Genetic Variation for Subsoil Toxicities in High pH Soils

Abstract

Alkaline soils (pH > 7) are common throughout the world in semi-arid to and climates (< 500mm rainfall/year) with soil types predominantly calcarosols (calcareous soils) and sodosols (sodic soils). The pH of calcareous soils is buffered in the range of pH 7.5 to 8.5 by the presence of CaCO3, while sodic soils have a high exchangeable sodium percentage (ESP >= 6) and generally contain Na2CO3. The higher solubility of Na2CO3 compared to CaCO3 increases the disassociation of CO3 (2-) and HCO3- in sodic soils, leading to pH values > 8.5 Solution screening methods have been used for the identification of HCO3- /CO2- (3) tolerance in plants, with significant variation found in root length within both commercial and landrace lines. A moderate level of tolerance was found in much of the southern Australian bread wheat (Triticium aestivum) germplasm. Durum wheats (Tritictum turgidum. ssp. durum) showed much lower tolerance to HCO3 (-)/CO32-(approximate to 50%), consistent with the shorter breeding history of durum wheat in southern Australia and their poor adaptation to alkaline soils; this is reflected in their confinement to higher rainfall regions. In field trials the durum variety Tamaroi (approximate to 89% of S.A. commercial production) suffered a > 1 t/ha yield penalty from increasingly higher subsoil pH (Cooper 2004). Several durum lines have been identified with significantly greater tolerance to HCO3 (-) /CO32- than Tamaroi. Significant correlations between HCO3-/CO32- tolerance and yield have been identified in a double haploid bread wheat population RAC875/Cascades grown at a number of high pH field sites across S.A. A second population Frame/Yarralinka//Pugsley has high variation for HCO3-/CO3 (2-) tolerance and is currently in field trials,