Physiological and genetic approaches for the development of waterlogging tolerance in wheat on sodic/alkaline and neutral soils in India and Australia

• University of Western Australia, Australia
• Central Soil Salinity Research Institute, India
• Narendra Deva University of Agricultural Technology, India
• Directorate of Wheat Research, India
• Department of Primary Industries, Victoria, Australia

Waterlogging adversely affects 10-15 million ha of wheat each year, and this occurs in diverse environments ranging from the acidic sandy duplex soils of Western Australia to the heavy clay alkaline/sodic soils of northern India. Unless physically drained, wheat plants may remain submerged for up to 10 days or more, completely killing intolerant varieties and resulting in large losses.
Waterlogging inhibits the exchange of oxygen and carbon dioxide between the roots and the atmosphere. In addition, the activity of soil microbes in the anaerobic environment then changes the soil chemistry, which in turn alters nutrient availability and releases potentially toxic substances. Different soil types may react differently. After water-logging, there is often less nitrogen available and this may limit recovery in some situations. Plant species vary considerably in their ability to tolerate the oxygen deficiency and the soil chemistry aspects of waterlogging. Because of this large genetic variation, improving the tolerance of crops to waterlogging has considerable potential for success. Genetic evaluations of wheat crosses have shown that the heritability of waterlogging tolerance is quite high, and this project sought to find the most tolerant lines.

The aims of this research were to characterise waterlogging-prone environments and determine the genetic diversity for waterlogging tolerance in wheat, evaluate mechanisms of tolerance, and with this knowledge develop new wheat breeding lines with waterlogging tolerance for specific target environments.

This large and complex project is divided into seven sub-projects. The first two will characterise the nature of waterlogging damage in wheat in India and Australia, noting differences and similarities in the environmental factors that impinge on waterlogging, in particular the alkalinity and sodicity of the soil. The scientists will also prioritise the various waterlogging environment and regions. Key field sites and the suitability of field station trials will be determined, and specific germplasm types will be assessed for breeding.

The third sub-project concentrates on understanding the physiology of waterlogging tolerance, while the fourth will identify physiological traits that could be used by plant breeders to screen for tolerance. In the fifth, breeding trials will be established and waterlogging-tolerant lines will be identified. The team will look both at yields and quality of harvest.

In the sixth sub-project the team will make use of facilities at Agriculture WA that enable development of new germplasm to occur within 1-2 years (in contrast to the normal 10-12 year timeframe). Physiological traits will be evaluated for any synergistic or antagonistic effects.

The final component of the work is concerned with increasing the research capacity of the project partners.

This project successfully formed the basis of developing screening protocols, identifying and prioritising physiological traits, exchanging germplasm, establishing a genebank for waterlogging tolerance of wheat adapted to diverse target environments, increasing waterlogging tolerance of wheat through the development of breeding lines and increasing research capacity. The work is now at an excellent stage for capturing the benefits of the research through the development of elite germplasm.
Project highlights and achievements included:
the determination that waterlogging is, and will continue to be, an important constraint to wheat production in India and Australia
evidence that every time wheat is irrigated in the sodic/alkaline soils of India, it becomes waterlogged
development of tools for environmental characterisation and germplasm evaluation that were successfully applied in this and other projects
the discovery that element toxicities are critically important during waterlogging - including aluminium, sodium, boron, manganese and iron (evidence for this came from 10 different sources including plant and soil analyses)
development of a current hypothesis that waterlogging tolerance is a product of: (1) tolerance/avoidance of anaerobiosis and (2) tolerance to specific element/microelement toxicities that are indigenous to the target environment(s)
determination that the presence of aerenchyma (plant tissue made of air filled spaces that transports air from the leaves and stems to the roots), which was initially considered a high priority for waterlogging tolerance, showed little or no correlation with waterlogging tolerance in wheat grown in acidic or neutral soils in Australia or India
identification of simple visual selection criteria for waterlogging tolerance, including plant height, tiller number and shoot biomass
genetic studies that developed 13 doubled haploid populations, including over 2600 genetically fixed lines, some with excellent waterlogging tolerance
development of over 150 populations segregating for waterlogging tolerance, which will be screened and further developed for waterlogging tolerance over the next few years as part of ongoing research.