Ion toxicity tolerance may tame hostile soils
GroundCover™ Issue: 115 | Author: Nicole Baxter
- Soil acidity affects 80 to 90 million hectares of Australian farmland
- Transiently waterlogged acidic soils have high concentrations of aluminium (Al), manganese (Mn) and iron (Fe) that may cause toxicity
- These ion toxicities restrict crop growth and yield if followed by drought
- Scientists are screening wheat for tolerance to Al, Mn and Fe toxicity to develop varieties able to yield well in acid soils prone to waterlogging and terminal drought
Acidity, waterlogging and drought all limit wheat yield, but researchers have identified a potential genetic solution
Australian researchers have confirmed a link between wheats that are tolerant to toxic ions and yield performance in acidic soils prone to waterlogging and drought.
Dr Hossein Khabaz-Saberi, from the University of Western Australia (UWA) Institute of Agriculture, has shown that wheat with a genetic resilience to toxic ions such as aluminium (Al), manganese (Mn) and iron (Fe) has enhanced root and shoot growth during transient early-season waterlogging compared with intolerant varieties.
The finding opens the way to breeding ion-tolerant varieties able to perform much more profitably in these adverse conditions.
Tolerant plants have been shown to have well-developed, deep root systems, allowing them to access water from deep within the soil profile. In terminal drought, these tolerant wheat plants are less affected because they tap into deeper water supplies for grain filling.
The findings, published in Crop & Pasture Science, come 10 years after Dr Khabaz-Saberi first raised the concept and pioneered the idea that breeding wheat with tolerance to toxic concentrations of Mn and Fe was just as important as breeding for tolerance to Al toxicity.
When he raised this 10 years ago, some researchers questioned his views; however, Dr Khabaz-Saberi says he found an abstract of a Portuguese article written by a Brazilian wheat breeder, which had a similar observation of high concentrations of toxic Al, Mn and Fe in acid soil.
The Brazilian wheat breeder’s article provided Dr Khabaz-Saberi with the names of the indicator wheat genotypes (very tolerant and very intolerant checks) for tolerance to Fe toxicity required to optimise the screening technique, saving him a year of research.
Retired wheat breeder Robin Wilson, formerly with InterGrain, says one of Dr Khabaz-Saberi’s most valuable achievements has been the development and optimisation of screening methods to determine which varieties are better able to cope with Al, Mn and Fe toxicity.
The screening methods were developed and optimised with UWA Winthrop Professor Zed Rengel, with support from an Australian Research Council Linkage Project.
In 2010, after Dr Khabaz-Saberi and Professor Rengel characterised and identified genotypes with contrasting tolerance to ion toxicities, the next step was to assess the yield advantage of tolerant versus intolerant genotypes and also yield potential using two low-yielding Western Australian sites (Merredin and Wongan Hills) and one high-yielding site (Esperance).
Grain yields were evaluated at three acidic sites in replicated plots with and without lime. Dr Khabaz-Saberi says extremely dry growing seasons at Merredin (104 millimetres) and Wongan Hills (119mm) and close to long-term average rainfall at Esperance (400mm) provided excellent conditions to evaluate the performance of the genotypes under combined drought and soil acidity, and the yield potential under optimum conditions.
The researchers observed that the combined effect of soil acidity and drought reduced grain yield less in Al and Mn-tolerant genotypes than intolerant genotypes – 2.34 tonnes per hectare versus 2.86t/ha.
The liming also reduced surface soil acidity and increased grain yield more in wheat varieties that were tolerant to toxic ions than those that were intolerant.
The GRDC has commissioned Dr Khabaz-Saberi and Professor Rengel to characterise commercially available varieties and advanced breeding lines from wheat breeding companies for variations in tolerance to Al, Mn and Fe toxicity.
To date, they have evaluated 75 entries out of 150 genotypes and found some distinct tolerance to individual ion toxicities.
“We have shown that tolerance to individual ion toxicity could increase grain yield by five to 10 per cent,” Dr Khabaz-Saberi says.
“The next exciting stage would be to test whether wheat with combined tolerance to ion toxicities could increase grain yield even further.”
The researchers have developed the required tools (doubled-haploid populations and near-isogenic lines) and hope to test whether combined tolerance to ion toxicities could enhance grain yield significantly in acid soils prone to waterlogging and terminal drought.
Beyond this, Mr Wilson hopes molecular experts will join the team to look for genetic differences between the intolerant and tolerant genotypes to develop markers based on single nucleotide polymorphism or SNP (pronounced ‘snip’) markers.
Having SNP-based markers, which he says may be identified in three years, would enable plant breeders to screen a large range of genetic material quickly to identify those tolerant to Al, Mn and Fe toxicity.
Russell Eastwood, wheat breeder with Australian Grain Technologies, is keen to see the results of Dr Khabaz-Saberi’s evaluation work and says having molecular markers would be ideal for assessing material with tolerance to Al, Mn and Fe toxicity.
Once markers are found, Mr Wilson says growers may see new wheat varieties with tolerance to Al, Mn and Fe toxicity within six to eight years.
Canola and barley
Dr Khabaz-Saberi says the work has implications for other crops such as barley and canola, which are more sensitive than wheat to acid soils prone to waterlogging and drought.
Canola breeder and UWA Institute of Agriculture’s Professor Wallace Cowling says ion toxicities in waterlogged, compacted layers may account for the underperformance of canola in many high-rainfall areas of southern Australia.
More information:Dr Hossein Khabaz-Saberi,
0401 684 459,
0428 939 503,
0427 716 632,
Professor Wallace Cowling,
08 6488 7979,
GRDC Project Code UWA00166