**1. Introduction**

The conservation of crop genetic resources is a fundamental step for further breeding of traits of interest. Common bean (*Phaseolus vulgaris* L.) is the major legume for human consumption

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throughout the world [1, 2]. It is naturally distributed from northern Mexico to northern Argentina, with a marked genetic structure. From the classic to the most recent reports, two major gene pools have been recognized for the species, the Mesoamerican and the Andean [3, 4]. Domestication has been independently performed within each gene pool [5, 6], selecting specific genes for growth habit, seed size, color and yield, a phenomenon described as the "domestication syndrome" [7]. Therefore, an enormous panel of diversity can be observed from wild to domesticated genotypes of common bean, making it as a model for understanding crop evolution [8].

farms at that area, De Oliveira et al. [11] were able to collect seeds with three main patterns of colors such as gray background with black strips (Serro Azul Malhado—SAM), light brown with glossy seed coat (Serro Azul Brilhante—SAB) and dark gray with dull seed coat (Serro Azul Fosco—SAF). Interestingly, at one of the farms, from a fresh sample of SAF seeds collected (approximately 1 kg), only 10 seeds presented the SAB pattern (**Figure 1A** shows the phenotypes of SAB and SAF). Seeds with the SAB pattern were crossed to the SAF pattern and

Genetic Variation of Landraces of Common Bean Varying for Seed Coat Glossiness and Disease…

Serro Azul has been the object of a few studies, considering its importance to local farmers and the need of improving its productivity. It has been subjected to many diseases, such as anthracnose, and pests. De Oliveira et al. [11] and De Oliveira and Tsai [13] showed low yield from this variety from experiments performed at different farms in Cunha, SP, when no fertilizer was applied. This treatment represented the traditional way that farmers cultivated this landrace at their farms. However, when a sort of fertilizer treatments were applied in soil cultivated with this variety, along with one commercial standard at the time (IAC-Carioca 80SH), the yield was significantly improved from around 930 kg ha−1 (without fertilizer) to 1360 kg ha−1

The genetic control of seed coat color, pattern and glossiness in common bean has been a major issue for scientists in decades. Frequently, the gene nomenclature for loci related to such traits was confusing, leading to a series of meetings for establishing standard nomenclatures (Bean Improvement Cooperative meetings). As regards seed glossiness, Bassett [14] has clarified the differences between glossy and opaque seed coats through a series of genetic crosses, providing genetic stocks (pure lines for specific alleles of seed coat loci) that have

Landraces might be the source of additional alleles or allele combinations for studying genes related to color, pattern and glossiness of the seed coat. Moreover, these new sources might be interesting for being added to the breeding programs concerned with such traits. The study of Konzen and Tsai [12] examined the particular aspect of Serro Azul of segregating for seed glossiness and color patterning. The population developed from the cross SAF × SAB was analyzed

of glossiness was attributed to two alleles at the *Asp* locus, usually referred as the gene controlling glossiness in common bean [14]. SAB carries the dominant allele *Asp*, which confers the intense glossy aspect of the seed coat, while SAF has a dull seed coat [12] (**Figure 1A**). This gene is known to be located in chromosome 7 [15], where genes associated with anthracnose and angular leaf spot resistance [16, 17], common bacterial blight [17] and nodulation [18] are also located.

generation for the segregation of these traits. The variation

been used since then for unraveling the genetic and biochemical aspects of the trait.

(fertilizer application along with lime and foliar spray of molybdenum) [13].

**3. Unraveling the genetic control of seed glossiness and its** 

generation, revealing consistent

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the reciprocal as well, and populations were advanced to F<sup>4</sup>

patterns of segregation for seed glossiness and color [12].

**importance taking Serro Azul as an example**

**3.1. Genetic control of seed glossiness**

from the parental genotypes to the F<sup>4</sup>

The introduction of common bean to other areas than its natural habitat, such as in Brazil [9], led to new combinations of seed and flower colors, shapes and sizes, growth habits, cycle, photoperiod and yield [10]. It has also shaped the interaction between beans and the environment, leading to new diseases and pests.

In Brazil, common bean is a staple food among most citizens along with rice. Usually, its cultivation is performed in small farming systems along with other crops and animal production systems, providing self-sufficiency for farmers in various regions of the country. Several cycles of selection by local farmers in specific environments have generated new landraces, which are not yet known and available from core collections such as the ones from Centro Internacional de Agricultura Tropical (CIAT, Colombia), United States Department of Agriculture (USDA, USA) and Empresa Nacional de Pesquisa Agropecuária (EMBRAPA, Brazil). Landraces have singular aspects that might assist breeding programs for disease resistance, abiotic stress tolerance, improvement of nutrition facts, among several other desirable aspects of common bean grains.

A particular landrace has been discovered with local farmers from the municipality of Cunha, Sao Paulo state, Southeast Brazil. The farmers referred this landrace as "Serro Azul" and have been cultivating it along with other varieties [11]. Serro Azul shows considerable morphological variability, revealing different types of seeds. It shows high genetic variation for seed colors and patterns [12], disease and insect resistance and nodulation ability [11, 13], which are among the main aspect studies in breeding programs of common bean.

We drive the topic of this chapter highlighting Serro Azul as a case study of how the conservation of landraces might be important for further breeding strategies. First, we describe the importance of landraces of common bean in the discovery of new allele combinations for seed color and pattern genes, using the example of Serro Azul. Then, we briefly discuss the implications of the research of common bean landraces for nutrition and health. Moreover, we outline a significant number of original findings about our landrace in focus, which serve as examples of disease resistance as well as indications of insect resistance. Finally, we guide the reader through other perspectives of the importance of a better knowledge of landraces, their collection and conservation for future endeavors in breeding programs.
