Early growth of wheat is more sensitive to salinity than boron at levels encountered in alkaline soils of south-eastern Australia

The early vegetative growth of 3 wheat (Triticum aestivum L.) cultivars, Frame, BT Schomburgk and Schomburgk, was evaluated over a range of soil salinity and soluble boron (B) concentrations in pots. Additions of boric acid and mixed salts to a sandy clay soil produced extractable B levels of 2, 13, 24, 51 and 129 mg/kg and salinities (ECe) of 0.8, 8, 15, 23 and 29 dS/m. In both cases, the levels produced in the first 4 treatments corresponded well with those commonly observed in subsoils of the southern Mallee. Within the ranges tested, wheat cultivars had relatively greater tolerance to B toxicity than to salinity. Significant differences in tolerance also existed among the 3 cultivars for B, but not for mixed salts. For Frame, BT Schomburgk and Schomburgk, critical concentrations of soil soluble B were estimated at 53, 32 and 27 mg/kg, respectively, in the absence of salinity. For salinity tolerance, the 3 wheat cultivars could all tolerate an ECe up to about 9 dS/m equally well. In combination with B, salinity still dictated overall response in growth with the interactive effect of B being to increase sensitivity of plants at low levels of salt. Shoot B concentrations in Frame ranged from 15 to 947 mg/kg for increasing soil B treatments but these responses did not correlate well with growth reduction. Shoot Na contents ranged from 0.02 to 0.58%, but was not a reliable indicator of Na+ toxicity due to interactive effects of B: increasing B reduced Na+ uptake. Generally, differences in B tolerance among the cultivars highlighted the existence of genetic variation in adaptation of wheat to high levels of soil B; however, this does not appear to be the case for salt tolerance in wheat. Because high levels of B and salt usually co-exist in the field, plant tolerance to these limitations need to exist in combination.