Data from several trials with large numbers of barley and durum wheat varieties conducted mainly under dryland conditions in a Mediterranean climate were used to study the effects of heading date and its stability on consistency of performance.
Heading date was expressed in relation to one or more control varieties, because of the significant genotype × environment interactions. Data from trials during 1969–85 were used to determine optimum heading date in order to aid selection for consistently high-yielding varieties. For rainfed barley in Cyprus this optimum range was between 2 days after and 5–8 days before heading of Kantara barley and for rainfed wheat 1 day after to 4 days before heading of Karpasia durum wheat. It is suggested that by selecting at one environment single plants from segregating populations or lines from nurseries and yield trials, having heading date within the optimum range, the chances of selecting consistently high-yielding lines are increased.
The genotype and environment significantly affected heading date. Stability of heading date was genetically controlled. Early varieties tended to be more variable than late varieties of both barley and durum wheat. Lines with the lowest values for variance of heading date gave low yields under variable conditions because they were very late. The consistently high-yielding lines of barley and durum wheat had variance of log transformed heading (s2log2) 0·025–0·050.
In durum wheat, lines with the lowest variance were later in heading date than the optimum for Cyprus environments. The absolute values of variance of heading date of varieties varied with year, but significant positive correlations were obtained between years (r = 0·84 for durum wheat and r = 0·55 for barley, P < 0·01).
Barley, which is considered a safer crop for the driest parts of the Mediterranean countries, heads a few days earlier than durum wheat but its better performance may be attributed also to its ability to grow faster than wheat in the winter months.