What are breeders selecting for?

ResearchBlogging.org One of the arguments in the organic-can-feed-the-world oh-no-it-can’t ding dong is about the total yield of organic versus non-organic. Organic yields are generally lower. One reason might be that, with a few exceptions, mainstream commercial and public-good breeders do not regard organic agriculture as a market worth serving. The increase in yield of, say, wheat over the past 70-80 years, which has been pretty profound, has seen changes in both agronomic practices — autumn sowing, simple fertilizers, weed control — and a steady stream of new varieties, each of which has to prove itself better to gain acceptance. Organic yields have not increased nearly as much. A new paper by H.E. Jones and colleagues compares cultivars of different ages under organic and non-organic systems, and concludes that modern varieties simply aren’t suited to organic systems.

The basics of the experiment are reasonably simple. Take a series of wheat varieties released at different dates, from 1934 to 2000. Plant them in trial plots on two organic and two non-organic farms for three successive seasons, measure the bejasus out of everything, and see what emerges. One of the more interesting measures is called the Cultivar superiority (CS), which assesses how good that variety is compared to the best variety over the various seasons. As the authors explain, “A low CS value indicates a cultivar that has high and stable performance”. The expectation is that a modern variety will have a lower CS than an older variety, and for non-organic sites, this is true. At organic sites, the correlation is much weaker.

You can see that in the figure left (click to enlarge). For the open circles (non-organic) more modern varieties have lower CS (higher, more stable yield), while for filled circles (organic) there is no relationship. Why should this be so. Because of those changes in agronomic practices mentioned above.

[M]odern cultivars are selected to beneļ¬t from later nitrogen (N) availability which includes the spring nitrogen applications tailored to coincide with peak crop demand. Under organic management, N release is largely based on the breakdown of fertility-building crops incorporated (ploughed-in) in the previous autumn. The release of nutrients from these residues is dependent on the soil conditions, which includes temperature and microbial populations, in addition to the potential leaching effect of high winter rainfall in the UK. In organic cereal crops, early resource capture is a major advantage for maximizing the utilization of nutrients from residue breakdown.

To perform well under organic conditions, varieties need to get a fast start, to outcompete weeds, and they need to be good at getting nitrogen from the soil early on in their growth. Organic farmers tend to use older varieties, in part because they possess those qualities. Concerted selection for the kinds of qualities that benefit plants under organic conditions, which tend to be much more variable from place to place and season to season, could improve the yileds from organic farms.

Drought resistance: “it’s complicated”

In case anyone out there is still wondering why all those early promises of drought-resistant crop varieties have been so long arriving, Ford Denison has a wonderfully clear explanation. He takes as his starting point a 2004 paper about the development of Drysdale wheat, bred in Australia for water use efficiency. And he came to that in search of counterexamples to his default view.

I’m always skeptical when someone speculates that we could double crop yield just by increasing the expression of some newly discovered “drought-resistance gene.” My rationale is that mutants with greater expression of any given gene are simple enough to have arisen repeatedly over the course of evolution.

The question Denison asks of Drysdale wheat is whether the tradeoffs that in the past prevented the selection of greater productivity — for example the ability to withstand drought being penalized in average and wetter years — are no longer relevant.

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Rather than give away the answer, or attempt to summarize the key arguments, I just urge you to go and read the full post. I will, however, add a little tidbit I discovered all on my own (with Google’s help). You might think that naming a drought-resistant wheat Drysdale marks a marketing triumph. You would be wrong. It recalls Russell Drysdale, an Australian artist whose paintings of rural life in general and drought in particular captured the land and its people.

Plan of action against UG99

Despite reassuring words from the Indian Minister of Agriculture at the start of the meeting, FAO announced that delegates of the 31 countries represented at the “International Conference on Wheat Stem Rust Ug99 – A Threat to Food Security” in New Delhi have pledged to support prevention and control of UG99. They agreed:

  • to share surveillance information;
  • that a global early warning system should be immediately established;
  • that plant breeding research should be intensified; and
  • that rust resistant wheat varieties should be distributed to farmers.

Resistance (to UG99) is futile

The Pakistan Biotechnology Information Centre has good news to share:

LAHORE: The scientists of Ayub Agricultural Research Institute, Faisalabad has successfully developed a new variety of wheat ‘UG99’ which is resistant to stem rust disease of wheat. The disease poses world-wide threat to wheat productivity and productive approach of AARI scientists to solve this problem would prove highly beneficial for the country.

Unfortunately, no more details are forthcoming. Where did they find the resistance? How did they get it into a productive variety? The world needs to know.

Wheat database heaven?

The USDA is promising people like Luigi a get out of hell free card. Shiaoman Chao, a molecular geneticist, sequences and fingerprints thousands of wheat and barley samples sent to her by breeders around the country. The results can help breeders to decide whether a particular seedling is worth persevering with.

But those data on their own become much more valuable when they can be married to other kinds of information from other kinds of laboratory. Enter GrainGenes, “a treasure trove of genetic information about wheat, barley and other ‘small grains’ like rye, oats and triticale”.

Personally, I don’t have the knowledge to make use of GrainGenes, or any of the other massive portals dedicated to just a few crops each: maize, strawberry, potato and others. But there is help out there.

The bigger question is the extent to which all those portals can be brought together and interlinked with other kinds of data: where selections grow, their visible characteristics, their utility, etc. etc. I know there are people coming at this from the non-molecular side of things, but I do sometimes wonder whether they really have the chops (and the resources) to pull it off. If some of the gene-jockeys decided they wanted to do it, and could throw some of their brains, brawn and bucks at the problem, I reckon Luigi would have his lifeline sooner. And it might be more reliable.