Description of the study area

This work was carried out in the Spring Summer 2014 cycle in the Barrio de Guadalupe, Municipality of San Mateo Atenco, State of Mexico, Mexico, located at 99⁰ 31’ 10’’ North latitude and 99° 34’ 05’’ West longitude, at 2 570 masl. The predominant soils are of alluvial origin and 87% of its surface are of the feozem type. The common climate is C (w₂) (w) b (i’’) g; that is, temperate sub-humid, with long summer and winter rain. Its average temperature varies from 10 to 12 °C and the precipitation ranges between 700 and 900 mm (^{García, 1988}).

Genetic material

39 cultivars of faba bean, 35 of these were collected in the Mexiquenses Municipalities of Acambay, Jocotitlan, Calimaya, Mexicaltzingo, Santa Cruz Atizapan, Santiago Tianguistenco, Almoloya del Río, Toluca, Zinacantepec, Metepec, Lerma and San Felipe del Progreso were considered. The other four were formed by the Agricultural, Aquaculture and Forestry Research and Training Institute of the State of Mexico (ICAMEX). In the Table 1 shows the identification code, the place of collection, the characteristics of the seeds, the altitude and the geographic coordinates of the municipalities where they were collected.

Experimental design and size of the plot

The 39 cultivars were established in the field in a randomized complete block design with three replications. The plot consisted of three rows of 4 x 0.8 m and the central furrow was the useful plot (3.2 m²).

Agronomic management

The preparation of the land was mechanical. Planting took place on April 20, 2014. Organic fertilization consisted in applying 2.5 t ha^-1 of cattle manure. Two irrigation assistance was provided after sowing (May 7 and June 7), two weeds were made (May 17 and June 8) and weed control was manual. The harvest was made after the genetic material reached physiological maturity.

Registered variables

Ten plants were chosen as a sampling unit in each of the useful experimental units and 23 variables were recorded: 12 qualitative and 11 quantitative. The quantitative variables were number of stems (NT), number of knots (NN), number of leafs (NF0), percentage of flowering (PF), number of flowers per node (NFN), number of pods per plant (NVP), pod weight (PVP, g), number of seeds per pod (NSV), weight of 100 seeds (P100S, g). The seed weight was recorded by experimental plot (PSP) and with this the grain yield per hectare (RHA) was estimated. The qualitative variables registered with the technical guide for the varietal description of faba beans of the national service of inspection and certification of seeds (SNICS, 2000) were: habit of growth (HC), height of plant (AP), coloration of anthocyanins (CA), color of the foliage (CF) extension of the anthocyanin coloration in the flower (ECA), presence of the melanin spot in the wing (PMM), color of melanin spot in the wing (CMMA), melanin spot in the standard (MME), anthocyanin coloration on the standard (CAE), pot size (PV), degree of pod curvature (GCV), green pod coloring intensity (ICVV), seed shape (FS), color of the seed (CS) and presence of hilium (PH).

Statistical analysis

An analysis of variance was made, and its mean squares were used to calculate the components of variance and broad-spectrum heritability (H²), the latter considered as an estimator of the genetic variability between accessions (^{Pérez et al., 2007}). A comparison of means between cultivars was also performed with the Tukey test (α= 0.01). The arithmetic means of each cultivar for the 11 quantitative variables were used to obtain a data matrix: the cultivars were assigned to the rows and the values of each variable to the columns. With this matrix we obtained the analysis of the main components (ACP, ^{Sánchez, 1995}) and conglomerates (method of the unweighted arithmetic mean, UPGMA Method). Both analyzes were performed with the statistical analysis system Statistical Analysis System (^{SAS, 1988}), but the biplot graph was made with Microsoft Excel 2010, using the scores of the first two main components (^{Pérez et al., 2009}).

Variance analysis

In the present study (Table 2) it was observed that the effects between cultivars were highly significant in number of knots (NN), percentage of flowering (DAF), number of flowers per plant (NF), pods per plant (NVP), weight of pod per plant (PVP), number of seeds per pod (NSV), weight of 100 seeds (P100S), weight of seed per plot (PSP) and yield per hectare (RHA). These results are similar to those reported by ^{Yahia et al. (2012)} and allow to deduce that for these variables the identification of outstanding genetic material is possible.

Components of variance and heritability

The components of variance (CV) are evaluated in terms of response to the selection and the use of the moment method, calculated with its linear functions, allows estimating the genetic variability (H²) that exists between cultivars when using the mean squares of the analysis of variance (^{Shimelis and Shringani, 2010}). In the present study it was observed that in the majority of quantitative traits the H² varied from 30.7 to 99.8% (Table 3).

In quantitative traits, such as seed yield, it is desirable that H² values are greater than 50% (^{Filippeti and Ricciardi, 1988}; ^{Khare and Singh, 1991}; ^{Bakheit, 1992}) to contribute to a greater response to selection or to optimize the genotype x environment association. ^{Alan and Geren (2007)} reported heritabilities less than 50% in plant height (29%), number of stems (17.6%), pods per plant (3%), seeds per pod (47%) and weight of 100 seeds (30%).

Principal component analysis

In the biplot that was constructed with the cultivars and the variables, it was observed that the main components 1 (41.6%) and 2 (23.6%) explained 65.2% of the original total variation (Figure 1).

Figure 1 Interrelations between 39 faba bean cultivars (in number) and 11 agronomic variables (in letter).  

^{Sánchez (1995)}; ^{Pérez et al. (2009)} mentioned that this percentage is desirable to interpret reliably the approximate correlations that exist between both. The dispersal of the 39 cultivars in the four quadrants of the biplot suggests that there is genetic variability that is available to initiate a new breeding program. Phenotypic variability was detected in 39 collections faba bean was higher in NN, PF, NF, NVP, PVP, P100S, PSP and RHA. Collecting 8 (T8) from Tixmadejo, Municipality of Acambay, he showed a yield of 4.16 t ha^-1, more than the national average value is 0.99 t ha^-1. T8 also showed superiority in number of knots (11.76), flowering percentage (90%) and pod weight per plant (152.83 g), followed by P5 (Pueblo Nuevo, Acambay) and P27 (Santa Cruz Cuauhtenco, Zinacantepec) (Table 4).

These results are similar to those observed by ^{Neal and Mcvetty (1983)} who concluded that 68.5 to 76.4% of the variability in seed yield is due to the number of pods produced per plant (^{Singh et al., 1987}; ^{De Costa et al., 1997}; ^{Chaieb et al., 2011}), to seeds per pod (^{Alan and Geren, 2007}), to the weight of 100 seeds (^{Baginsky et al., 2013}) and to the size of the seed (^{Al-Refaee et al., 2004}; ^{Mohammed et al., 2013}). Although the number of pods per plant has been considered by many authors as the main source of variation in the yield of the faba bean crop (under very favorable conditions there is an excess of pods and also of abortions), the number of seeds per square meter (depending on the number of pods) is the factor that most affects performance.

Conglomerate analysis

In the dendrogram of Figure 2, when cutting at an average distance between conglomerates of 0.8 units, four groups were identified. In group IV only cultivar 24 was observed, from Santiago Tianguistenco, with significant values in NN, NFo, NFP and P100S, it was the highest with respect to all populations and had 3.53 t ha^-1.

Figure 2 Grouping of 39 faba bean cultivars based on 11 agronomic variables. Method of grouping unweighted pairs with arithmetic means (UPGMA method).  

These results are similar to those found by ^{Alan and Geren (2007)} and ^{Baginsky et al. (2013)}, who commented that these characters have an important influence on performance.

In group II, cultivars identified as T7 and T29, from Los Reyes, Jocotitlan and San Isidro de Metepec variety, respectively, showed desirable characteristics in NT, NFo, PVP and produced more than 3 t ha^-1, group I was made up of T1, T32, T9, T36, T5, T8, T2, T27, T4, T30, T3, T26, T31, T17, T20 and T25, the first 13 belong to the northern and central part of the Valley Toluca-Atlacomulco, the last three to the south-east zone, in terms of the agronomic traits evaluated is the most important group because it agglomerates the best populations. In contrast, in group III the rest of the cultivars were classified with the lowest average values. Such results coincide with ^{Duc et al. (2010)}, who commented that the response of genotypes is differential, since the adaptation to the environment and its interaction with it is determinant in a desirable phenotypic expression.

Qualitative characteristics

The identification of genetic variability between and within cultivars allows selecting varieties with desirable agronomic characteristics and contributes to the partial increase of the production and quality of the faba bean seed. The varietal description allows an easy and rapid discrimination between phenotypes (^{Franco and Hidalgo, 2003}), they are generally considered highly heritable characteristics, easily detected with the naked eye and with little or no variation through the environments (^{Pérez et al., 2007}). In this investigation, phenotypic differences were observed in the 39 populations in determinate (D) growth habit (HC) and gray-green color, except for T29 (San Isidro) that was green and T35 that was bluish green, 12 cultivars showed anthocyanin coloration in foliage, the extent of anthocyanin coloration was large only in T8, in 23 populations was medium and in 15 small, the presence of melanin spot was recorded by all populations, the color of the spot was brown, there was presence of melanin spot but with absence of coloration (Tables 5 and 6).

The pod size was semi-erect in 26 populations, erect in eight and horizontal in five, this is important for producers since an recto angle of the pod favors physiological maturity, mechanized harvest and resistance and tolerance to drought (^{Gresta et al., 2009}), there was no degree of curvature in 24 populations, two were of medium curvature and 13 weak, the green intensity of the pod was medium in 20 populations, weak in 13 and strong in six. The shape of the seed was ovate in 21 populations, oblong in 15, elliptical in two and only in T29 was rectangular, the color of the seed was light brown in all the populations except in T30 that was marbled, all the materials presented hilium (Table 7).

The morphological characters of qualitative type, such as habit of growth of the leaves and flowers, among others, are those that allow the visual identification of the genotypes in the field, but a greater or lesser uniformity and adaptation of the genotypes will influence their use final by the producers (^{Madriz and Luciani, 2002}).