Barley mutants with increased tolerance to aluminium toxicity

Acid soil and associated aluminium toxicity are considered as the number on e abiotic factor limiting crop production. Over 2 billion hectares of acid soils exist world-wide, both in tropical and moderate climatic zones. In Po land acid soils represent up to 60% of arable land. At soil pH < 5.0 Al ion s become soluble in water and toxic to plants. Genetic improvement of Al to lerance in crops is the only alternative to soil liming, a traditional but short term and expensive agricultural cure to raise soil pH. Of the various cereals, barley is the most sensitive to Al toxicity. The known sources of Al tolerance in barley are limited to old cultivars and landraces. While t hey represent multiple alleles of a single locus, there is no potential to improve Al tolerance through recombination of non-allelic additive genes. I n the Department of Genetics, Silesian University we have employed induced mutations for rapid creation of variability for Al tolerance in barley. Thi rteen mutants with increased levels of tolerance to Al toxicity have been s elected in M-3 generation after mutagenic treatment of four barley varietie s with N-methyl-N-nitroso urea (MNH) and sodium azide. Six further Al toler ant mutants were identified in the collection of semi-dwarf mutants of the Department. All selected mutants confirmed Al tolerance with the use of thr ee different methods of screening, i.e., root re-growth, root tolerance ind ex and hematoxylin staining. Fourteen mutants exhibited significant root re -growth after 48 hour incubation with 3 ppm Al+3 and two of them, namely RL 819/2 and RL820/6 were tolerant even to 6 ppm Al+3. Crosses of two selected mutants with their respective parent varieties indicated that Al tolerance in each mutant was controlled by a single recessive gene. Out of three met hods tested, the root re-growth method facilitated by hematoxylin staining proved to be the most reliable technique for large scale testing. Double tr eatment with MNH or combined treatment with sodium azide and MNH and 6h int er-incubation germination between treatments were the most successful treat ment combinations for induction of aluminium tolerance in barley.