Description of the management of native varieties
The bean materials were found at altitudes ranging from 431 to 1 644 masl; that is, a difference of 1 233 m in altitude, between the Noche buena variety and those from Chocamán, Veracruz. This agrees with
Miranda (1967), who reported wild and domesticated varieties of
P. vulgaris between 500 and 1 800 masl in the Sierra Madre Occidental. The native bean varieties presented a biological condition called traditional cultivar, that is, they are considered creole and/or native varieties and were frequently observed in small plots managed as monocultures or associated with maize due to their climbing habit, such as the Noche buena, Negro milpa and Amarillo milpa varieties. In Mexico, the maize-bean association is common and it is possible to intercrop with other crops such as banana, coffee and sugarcane; mainly in agricultural farms with crop diversity
(Ngoya et al., 2023). The main reported use of beans in the study was for self-consumption, although the harvest of the Amatlán de los Reyes varieties is commercialized in the local market (Table 1). It is noteworthy that farmers maintain the tradition of selecting seeds as germplasm to be used in the sowing of the next agricultural cycle. According to
INEGI (2016), it was found that the varieties are cultivated under three land uses: 1) permanent rainfed agriculture (Chocamán), 2) semi-permanent rainfed agriculture (Amatlán de los Reyes) and 3) secondary arboreal vegetation of high evergreen rainforest for the municipality of Tezonapa, Veracruz.
Description of edaphoclimatic conditions
Environmental conditions affect the rate of development and agronomic behavior of bean cultivation
(Sozen et al., 2018; Maqueira-López et al., 2021). In this regard, it was found that bean varieties are cultivated under a semi-warm humid (A)C(m)(f), (A)C(m) and warm humid (Am) climate (
García, 2004), which comprise ranges between 18.4 to 25.5°C of mean annual temperature (Table 2) and maximum temperatures of the warmest and coldest month with 27.8 to 35.2°C and 8.36 to 16.1°C, respectively. Based on the above, the environmental interval where the bean expresses its productive potential is between 15 to 21°C, since sites with frost are not suitable for the species, while sites with conditions <4°C, are detrimental to germination, flowering and fruiting, while seed formation is affected when temperatures >35°C occur (
FAO, 2001). In this sense, the bean varieties in the present study show tolerance to the climatic extremes where they are cultivated, which can generate adaptations and evolve towards necessary characters that tolerate those extreme conditions.
Regarding humidity, the field records where the collected bean varieties were cultivated ranged between 1 827 to 2 610 mm of annual precipitation, while in the wettest month and the warmest month precipitation ranged between 338 to 526 mm and 38.67 mm, respectively (Table 2). This environmental condition allows the bean crop to develop under rainfed conditions; that is, with the residual moisture produced by the rains
(Ayala et al., 2021). One aspect that should be highlighted is that the precipitation range was wider than that reported for the species (Table 2), since the recommended optimum for sowing this species is between 1 600 to 2 500 mm, since precipitation below 1 000 mm and above 3 000 mm limit development and yield (
Ramírez-Jaramillo et al., 2023). For good crop development, a balance is required between the distribution and availability of rainfall in relation to the phenological cycle in the flowering, pod formation and grain filling phases
(Ugalde-Acosta et al., 2005), due to the demand for assimilates required by the reproductive structures
(Manjeru et al., 2007; Tosquy-Valle et al., 2014). However, the bean varieties studied showed their tolerance and ability to survive short periods of drought, which could increase the proline content generated by water stress, making it a resilient and adaptable crop to climate change
(Batool et al., 2023), so its management and conservation is necessary.
Regarding the edaphic characterization, the medium organic matter contents (1.98 to 2.83%), with moderately acidic to neutral pH (5.89-7.04), as well as variable concentrations and amounts of minerals such as Ca (0.49 to 0.69 cmol L
-1), OC (6.16 to 9.31 kg m
-2) and Na (0.13 to 0.24 cmol L
-1), present in the sites where the bean varieties are cultivated (Table 3). The edaphic conditions are within the favorable ranges for crop development, since the optimal acidity for cultivation ranges between 5.5 to 6.5 (
Ramírez et al., 2023); while the nitrogen and phosphorus contents are adequate for production
(Dorcinvil et al., 2010), this shows the species ability to adapt to a wide variety of edaphic conditions. However, it is likely that the high soil acidity (>5) has negative effects on the maturity, growth and yield of the bean varieties, reducing grain yield by 26% due to this factor
(Legesse et al., 2013). Similarly, reproductive fertility decreases in the plant due to low nutritional quality, which causes bean plants to develop thin stems and low seed weight, due to a decrease in Zn
(Rocha et al., 2020). In this regard, in plant breeding programs, some limiting parameters such as low soil fertility and acidity are taken as a reference; in this way, experimental genotypes with adaptation to strongly acidic soils (pH= 4.67) and low OM content (0.86%) are reported
(Tosquy-Valle et al., 2020); therefore, the materials evaluated in this study are considered feasible to be incorporated into a regional genetic diversity management and conservation program, as well as to increase exploration efforts for other bean varieties in other municipalities.
Qualitative characteristics of bean varieties
Qualitative characteristics have an impact on the
in situ conservation of bean diversity, such as the shape, color and size of the seed; meanwhile, the preference for varieties is linked to culture and geographic area
(Stoilova et al., 2013; García-Narváez et al., 2020). It was observed that the native varieties stand out for their seed shape in longitudinal section, which is reniform (50%) and elliptical (33.33%); flattened (50%) with respect to the seed shape in cross-section; seeds of a single color on the testa (83.33%) and classified as black, yellow, sulfur and red, in addition to different color of the hilum on the testa (100%). It is noteworthy that the Negro and Amarillo milpa varieties are characterized by a high luster on the seed, while the rest, including the commercial ones, report medium or absent luster (Table 4).
The importance of seed coat color is a useful characteristic to guide plant breeders on the morphological traits that need to be improved to increase productivity and ensure their adoption by farmers and consumers is viable
(Loko et al., 2018). In this sense, the ecotypes based on testa color in the
P. vulgaris varieties present in the three municipalities studied were yellow, red, cream, olive, purple, black, brown, gray and their different shades
(Jan et al., 2021), representing different bean morphotypes (Fig 2).
The correspondence analysis indicated that the qualitative characters evaluated in the bean varieties presented an accumulated variation of 58%. The Negro milpa variety presented the qualitative characteristics with the greatest dissimilarity, while the Pinto bean presented yellow-brown colorations that stand out compared to the other bean varieties; it is important to highlight the Güero Amatlán variety with brown coloration and narrow elliptical shape and which differs from the other varieties. The Negro Amatlán, Amarillo Milpa, Michigan and Noche buena bean varieties presented similarity due to seeds with yellow and black coloration (Fig 3).
Quantitative characteristics in bean varieties
Significant differences were found in the variables, number of seeds per pod and 100-seed weight (p≤0.01) in the bean varieties. The coefficients of variation were between 11.40 and 41.03% (Table 5), an interval that is considered an excellent indicator of the existing variability between populations and is an important tool in plant breeding (
Franco and Hidalgo, 2003;
Arteaga et al., 2019). High values were found for the NPODS and YPLAN traits and although they did not show significant differences (Table 5), these are sources of genetic variability that can be selected to develop varieties with desirable characteristics and conserve them through the promotion of their cultivation.
Variability was found among the accessions, with highly significant differences for all seed dimensions and indices (Table 6, p≤0.01). In this regard, seed length, width and thickness are morphological traits of importance due to their discriminatory power among bean populations (
Espinosa-Pére et al., 2015). Regarding the coefficients of variation, they were between 2.54 and 6.59, which demonstrates, on the one hand, the reliability of the data because the sample size reduced the error, as well as the normality and homogeneity (
Castillo, 2007).
Comparison of means in morpho-
agronomic variables of bean seeds
The Pinto variety stood out in seed length with 12.77±0.18 mm (Fig 4a), followed by the native variety Noche buena (11.10±0.23 mm), while Negro milpa, Amarillo milpa, Tlalchete, Negro and Güero Amatlán varied from 9.68 to 10.43 mm, dimensions similar to those found in the varieties from Costa Rica named as Mantequilla, Nica, Revuelto, Sesenteno, Turrialba and Vaina Blanca
(Oreamuno-Fonseca et al., 2023); likewise, they coincide with the length of genotypes from the western Himalayas of Mesoamerican origin (12.97±2.63 mm)
(Jan et al., 2021).
Likewise, the Pinto variety was characterized by a greater dimension in seed width with 7.35±0.15 mm, followed by Güero Amatlán, Negro Amatlán, Negro INIFAP, Negro milpa and Tlalchete with 6.35±0.16, 6.46±0.12, 6.34±0.17, 6.49±0.15 and 6.35±0.11 mm, respectively (Fig 4b), this group had lower values compared to the Creole Negro (6.60 mm) collected in the Hopelchén region in the state of Campeche, Mexico
Mex-Álvarez et al., (2021) and advanced lines (6.50±0.70 mm) from Peru
(Pumalpa et al., 2020). The varieties studied were superior (6.20±0.10 mm) to those reported in 57 creole bean accessions collected in the central region of the Republic of Benin
(Loko et al., 2018).
Also, The Pinto bean seeds had the highest value in their thickness (5.41±0.16 mm), while lower values were found in the Tlalchete variety at 4.30±0.09 mm (Fig 4c); however, the difference between these is reduced since in other reports such as that of
Sinkoviè et al., (2019) in which germplasm from Slovenia (953 accessions) presents thickness values ranging from 4.24 to 9.56 mm.
The comparison of means (Table 7) showed that for the case of the estimated indices directly related to seed shape, the maximum seed length/width index was observed in the Noche buena variety with 1.88±0.14. In this sense, all varieties presented values greater than 1.5, indicating that they have an elongated shape
(Oreamuno-Fonseca et al., 2023). The highest value in the seed width/thickness index which gives a reference on the cylindrical shape of the seeds was presented in the Tlalchete variety with 1.49±0.04. The results of both indices are similar to those presented as an average of 953 accessions of
P. vulgaris in which values of 1.69±0.28 and 1.24±0.16 are reported, respectively (
Sinkoviè et al., 2019). Regarding the seed length/thickness index, the highest value was recorded in the Tlalchete variety and the lowest in the Amarillo and Negro milpa varieties with 2.41±0.05, 2.05±0.10 and 2.05±0.03, respectively.
The number of pods was similar across the bean varieties, ranging from 15.60±0.58 to 28.62±1.12, values that are relatively low compared to the French bean variety, which reported between 59.2±9.76 and 71.0±9.07 under different population densities (
Sundar and Lal, 2022). Additionally, the Amarillo milpa bean variety reached the highest number of seeds per pod, in this case with 7.33, higher than the other varieties. Regarding the weight of one hundred seeds, the Pinto variety stands out, with a value of 33.41 g, lower than the Pinto Saltillo (40.99±1.99 g) cultivated in its area of adaptation
(Corzo-Rios et al., 2020), which is probably due to the high values in the parameters of seed length, width and thickness, For the native varieties and the Michigan commercial grain, these presented a weight of 18.80 to 20.74 g (Table 7). According to the above, small seeds (<25 g per 100 seeds) and the presence of 6 to 8 seeds per pod indicate a strong resemblance of the varieties to the Mesoamerican race
(Singh et al., 1991). Likewise, the seed weight values (WHSE) were lower than the advanced and commercial black bean lines (21 to 26 g) generated by the National Institute of Forestry, Agricultural and Livestock Research under acidic soil conditions, reflecting the genetic improvement of the materials under stress conditions
(Tosquy-Valle et al., 2020); additionally, these values were lower than those achieved in seven native varieties under Mediterranean conditions (29.25 to 39.69 g)
(Kargiotidou et al., 2019). However, WHSE of up to 98.39 g has been reported (
Sinkoviè et al., 2019); these differences are attributed to both the variety and climatic conditions (
Sánchez-Reynoso et al., 2020). The Noche buena variety was not considered due to germination problems and lengthening of the cycle. Meanwhile, the similar yield between the native varieties, the grains and the improved variety show climatic plasticity, highlighting the Negro milpa and Tlalchete varieties with yields equal to Negro and Güero Amatlán, the latter as varieties adapted to the experimental site.
