Genetic Structure of Landraces

Abstract

Domestication, geographical dispersal to new environments and selection by farmers resulted in numerous landraces of cultivated plants. Simplified models of landraces lead to some useful conclusions. Depending on their mode of reproduction (sexual or asexual) and mating system (extent of self-pollination versus cross-pollination), landraces consist of mixtures of inbred lines (wheat, rice and barley), or hybrids (maize), or inbred lines and hybrids (oilseed rape and field beans), or vegetatively propagated clones (cassava, potatoes and yams). These factors also determined the types of cultivar bred from landraces during the 20th century. Theoretical considerations of mixed selfing and random mating confirm that predominantly self-pollinating (>95 %) landraces will be mixtures of inbred lines with a high degree of homozygosity whereas predominantly cross-pollinating (>95 %) ones will be mixtures of hybrids with a high level of heterozygosity. Greater complexity can be expected with a mixture of self-pollination and cross-pollination under both disomic and tetrasomic inheritance.