No abstract

Assessment of dormancy inception, maintenance and release was studied for artificially dried immature seeds harvested throughout seed development in the barley cv. Triumph and its mutant line TL43. Each was grown in Spain and Scotland under low and high dormancy inducing conditions, respectively. Both TL43 and Triumph followed a similar pattern of release from dormancy across the seasons, although seeds of TL43 were able to germinate at an earlier seed development stage. Abscisic acid (ABA) content was also studied in immature grains throughout the seed development period. Total amount of ABA in seeds of Triumph and TL43 was higher in plants grown in Scotland than in Spain. However, no clear genotypic differences in ABA pattern in the course of grain development could be detected whilst significant genotypic differences were observed for germination percentage (GP). Endogenous ABA content alone throughout grain development did not explain genetic differences in GP within environments. Environmental and genetic differences in dormancy were also observed on mature seeds throughout the after-ripening period. The initial germination (GP(0)) played a key role in the sensitivity to ABA of post-harvest mature seeds. For the same after-ripening stage, TL43 was more insensitive to exogenous ABA than Triumph. However, ABA responses in seeds of the two genotypes with similar GP(0) at different after-ripening stages were comparable. Therefore, differences in exogenous ABA sensitivity of post-harvest mature grain of these two genotypes seemed to be determined by, or coincident with, the initial germination percentage.

To examine environmental differences between southern and northern European malting barleys, particularly relating to protein and hordein influences on malt extract development, samples of the malting barley cultivar Alexis, from the Nordic countries and from the Iberian Peninsula, were used. Fractionation ofhordeins was carried out on barley grains, prior to micromalting and malt analyses, using high performance liquid chromatography (HPLC). Different mechanisms for extract development, in malting barleys from the North and South of Europe, have been demonstrated. Barley protein content determined a significantly greater decrease in malt extract in the Nordic samples, compared with those from the Iberian Peninsula, while apparent final attenuation showed a more pronounced positive association with extract in the South than in the North. B-hordein was associated with a significanlty greater decrease in malt extract in the Nordic compared to the Mediterranean samples.

No abstract

Mildew-resistant mutants were induced with sodium azide in three North American malting barley cultivars, two in the six-rowed Ursula (URS1 and URS2), one in the six-rowed Gertrud (GER1), and one in the two-rowed Prudentia (PRU1). Two of the mutants, URS1 and PRU1, showed complete resistance and were shown to have two new alleles at the mlo locus; these were designated, respectively, mlo31 and mlo32. Mutant URS2, showing partial resistance, was inherited as a dominant gene, but was not an allele at the Mla locus. The mean yield of each mutant was higher than that of its parental line, but yield levels varied across environments, although this was independent of the severity of the mildew attack. Other reasons, for example, the severity of the necrotic lesions in the mutants, may account for yield variations. The malting quality of the GER1 mutant proved similar to that of Gertrud, but both URS1 and URS2 showed lower malt extract than Ursula. This lower extract might be due to the smaller grain size of the mutants that could, in turn, result from necrotic lesions in the leaves, as implied by the effects on grain yield.