Variation in tolerance in Phalaris aquatica L. and a related species to aluminium in nutrient solution and soil

Abstract

The range of aluminium tolerance in P. aquatica and P. arundinacea L. was examined and compared with the range in some crop and pasture species of known tolerance. In nutrient solution and aluminium-toxic soil, a distinct class of P. aquatica plants extremely sensitive to aluminium was resolved. The tolerance of each P. aquatica line was correlated with the frequency of sensitive plants, which ranged from 0 to 100%. Significant variation in tolerance remained after exclusion of the sensitive class. The aluminium concentration in nutrient solution required for 50% growth reduction varied from approximately 2 to 6 ppm Al among P. aquatica lines. The more tolerant lines, which included Sirosa and Sirolan, were markedly less tolerant than cocksfoot, tall fescue, subterranean clover and known tolerant cereal cultivars. Root extension was the most sensitive character. However, ranking of P. aquatica lines according to yield in solution gave better agreement (r = 0.81, P < 0.01) with ranking according to relative yield in unlimed versus limed aluminium-toxic soil than did root extension in solution (r = 0.69, P < 0.01). Reference to yield is thus considered necessary for selection among more tolerant plants in a breeding program. The aluminium tolerance of P. arundinacea was superior to that of P. aquatica, and P. arundinacea CPI 69103 was as tolerant as tall fescue in aluminium solutions. Significant improvement of P. aquatica appears possible in the longer term by hybridisation with P. arundinacea, whereas limited improvement should be achieved in the short term by intraspecific recombination and selection.