Two centuries of isolation/cloning breeding method

摘要

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 19th 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.