Multivariate analysis and clustering reveal high morphological diversity in Tunisian autochthonous grapes ( Vitis vinifera ): insights into characterization, conservation and commercialization

摘要

Aim: To characterize autochthonous grapevine cultivars from a national germplasm collection, to estimate the phenotypic diversity among and within the cultivars, and to identify the traits that contributed to cultivar heterogeneity.Methods and results: Seventy major ampelographic descriptors comprising shoot, leaf and fruit traits were investigated to determine the overall degree of polymorphism among 61 autochthonous Tunisian grapevine genotypes. Based on the correlation values obtained between the characters, all descriptors must be considered for the characterization/clustering of the grapes, of which 12 descriptors were identified as the most important. Based on principal component analysis (PCA) and hierarchical cluster analysis (HCA), all cultivars were discriminated and high morphological variation was observed among the accessions. ANOVA demonstrated that most of the morphological variation was found within (89.31 %) rather than between the groups (10.69 %). The Khalt Bouchemma Gabès, Blanc 3 and Blanc 2 genotypes were identified as the barycentres of the groups, representing all the morphological variation observed within autochthonous grapes in Tunisia. These genotypes exhibited all the required characteristics to be introduced into the market and commercialized as table grapes and stand out as the most promising for commercial cultivation.Conclusion: The detailed ampelographic description presented herein highlighted clear morphological differentiation between Tunisian autochthonous grapevines, investigated for the first time using 70 OIV descriptors, and allowed us for the first time to easily split the Tunisian autochthonous grapevine accessions into wine and table grapes. Numerical analyses showed that the number of morphological traits that are effectively contributing to the characterization of the cultivars could be reduced to 12.Significance and impact of the study: In this investigation, we highlight the importance of importance of breeding programs, commercialization and evaluation of economically valuable characteristics of the highly diverse autochthonous grapevine cultivars from Tunisia. IntroductionIn Tunisia, viticulture is very ancient and the first historical record of grapevines dates back to 6000 BC (Zohary and Hopf, 2000). Autochthonous grapes are often grown by poor farmers in marginal, low-input and drought-stressed environments. These genetic resources, which may represent valuable reservoirs of interesting genes for crop improvement such as adaptation to biotic and abiotic stresses (Brush, 1995), represent a small population with a high risk of extinction due to the introduction of commercial high-yield foreign varieties (Hjalmarsson and Ortiz, 2000). All these factors contribute to the need for a detailed description and evaluation of the Tunisian grapevine genetic resources.Initial efforts to identify genetic diversity in Tunisian grapevine cultivars were mainly based on molecular tools (Zoghlami et al., 2001; 2009). Despite the use of molecular markers, knowledge of the phenotype given by morphological and agronomical descriptors is still important for breeding programs, conservation and commercialization of new varieties (Franco et al., 2005; Gon?alves et al., 2008; Laurentin, 2009).The description of the morphological characteristics is the usual methodology accepted from a legal point of view for patenting and registration of varieties (Badenes, 1991). In fact, ampelography is the first step in grapevine identification and selection and for resolving different classification problems (Martinez de Toda and Sancha, 1997). The complete characterization as well as the conservation of autochthonous cultivars is of great importance to prevent the loss of diversity (Rodrigues et al., 2008).In the last years, morphological data have been used to resolve the complex problem of the definition and classification of crop accessions using multivariate statistical analyses such as principal component analysis (PCA) and hierarchical cluster analysis (HCA) (Manjunatha et al., 2007; Aghaei et al., 2008). These methods assist in the successful management of plant genetic resources and contribute to the determination of the agronomical value of the accessions in the germplasm collection (bank).Morphological characterization continues to be the first step for the description and classification of germplasm accessions and statistical methods like PCA are useful tools for screening the accessions of a collection (Badenes et al., 2000). PCA transforms the original variables into a limited number of uncorrelated new variables. As reported by Martínez-Calvo et al. (2008), this method allows the visualization of differences among individuals, the identification of groups, and the identification of relationships among individuals and variables.Keeping in mind the importance of morphological characteristics in varietal identification and registration, the characterization of the worldwide Vitis