**2. Historical background of landrace origin**

The origin of landraces encompasses both the temporal and spatial components of where landraces were first developed. They (landraces) have a relatively long history, significantly more than the ephemeral lifespan of modern cultivars. Many authors suggest that landraces have been growing 'since time immemorial' [11], 'over long periods of time' [9], 'over hundreds even a thousand years' [12], 'for many years even centuries' [13], 'for generations' [14], 'for many centuries' and 'over a period of time' [15]. Nevertheless, few are explicit about the amount of time a landrace must be grown to be considered a landrace. However, Louette [16] indicated for maize that the period of time must be 'for at least one farmer generation (i.e. more than 30 years)', while Astley referred to vegetable landraces being grown for '50–70 or even 100 years'.

Hawkes [17] opined that landraces are associated with one specific geographical location, in contrast to cultivars which are bred remotely, trialed in several locations and subsequently cultivated in diverse locations. Therefore, landraces are closely associated with 'specific locations' and often will take the name of the location [11]. Examples of this are Kent Wild White Clover from the UK county of Kent and Tuxpenõ maize from the Tuxpan region in Mexico. However, migrations (seed flow) of established landraces from their region of origin to new regions have also occurred as local informal variety introductions. Zeven [3] proposed two types of landraces: **autochthonous** (landraces cultivated for more than a century in a specific region) and **allochthonous** (a landrace that is autochthonous in one region introduced into another region and becoming locally adapted). In that case, the examples of Kent Wild White Clover and Tuxpenõ maize are cultivated in regions other than where they originated. Kent Wild White Clover is grown in some hilly areas of Scotland and Tuxpenõ maize in several regions of Southern Mexico. A third type known as a 'Creole' landrace may be derived from an originally bred variety [18, 19], which then becomes an effective landrace following numerous repeated cycles of planting and farmer seed selection in a specific location. For instance, Square Head Master Wheat, identified as a cultivar in the National List of the UK, has been grown continuously since 1930 by the family of Paul Watkin (a farmer from Suffolk, UK) saving seed each year.

Continuity and individual cultivation and discontinuity and collective cultivation are both significant. Individual farmers commonly lose and recover landraces as a result of their management of a dynamic portfolio of landraces [19] and seed replacement [20] and because of various stochastic events such as drought, floods, pests and diseases. Village or local community continuity may be maintained through farmer's seed exchange networks if cultivation is by more than one farmer. In fact, several papers have highlighted the relevance of seed exchange for the maintenance of landraces [20–22]. Such localized farmer exchange activities may help to define and ensure continuity of a landrace. However, the introduction of 'exotic' landraces to a locality is likely to adulterate the uniqueness and local adaptation of the local landraces. Therefore, many believe that the maintenance of an 'open' cultivation system, with routine local or more remote introductions of germplasm, is likely to be responsible for the maintenance of genetic diversity in landraces.
