Dwarf wheat and rice on the shoulders of giants

“If I have seen further it is by standing on the shoulders of giants”
—  Isaac Newton, possibly paraphrasing Bernard of Chartes

In 1966, farmers — 2359 of them — came to the International Rice Research Institute from all over the Philippines, to get seeds of IR8 rice, which had double the yield potential of existing varieties.  Achieving that potential usually required nitrogen fertilizer, but fertilizer actually decreased yield of earlier varieties  (Rice Today v. 5 p.36).

RiceYieldPetaVsIR8

Norman Borlaug got the Nobel Prize for similar results with wheat a few years earlier, so why is Peter Jennings, the plant breeder who developed IR8, not equally famous?  I think Jennings is still alive, but the Nobel Committee had better hurry.

IR8riceParents

I’m afraid my book, Darwinian Agriculture, perpetuates this injustice.  I devote most of page 121 to Norman Borlaug and the Japanese and American plant breeders (Gonjiro Inazuka and Orville Vogel) who were the proximate source  of the short-stemmed materials that were key to the high yield of Borlaug’s varieties.  Some of the key genes apparently came from wheat varieties developed by the Italian plant breeder, Nazareno Strampelli, 30 years earlier [1], as discussed in this podcast.  I neglected to name Peter Jennings in the main text of my book, although I do cite one of his papers, which showed that IR8 was less competitive than older, lower-yielding varieties [2].

SunesonJenningsRice

Such tradeoffs between yield potential and competitiveness are a major theme of my book.  Although tradeoffs are now a central theme in evolutionary biology, I got the idea from a 1968 paper by Colin Donald [3], to which I was introduced by my postdoctoral mentor, the late Bob Loomis, author (with David Connor and Ken Cassman) of Crop Ecology.

So I’m standing on Donald’s shoulders, with a boost from Loomis, but whose shoulders did Donald stand on?  Donald cites several papers by Jennings, including a paper that correctly identified traits he thought would be key to high yield potential in rice, including short stems and erect leaves [4].   Jennings then proceeded to make a rice variety with those traits, through crossing and selection, and the result was IR8.  Donald also cites two technical bulletins by Akiro Tanaka, who Jennings credits (in this interesting interview) with helping him design IR8.

What other shoulders did Jennings stand on?  Well, he cites papers by S.A. Tsunoda, who identified short stems and erect leaves as key to high yield in sweet potato, soybean, and rice [5].  Neither Donald nor Jennings cite Borlaug, who doesn’t seem to have published much, but Donald does cite a paper by Vogel et al. on semi-dwarf wheats that Borlaug used [6].

The value of short stems may have been widely recognized at the time.  A historical account in the International Rice Research Institute’s magazine, Rice Today, quotes plant breeder Henry Beachell as advising Jennings to “be on the lookout for a dwarf rice,” and says that IRRI’s first Director, Robert Chandler, was calling for a short stem as early as 1962 [7].  He didn’t mention erect leaves, and attributed the yield benefit of short stems to their ability to support larger, fertilizer-supported grain heads without lodging (falling over).  Shorter stems could also use fewer resources, freeing carbon or nitrogen for more grain, although that would depend on stem diameter as well.

Colin Donald seems to have been the first to generalize from specific traits to a tradeoff “between the competitive ability of cultivars on the one hand, and their capacity for yield in pure culture on the other.” [3]  For example, Jennings mentions prolific tillering  as a positive trait in his interview, whereas Donald suggests fewer stems per plant (maybe only one) as a route to increased yield potential.  Plants with fewer stems (spaced closer together) could capture all available sunlight sooner than slowly-spreading multistem plants (spaced farther apart).

Jacob Weiner has shown that increased planting density (more crop plants per square meter) can also help  suppress weeds, because the weeds then encounter crop plants earlier, when the crop’s larger seed reserves give them a competitive advantage [8].  Maximizing this benefit requires within-row spacing to be more similar to between-row spacing.  Today, between-row spacing is usually greater — plants are usually spaced close enough within rows that they compete with each other before they have a chance to suppress between-row weeds.  For example, this time-lapse movie shows lots of space between rice rows for much of the growing season, so a lot of sunlight is wasted, evaporating soil water rather than hitting leaves, where it would contribute to photosynthesis and yield.

In summary, both Borlaug and Jennings relied on other plant breeders or plant physiologists for materials and/or ideas.  Their accomplishments, in turn, helped Donald develop his more-comprehensive approach.  Maybe all three deserved Nobel Prizes.

As for the future, I argue in my book, in journal articles [9], and in talks that variations on Donald’s approach are still our most-promising route to increasing crop yield potential.  Scroll down my main blog page for links to other talks, including a series at the International Rice Research Institute.

1] Salvi, Sergio et al. (2013) Nazareno Strampelli, the ‘Prophet’ of the green revolution. The Journal of Agricultural Science 151 :1-5

[2] Jennings, P. R., de Jesus, J., (1968) Studies on competition in rice. I. Competition in mixtures of varieties. Evolution 22 :119-124

[3] Donald, C. M., (1968) The breeding of crop ideotypes. Euphytica 17 :385-403

[4] Jennings, P. R., (1964) Plant type as a rice breeding objective. Crop Science 4 :13-15

[5] Tsunoda, S., (1959) A developmental analysis of yielding ability in varieties of field crops. II. The assimilation system of plants as affected by the form, direction, and arrangement of single leaves. Japanese Journal of Breeding 9 :237-244

[6] Vogel, OA et al. (1963) Plant and performance characteristics of semidwarf winter wheats producing most efficiently in Eastern Washington. Agronomy Journal 55 :397-398

[7] Hargrove, T., Coffman, W.R., (2006) Breeding History. Rice Today 5 :34-38

[8] Weiner, J. et al. (2001) Suppression of weeds by spring wheat Triticum aestivum increases with crop density and spatial uniformity. J. Appl. Ecol. 38 :784-790

[9] Denison, R. F., (2015) Evolutionary tradeoffs as opportunities to improve yield potential. Field Crops Res. 182 :3-8

 

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