Common bean landraces with bicolored seed represent a small fraction of those surviving on-farm in Italy [
1]. Among the bicolored types, “Badda” bean has a preeminent position being able to boast structures, such as the “Slow Food presidium” and the “Farmers’ Consortium”, aimed to support the continuation of its cultivation. A detailed characterization of “Badda” bean can help to better safeguard its genetic structure, as well as to support its distinctiveness respect to other landraces or cultivars with similar coat pattern.
3.1. Seed Storage Protein Variation
When analyzed by SDS/PAGE, protein extracts showed some major bands around 45 kDa, corresponding to PHAS, the major seed storage protein. The PHAS pattern type allows the attribution of landraces to the Mesoamerican or to the Andean gene pool [
15]. All “Badda” accessions analyzed were homogeneous for this character, showing only the C phaseolin pattern type, which is associated to the Andean gene pool.
The European common beans arose from the introduction of domesticated forms from both the American gene pools. The proportions of the two gene pools within the European materials have been extensively investigated. The prevalence of Andean types was first described by Gepts and Bliss [
15], and confirmed by subsequent studies at national [
3,
27,
28] and regional [
1,
2,
11,
29] level. Probably, types belonging to the Andean gene pool, characterized by medium or large-seeded size, are widespread in Europe since they had a higher adaptation to the new environments and were preferred by both farmers and consumers [
1,
27]. The ratio between the two gene pools within the European germplasm is linked to geographical areas [
30]. A clear-cut prevalence of Andean phaseolin types was recorded in Iberian Peninsula, Italy, and the Balkan area, while in central and south-eastern Europe, the proportion of Mesoamerican types tends to increase [
31]. As concerns Italy, studies carried out at regional level, proved the presence of the three major phaseolin types (C, T, and S). The recorded frequencies were 40%, 28%, and 32% for C, T, and S type, respectively [
1,
8,
32,
33]. The C phaseolin type is the predominant one in Sicily as well as in other southern Italian regions [
11,
34,
35]. In a recent study on twenty-five landraces cultivated in the Nebrodi mountains (northeast Sicily), the C phaseolin type was detected in 17 landraces [
11].
The electrophoretic bands corresponding to phytohaemagglutinin (PHA), the lectin protein representing the second storage protein of common bean seeds, were detectable in the protein profile around 34 kDa. Eleven PHA pattern types have been described in cultivated common bean; their nomenclature was coded by Brown
et al. [
36]. The “Badda” accessions showed as unique PHA pattern the TG
2 type. Although the gene families coding for PHAS and PHA are not linked, it has been proved that in cultivated materials there is a close association between their pattern types. Experimental results collected in this study agree with the described narrow association between C and TG
2 patterns (PHAS and PHA protein fraction, respectively) [
37].
3.2. Genetic Variation Based on Molecular Markers
Molecular markers of SSR type, which are specific in target, are commonly used to assess diversity among common bean landraces [
19,
38,
39]. The polymorphism revealed by SSR markers or microsatellites was variable depending on the
locus. In this study, the number of alleles per
locus ranged from 1 to 14 (
Table 1).
Overall, 65 alleles were identified at the 16
loci examined, with a mean of effective alleles per locus equal to 1.50 (
Table 2). The mean value of the percent of polymorphic
loci (P, 5% criterion) was 32% with values ranging between 19% and 44%. A particularly high level of polymorphism was observed at the
locus PVME1G with 14 alleles, and at the loci PV18791 and PVGLND5 with 13 and 12 alleles, respectively (
Table 1). The mean genetic diversity or expected heterozygosity (H
e) values were calculated for each accession, and ranged from 0.27 to 0.07, with a mean value of 0.17 (
Table 2).
Table 2.
Genetic diversity statistics relating to Simple Sequence Repeats (SSR) markers for each accession of “Badda” bean examined.
Table 2.
Genetic diversity statistics relating to Simple Sequence Repeats (SSR) markers for each accession of “Badda” bean examined.
Work Code | no a | ne b | P c | He d | Ho e |
---|
Badda bianco |
PH05 | 1.75 | 1.34 | 38 | 0.17 | 0.01 |
PH06 | 1.81 | 1.54 | 44 | 0.21 | 0.01 |
PH07 | 2.19 | 1.92 | 38 | 0.24 | 0.00 |
PH08 | 2.38 | 2.10 | 38 | 0.27 | 0.00 |
Mean | 2.03 * | 1.66 | 40 * | 0.22 * | 0.005 |
Badda nero |
PH09 | 1.88 | 1.56 | 44 | 0.21 | 0.00 |
PH10 | 1.31 | 1.14 | 19 | 0.07 | 0.01 |
PH11 | 1.75 | 1.57 | 25 | 0.16 | 0.00 |
PH12 | 1.56 | 1.30 | 19 | 0.12 | 0.00 |
PH13 | 1.31 | 1.19 | 19 | 0.09 | 0.00 |
Mean | 1.56 * | 1.33 | 25 * | 0.13 * | 0.002 |
Total mean | 1.77 | 1.50 | 32 | 0.17 | 0.003 |
Six out of the accessions exhibited homozygosity across all loci (H
o = 0.0). In the others, a scarce number of heterozygotes were observed (H
o), according to the predominantly autogamous mating system of common bean (
Table 2). When analyzed separately, the mean values of genetic diversity parameters resulted higher for “Badda bianco”, indicating that these accessions showed a higher level of genetic variability. The quantification of genetic diversity within and between “Badda bianco” and “Badda nero” bean, based on Nei’s genetic diversity statistics is shown in
Table 3.
Table 3.
Genetic diversity statistics of “Badda” bean accessions.
Table 3.
Genetic diversity statistics of “Badda” bean accessions.
Morphotype | Nei’s genetic diversity analysis |
---|
HT | HS | DST | GST |
---|
Badda bianco | 0.25 | 0.22 | 0.03 | 0.12 |
Badda nero | 0.21 | 0.13 | 0.08 | 0.38 |
The total genetic diversity (HT) was slightly higher in “Badda bianco”. The observation that intrapopulation diversity (HS) was higher than the interpopulation genetic diversity (DST), suggests that the diversity among accessions is lower than that within them. The coefficient of genic differentiation (GST) among populations was 0.12 and 0.38 in “Badda bianco” and “Badda nero” bean, respectively. These results indicated that 12% of “Badda bianco” total genetic diversity is among accessions, while this value increased to 38% in “Badda nero”.
Pairwise comparison of Nei’s genetic distances is reported in
Table 4. The average genetic distance among the nine “Badda” accessions was 0.119. The smaller values were observed between PH07 and PH08 (0.032), and PH11 and PH12 (0.033), belonging to “Badda bianco” and “Badda nero” bean, respectively.
Table 4.
Pairwise comparison of Nei’s genetic identity (above diagonal) and genetic distance (below diagonal) between common bean “Badda” accessions.
Table 4.
Pairwise comparison of Nei’s genetic identity (above diagonal) and genetic distance (below diagonal) between common bean “Badda” accessions.
Accession | PH05 | PH06 | PH07 | PH08 | PH09 | PH10 | PH11 | PH12 | PH13 |
---|
PH05 | - | 0.943 | 0.924 | 0.919 | 0.894 | 0.771 | 0.871 | 0.866 | 0.777 |
PH06 | 0.059 | - | 0.960 | 0.951 | 0.879 | 0.808 | 0.901 | 0.889 | 0.820 |
PH07 | 0.079 | 0.041 | - | 0.969 | 0.921 | 0.842 | 0.935 | 0.939 | 0.856 |
PH08 | 0.084 | 0.051 | 0.032 | - | 0.910 | 0.878 | 0.913 | 0.905 | 0.899 |
PH09 | 0.112 | 0.123 | 0.082 | 0.095 | - | 0.819 | 0.946 | 0.939 | 0.830 |
PH10 | 0.260 | 0.213 | 0.172 | 0.130 | 0.200 | - | 0.876 | 0.825 | 0.963 |
PH11 | 0.138 | 0.102 | 0.067 | 0.091 | 0.055 | 0.133 | - | 0.968 | 0.886 |
PH12 | 0.143 | 0.117 | 0.063 | 0.100 | 0.062 | 0.192 | 0.033 | - | 0.840 |
PH13 | 0.252 | 0.198 | 0.156 | 0.106 | 0.186 | 0.037 | 0.121 | 0.174 | - |
The UPGMA dendrogram, based on Nei’s genetic distances as defined by SSR markers, is shown in
Figure 3. The nine “Badda” accessions were grouped in three sub-clusters. The first one included all the “Badda bianco” accessions, while the “Badda nero” ones were grouped in two well-distinguished sub-clusters. The PH10 and PH13 accessions, located in a well-separated branch, showed fairly different results than the other materials analyzed, thus indicating more distant genetic relationships with the other two groups (see
Table 4).
Figure 3.
Dendrogram based on Nei’s genetic distances as defined by SSR markers showing the genetic relationships among the “Badda” bean accessions. Support values are shown.
Figure 3.
Dendrogram based on Nei’s genetic distances as defined by SSR markers showing the genetic relationships among the “Badda” bean accessions. Support values are shown.
Recently, Paniconi
et al. [
10] studied three “Badda” bean accessions using morpho-physiological traits and ISSR (Inter Simple Sequence Repeat) molecular markers. Although different accessions and marker types were used, they also recorded the presence of a more distant population among the three analyzed and attributed this result to a different introduction or contamination by foreign germplasm. Results presented in this study confirm the possibility that two constitutive nuclei contributed to the genetic background of “Badda nero” bean. The co-existence of two or more nuclei within a single landrace was described for “Fagiolo del Purgatorio”, an Italian landrace traditionally cultivated in Central Italy [
19]. The authors reported that the differences between the two nuclei identified within “Fagiolo del Purgatorio” were at agronomic, biochemical, morphological and genetic level. It is interesting to underline that this landrace belongs to the Mesoamerican gene pool, suggesting that the presence of more nuclei within the same landrace could not be prerogative of the Andean gene pool. To explain the co-existence of different nuclei within a landrace, different scenarios can be hypothesized: (a) genetically different individuals were already present in the original material; (b) presently detectable different nuclei are the result of selection processes operated over the time by environment and/or farmers; (c) introduction of foreign materials, morphologically similar to the original one, has occurred.
3.3. Nutritional and Technological Seed Traits
The nutritional and technological seed quality of the “Badda” bean were investigated by analyzing nine traits. As shown in
Table 5, for all traits the range of variation relative to “Badda bianco” and “Badda nero” bean overlapped to a great extent. This suggests that the two “Badda” bean morphotypes have a comparable seed quality.
Table 5.
Grain quality traits. Seed composition values are referred to dry matter.
Table 5.
Grain quality traits. Seed composition values are referred to dry matter.
Work code | 100 seed weight (g) | Seed density (g mL−1) | Coat (g kg−1) | HI (%) | SI (% 24 h) | Moisture (g kg−1) | Protein (g kg−1) | Ash (g kg−1) | Cooking time (min) |
---|
5 h | 24 h |
---|
Badda bianco | | | | | | | | | |
PH05 | 56.2 | 1.20 | 59.2 | 45.4 | 106.4 | 100 | 111.2 | 258.0 | 47.7 | 41 |
PH06 | 44.2 | 1.07 | 57.6 | 2.5 | 80.1 | 92 | 108.7 | 243.8 | 41.0 | 42 |
PH07 | 46.5 | 1.26 | 56.0 | 4.4 | 87.4 | 136 | 110.4 | 232.7 | 40.6 | 42 |
PH08 | 52.2 | 1.13 | 52.8 | 15.2 | 89.7 | 92 | 101.7 | 245.7 | 46.1 | 45 |
Mean | 49.8 | 1.16 | 56.4 | 16.9 | 91 | 105 | 108.0 | 245.0 | 43.8 | 42.5 |
Std Dev | 5.45 | 0.08 | 2.73 | 19.82 | 11.11 | 21.01 | 4.33 | 10.36 | 3.59 | 1.73 |
Badda nero | | | | | | | | | |
PH09 | 45.7 | 1.27 | 59.1 | 12.5 | 87.0 | 127 | 110.2 | 242.0 | 42.0 | 38 |
PH10 | 59.1 | 1.09 | 57.0 | 59.7 | 85.5 | 94 | 106.5 | 243.1 | 38.8 | 44 |
PH11 | 44.1 | 1.10 | 59.3 | 8.2 | 87.9 | 75 | 112.5 | 224.8 | 40.9 | 42 |
PH12 | 41.7 | 1.11 | 60.5 | 5.6 | 90.4 | 100 | 111.3 | 222.7 | 43.0 | 48 |
PH13 | 59.3 | 1.18 | 57.1 | 30.2 | 92.4 | 123 | 103.1 | 249.4 | 45.8 | 50 |
Mean | 50.0 | 1.15 | 58.6 | 23.2 | 88.6 | 104 | 108.7 | 236.4 | 42.1 | 44.4 |
Std Dev | 8.54 | 0.08 | 1.51 | 22.53 | 2.75 | 21.49 | 3.86 | 11.91 | 2.59 | 4.78 |
The 100 seed weight, ranging from 42 to 59 g, is in agreement with its assignation to Andean gene pool, that generally contains large-seeded types. The coat content showed a low variation (52.8–60.5 g kg
−1), and was not related to seed size. It is well known that common bean seeds need a period of soaking before cooking, and that short soaking times are preferred by consumers. On the base of HI values recorded after 5 h of soaking, the “Badda” accessions can be divided in two groups (
Table 5). The first one was constituted by accessions having a very low hydration rate (HI ≤ 30%), while the second comprised the accessions PH05 and PH10 that had high hydration rates (HI ≥ 45%). The detection of low and high HI values within both “Badda bianco” and “Badda nero” bean indicated that hydration rate was not related to coat color. The detection of genotypes having high hydration rates could discourage the cultivation of those that do not possess this trait. However, a similar choice is questionable in relation to genetic resources safeguard, which is devoted to the conservation of the original genetic background of a landrace. The difference of hydration rate among the accessions disappeared when the soaking time was long as 24 h (
Table 5). At that time, seeds have absorbed as much water as almost their dry weight (HI > 80%). Moreover, prolonged soaking allowed a high increase of seed size (SI > 90%), with the only exception of PH11 accession (SI = 75%).
As predictable for large seeds, high cooking times were recorded for the “Badda” bean, though this trait was shown not to be significantly correlated to seed size. Mean cooking time value of “Badda nero” slightly exceeded that of “Badda bianco” (
Table 5). In order to estimate the nutritional quality of “Badda” bean, the protein content was determined. This trait varied little among the accessions (CV ≤ 5%), but is significantly correlated to 100 seed weight (R = 0.74,
p < 0.05). The highest value was recorded for the “Badda bianco” PH05, while the lowest one was that of the “Badda nero” PH12. Finally, ash content showed a low degree of variation, from 38.8 to 47.7 g kg
−1, and the calculated CV was ≤8.2%.
When the “Badda” seed quality traits were compared with those relative to 25 landraces traditionally grown in northeast Sicily, it appears a certain resemblance with the landrace named “Monaca” [
11]. In detail, the percentage of coat, protein, and ash were comparable, while 100 seed weight, cooking time and HI after 5 and 24 h of soaking, showed differences.
Seed morphology of “Badda” bean results attractive for consumers being a round large-seeded type with partially colored coat. It is widely accepted that only some landraces surviving on-farm possess quality traits that can justify their promotion as niche products. Consumers are attracted by visual, textural, and sensory seed traits. Nutritionists focused their attention on the evaluation of the main seed components, as well as on the minor ones having potential nutraceutical value. Data reported in this study, far from a complete nutritional evaluation of the “Badda” bean, represents a starting point for its promotion as niche product.