Nibbles: Potaghurt, Yams, New fodder crops, Enset, Cowpea migrations, Trees

by Jeremy Cherfas on April 3, 2012

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Dave Wood April 4, 2012 at 7:11 pm

Yams: will they never learn? The project is to improve indigenous yams. It is noted: “a variety of pests and diseases have now depressed yields to a mere 14 percent of potential harvests”. Purseglove (`Monocotyledons’, p. 98 – 40 years ago) says for yams in West Africa: “their relative importance has declined substantially in recent times, a process which may be expected to continue, both in this region and elsewhere in the world.”

But Purseglove also knew the reason. In his `Dicotyledons’ p. 14 (44 years ago) he says “… the main areas of production of the major economic crops are usually far removed from the regions in which they originated.” And why? He goes on: “…undoubtedly the most important [reason] is the introduction of crops into the new areas without the major diseases and pests which attack them at their centre of origin.” I’ll formally dub this “Purseglove’s Rule”.

The take-home lesson is not to spend $12 million on African yams in West Africa but to introduce Asian yams and non-African Aroid yams (cocoyams) which can escape by distance their co-evolved pests and pathogens (and take the African yams somewhere else).

Incidentally, `Purseglove’s Rule’ seems to be far more `agro-ecological’ in its explanatory value for biological relationships and crop productivity than most of the current multitude of somewhat dodgy arguments for agro-ecology, which ignore crop introduction.

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