The inheritance of aluminium tolerance in P. aquatica was investigated in solution culture, and correlations with other screening systems were determined. In the Israeli cultivar, Noy, the difference between the highly sensitive and moderately tolerant classes, which had been resolved in earlier experiments, can be largely explained by a two-gene hypothesis in which tolerance requires at least one dominant allele at each locus. Modifiers of these genes may also be involved. Assuming that the extensive continuous variation within the moderately tolerant class is polygenic, a quantitative inheritance study was conducted in a population of half-sib families in a diverse breeding population, the sensitive class being eliminated on performance in solution. Heritability estimates for relative root extension in solution ranged from 0.48 to 0.75, and estimated response to selection was high. However, heritability estimates for shoot growth of the same plants on a field site high in aluminium were low and non-significant (0.07-0.26). The highest estimate of genetic correlation between solution and field was not significant at 0.56. Variability in soil aluminium concentrations appeared to be a major cause of these low values. Prior screening of the population using a haematoxylin root-staining procedure gave a significant genetic correlation with solution responses (0.48). However, the technique requires further development for screening phalaris. In breeding for improved tolerance, the highly sensitive class could be eliminated by test crossing potential parents with homozygous sensitive plants. Several generations of selection could then be imposed, which, on the basis of genetic parameters estimated from solution screening, should yield a population appreciably more aluminium-tolerant than existing cultivars.
Genomic association and further characterisation of faecal immunoglobulin A deficiency in German Shepherd dogs