The growth and yield of seven wheat and two barley cultivars or lines, previously found to show different degrees of boron tolerance under field conditions, were compared in a pot experiment at a range of soil boron treatments . Soil treatments ranged up to 150 mg/kg applied B . Extractable B in soils ranged up to 103 mg/kg . At the highest B treatment seedling emergence was delayed, but the percentage emergence was not reduced . The degree of boron toxicity symptom expression varied between the wheat cultivars and lines, with the two most tolerant, Halberd and (Wq*KP)*WmH)/6/12, displaying the least symptoms .The concentration of boron applied to the soil which produced a significant depression of growth and yield varied between cultivars . For example, the yield of (Wq*KP)*WmH)/6/12 was not affected at the 100 mg/kg applied boron treatment, while the grain yield for (Wl*MMC)/W1/10 was significantly reduced at the 25 mg/kg treatment.There was a linear increase in boron concentration in tillers at the boot-stage with increasing concentration of boron in the soil . The most boron tolerant genotypes had the lowest tissue boron concentrations in each of the treatments . Halberd and (Wq*KP)*WmH)/6/12 had approximately half the boron concentrations of the more sensitive genotypes at the 25 and 50 mg/kg treatments . Differential tolerance of boron within the tissue was also observed . Both Stirling and (WI*MMC)/W1/10 had significantly reduced total dry matter and grain yields at the 25 mg/kg treatment, while the concentrations of boron in boot stage tillers at this treatment were 118 and 100mg/kg, respectively . On the other hand, Halberd and (Wq*KP)*WmH)/6/12 had tissue boron concentrations of 144 and 131 mg/kg, respectively, at the 50 mg/kg treatment but yield was unaffected .The relative responses in the pot experiment, for wheat, were in close agreement with field results . Halberd and (Wq*KP)*WmH)/6/12 had the highest grain yields, with the lowest concentrations of boron in the grain when grown under high boron conditions in the field . In pots these two genotypes proved to be the most tolerant of boron . For barley the advantage in grain yield in the field, expressed by WI-2584 compared with Stirling, was not repeated in pots . WI-2584 was, however, more tolerant than Stirling on the basis of total dry matter production .The results show that useful variation in boron tolerance exists among wheat, and that breeding should be able to provide cultivars tolerant to high levels of boron .
Severe leaf blotching in a crop of barley growing on a red-brown earth (Calcic Rhodoxeralf) was closely associated with high concentrations of boron in the soil. No infection by fungal pathogens capable of accounting for the symptoms was found. Of 14 elements determined in the plants only accumulation of high-concentrations of boron was associated with the disorder. Boron concentrations in saturation extracts of subsoil ranged up to 17.9 �g boron/cm3 under plants that were severely affected, and plants sampled just prior to anthesis contained up to 96 fig boron/g (mean 62.4). Plants that were only slightly affected contained less than 15 �g boron/g (mean 13.8). Grain yield was depressed by 17% due to the boron toxicity. This is only the second report of boron toxicity due to naturally occurring boron in Australia, and the first for a red-brown earth.
Boron toxicity was identified in barley crops grown on a range of soils at 16 widespread locations in South Australia, and also at one site in western Victoria. The soils on which boron toxicity occurred included red-brown earths (Calcic Natrixeralf), calcareous earths (Xerollic Calciorthid and Calcic Paleorthid), and calcareous sands ('Petrocalcixerollic' Xerochrept). At one site the soil was a grey clay (Palexerollic Chromoxerert). The properties of some examples of normal and high-boron soils which were sampled in close proximity are discussed. For individual high-boron soil profiles it was possible to demonstrate statistically significant relationships between extractable boron and ESP, CEC and clay content. However, these relationships did not hold generally for comparisons between normal and high-boron soils. Boron concentrations in affected barley ranged from 56 mg/kg in mature straw to 323 mg/kg in whole tops at Feekes stage 10.1. In control samples the mean boron concentration was 22.8 mg/kg. The concentrations of other nutrient elements (P, K, S, Mg, Cu, Zn, Mn, Mo) were within normal ranges, and did not differ between control samples and plants with toxicity symptoms. Barley plants affected by the toxicity had increased concentrations of Na and Cl, and decreased concentrations of Ca compared with control plants. These effects were small, but statistically significant, and were consistent with the notion that the toxicity was associated with sodic soils. The findings extend our earlier work on boron toxicity at a single site, and demonstrate that the toxicity is widespread in South Australia.
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