**5. High genetic diversity**

others believe that landraces can even be selected from cultivars [18, 19], terms such as creolization or rustication are applied, and 'in the absence of traditional and formal maintenance breeding, any improved landrace (cultivar), including a hybrid variety, will regress with time into a landrace' [27]; 'a cultivar that has been growing under a low selection pressure for specific traits but not uniformity for a long time could be considered a landrace' (**Figure 2**).

**Figure 2.** Types of landraces of maize [27].

8 Rediscovery of Landraces as a Resource for the Future

The characteristics of landraces in relation to the magnitude of allelic and genetic diversity in contrast to cultivars are considered to be significantly more genetically diverse [37]. Thus, a landrace is a 'highly variable population in appearance' [7], 'highly diverse populations and mixtures of genotypes' [38], 'genetically heterogeneous' [13], 'not genetically uniform and containing high levels of diversity' [14], 'local diverse crop varieties' [26], 'heterogeneous crop populations' [39] and 'materials with variable levels of heterogeneity'. Frankel and Soule [40] indicated that the genetic diversity of landraces has two dimensions: between sites/populations and within sites/populations. The former is generated by heterogeneity in space and reproductive isolation, while the latter is generated by heterogeneity in time associated with both shortterm variations between seasons and by longer-term climatic, biological and socio-economic changes.

Some authors have used the term 'meta-population' when referring to the diversity structure of a landrace. As such, a landrace constitutes a group of farmers' seed lots that are highly diverse both between and within themselves. In contrast however, Sanchez [41] when evaluating the genetic diversity of maize landraces of Mexico found that some landraces had very low levels of genetic diversity, and it was suggested that comparatively low diversity may be more associated with selfing crops. Bere barley, one of the oldest cereal varieties in Europe, is 'surprisingly homozygous', possibly because it has been maintained in isolation in marginal lands since the sixteenth century [42]. A similar picture is provided by Tibetan barley landraces which proved to be much less diverse than modern barley cultivars due possibly to their relative geographic isolation, their relatively recent introduction to Tibet and the fact that they have been subject to very little natural or man-made selection [43]. Therefore, the dynamics of genetic diversity and changes over time of the genetic structure of landraces are likely to be crop specific. It is also likely to be associated with the mode of fertilization (self- versus cross) and propagation (sexual or asexual), which has over time resulted in genetic bottlenecks, varying outcrossing rates, recombination and gene flow. Thus, as Almekinders and Louwaars [24] conclude, 'a landrace is usually a complex heterogeneous population, but not necessarily so'.

adapt themselves only to a few environments'. Wood and Lenne [19] disagree with the assumption 'that all traditional varieties are locally adapted' and state that 'evidence against specific local adaptation in crop varieties is provided by the extensive interchange of traditional varieties of all crops'. Farmers employing an 'open' cultivation system where there is regular local or more exotic landrace introduction are less likely to have locally adapted landraces. Zeven [20] provided evidence of farmers' traditional practice of periodic seed replacement to combat socalled degradation, which indicates that in certain situations a 'closed' cultivation system that results in local adaptation of landraces may be deleterious. The farmer's criteria for seed selection also do not necessarily lead to selection for local adaptation; the varying environmental conditions under which traditional agriculture is carried out may in certain conditions not actually favor specific local adaptation. In this sense, some authors consider that local adaptation can comprise both wide adaptation in certain landrace characters and narrow adaptation in others.

Landraces and Crop Genetic Improvement http://dx.doi.org/10.5772/intechopen.75944 11

Traditional farming systems have often been considered beneficial reservoirs of landraces and intra-crop diversity [45]. Traditional farming systems involve traditional cultivation, storage and use practices, and integrated with these practical skills, traditional knowledge about landrace identification, cultivation, storage and uses is incorporated. In this sense, one important element of landraces conservation that has recently been the focus of researchers' attention is the way that landraces studies have focused on farmers' variety selection [46], farmers' seed exchange [22], farmers' seed networks [22], farmers' seed replacement [20], farmers' portfolios of varieties [19], farmers' landraces identification [47]and farmers' landrace uses [48].

In fact, Zeven [27] suggested that landrace diversity can be explained by the combination of farmers' selection criteria on specific local landrace genotypes by means of farmers' seed saving and the introduction of variation by means of exchange with other farmers of other genotypes of the same crop. This indicates that landraces are more inherently dynamic than cultivars as they are maintained through repeated cycles of sowing, harvesting and replacing seed selection by farmers [49, 50] within complex informal systems. However, it is also important to consider that traditional farming systems are themselves also dynamic and that the frontier between them and other farming systems is not well defined. As such, traditional farming systems are subject to change, incorporating in some cases modern cultivars into their systems, growing them alongside landraces of the same species [51]. These have been

The current industrial agriculture system may be the single most important threat to biodiversity [2]. Also, Sarker and Erskine [52] opined that a serious consequence of biodiversity loss is the displacement of locally adapted landraces with adaptation traits to future climates by

Each has shown the role of farmers for the creation and maintenance of a landrace.

**7. Association with traditional farming systems**

managed and maintained by farmers.

**8. Threat to landrace diversity**
