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14 March 2006
Research paper questions current approaches to breeding aluminium-resistant cultivars
Soil scientist Mark Conyers and his E H Graham Centre colleagues have questioned the rationale behind current approaches to breeding aluminium-resistant cultivars and have recommended new techniques be developed to identify best-performing varieties. Their controversial paper was published late last year in the journal Plant and Soil (v. 278, p. 195-204).
In their paper, Mark Conyers, Keith Helyar and Sergio Moroni explain that plants have two strategies for coping with Al-toxicity, avoidance or tolerance. Their paper examines the 'cost' of the three different options for avoiding Al-toxicity. The 'currency' they used was carbon: C is acquired by leaves via photosynthesis and thus provides an index for the amount of energy that is spent protecting roots from Al.
The first C-currency they examined was that associated with the root exudation of organic anions such as malate, oxalate and citrate. What they found was that the second mechanism examined, microbial oxidation of the organic anions, was more C-efficient than the exudation of these compounds alone. This second mechanism is even more efficient in the presence of manganese oxide (MnO2).
The third mechanism they examined was the complexation of Al with organic anions. However, the authors suggested this mechanism might be a 'race against time'. Microbes could oxidise the Al-complexes, making the remediating effects of the organic anions short-term only.
The researchers explained that the reason why cultivars that perform well in the laboratory often don't exhibit Al-resistance in field trials, and vice versa, is because of the importance of microbes and MnO2 in making Al-resistance C-cost effective. The laboratory experiments are often based on plants grown in a solution culture. The implication is that Al-resistance is not simply under the direct control of plants, but there is also an important environmental influence. Mark and his colleagues therefore concluded that plant breeders must develop new soil-based protocols in order to improve the identification of cultivars resistant to toxic concentrations of aluminium.
For more information contact Mark Conyers (02 6938 1830).