**5. Analysis and conservation of the genetic diversity of landraces**

*Colletotrichum lindemuthianum*. The genetic architecture and mechanisms of resistance to such diseases have been studied at genomic scales, identifying specific genes, pathways and QTL associated to each one (see [16, 36, 37]). As landraces are usually genetically structured and locally adapted, they might be the source of new alleles for disease resistance, which could be

Here, we present new findings obtained with experiments conducted with Serro Azul Brilhante and Serro Azul Fosco, as regards their variation for anthracnose resistance. The resistance degree to *C. lindemuthianum* was evaluated using the method of detached leaves [38], with modifications. Seeds of each parental line (SAB and SAF) and control standards from the literature (cultivars Rosinha G2 and G2333 are highly susceptible and resistant, respectively) were germinated and transferred to pots with substrate (Plantmax) in a greenhouse, and irrigated properly until the establishment of the first trifoliate (around 21 days). One leaf was collected

*thianum* races 65 and 73 [39]. After 1 min, the leaves were placed in Petri dishes containing two layers of moistened filter paper. The plates were then incubated in a BOD type chamber and maintained in a photoperiod of 12 h at 21°C (± 2°C) for 7 days. For analysis, plant resistance was inferred according to the standards proposed by CIAT, using a scale from 1 (resistant—no

The results revealed an interesting difference between the parents SAF and SAB, used to constitute the segregating populations. The detached leaf method clearly showed that SAB was highly resistant to both races studied (65 and 73), while SAF showed high susceptibility to the *Colletotrichum* races, especially race 65 (**Figure 3**). The scores for disease resistance were significantly different among the two parents (SAB and SAF) for the race 65, but the average score with the race 73 also suggested higher degree susceptibility in SAF (**Table 1**). It is interesting to notice that the score for SAF was higher than the standard, which is used as a control for anthracnose susceptibility (Rosinha G2). In a similar manner, SAB was even more resistant

G2333 (resistant control) 2 ± 0.8 1 ± 0.5 Rosinha G2 (susceptible control) 5 ± 0.4 4 ± 0.2 SAB 1 ± 0.0 3 ± 0.6 SAF 7 ± 3.0 5 ± 1.1

G2333 × Rosinha G2 p = 0.012\* p = 0.001\* SAB × SAF p = 0.0001\*\* p = 0.081 ns

**Table 1.** Average scores of *Colletotrichum lindemuthianum* infection in leaves of the variants Serro Azul Brilhante (SAB)

and Serro Azul Fosco (SAF), compared to G2333 (resistant control) and Rosinha G2 (susceptible control).

conidia mL−1 of *C. lindemu-*

**Race 65 Race 73**

added to the disease resistance breeding programs.

186 Rediscovery of Landraces as a Resource for the Future

symptoms) to 9 (susceptible—evident necrosis).

than the standard resistant line G2333 (**Table 1**).

Mean comparisons—Tukey's test

\*Significant at *P* < 0.05, \*\*Significant at *P* < 0.01.

**Genotype Mean score**

from each plant and immediately placed in a suspension of 1.2 × 10<sup>6</sup>

The genetic diversity of common bean landraces, cultivars and wild accessions has been investigated in multiple studies, mainly based on morphological and molecular markers in the last two decades (from 1995 to 2017). In the 1990s, studies have shown high genetic diversity based on morphological, enzyme and DNA-based markers (RAPD and microsatellites) [41–43]. After 2000, several studies involving amplified fragment length polymorphic (AFLP) [44, 45] and microsatellite [24, 46, 47] markers have been conducted. After 2010, with the advances of the sequencing technology, numerous papers have addressed the molecular diversity of common bean based on SNP markers [4, 48–51]. In general, most of the studies revealed that common beans are divided into two main gene pools, the Mesoamerican and Andean. In the case of Brazil, where common beans were introduced and have been cultivated mainly in small farming systems, varieties of both pools have been encountered. However, Burle et al. [24] investigated the genetic diversity of almost 300 landraces cultivated in Brazil and demonstrated that almost 80% of the genotypes have a Mesoamerican background, based on a population structure analysis with microsatellite polymorphisms.

In the case of Serro Azul, we also examined the molecular diversity of a sample of plants from both the variants (Serro Azul Brilhante and Serro Azul Fosco) by using the AFLP markers. Selective amplifications were done with four primer combinations (*EcoRI-A*/*MseI-CC*; *EcoRI-AC*/*MseI-CC*; *EcoRI-AT*/*MseI-CA*; *EcoRI-T*/*MseI-CA*). The AFLP gels revealed a considerable variation within and among SAB and SAF plants (**Figure 4**). An UPGMA tree was designed using Bionumerics software (**Figure 5**). Our data revealed a good separation among SAB and SAF samples, although some mixture was detected. In general, the SAB subgroup presented 75% of similarity with the SAF subgroup. Two plants of the SAF, however, were grouped within the SAB subgroup. From the analysis of the UPGMA tree, it is possible to infer that SAB plants were derived from SAF, which is consistent with the prior observation that SAB seeds were observed within 1 kg of SAF seeds harvested at a farm in Cunha, SP. Hereby, the high variability at the morphological levels can be verified at the molecular level, revealing a landrace with considerable genetic diversity to be explored. The development of the SAF × SAB population, for instance, revealed a high variation for seed size, color and water uptake [12]. Moreover, we showed that the parental lines have noticeable differences for disease resistance.

**6. Perspectives of the conservation and use of bean landraces**

the AFLP profiles. An examination of AFLP polymorphisms among F<sup>4</sup>

The findings about Serro Azul provide interesting insights of the use and application of landraces in common bean breeding. A distinguishable morphologic diversity is noticeable within the landrace, which can be further explored to investigate genes responsible for color and glossiness [12]. SAB and SAF are consistently different at the molecular level as well, as revealed by

**Figure 5.** UPGMA tree based on Jaccard similarity analysis and AFLP profiles of the two variants of the landrace Serro Azul.

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SAB revealed a potential discrimination of color classes in the population by the molecular approach [12]. Furthermore, Serro Azul and the population developed might be used to investigate the genetic control for such incredible difference in anthracnose resistance between SAB and SAF. Another interesting observation comes from field observations where the SAF × SAB population was being tested. Usually, lines with similar features to the SAB parental line, especially the seed glossiness, presented very low incidence of bruchid attacks. On the other hand, SAF-derived lines were usually susceptible to the insects, leading to damages to the seeds.

lines of the cross SAF ×

**Figure 4.** AFLP profile (primer combination *EcoRI-A*/*MseI-CC*) of individual plants from SAB (Serro Azul Brilhante) and SAF (Serro Azul Fosco). M stands for the ladder DNA of 100 bp.

Genetic Variation of Landraces of Common Bean Varying for Seed Coat Glossiness and Disease… http://dx.doi.org/10.5772/intechopen.73425 189

**Figure 5.** UPGMA tree based on Jaccard similarity analysis and AFLP profiles of the two variants of the landrace Serro Azul.
