Variation existed between plants of the lucerne (Medicago sativa L.) cultivar CUF 101 for dry matter production, shoot number and length, and leaf damage when grown for 70 days under 250 mM NaCl (15 h photoperiod, 20�C day, 10�C night). Salt tolerance evaluation using the criteria percentage leaf damage (percentage of total number of leaves with complete or partial necrosis) and length of the main shoot, isolated plants which showed salt tolerance of reasonably high heritability (h2=0.41). Two generations of recurrent selection for tolerance significantly increased the mean population tolerance without decreasing production under non-saline conditions. While both sodium and chloride concentrations of the shoot were lower in the tolerant than in less tolerant plants, chloride was more closely associated with salt tolerance than sodium. Sodium and chloride concentrations in the roots did not vary with the level of salt tolerance. No association of shoot and root potassium concentration with tolerance was evident. Selection for salt tolerance in lucerne plants using percentage leaf damage of less than 10% as the main criterion should give a rapid response to selection. The efficiency of selection may be increased if selection is based on the efficiency of chloride exclusion from the shoots and/or the level of chloride tolerated by the shoots prior to leaf damage becoming evident.

The translocation efficiency of plant nitrogen to the grain was examined in six lines of bread wheat (Tvtticum aestivum L.) under four levels of soil nitrogen (48, 556, 810 and 1065 ppm). Translocation efficiency, both within the primary tiller and within the whole plant, was significantly different between cultivars; the within-tiller value was higher than the corresponding whole-plant value for each cultivar. There were marked differences in trends in translocation efficiency between certain cultivars as the soil nitrogen availability increased. A reasonably close positive correlation (r = + 0.74, P < 0 . 0 1 ) existed between the within-tiller and whole-plant values for translocation efficiency over the four nitrogen levels.It is suggested that wheat breeders use within-main-tiller translocation efficiency of nitrogen, in parental or crossbred selection to increase grain nitrogen yield in wheat. Because nitrogen translocation efficiency varied with soil nitrogen level, such selection would need to be conducted under soil nitrogen levels appropriate to field conditions. The relationship between total plant dry matter and total grain nitrogen across cultivars and nitrogen levels was not close (v = +0.41, P < 0.01), which suggests that a good potential exists for selecting for increased total grain nitrogen levels in wheat at existing levels of total dry matter production. The implications of these findings for further genetic and biochemical study of nitrogen metabolism in wheat, are outlined.

The first of 2 studies reported in this paper investigated the variation in 15 barley genotypes for the durations of 3 periods of pre-anthesis development [leaf initiation (LI), spikelet initiation (SI), and spikelet growth (SG) phases], and the degree of independence of the duration of the SG phase from each of the LI and SI phases. There were differences between genotypes in the duration of the SI and SG phases which were not closely correlated (r = – 0·58, P < 0·05) across genotypes, indicating the feasibility of genetically combining different durations of the 2 phases while maintaining a constant time to anthesis. The duration of the LI phase was closely correlated with time to anthesis (r = 0·82, P < 0·001) but not with the duration of either the SI or SG phase. The rate and duration of spikelet initiation were negatively correlated across genotypes (r = – 0·75, P < 0·01). There was little variation in the number of spikelet primordia formed over the range of genotypes but there was considerable variation in the number of aborted spikelet primordia. The study indicated the likelihood that in breeding to increase the yield potential of the spike in barley, there is more potential for reducing the level of spikelet primordia abortion during the SG phase than increasing the number of spikelet primordia per spike. The second study investigated whether 3 photoperiod regimes (15·5, 14, and 12–13 h), imposed for the duration of the LI and SI phase, had any subsequent effect on the duration of the SG phase in 2 cultivars, Bandulla and Galleon. There were no major effects, suggesting that the duration of the SG phase was largely independent of the duration of the 2 previous phases.

The seasonal patterns of leaf nitrate reductase activity were compared in five wheat cultivars which differ widely in their capacities to accumulate grain nitrogen. Significant differences in the average levels of nitrate reductase activity were observed between cultivars. Total seasonal nitrate reductase activity was closely related to total plant nitrogen at maturity. Grain nitrogen was only related to total seasonal nitrate reductase activity when allowance was made for significant differences between cultivars in nitrogen redistribution patterns. The significance of these results with respect to the possible use of nitrate reductase activity levels as a selection criterion for nitrogen productivity is discussed.

The disease reaction of seedlings (2 weeks old) from a field collection of subterranean clover (Trifolium subterraneum) to clover scorch (Kabatiella caulivora (Kirch.) Karak), revealed 89 immune plants out of a total of 1530. However, with adult plants (15-16 weeks old) only one plant remained immune. In the F2 population of the cross of the cultivars (Daliak X Woogenellup (D X W), seedling resistance was conditioned by a single dominant gene and in the cross (Enfield X Woogenellup) (EX W) by a single recessive gene. However, with adult plants, resistance in the (D X W) F2 was conditioned by a single recessive gene and that in the (EX W) F2 by two recessive genes. The effect of increasing age in reducing the proportion of plants resistant to clover scorch in both studies indicates that caution is needed in evaluating resistance to clover scorch in epidemiological, breeding and genetic studies.