Recently in plant breeding Category

In Darwinian Agriculture, I argued that accepting tradeoffs rejected by past natural selection is key to past and near-future crop improvement, whereas novel phenotypes never tested by natural selection may eventually make major contributions. In this post, I will briefly discuss two recent papers relevant to this hypothesis.

Lee DeHaan and David Van Tassel published "Useful insights from evolutionary biology for developing perennial grain crops", in American Journal of Botany, while Lin et al. published "A faster Rubisco with potential to increase photosynthesis in crops" in Nature.

Perennial plants often develop more extensive root systems than annuals, reducing the risk of erosion. Well-managed perennial forages (pastures and hay fields) are arguably our most-sustainable agricultural system, supplying milk, meat, wool, and leather, and often getting most of their nitrogen from symbiotic rhizobia bacteria (the main focus of my own research) rather than external inputs.

The Land Institute, where DeHaan and Van Tassel work, has been attempting to develop perennial grain crops. I have argued that greater investment of photosynthate or nitrogen in roots will usually leave less of these limiting resources for grain (seeds). All else being equal, DeHaan and Van Tassel apparently agree:

"where annual crops can use a similar amount of water, light, and nutrients as the perennials... annuals will indeed have greater yield potential"
But they have argued (and I agree, on p. 97 of my book) that perennials may sometimes capture more of these resources than annuals can. The last chapter of my book, on diversity and bet hedging, therefore included perennial grains as an example of high-risk approaches deserving some funding.

The potential of perennials to photosynthesize more months per year than annuals also implies using water more months per year, but their superior root systems can sometimes help water soak into the soil rather than being lost to runoff.

Actual results so far are somewhat discouraging, however. DeHaan and Van Tassel cite a paper by Culman et al., which found greater above-ground biomass in a perennial grass, kernza, relative to wheat. So it might be a better forage than wheat, but its grain yield (with moderate fertilizer) was only 4% that of wheat in year 1 and 39% in year 2. So it would take about 5 acres of kernza to produce as much grain as 1 acre of wheat. Where are those extra 4 acres (and the water to irrigate them) going to come from? Or can we realistically expect significant yield increases without losing the benefits of perenniality?

I have argued that while some tradeoffs (e.g., root vs. grain) constrain crop improvement, other tradeoffs can represent opportunities. For example, the fastest versions of the key photosynthetic enzyme work best at CO2 concentrations greater than atmospheric. Lin et al. transferred genes for one of these enzymes from cyanobacteria into tobacco. The resulting plants grew more slowly than unmodified tobacco, even at 9000 ppm CO2 (atmospheric is now 400 ppm). So this looks like a step in the wrong direction, but it's only a first step. The cyanobacterial enzyme works well in cyanobacteria because they also have a CO2-concentrating mechanism. Some plants, including corn, have different CO2-concentrating mechanisms. If someone could combine the faster cyanobacterial enzyme with a plant or cyanobacterial concentrating mechanism, they might achieve significantly greater photosynthesis.

That could take a decade or more, but it's worth noting that perennial grains have been a significant focus of the Land Institute for most of their 38-year history.

Both talks are part of symposia with other interesting speakers.

August 18: Student Organic Seed Symposium, NY Finger Lakes Region

October 28: minisymposium (with Emma Marris, author of "Rambunctious Garden: Saving Nature in a Post-Wild World") on "Saving Nature and Improving Agriculture: Where does Nature's Wisdom Lie?" Washington State University, Pullman

Improving on nature?


I have two invited reviews due this summer, building on the theme from my book, that past natural selection improved trees (and the wild ancestors of our crops) much more than it has improved the overall organization of forests (and other natural ecosystems):

In Global Food Security, Andy McGuire and I will ask, "What can agriculture learn from nature?" If natural selection or some other process had consistently improved the overall organization of natural ecosystems, then agriculture might benefit from copying that organization. If every natural ecosystem had some process that adjusted the relative abundance of species to maximize ecosystem-level productivity and/or stability, then we could (for example) try to match the ratio of grasses and legumes in our pastures to those in nearby grazed meadows. I expect to argue, however, that nothing has consistently improved natural-ecosystem organization, so mindless mimicry of natural ecosystems is unlikely to improve agriculture. The wild ancestors of key crops grew naturally as monocultures, but that doesn't necessarily mean polyculture wouldn't be better. It's still worth studying how natural-ecosystem organization affects productivity and stability, and thinking about which features of natural ecosystems might be worth copying.

In "Evolutionary tradeoffs as crop-improvement opportunities", intended for Field Crops Research , I will argue that past natural selection has been improving individually-beneficial plant traits like drought tolerance for millions of years, leaving few simple, tradeoff-free options for further improvement. Accepting tradeoffs rejected by past natural selection has been key to past crop improvement and that is probably still true.

For a preview, see my discussions with farmer/blogger Chris Smaje and soybean-breeder Clem Weidenbenner in the comments for this post on Small Farm Future.

Chris argues that rotating annual crops with pasture is copying nature. I don't see any close analogs to such rotations in nature, so disagree. The pasture phase might benefit from copying some aspects of natural grazing systems, though.

Clem has various examples of plant breeding improving crops in ways that natural selection hasn't. I agree, but would any of those changes have improved individual-plant fitness in nature? If not, what are the prospects for improving traits like stress tolerance, which would (if tradeoff-free) have improved individual fitness?

Increasing or decreasing oil content beyond its natural range would presumably decrease fitness, even though it may be useful to us. Clem mentions range expansion of crops, which could show that humans can improve traits like cold tolerance in ways that past natural selection on the crop's wild ancestors didn't. I need to read more about this, but I find it interesting that high-altitude maize picked up cold-tolerance genes from teosinte, not the other way around.

UPDATE: a Faculty of 1000 selection.

That's the title of a paper Toby Kiers and I just published in Philosophical Transactions of the Royal Society. We argue that:

"[despite] past selection for inclusive fitness (benefits to others, weighted by their relatedness)... [and despite some] evidence for kin recognition in plants and microbes... there is still ample opportunity for human-imposed selection to improve cooperation among crop plants and their symbionts"

Wednesday I'm off to the University of Illinois, where Michelle Wander and the Agroecology and Sustainable Agriculture program are using my book in a grad course on the Future of Agriculture.

That's the topic of a thoughtful essay by Nathanael Johnson on the Grist website. He gives a reasonable summary of my argument that many hoped-for improvements either involve tradeoffs (some of them acceptable) or radical enough changes that their effects will be hard to predict.

He also cites my colleague Jonathan Foley's suggestion that "we" should "Reduce food waste, eat less meat, and make fertilizer and irrigation available to the farmers that need it."

OK, but who's "we"? Any "solution" that requires billions of people to change what they're doing -- because they read Foley's article in Science? -- will be a long time coming. For example, a few million rich consumers eating less meat -- this would lower the demand for meat so that meat prices decrease so that slightly-less-rich consumers eat more meat, but let's pretend total meat consumption goes down a few percent -- would not have much effect on global greenhouse gas production or food security for the billion or two in greatest need. Similarly, if a couple billion consumers wasted less food, that would free up some resources. But if you and a few friends reduce your waste, it's a drop in the ocean.

Reducing pre-consumer food waste has more potential. Because reducing pre-consumer waste could mean larger profits for farmers, food companies, etc., near-universal adoption of practical waste-reducing methods is at least conceivable. Motivation linked to higher profits also means, however, that the obvious improvements have already been made. Less-obvious improvements are already a major research focus, but more likely to be invented by engineers than ecologists.

Expanding access to irrigation might greatly increase food security, but it would be a big project, perhaps costing a significant fraction of what we spend on war or video games. So I'm not holding my breath.

Increasing access to fertilizer can start small and scale up -- avoiding over-fertilization -- so that's an area where contributions from a few million people (or a handful of rich people) could really make a difference. But I worry about solutions that require on-going subsidies.

And then there's plant breeding. Develop a cultivar that out-performs what's available now, and watch it spread.

Near the beginning of the question period for this recent lecture at the University of Minnesota, I suggested that:

1) nobody has done a good comparison of ideotype breeding with breeding for yield, and
2) many plant breeders who use the word "ideotype" ignore tradeoffs.

The main point of Donald's 1968 paper, which coined the term, "ideotype" was that there are often tradeoffs between individual-plant competitiveness and the collective performance of plant communities, so we can improve the latter by sacrificing the former. That's a major theme of my book, as well.

But both my numbered points above turn out to be wrong, at least partly.

Yuan et al. (2011) compared ideotype breeding with breeding for yield. I criticized some of their choices for "ideotype traits" in my third lecture at the International Rice Research Institute, but it's still an impressive study.

And, rereading Rasmusson's 1984 paper on ideotype breeding, I find extensive discussion of tradeoffs, though he doesn't explicitly mention the tradeoff between competitiveness and yield potential hypothesized by Donald (1968).

I am correcting these errors in an perspective I'm writing for the journal, Evolution.