Abstract:
Sixty-five accessions, including diploids, tetraploids and hexaploids, of the African grass Digitaria milanjiana, were grown in a grass garden in south-eastern Queensland, and sodium (Na) and potassium (K) concentrations of herbage were determined after regrowth periods of either 6 weeks or 6 months. The accessions were originally obtained from sites in Africa from l�_S. to 25�_S., and over 400-1700 mm mean annual rainfall. The Na concentration of herbage ranged from 0.01 to 2.30% (w/w) and was inversely correlated with K concentration. There was a clearly defined geographic distribution of accessions which had high or low Na concentrations. Accessions from coastal sites had high concentrations of Na in the dry matter (>0.25% DM), those from inland sites south of 20�_S. had low concentrations of Na (usually <0.24% DM), and all those from inland sites north of latitude 20' S. were invariably very low in Na concentration (<0.09% DM). Accessions with high and low levels of Na occurred at all three ploidy levels. Genetic studies at the diploid level, using generation means analysis, showed differing patterns of inheritance of Na and K concentration for two crosses, even though they had one parent in common. Both additive and dominance effects were evident for Na and K; in addition, significant inter-allelic interactions occurred, especially involving dominance. The results are discussed in relation to the adaptive significance of Na accumulation, to its significance in animal production, and to the possibilities of breeding cultivars that have adequate Na concentration and are adapted to low rainfall regions.