If you’ve just arrived from Tangled Bank, welcome. And be aware that there’s a follow-up post.
A couple of meta-analyses on the menu today.
Devra Jarvis and Bioversity International colleagues, together with numerous co-authors from national programmes around the world, have a paper in PNAS summarizing the results of a 10-year effort to establish the scientific bases of on-farm conservation of agrobiodiversity. ((Jarvis, D.I., Brown, A.H., Cuong, P.H., Collado-Panduro, L., Latournerie-Moreno, L., Gyawali, S., Tanto, T., Sawadogo, M., Mar, I., Sadiki, M., Hue, N.T., Arias-Reyes, L., Balma, D., Bajracharya, J., Castillo, F., Rijal, D., Belqadi, L., Rana, R., Saidi, S., Ouedraogo, J., Zangre, R., Rhrib, K., Chavez, J.L., Schoen, D., Sthapit, B., Santis, P.D., Fadda, C., Hodgkin, T. (2008). A global perspective of the richness and evenness of traditional crop-variety diversity maintained by farming communities. Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.0800607105))
Varietal diversity ((The unit of analysis was the farmer-recognized and named variety.)) data on 27 crops grown on 64,000 ha by 2,041 households in 26 communities in 8 countries on 5 continents were pulled together in a stunning feat of synthesis. Are any generalizations possible from such a massive dataset? Well, perhaps surprisingly, yes. Let me pick out the highlights:
- Households growing traditional varieties generally grow more than one (1.38-4.25).
- Households within a community tend to grow somewhat different sets of traditional varieties.
- Larger fields generally have more traditional varieties, but smaller fields tend to be more different in varietal composition.
There’s much more to this rich analysis than that, but the take-home message can be pretty easily stated: crop genetic diversity can still be found on-farm because even neighbouring families choose to grow different traditional varieties, and generally more than one. Especially families tending smaller fields, who will presumably be poorer and living in more marginal conditions. The conoscenti will recognize a familiar meta-narrative, but it is good to have solid data from a wide range of crops and from all over the world.
The next paper I want to talk about looked at genetic diversity in wild clonal species as it relates to their breeding system. ((Honnay, O., Jacquemyn, H. (2008). A meta-analysis of the relation between mating system, growth form and genotypic diversity in clonal plant species. Evolutionary Ecology, 22(3), 299-312. DOI: 10.1007/s10682-007-9202-8))
Summarizing 72 genetic diversity studies, including of a couple of crop relatives, the authors found that populations of self-incompatible clonal species tended to have fewer genotypes, more unequally distributed (i.e., with a few dominant clones), than populations of self-compatible clonal species. It would be interesting to see if this relationship is also present in vegetatively propagated crops. I don’t think the previous dataset would help with that, however. Only two clonal crops were included in the on-farm analysis, cassava and taro. Interestingly, they had the highest average levels of community-level varietal richness (33) compared to seed-propagated species.
