Two centuries of isolation/cloning breeding method

ABSTRACT

The Industrial Revolution led to replacing peasant mass selection by individual selection. In 1836 John Le Couteur on the suggestion of the Spanish botanist Mariano LaGasca codified the isolation method, empirically practiced since the early 19^th century. It consists in replacing varieties or populations by “copies” of a better plant – by a (quasi) clone. It requires plants that “breed true to type,” namely that are individually reproducible as is the case for small grain cereals. It exploits the natural variation of populations. George Shull’s “hybrid corn” extended the isolation method to maize thus exploiting the natural variation of maize population but took great care to hide it behind genetic considerations on the exploitation of the elusive heterosis. To anyone focusing on what breeders do, this sleight of hand would have been clear as early as January 1909, when Shull detailed the breeder’s task: building a random sample population of individually reproducible plants (reproducible by the breeder and only the breeder) by “making all possible crosses among different pure strains” obtained by “as many self-fertilization as practicable.” Although only a marginal and unique genetic yield increase could be expected from such an extravagant proposal, it solved the overdominant problems of an industrial agriculture, crop uniformity and breeders’ property rights. Shull was clear about his goals, but these crucial aspects were ignored while all attention went to the non-existent yield increase of the exploitation of heterosis.

KEYWORDS:

• George Shull’s composition of a field of maize (January 1908)
• Shull’s pure line method in corn breeding (January 1909)
• isolation method (1836)
• “hybrid corn” as the maize isolation method
• economics of hybrid corn
• seeding rate or heterosis? natural variations or heterosis?

Acknowledgments

This article concludes of a long process begun in the early 1980’s when Richard Lewontin invited me, an economist, to develop what were mere intuitions about hybrid corn in his intellectually ebullient Harvard population genetics laboratory where even technical issues were cast in their proper philosophical, historical, epistemological context. Diane Paul, historian of sciences, introduced me to her field and was supportive intellectually and morally, particularly during the discouraging years when, one after the other, biological journals declined to publish my views. Diane declined to be a coauthor. I also wish to thank the editors and reviewers of the Journal of Genetics for their scientific openness: not only they dared to open the debate about “Hybrid corn and the unsettled question of heterosis” (Berlan 2018), but they greatly helped improving my manuscript.

Disclosure statement

I never received any grant from the seed industry.

Author contribution

Solving the inconsistency between theory (exploiting heterosis) and practice (exploiting once a small part of corn populations variation with the isolation method) required much creativity, neglect of facts and word juggling to fit the legend of a heterosis manna. My book La planète des clones (Berlan 2019), offers a political economy overview of breeding since the Industrial Revolution to the so-called Gmos and Dolly, the first mammal clone.

Notes

1. Citations are from distinguished scientists, geneticists, breeders, agronomists, most of them members of the Academy of Sciences (James Crow, Paul Mangelsdorf, Lewis Stadler, George Sprague, Donald Jones, Arnel Hallauer, Donald Duvick). In this article, I will stick to the unfortunate habit considering that hybrid vigor and heterosis are synonymous. Addendum one describes how this confusion arose.

2. My article Beyond heterosis: reading George Shull’s hybrid corn articles (1908–1909) accepted for publication in the Journal of Genetics analyses Shull skillful rhetoric and semantic (Berlan 2021).

3. This addendum draws heavily on my article Hybrid corn and the unsettled question of heterosis, J. Gen. December 2018.