Physiological studies of a hybrid between populations of Dactylis glomerata from contrasting climatic regions. II. Intra population variation

SUMMARY Considerable intra‐population variation was found for leaf expansion characteristics of three populations of Dactylis glomerata grown in a cool glasshouse during winter. The rates of leaf area expansion of a winter‐dormant population of North European origin were very low, while a colchicine‐induced autotetraploid of a winter‐growing Portuguese population had high rates. The progeny of a cross between these two populations had intermediate rates with a population mean significantly different from the mean rates of its parents. Some of the individual hybrid plants had rates greater than the mean rate of the Portuguese parent and selections were made based on these plants with the aim of improving the rate of leaf area expansion of the hybrid under winter conditions. Some of the F1 polycross progenies from the first cycle of selection showed a marked improvement with mean rates of leaf area expansion for certain maternal lines approaching the mean rate of the Portuguese parent.