Introduction

Pumpkin (Cucurbita spp.) along with maize (Zea mays) and beans (Phaseolus vulgaris) were among the first crops domesticated by man (^{Smith, 1997}). Mexico is a major centre of origin, domestication and diversification of the genus Cucurbita (^{Whitaker, 1968}; ^{Acevedo, 2009}). In the country, numerous varieties of four of the five domesticated species are cultivated in Mesoamerica: Cucurbita pepo, C. moschata, C. argyrosperma and C. ficifolia (^{Lira-Saade, 1995}).

Nationally, in 2012, 65 965 ha were planted; in Nayarit, in the same year 1524 weres cultured, of which 9.7% were used for vegetables, 23.5% for use in pastry and 66.8% for seed extraction (^{SAGARPA, 2013}).

Farmers use different strategies to ensure the survival of the family throughout the year, due among other factors to the prevailing agro-climatic conditions, such as rainfall, which have highly random behaviour in quantity and distribution. In order to overcome this randomness, the farmers plant different species and local varieties, which are characterized by different production cycles and habits of development (^{Chavez et al., 2004}). Nevertheless; in most of Mexico, local varieties, including squash have disappeared for lack of continuity of use to be preferred by most productive new selections; some remain isolated and others require characterization, selection and improvement to identify outstanding features (^{Villanueva, 2007}).

Morphological characterization is the first step for improving crops and conservation programs; morphological characteristics have been used to study the genetic diversity, cultivated plants identify and conserve genetic resources (^{Onamu et al., 2012}).

In Mexico, there have been important work on morphological characterization and genetic diversity in Cucurbita; ^{Montes and Eguiarte (2002)}; ^{Canul et al. (2005)}; ^{Rodríguez-Amaya et al. (2009)}; ^{Cerón et al. (2010)}; ^{Jacobo-Valenzuela et al. (2011)}; Moreover, ^{Mera et al. (2011)} conducted a diagnostic document cultivated species of Cucurbita where the current distribution and use in Mexico is described. Internationally these investigations have been made by ^{Montes et al., (2004)}; ^{Ferriol et al. (2004)}; ^{Tsivelikas et al. (2009)}; studies show varying degrees of diversity between and within the species.

Although there have been several studies, these accessions have used much of the country, but contain few examples of the areas under study and not expose her wealth that are available in some areas in particular.

In Nayarit, various species of pumpkin are cultivated; in the region of the coast and valleys are cultivated on a large scale, mainly to be sent to market; while in the mountainous area of the State is grown for consumption along with maize and beans and are an important part of their diet, which could be improved and complement the nutrition due to its characteristics as a vegetable and the advantage of consuming its seeds.

The aim of this study was to establish the level of morphological diversity in four species of pumpkin grown in Nayarit; and the definition of the characteristics of more descriptive value for these species.

Materials and methods

Sites collections of accessions

From the year 2009 started with the collection of accessions in the coastal and mountainous area of Nayar and in 2012 was collected in the north and south of the State; accessions were obtained from 25 sites (Table 1 and Figure 1), which consisted in obtaining fruits and seeds producers in houses, fields and local markets.

Table 1 Geographical location of the collections sites of pumpkin species (Cucurbita spp.) in municipalities in the State of Nayarit. 

*C. mos = Cucurbita moschata, C. fic = Cucurbita ficifolia, C. pep = Cucurbita pepo y C. arg = Cucurbita argyrosperma. Se utilizó además el hibrido comercial tipo Zuchini (C. pep28) como material contrastante al resto de las accesiones.

Figure 1 Geographical location of the collections sites of accessions of pumpkin species grown in Nayarit. 

Results and discussion

The three principal components (PC) explained 53.3% of the total variability of the evaluated characteristics (Table 2). CP1 was the most important with the highest percentage of participation (26.75%). Table 2 shows in the same variables that most influenced the variability of the three main components are recorded, with those who expressed the greatest correlation values; therefore, the CP1 was associated with fruit characteristics (height, width and colour of the flesh), seed characteristics (thickness and number of seeds per fruit) and leaf size. These results agree with the findings of ^{Balkaya et al. (2010)}, ^{Delgado-Paredes et al. (2014)} and ^{Azurdia (1999)}, who mentioned that diversity pumpkin is cultivated in morphology, size of fruits and seeds, as well as colour and flavour of mesocarp.

Table 2 Values and vectors-features on three principal features components of 43 features to 33 accessions of pumpkins (Cucurbita spp.). Mexpan joint analysis and Xalisco, Nayarit. Spring-summer 2012. 

*Indica los mayores valores positivos señalados en negritas para cada componente.

Table 2 Values and vectors-features on three principal features components of 43 features to 33 accessions of pumpkins (Cucurbita spp.). Mexpan joint analysis and Xalisco, Nayarit. Spring-summer 2012 (Continuation). 

*Indica los mayores valores positivos señalados en negritas para cada componente.

CP2 was associated with characteristics and dimensions of the peduncle (base thickness and thickness of the middle) and seed characteristics (length and weight of 100 seeds). In the basal characteristics CP3 fruit shape and colour of the flower had the highest correlation values. Thus, the morphological characteristics of fruit, seed and stem were determinants of the diversity shown by the different accessions pumpkin.

The graphical representation of the distribution of accessions studied pumpkin, the CP1 (Figures 2 and ³) indicate that the population distributions on this axis is related to the largest correlation values concerning the evaluated characteristics, so stocks 17, 10, 25, 15 and 27 of C. moschata on the positive end of the axis, the recorded heaviest and widest fruit pulp colour salmon, larger number of seeds, seed thickness and larger leaf; while those located on the negative end of the shaft (C. argyrosperma, C. ficifolia and C. pepo) showed lower values in the same variables. In this regard, according to ^{Montes (1991)}, C. moschata is characterized by the amount of seed produced superior to C. argyrosperma and C.ficifolia, and in the same sense as shown in C. pepo in this study.

Figure 2 Dispersion of 33 accessions based on two major components. Mexpan locations and Xalisco, Nayarit. 2012. 

Figure 3 Sense-vector magnitude and characteristics in accessions 33 based on two major components. Mexpan set and Xalisco, Nayarit analysis. Spring-summer 2012. 

Considering the axis of CP2, the management of accessions populations located in the positive part of the axis, thereof have the characteristics of more values in features and dimensions of the stem (thickness of the middle and basal part), outstanding arg-07, arg-19, arg-23, arg-04, arg-32 and arg-12, which showed enlarged and flared stems not excel in characteristics of greater length and weight of 100 seeds; characteristic of this species to have larger seeds.

In the end portion of the negative axis, the accessions of lowest value (C. pepo, C. moschata and C. ficifolia), which showed the lowest averages in terms of seed characteristics (length and weight of 100 seeds were placed), hard stems and flared with smaller at the bottom and middle. The absence of accessions in the central axis (Figure 2) suggests that the distinctive features of the species are widely marked by the features mentioned and that distinguish them.

The cluster analysis (Figure 4) formed six groups with 33 accessions of pumpkin with Euclidean distance of 0.06. Group I was formed with the accession C. pepo-28 used as contrast control (commercial hybrid), as some of its salient features were of erect habit (tree), more precocious and no earrings, no common to other accessions.

Figure 4 Dendrogram generated with 33 accessions of pumpkin (Cucurbita spp.) grown in Nayarit. Using the Ward method. Mexpan set and Xalisco, Nayarit analysis. Spring-summer, 2012. 

Group II was formed by three accessions of the species C. pepo (06, 14 and 21) that had low values in weight and width characteristics of fruit, stems and fewer seeds per fruit and cream flesh colour, with lower values than the other accessions (D, E and F Table 3 and Figure 4).

Table 3 Values of descriptive statistics for quantitative and qualitative characteristics of groups based on the dendrogram formed for pumpkin accessions in Nayarit. 

¹Grupo. ²Estadístico (=medida, S=desviación estándar). ³GPMP= grosor de la parte media del pendúnculo; GBP=grosor de la base del pendúculo, AF= ANCHO DE FRUTO; PF= peso de fruto; NSF=número de semillas por fruto; LS= longitud de semilla; GP= grosor de semilla; P100S= peso de 100 semillas. TH= tamaño de hoja (1: pequeña; 2: intermedia; 3: grande); CP= características del pedúnculo (1: duro no acampanado; 2: duro y acampanado; 3: no acampanado agrandado por corteza dura; 4: no acampanado agrandado por corteza suave); CPF= color de la pulpa del fruto (1: blanca; 2: verde; 3: amarilla; 4: anaranjada; 5: salmón).

Accessions in the group III belong to C. ficifolia 22, 02 and 26, just like the previous group, presented lower values of distinctive character in the current study allowed us to distinguish groups of accessions, these accessions had small leaves and white pulp of the fruit, typical of the characteristics species to which they belong. The morphological data agree with those reported by ^{Delgado-Paredes et al. (2014)} in shape and colour of fruits cream coloured green and soft and smooth texture (Figure 4: J and K).

Concerning the group IV, all accessions belonging to C. argyrosperma (Figure 4 G, H and I), they showed differences in length and seed weight (Table 3), which shows improvement processes by producers for these features as accessions correspond to places where it is produced for this finish; which is consistent with that reported by ^{Canul et at. (2005)} and ^{Rodríguez-Amaya et al. (2009)} who pointed out characteristics such as large seeds and fruit gross margin of small to medium size for this species.

The accessions of group V and VI belong to C. moschata (Figure 4: A, B and C), both groups differ in weight and width of fruit, the group V showed the highest values of these characteristics; with respect to the group VI, previous values were on a smaller scale (Table 3), both groups had salmon flesh; Moreover, a characteristic feature within both groups of this species is fruit shape; the group V presented fruits of globular or flattened with ribs, while the sixth had curved shapes (of crop) and in both groups the number of seeds per fruit showed the highest values.

Figure 5 Accessions of squash grown in Nayarit: Cucurbita moschata (A, B and C), Cucurbita pepo (D, E and F), Cucurbita argyrosperma (G, H and I), and Cucurbita ficifolia (J and K). 

Conclusions

We found morphological variability between and within the species of Cucurbita, establishing the diversity of species that are grown in the State of Nayarit. C. moschata showed the highest diversity, followed by C. argyrosperma, C. pepo and C.ficifolia. The characteristics that contributed on a larger scale for explaining the diversity found and that also allowed to distinguish between species were for C. moschata, it was quite contrasting to other species regarding leaf size, thickness and number of seeds, weight and width of fruit, C. argyrosperma in features and dimensions of the stem, width, length and weight of 100 seeds, C. ficifolia in colour of the fruit pulp and C. pepo weight and dimensions of fruit and seed with the lowest values than other species under study.