**4. Conclusions**

**Figure 3.**

vertical boxes indicate the 1000

gray dot at the top of the figure mark the centromeres. Modified from Cortés & Blair [66].

Patterns of genome-wide diversity in common bean accessions based on SNP markers. A sliding window analysis was used to compute (A) SNP density, (B)

millions of base pairs (Mb). Black and gray colors highlight different common bean (Pv) chromosomes. Gray dashed horizontal lines indicate genome-wide averages. Gray

bp flanking region of each marker that was associated with the bioclimatic-based drought index. Horizontal gray lines with a central filled

Results of all windowed analyses are plotted against window midpoints in

122 Rediscovery of Landraces as a Resource for the Future

nucleotide diversity as measured by π, (C) Watterson's theta estimator (θ), and (D) Tajima's D.

Wild accessions and landraces of common bean occupy more geographical regions with extreme ecologies [2] and extensive drought stress [12] than cultivated accessions. Those regions include the arid areas of Peru, Bolivia and Argentina, and the valleys of northwest Mexico. Hence, a broad habitat distribution for wild common bean has exposed these genotypes to both dry and wetter conditions, while cultivated common bean has a narrower distribution and is traditionally considered susceptible to drought. These differences in the ecologies of wild and cultivated common bean have been associated with higher genetic diversity in the former group when surveying candidate genes for drought tolerance such as the ASR [47], DREB [48], and ERECTA [49] gene families, once the population structure [41] and the background distribution of genetic diversity have been accounted for.

Also, as identified through the genome-environment association approach that was illustrated in this chapter, there are notorious differences between the adaptations of wild accessions and landraces found in arid and more humid environments, in congruence with natural divergent selection acting for thousands of years. Several of these differences might be valuable for plant breeding. Therefore, we reinforce, as was envisioned by Acosta [50], that wild accessions and landraces of common bean be taken into account to exploit naturally available divergent variations for drought tolerance. We envision that this lesson from common bean will inspire the exploitation of wild relatives and landraces of other crops to face the threats imposed by current climate change.

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