Introgression from modern hybrid varieties into landrace populations of maize (Zea mays ssp mays L.) in central Italy

Landraces are domesticated local plant varieties that did not experience a deliberate and intensive selection during a formal breeding programme. In Europe, maize landraces are still cultivated, particularly in marginal areas where traditional farming is often practiced. Here, we have studied the evolution of flint maize landraces from central Italy over 50 years of on-farm cultivation, when dent hybrid varieties were introduced and their use was widespread. We have compared an 'old' collection, obtained during the 1950s, before the introduction of hybrids, and a recent collection of maize landraces. For comparison, a sample of maize landraces from north Italy, and of improved germplasm, including hybrids and inbred lines were also used. A total of 296 genotypes were analysed using 21 microsatellites. Our results show that the maize landraces collected in the last 5-10 years have evolved directly from the flint landrace gene pool cultivated in central Italy before the introduction of modern hybrids. The population structure, diversity and linkage disequilibrium analyses indicate a significant amount of introgression from hybrid varieties into the recent landrace populations. No evidence of genetic erosion of the maize landraces was seen, suggesting that in situ conservation of landraces is an efficient strategy for preserving genetic diversity. Finally, the level of introgression detected was very variable among recent landraces, with most of them showing a low level of introgression; this suggests that coexistence between different types of agriculture is possible, with the adoption of correct practices that are aimed at avoiding introgression from undesired genetic sources.