Back at the day job, we are often asked by journalists and others how many different types, or varieties, of this or that crop there are in a country, or indeed the world. And, with help from our friendly crop experts, we have tried to provide answers. But it is as well to remind ourselves sometimes how slippery the question is. Because, to paraphrase Bill Clinton, it really does depend on what your definitions of “different” and “variety” are. For example, take rice in a particular part of Thailand, as the authors of a recent paper in GRACE did. ((Oupkaew, P., Pusadee, T., Sirabanchongkran, A., Rerkasem, K., Jamjod, S., & Rerkasem, B. (2010). Complexity and adaptability of a traditional agricultural system: case study of a gall midge resistant rice landrace from northern Thailand Genetic Resources and Crop Evolution DOI: 10.1007/s10722-010-9579-z))
They looked at 20 accessions of a single landrace, defined as a “geographically and ecologically distinctive population, identifiable by unique morphologies and well-established local name.” That is, these 20 samples, though collected from different farmers and even villages, all basically looked the same, and were recognized as belonging to the same type by farmers, who gave them all the same name — Muey Nawng.
But the authors found significant, non-random, patterned variation within the material, not only in microsatellite markers, which wouldn’t perhaps be so bad, but also in endosperm starch type, days to heading and, interestingly, gall midge resistance. So how many varieties were there among the 20 samples of Muey Nawng? Answers on a postcard, please.
Hum… But just wait: varieties may not simply be cut down up to every single set of genotypes producing distinct phenotypes. That would be way too heavy splitting, wouldn’t be?
So far, as a species is “whatever specialists think is a species”, shouldn’t varieties be defined as “whatever farmers think is a variety”?
If we agree on the definition, I would say there’s one variety in the samples of Muey Nawng… :)
Else, we would have to investigate whether genetic variation within the so called variety is mostly distributed geographically or within local samples, and whether some samples seem genetically distinct from others or from a theoretical common stock.
That is, does differentiation probably arise from local adaptation or from mixing of different/unrelated resources? And if the latter, did it arise from hybridisation and introgression of variety-characteristics “once” or recurrently? At one place or at several places?
The evolution of domestic varieties via farmers phenotypic preferences/choices or practices is such a tricky but interesting research theme!
I haven´t read the paper, but I wonder if the differences in endosperm starch type, days to heading and gall midge resistance are big enough to be recognized in a variable environment.
Farmer variety naming is not arbitrary but tends to depend on observation and seed/knowledge exchange practices that give rise to a shared classification scheme.