Stable cereal grains domesticated in Africa: pearl millet and sorghum. Grain-packing on the panicle. Drought resistance compared to maize.
The north Atlantic croplands know well wheat, barley and oats, also rye, but some of the most important cereal grains do not grow here. It’s too cold. Of great importance to future food are the grain crops millet and sorghum – out of Africa.
Maize, domesticated in the Americas, came to dominate cereal production in Africa, but only in the last few hundred years. Maize came to the fore because it yields well in moist, fertile soils, its cobs can be easily tranported and its seeds easily cooked.
Before maize, people grew sorghum (Sorghum bicolor), pearl millet Pennisetum typhoides), and related crops such as finger millet (Eleusine coracana). With the rise of maize, they were reduced in area, sometimes found only where it was too dry for maize to yield reliably.
But now their value is being appreciated where maize has come to yield poorly or fail in soils that are not rich enough in nutrients and in climates that are getting drier.
Compared to the cereals we know, the sorghums and millets have unusual grain-bearing structures – commonly called panicles. They hold far more grains than the typical ‘ears’ of wheat and barley.
Pearl millet
Pearl millet panicles are long and round, the grains tightly packed around the outside of a central stem (fig. 1). The grains are held in pairs at the end of short stalks, each having a ring of hairs just in from the grains and more, smaller hairs on the stalk. The grains are protected when young by bracts, just as in our cereals, but the grains elongate and hide the bracts from view. They can be seen if some of the grain falls out.
Figure 1. Structure of panicles of pearl millet: lower shows part of a panicle as seen from the outside; middle right, the outside with some grains present, others having fallen out revealing the holding bracts; top, inside the panicle, grains held in pairs on short hairy stalks grown from the central stem.
Sorghum
Sorghum panicles are looser than those of pearl millet. Some older varieties and landraces are very loose whereas modern varieties tend to be more compact but not as much as pearl millet. Panicles of three sorghum varieties are shown in Fig. 2. The centre one a little more compact than the one on the left. That on the right is very loose – the
Fig. 3. Grain on panicles of (left) pearl millet, and three varieties of sorghum with (rightwards) decreasing grain packing. The square is 10 mm by 10 mm.
Comparison with temperate cereals
How do the panicles compare with wheat and barley? They are all usually much larger (Fig. X)..
Panicles, spikes or ‘ears’ of cereals: 1) emmer wheat, 2) bere barley, 3) bread wheat landrace, 4) and 5) pear millet, small and large panicles, 6) sorghum, intermediate grain packing, 7) sorghum, tight packing, 8) traditional sorghum, loose packing. Origins: 1, 2 and 3 grown in the Living Field garden; 4 to 8 provided by International Crops Research Institute for the Semi-Arid Tropics.