Review of wheat improvement for waterlogging tolerance in Australia and India: the importance of anaerobiosis and element toxicities associated with different soils

Abstract

Background and aims: The lack of knowledge about key traits in field environments is a major constraint to germplasm improvement and crop management because waterlogging-prone environments are highly diverse and complex, and the mechanisms of tolerance to waterlogging include a large range of traits. A model is proposed that waterlogging tolerance is a product of tolerance to anaerobiosis and high microelement concentrations. This is further evaluated with the aim of prioritizing traits required for waterlogging tolerance of wheat in the field.

Methods: Waterlogging tolerance mechanisms of wheat are evaluated in a range of diverse environments through a review of past research in Australia and India; this includes selected soils and plant data, including plant growth under waterlogged and drained conditions in different environments. Measurements focus on changes in redox potential and concentrations of diverse elements in soils and plants during waterlogging.

Key results: (a) Waterlogging tolerance of wheat in one location often does not relate to another, and (b) element toxicities are often a major constraint in waterlogged environments. Important element toxicities in different soils during waterlogging include Mn, Fe, Na, Al and B. This is the first time that Al and B toxicities have been indicated for wheat in waterlogged soils in India. These results support and extend the well-known interactions of salinity/Na and waterlogging/hypoxia tolerance.

Conclusions: Diverse element toxicities (or deficiencies) that are exacerbated during waterlogging are proposed as a major reason why waterlogging tolerance at one site is often not replicated at another. Recommendations for germplasm improvement for waterlogging tolerance include use of inductively coupled plasma analyses of soils and plants.

Fig. 1.

Waterlogging tolerance screening ponds at Katanning, Western Australia. Separate ponds enable screening of genetically fixed or segregating populations under controlled conditions. In this case up to 10 000 pots were used to screen approx. 450 genotypes in four soils. The insert shows normal (left) and specially designed pots (right) to minimize root escape during waterlogging treatments (see Materials and Methods).

Fig. 2.

Varietal tolerance of wheat to waterlogging in Katanning soil. Varieties were waterlogged for 49 d at 21 d after sowing. Varieties are ranked according to ‘waterlogging tolerance,’ values, i.e. waterlogged/drained shoot dry weights given in parenthesis. Data are the same as for Table 2 (2004).

Fig. 3.

Comparison of shoot dry weight per plant (DW/pl) in different experiments (A and B) for ten wheat genotypes at the end of 49 d waterlogging or drained treatments. The r² value is for all data; the r² value for waterlogged treatments only in these two experiments is 0·56.

Fig. 4.

Soil redox potentials of eight soils during waterlogging in the field at Katanning, Western Australia. Soils are the same as used in Tables 1 and 4; some soils with intermediate values are not shown for clarity. Data are standardized to pH 7 (see Materials and Methods); and soils are considered anoxic at redox potentials of ≤350 mV at pH 7 (Marschner, 1984). There was an intermittent period of rainfall during the drainage period at 52–55 d after waterlogging (which is why redox decreased over this period). The horizontal black bar indicates waterlogging duration; the standard error of the mean of individual values was always less than ±20 mV.

Fig. 5.

Concentrations (mg kg⁻¹ ± s.e.m.) of (A) shoot Mn, (B) shoot Fe and (C) shoot Al of three wheat varieties grown under drained and waterlogged treatments in Katanning, Esperance and South Stirlings (Warburton) soil or in potting mix. Plants were grown in waterlogged soil for 49 d. Dashed lines indicate critical concentrations for toxicity (see Materials and Methods).

Fig. 6.

Concentrations (mg kg⁻¹ ± s.e.m.) of (A) shoot Al, (B) shoot B, and (C) leaf Na ( % ± s.e.m.) of wheat varieties exposed to 12 d under drained and waterlogged treatments in Karnal soil at pH 7·8–8·2 or 9·2–9·4 (Karnal, India). Plants in (C) were in a different experiment from (A) and (B) so the soil pH was slightly different. Dashed lines indicate critical concentrations for toxicity (see Materials and methods).

Fig. 7.

Varietal tolerance to high Al concentrations based on mean maximum root length. Varieties were exposed to high Al concentrations (12 ppm) in aerated solution culture for 10 d (Materials and methods). Vertical lines indicate standard error of the mean.

Fig. 8.

Effects of waterlogging on element toxicities due to (a) direct effects of low redox potentials on changes in concentrations (affecting concentrations of Fe²⁺, Mn²⁺ and S^2– ); (b) indirect effects of anaerobiosis on root energy supply and/or membrane integrity affecting the ability to exclude or compartmentalize ions such as Al, B and Na.

Fig. 9.

Shoot ethanol-insoluble dry weight (EIDW) of wheat grown at a range of NaCl concentrations (0–120 mm; 0–12 dS m⁻¹) under either aerated or hypoxia conditions (nitrogen bubbled). Plants were grown under aerated or hypoxia conditions for 33 d and then allowed a further 13 d recovery (as per Barrett-Lennard et al., 1999); data plotted are for EIDW increases over the recovery period. The dotted line depicts the predicted results for hypoxia treatment (a) assuming that hypoxia reduces EIDW as per values at 0 mM NaCl, and (b) based on the relative reductions of the aerated treatment at 0–120 mm NaCl, i.e. assuming there is no NaCl –hypoxia interaction. The standard error of the mean is ≤10 % of individual values.