Abstract:
The olive tree (Olea europaea L.) is considered as one of the oldest and the most important
fruit crops of the Mediterranean basin, which is characterized by the existence of a
considerable number of different olive cultivars. Therefore, the olive cultivar identification is
crucial to safeguard the genetic patrimony of this species. Different morphological and
molecular markers were used to discriminate among cultivars. The aim of the present work
was to describe different pollen morphological and ultrastructural parameters (shape, size and
exine pattern) as an additional tool for the identification of olive cultivars. Observations were
carried on seventy centennial olive accessions grown in the Central Eastern part of Tunisia
using Scanning Electron Microscopy (SEM) and Image analysis (ImageJ). Pollen were threezonocolpate
and elliptical-prolate or subprolate. Pollen morphological qualitative traits
revealed specific differences among the studied genotypes including variation in whole grain
shape and also exine pattern ornamentation as meshes profile and regularity and muri
thickness. The quantitatively measured traits were significantly different among pollen from
diverse genotypes. Polar and equatorial diameters varied from 21.80 to 29.88 μm and from
14.47 to 21.14 μm, respectively, while the pollen area ranged between 274.58 and 466.35 μm2.
Frequency distributions of most measured pollen parameters depicted a normal distribution.
The three principal components of the Principal Component Analysis (PCA) accounted for
more than 97% of the total variation. The first Principal Component (PC1) was correlated to
pollen size. The second (PC2) and the third (PC3) were correlated to exine texture and to
pollen shape, respectively. Both morphometric features and exine pattern observations were
potentially relevant tools to discriminate among the studied genotypes. Further combination
between pollen ultrastructural analysis, morphological and molecular markers is fully
desirable, in subsequent work, to improve both reliability and discriminative ability for
cultivars classification.
Keywords: Exine pattern, Olea europaea L., Pollen micromorphology, Scanning electron.
Microscopy.
