Sorghum endures

How much crop genetic diversity have we lost? At one level, the question is easy to answer: three quarters over the last century. That’s certainly the number that’s most often quoted.

But that doesn’t make it right. In particular, I have it on very good authority that the figure may in fact be traceable back — a la Chinese whispers — to a statement in Fowler & Mooney’s 1990 book Shattering: “As the mid-1970s were reached, three-quarters of Europe’s traditional vegetable seed stood on the verge of extinction.”

Not quite the same thing. Anyway, be that as it may, the existence of a dominant narrative hasn’t stopped people going out into the field and — the horror! — actually collecting data.

I came across a couple of examples of this when hanging around the library with a colleague the other day. He had arrived a bit early and had been browsing the journals on display while waiting for me to turn up for a meeting. He was struck by two papers in the latest issues of two separate journals, by different people but both about genetic erosion of sorghum in Ethiopia. The interesting thing is that, at least judging by a rapid scan of the abstracts, they came to opposite conclusions. Intrigued, I took photocopies for later reading. It turned out not to be quite as simple as that.

Firew Mekbib of Haramaya University in Dire Dawa has been working in eastern Ethiopia. ((Firew Mekbib (2008) Genetic erosion of sorghum in the centre of diversity, Ethiopia. Genetic Resources and Crop Evolution 55: 351-364. DOI: 10.1007/s10722-007-9240-7)) He has asked farmers about loss of varieties and also compared a 1960 collection conserved at the Institute for Biodiversity and Conservation with one he made himself in the same area in 2000. He finds that although individual farmers have certainly stopped growing some varieties, there has actually been an increase in the number of distinct names of varieties in the area as a whole. That’s despite a decrease in the total sorghum area and the arrival of modern varieties. His conclusion:

…maintenance of the varieties for 40 years is a reality but [genetic erosion] is rhetoric.

H. Shewayrga is at the Sirinka Agricultural Research Centre in Woldia and worked in the highlands of central Ethiopia, just north of Addis Ababa. ((H. Shewayrga, D. R. Jordan and I. D. Godwin (2008). Genetic erosion and changes in distribution of sorghum landraces in north-eastern Ethiopia. Plant Genetic Resources Characterization and Utilization 6:1-10. DOI: 10.1017/S1479262108923789.)) Together with Australian co-authors, he/she also compared a historical collection at the IBC (this one from 1973) with a later one (made in 2003). But, unlike in the previous study, which was based on local names, both collections were grown out and characterized using standard descriptors (molecular work is taking place but was not reported on in this paper). Farmers were also surveyed.

Significant changes were documented in the means of many descriptors (in particular, there has been a marked shift toward earlier flowering varieties), and previously important varieties were found to have disappeared or become marginalized. The authors thus talk of an “alarming trend of loss of traditional landraces.” But their figures for the range and diversity of morphological descriptors show no such negative trend. So while varieties may have been lost, overall phenotypic diversity seems not to have suffered.

What to make of it all? Well, there are things to quibble about in both studies, questions of sampling strategy for example. But the impression I get is one of tremendous dynamism, of rapid turnover of varieties, of localized losses, yes, but also of gains. Whatever that “three-quarters” figure may apply to, it does not seem to apply to sorghum in these areas of Ethiopia in the past few decades.