The Relation Between the Date of Heading of Nigerian Sorghums and the Duration of the Growing Season

An indigenous variety of sorghum in Northern Nigeria yields best in its own locality. All the local varieties of a locality tend to flower at the same time each year, and this time is associated with the average date on which the rains end in the locality. When a variety is grown elsewhere than in its own locality, it still flowers at a time corresponding to the average end of the wet season in its own locality. Since the rains end progressively earlier from south to north, a variety moved south or north of its own locality will flower either before or after the end of the rains in the new locality, and as a result will yield less than the local varieties of that locality. The adaptation of flowering to the average end of the rains is probably a photoperiodic effect which normally operates several weeks before the end of the rains. It is not a reaction to a critical daylength, but it may be an effect of the number of successively shorter days which the plants experience.