Morphological characterization of ‘Oblačinska’ sour cherry by multivariate analysis

Abstract

A wide range of ‘Oblačinska’ sour cherry germplasm was collected from the most important growing regions in Serbia. Twenty nine variables were recorded in 41 accessions to determine the overall degree of polymorphism and to detect similarities among genotypes. The highest degree of variability was observed in traits related to number and composition of fruiting twigs, fruit set and yield. The majority of significant correlation coefficients were found in the characteristics representing fruit and leaf size. Principal component analysis (PCA) makes the phenotypical diversity determination and separation of similar genotypes possible. Variables with high discriminating values were those related to fruit and leaf size, yield efficiency, blooming time and flowering density. Based on the results from this study, the genotypes XI/3 and II/10 can be recommended for cultivation. The clonal selection and conservation of the highly diverse autochthonous population of sour cherry are also recommended.

Introduction

The ‘Oblačinska’ sour cherry (Prunus cerasus L.) is an autochthonous and heterogeneous cultivar, which is the most planted cultivar in Serbian commercial orchards. The ‘Oblačinska’ sour cherry tree is of low vigour and is suitable for dense planting and mechanical harvesting. This cultivar is self-compatible and characterized by regular and high yield. The fruit is of “morello” type, small to medium in size, with dark red and thin skin. The flesh is red, medium-firm, juicy, quite sour, aromatic and of high quality. The ‘Oblačinska’ sour cherry is highly resistant to leaf spot and to bitter rot (Grzyb and Rozpara, 2004). The numerous positive traits of this cultivar should make it interesting for plantation in other countries.

Long-term cultivation in diverse agroecologic conditions and the use of various types of propagation (both by suckers and by seeds) has caused the ‘Oblačinska’ sour cherry to become a mixture of numerous genotypes. Generative reproduction enabled the occurrence of individual trees with intermediate phenotypes (Coart et al., 2003), and in addition some genotypes underwent genetic erosion (Rhymer and Simberloff, 1996). The first selection from a diverse gene pool was conducted by local farmers in order to obtain certain desirable traits. Later, series of authors (Milutinović et al., 1980, Ogašanović et al., 1985, Nikolić et al., 1996, Nikolić et al., 2005a, Nikolić et al., 2005b, Rade et al., 2008) who studied this cultivar noticed a variability in the majority of pomological and technological traits. The heterogeneity of the cultivated population can create problems in production, so efforts have been made to identify selections with desirable properties. Also, autochthonous cultivars are in some cases at a high risk of extinction due to the introduction of foreign varieties, which may have a higher productivity or are better known in the foreign markets (Hjalmarsson and Ortiz, 2000). All these factors are creating a necessity for a detailed description and evaluation of ‘Oblačinska’ sour cherry.

The complete characterization as well as the conservation of autochthonous cultivars is considered of great importance in order to avoid the loss of their germplasm (Rodrigues et al., 2008). Morphological characterization continues to be the first step for the description and classification of germplasm and statistical methods like principal components analysis (PCA) are useful tools for screening the accessions of a collection (Cantini et al., 1999, Badenes et al., 2000). PCA is a method of data reduction that transforms the original variables into a limited number of uncorrelated new variables. The technique is thus a useful device for representing a set of variables by a much smaller set of composite variables that account for much of the variance among the set of original variables. It allows visualization of the differences among the individuals, identification of possible groups and relationships among individuals and variables (Martínez-Calvo et al., 2008).

The objective of this study is to describe the variability in 41 genotypes of the ‘Oblačinska’ sour cherry collection, to determine the correlation among the traits, to identify the most useful variables for discrimination among the genotypes and to detect relationships between the genotypes. We have also conducted an evaluation of economically valuable characteristics in order to identify the genotypes with a good potential for cultivation or for exploitation in breeding programs.