Apricot (Prunus armeniaca) pollen morphological characterisation through scanning electron microscopy, using multivariate analysis

Pollen grains of 11 Iranian apricot (Prunus armeniaca) cultivars were examined, using scanning electron microscopy (SEM). Pollen was collected in the 2002 growing season from mature apricot trees grown in The Apricot Collection Orchard, Ismailabad Horticultural Research Station, Qazvin, Iran. For SEM evaluation, pollen grains were observed and photographed at 1000x for whole grain and at 10 000x for sectioning of exine pattern (surface topography). The length (L) and the width (W) of grain, L/W ratio, distance between two furrows and the width of ridges in elliptical pollen, and the base, the altitude and the width of grain and ridges in triangular pollen were measured. Substantial variability in the size, shape, and exine patterns among pollen grains was clearly distinguished. The apricot cultivars were easily separated into two groups according to their pollen grain shapes: (1) elliptical trizonocolpate (five cultivars); and (2) obtuse-triangular (six cultivars). The pollen grains of all studied apricot cultivars were medium in size: 51.32 x 25.51 mu m (length x width) for the elliptical shape, and for the triangular shapes: 39.03 x 31.22 mu m (base x altitude). The resultant data from the two types of pollen shapes were analysed using completely randomised design (CRD) with unequal replications. Moreover, multivariate statistical analysis was carried out to distinguish morphometric information from measured parameters of the two pollen grain shapes. The projections of the loadings defined by the first two principal components allowed for the visualisation of the position of apricot cultivars, demonstrating between-cultivar-pollen shape variations. Hence, the differences in both exine pattern and surface topography, in particular ridges and pore characteristics, can potentially be used as a diagnostic tool to aid in the identification of apricot cultivars.