolerant and a number of options remain open to us. These include: genetic modification; the editing of the existing enzymes in wheat to make them more salt-tolerant; or the introduction of enzymes from outside wheat, such as barley, that are more salt-tolerant. It also includes traditional breeding approaches that have proved successful over many decades in Australia for breeding tolerance to a range of diseases. This would involve identifying local or international varieties or landraces (historical precursors of modern wheat) that contain structurally different versions of enzymes and then breeding these into modern Australian varieties. Additionally, we have an eye on the evolving regulatory landscape with respect to genetically modified organisms, genetically edited organisms, marker assisted selection and traditional breeding. In theory, if we can successfully improve the salt tolerance of wheat through the approach we have taken, then it should be possible to attempt similar approaches in other salt sensitive crops.

 

 

Dr Taylor: This is a difficult question to answer. The key to this is that we have found what we think is the most affected part of metabolism related to energy production. If we fix this we hope this will make the plants more tolerant, but will it make them grow like plants on non-salty soils? Unfortunately, that is unlikely, as other parts of a plant’s metabolism may also be affected. But we hope that by solving one problem, it is the first step in identifying other potential bottle necks to growth that can then be subsequently addressed to further improve tolerance.

 

While everyone would love to see a rapid fix, unfortunately there is more research to do to define the impact that changes to these enzymes could have. After that there will be many years of work in controlled environments for rapid generation advancement, followed by field trials in which you can only plant a single crop per year and it would take multiple seasons to confirm the benefit. So all in all, if everything went perfectly, you might imagine ten years, but we know in science not much ever goes perfectly.