Amount and quality of pollen grains in four olive (Olea europaea L.) cultivars as affected by ‘on’ and ‘off’ years

Olive pollination is anemophilous and an adult olive tree can produce large amounts of pollen grains spread in the air during the flowering period. Viability of pollen grains can be checked by using different methods such as cytoplasmic stains, enzymatic reactions or germination. The aim of the work was to verify either if quality and number of pollen grains were similar in 'off' year with respect to 'on' year or differences occurred among olive cultivars. In 2006 and 2007, the viability and number of pollen grains per anther have been investigated in four Italian olive cultivars: 'Ascolana Tenera', 'Cazzinicchio', 'Cima di Melfi' and 'Coratina'. Grains viability was estimated by using three different techniques: acetic carmine, fluorescein diacetate and germination. The three techniques obtained statistically different data, with acetic carmine always showing the highest values but staining also heat-killed pollen grains. Fluorescein diacetate and germination were significantly correlated with a high R2 (0.862). The number of pollen grains significantly varied among the cultivars and between the two years. The average number of pollen grains per anther ranged from 65,722 ('Ascolana Tenera') up to 97,160 ('Cazzinicchio'). A significant difference was detected between the two years for the number of pollen grains per anther, ranging from 98,037 in 2006 ('on' year) down to 70,630 in 2007 ('off' year). The study also showed that the viability (with all the techniques) of the pollen grains was significantly higher in the 'off' year with respect to the 'on' one, with important consequences on the fertilization process