Climate Change and the Importance of Maintenance Breeding

Variety IR8 is the original "Miracle rice" of the 1960s. This carefully-crafted variety has a stunted, semi-dwarf phenotype, which increases it's harvest index (the proportion of grain biomass to total biomass), and allows it to resist lodging (falling over into the mud), even when heavily fertilized. As with wheat, the creation of dwarf varieties of rice played a major role in the enormous yield gains of the Green Revolution.


But now it's in trouble!
IR8 originally produced yields of 9.5-10.5 tons per acre (twice the contemporary average), but recently it's been down to 7. The question is: did the genetic makeup of IR8 drift over time or has something in our environment changed? Some researchers tested this by growing out 30 year old stored IR8 seed from the International Rice Gene Bank and comparing it to its own great-great-great-grandchildren. As far as they could tell, the modern accessions of IR8 that have been self-pollinated for 30 years were identical to the original stock of IR8, but they both produced low yields (15% less than other modern rice varieties). Somehow IR8 is no longer as well adapted to its environment!

So how did the environment change?
The authors state that it could be due to air pollution, differences in modern agronomic techniques or climate change, but regardless of the cause it's a real-life demonstration of the need to continue breeding efforts even when there are great breakthroughs (and another good reason to support gene banks).


And climate change could make it a lot worse...
A second study collected microclimate and yield data from intensively-managed rice fields in 6 major rice growing countries in tropical and subtropical Asia. The authors found that both temperature and solar radiation had significant impacts on the vegetative and ripening phases of rice growth (though the impacts were different at different growth stages). Specifically, they found that high minimum temperatures reduced yield while high maximum temperatures increased it (plant physiology is complex!). The key here is that rice plants benefit from hot, sunny days and relatively cool nights. With sufficiently hot days though, yield is again depressed - suggesting that rice breeders have some work to do just to maintain current yields in a warming climate.


And they certainly have their work cut out for them.
A new report shows that climate change may be hitting the rice-growing regions of Southeast Asia especially hard (h/t). The blue areas in the poster indicate regions that are most environmentally, socially and politically vulnerable to the predicted changes. Of course the U.S. is bright green, but you'll notice Europe is not quite so. I was chatting with one of my boss' Dutch neighbors the other day and he told me that a big reason Europeans have accepted climate change so much faster than Americans is because they've been subject to more obvious weather changes over the past generation (e.g. failing ski resorts and all that recent flooding). I'm sure it doesn't hurt to have deep, extremely local cultural histories either.


It's funny how much humans respond to anecdotes and intuition.

h/t: Plant Breeding News

Peng, S., Huang, J., Cassman, K., Laza, R., Visperas, R., & Khush, G. (2010). The importance of maintenance breeding: A case study of the first miracle rice variety-IR8 Field Crops Research, 119 (2-3), 342-347 DOI: 10.1016/j.fcr.2010.08.003
Welch, J., Vincent, J., Auffhammer, M., Moya, P., Dobermann, A., & Dawe, D. (2010). From the Cover: Rice yields in tropical/subtropical Asia exhibit large but opposing sensitivities to minimum and maximum temperatures Proceedings of the National Academy of Sciences, 107 (33), 14562-14567 DOI: 10.1073/pnas.1001222107