Abstract
The olive trees (Olea europaea L.) have been cultivated for millennia in the Mediterranean basin and its oil has been an important part of human nutrition in the region. In order to distinguish between olive accessions, morphological and biological characters have been widely and commonly used for descriptive purposes and have been used to characterize olive accessions. A comparative study of morphological characters of olive accessions grown in Tunisia was carried out and analyzed using Bayesian Networks (BN) and Principal Components Analysis (PCA). The obtained results showed that averages of fruit and kernel weights were 2.27 grams and 0.41 grams, respectively. Besides, a relatively moderate level of variation (51.22%) being explained by four Principal components. BN revealed that geographical localisation plays a role in the increase of tree habit, size of lenticels and leaf shape. A dendrogram has been carried out in the aim to classify studied olive accessions. We proposed a novel method of analysis based on the three-step scheme, in which first the data set is clustered, then olive tree features are evaluated. The studied accessions can be divided into four main groups by cutting the dendrogram at a similarity value of 0.645. Different relationships are studied and highlighted, and finally the collected features are subjected to a global principal component analysis. Obtained results confirmed that core surface was negatively correlated with geographical location (r = -0.52, p<0.05) and maturation period r = -0.539, p<0.05). Number of lenticels was positively correlated to lenticels size (r = 0.632, p<0.05). Core shape had a negative correlation with fruit shape (r = -0.759, p<0.05). On the basis of these findings, this research confirmed that morphological markers are a preliminary tool to characterize olive oil accessions.
Highlights
The cultivated Olive (Olea europaea L.) is a long-lived evergreen tree native to the Mediterranean basin (Poljuha et al, 2008); it is found in several countries in Europe, North and South America, and Australia (Therios, 2009)
The aim of this study was firstly to evaluate the associations of autochthon olive accessions grown in Tunisia on the basis of a combination of morphologic and agronomic parameters by clustering, and to analyse accurately the type and origin of existing relationships between the studied parameters by Bayesian Networks (BN) and Principal Component Analysis (PCA) methods
This research indicated that morphological markers are a preliminary tool to characterize olive oil accessions
Summary
The cultivated Olive (Olea europaea L.) is a long-lived evergreen tree native to the Mediterranean basin (Poljuha et al, 2008); it is found in several countries in Europe, North and South America, and Australia (Therios, 2009). The size of the olive fruit is variable, even within the same tree, and depends on accession, fruit load, soil fertility, available water and cultural practices (Therios, 2009). Volatile and phenolic compounds found in the fruit are responsible for the aroma, taste and many of the health benefits associated with olive oil (Mez-Rico et al, 2006). The concentrations of these compounds change depending upon the degree of ripening of the fruit. The quality of pickling olives is greatly affected by the concentrations of organic acids and sugars found in the fruit due to the role of these compounds in the fermentation process (Patumi et al, 1999). The fruit maturation process is characterized by a change in the fruit
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