Abstract
Maize landraces (Zea mays subsp. mays) have evolved under the joint action of environmental factors and of the farmers who cultivated them. In this study, we aim to quantify the selection gradients exerted by farmers by proposing them a selection test consisting in choosing the ears they would select if they were to grow maize landraces the following year. The study focused on the Pyrenees region of France, where landraces were cultivated until the arrival of hybrids in the 1960s and conserved ex-situ ever since. We interviewed former Pyrenean farmers or their children who were cultivating landraces 60 years ago. The survey documented seed management practices and know-how. Our selection test showed that their selection was based solely on ears: old farmers selected healthy and productive ears by using ear length and volume as the first two selection criteria. Both were highly correlated with the kernel weight per ear. Heritabilities of ear traits at an individual plant level were estimated in one trial for four landraces and were found variable between traits and landraces (average 0.36 ranging between 0 and 0.76). We calculated the expected genetic change after one generation of mass selection, following farmer selection criteria. For ear length, genetic change was expected to reach about 3.4% (from 1 to 7.5% over the 17 selection tests). We investigated seed selection practices both east and west of the Pyrenees and compared them qualitatively with those of native American farmers.