Morphophysiological characterization in artichoke accessions aimed at selecting materials for in natura consumption

A morphophysiological characterization of 19 accessions within an artichoke germplasm collection was conducted with the aim of determining genetic variability and to select materials suitable for in natura consumption to be used in genetic breeding. The collection was composed of commercial accessions, materials collected in South Brazil, and of foreign origin. Twenty quantitative, five multicategorical and two binary traits were evaluated. Quantitative data were submitted to a multivariate analysis. Genetic variability was observed for almost all characteristics. The traits with the greatest relative contribution to genetic divergence, which accounted for 79.54% of the variability, were as follows: the thickness and diameter bottom, bottom fresh mass/head fresh mass ratio, external bract length, bracts base, leaves and primary head height and plant diameter, primary head diameter and bracts base thickness. A cluster analysis revealed four groups. Group I aggregated the accessions with characteristics for fresh consumption. The best accessions were Romanesco 1, Green Globe, and Improved Green Globe, all of which exhibited plants with a greater fresh mass, larger primary head diameter, greater fresh mass and bottom diameter, circular head shape, no thorns, round head tip and desired color, that are important traits for selection of superior genotypes for in natura consumption.


Introduction
The artichoke is a vegetable consumed in natura or industrialized.For in natura consumption, the fleshy bracts and the floral receptacle form the edible part of the artichoke.This crop also contains interesting medicinal properties, which benefit gastrointestinal, hepatic and cardiac activities.Because head contains high polyphenol and antioxidant levels (LOMBARDO et al., 2010;MOGLIA et al., 2010), the artichoke has been considered a functional food (CECCARELLI et al., 2010).This crop is also being studied as a new alternative for energy generation (solid biofuel) and Acta Scientiarum.Agronomy Maringá, v. 34, n. 4, p. 431-437, Oct.-Dec., 2012 as a forage plant in animal feed (IERNA;MAUROMICALE, 2010).Thus, the purpose of the artichoke can be considered in three areas: as a nutritional source, as a pharmaceutical and bioenergy source, and as an innovative crop for sustainable and economic development.
Italian immigrants first introduced the artichoke to Brazil.Currently, the State of São Paulo is Brazil's largest producer of artichokes, and the most widely grown in this region is cv.Roxa de São Roque, destined for in natura consumption (FILHO et al., 2009).In Southern Brazil, the cv.Nobre is cultivated exclusively for industrial purposes, and the genotypes adapted to the environmental conditions and possessing favorable characteristics for in natura consumption are scarce.
The genetic variability in this culture allows for the selection of superior genotypes that can be used as progenitors in the creation of hybrids and the development of new varieties (COINTRY et al., 1999) as well as in cloning because this species might be sexually or asexually reproduced.Therefore, knowledge of the genetic variability in a population with regard to characters of agronomic interest is fundamental to use the characters as selective criteria (ASPRELLI et al., 2001;CRAVERO et al., 2002).
The characterization is based on morphological descriptors, which enable the characterization and differentiation of accessions.For the artichoke, 57 vegetative, phenologic, and yield traits were established as descriptors for the characterization of cultivars (UPOV, 2001).
To satisfy the demands of the consumer market, the selection of plants for genetic breeding demands an analysis of a large number of characteristics (CRAVERO et al., 2002).A multivariate statistical analysis fulfills this need because it allows for an estimation of the genetic divergence between the accessions and their division in groups according to the degree of similarity among them (CRUZ, 2006).
The objective of this study was to conduct a characterization of the artichoke germplasm to determine the genetic variability and select accessions with the desirable traits for in natura consumption.

Material and methods
The evaluated germplasm collection was composed of accessions from the domestic gardens of rural properties in Rio Grande do Sul State, Brazil, and from commercial varieties and some foreign materials, which were established by seeds (sexually propagation) or buds (asexually propagation).The treatments were composed of 19 artichoke accessions (Table 1), represented by individual plants with varied numbers of replications.The experimental design used was a completely randomized design, with 0.60 x 1.00 m spacing between plants.
The study was conducted in Passo Fundo, Rio Grande do Sul State -Brazil at 28°15' S, 52º24'W, 687 m of altitude, between April and December, 2009.
The accessions were evaluated when the primary head (capitulum or inflorescence) reached commercial stage, D stage (FOURY, 1967), and they were characterized according to the artichoke descriptors established by Upov (2001).Twenty quantitative, five multicategorical, and two binary traits were used.The quantitative characteristics were the plant height, measured from the base to the top of the primary head; the plant diameter, measured from one end to the other of the lower leaf level; the floral peduncle length, measured from the plant base to the primary head insertion; the main stem diameter, measured 10 cm from the primary head insertion; the number of leaves at harvest; the length of the biggest leaf; leaf width, measured from the middle part of the blade; the number of lateral buds formed after harvest; the fresh mass, primary head length and diameter; the outer bract length; the length, width and thickness of the edible parts of the bracts (bract base selected from the fourth row of the main head); the thickness, fresh mass and diameter of the bottom; the number of secondary heads per plant; and the ratio of bottom fresh mass to primary head fresh mass.The multicategorical characteristics were as follows: (1) the primary head shape: circular,  The quantitative data were submitted to a variance analysis and then followed by a multivariate analysis in which the Mahalanobis distance matrix, the relative contribution of different characters towards genetic divergence and, using Ward's method, a dendrogram were obtained.The results of a grouping analysis were compared through an analysis of variance.The averages were then compared using Tukey's test (which has a 5% error probability), in which the groups constituted the treatments and the accessions constituted the replication.The statistical analyses were performed with Genes (CRUZ, 2001) and COSTAT (COHORT SOFTWARE, 2003) statistical software.For the multicategorical and binary variables, no statistical analysis was applied; only the accession characterization was conducted.

Results and discussion
For 19 of the 20 quantitative traits evaluated, the variance analysis indicated differences between the accessions (p < 0.05 and p < 0.01).The leaf number was the only trait that did not differ between them (data not shown).These results indicated the existence of a genetic variability in this collection.
Besides this pioneering work in Brazil, other studies referring to morphophysiological and molecular diversity were performed in the Mediterranean regions (the center of artichoke diversity), showing intra-and inter-population variability (CRINO et al., 2008;MAURO et al., 2009;PORTIS et al., 2005).Genetic diversity has also been observed in countries where this crop has been introduced, such as in Argentina (ASPRELLI et al., 2001;COINTRY et al., 1999;CRAVERO et al., 2002).
The morphological characters that contributed the most to genetic diversity in this study were bottom thickness, bottom fresh mass/head fresh mass ratio, bottom diameter, outer bract length, primary head length, bract base length, plant diameter, leaf length, primary head diameter, bract base thickness and plant height.These characters represented 79.54% of the variability present in the germplasm (Table 2).Many of these traits, such as bottom diameter and thickness, bottom fresh mass/head fresh mass ratio, primary head length and diameter, bract base length and diameter, are involved in the head quality for in natura consumption.
However, Mauro et al. (2009) found that the major trait responsible for the morphological variation among the Sicilian ecotypes was primary head fresh mass.Asprelli et al. (2001) reported that the variables associated with head shape and fresh mass, bottom fresh mass and market yield were the main traits explaining the existing variability in one artichoke clone population in Argentina.
The greatest diverging accessions were Romanesco 1 and Israel 4, with a Mahalanobis distance (D 2 ) = 131.68,and the most similar accessions were Green Globe and Improved Green Globe (D 2 = 1.40).Such similarity might be explained by the fact that cv.Improved Green Globe was derived from the selection within cv. Green Globe.The dendrogram showed the clustering of four groups (Figure 2).The cluster analysis is a suitable tool for evaluating inter-relationships among the variables, allowing identification of genotypes with high homogeneity and allowing their separation into different groups (AMARAL JUNIOR et al., 1996;ARIYO, 1993;SUGIYARTO et al., 1984).For the artichoke, this tool has been used in genetic variability studies in clone population, self-pollination families and hybrids (ASPRELLI et al., 2001;CRAVERO et al., 2002;MAURO et al., 2009).
The variance analysis between groups showed the existence of diversity for the most quantitative characteristics (p < 0.01), with the exception of leaf breadth and bottom thickness (Table 3).In each row, the averages are followed by the same letter and do not differ from one another in Tukey's test (with a 5% probability of error).*Plant height (PH), plant diameter (PD), flower peduncle length (FPL), main stem diameter (MSD), number of leaves per plant (NL), leaf length (LL), leaf width (LW), lateral buds number (LBN), primary head fresh mass (PHFM), primary head length (PHL), primary head diameter (PHD), bract base length (BBL), bract base width (BBW), bract base thickness (BBT), outer bract length (OBL), bottom thickness (BT), bottom fresh mass (BFM), bottom diameter (BD), number of secondary heads (NSH), ratio of bottom fresh mass to and primary head fresh mass (RBH).
Group I was composed of accessions with a higher fresh mass and primary head diameter as well as a higher fresh mass and bottom diameter compared to other groups.The fresh mass of the primary head is a good productivity indicator because if the fresh mass and the head diameter are higher, then the bottom is larger, which is an important feature for in natura consumption (Table 3).Thus, Green Globe, Improved Green Globe, Romanesco 1 and Violet de Sicilia could all be selected for in natura consumption.However, the other two accessions belonging to this group, although exhibiting features similar to the other accessions, should be discarded because they possessed thorns.
Group II differed from the other groups because it exhibited a higher primary head length and outer bracts length.The accessions from this group also exhibited an average lower plant height and floral peduncle length (Table 3).
Group III differed from the three other groups because it exhibited a greater bottom fresh mass and primary head fresh mass ratio.Group III also differed from Groups I and II because it demonstrated a greater bract base thickness.However, when compared to Groups I and II, Group III showed a smaller diameter of the main stem, primary head length, bracts base width, and outer bract length (Table 3).This group included only accessions of unknown identity (Espumoso 1, 2 and 3, Erechim, Colorado and Passo Fundo 2), which demonstrated lower values for the main characteristics of selective interest, and should be discarded.
Group IV contained accessions with average values lower than those of group I for main stem diameter, primary head fresh mass and diameter as well as bottom fresh mass and diameter.It also had lower values than those of groups I and II for primary head length, base width and outer bract length.
In a study performed by Cravero et al. (2002), the cluster analysis resulted in the formation of four groups of families evaluated in Argentina, and the best cluster joined together plants presenting a high number of secondary head, primary head fresh mass and diameter and market yield.
The selection of artichokes for in natura consumption is based on characters related to head dimension, bract base, and floral receptacle (bottom) because these are the edible parts of the plant.Therefore, in this study, the accessions of Group I could be used in hybridization programs aiming to develop varieties or for in vitro cloning because these accessions demonstrate such traits.Additionally, accessions belonging to Group III, due to exhibiting a greater bottom fresh mass and head fresh mass ratio, bract thickness and a higher number of secondary heads, could be included in crossing blocks aimed at the obtention of improved genotypes for these characteristics in the long term.
In addition to the quantitative characters, the qualitative, multicategorical, and binary characteristics are important traits to be considered in the selection of materials for in natura consumption because they also contribute to the product quality (BONASIA et al., 2010).With regard to the primary head shape (Figure 1), most accessions exhibited circular heads, which is a desirable characteristic for in natura consumption (Table 4).Heads of elliptical, oval and large transverse elliptical shape were also found.No triangular heads were observed in the collection.A greater variation was observed in relation to the primary head tip shape, with accessions having been found in the four classes described by the Upov (2001).In the collection, 58.5% of the plants exhibited a depressed shape of the primary head tip, which is an undesirable feature in materials destined for in natura consumption because it enables the infiltration of water and microorganisms, resulting in the compromise of the inner bracts and a consequent diminution of the head quality.The flat and rounded head tip shape are more suitable for commercial use.The accessions presenting these traits are listed in Table 4. Figures 3a and b present details of the head tip shape of flat and depressed types.In relation to the bract tip shape, the accessions demonstrated acute, flat and emarginated shapes (Table 4).Most accessions presenting a pointed bracts tip had thorns.
According to Mauromicale and Copane (1989) and Macua Gonzáles and Arce Tudanca (1996), the genetic improvement of artichokes for in natura consumption should meet market demands.Therefore, the external color of the bract is very important because in countries such as France, Italy, Argentina, and Brazil, violet colored heads are preferred.In the collection, violet-striped green and green were the colors found in most accessions (Table 5).

Table 3 .
Trait average and standard deviation for the four groups formed through a clustering analysis.

Table 4 .
Characterization of artichoke accessions based on multicategorical characters.