It is essential that the pollen grains moved by insect vectors, wind or artificially by man, between the pollen donor (pollinating variety) and the main commercial variety, remain viable and capable of germination and growth down the style into the ovary and micropyle of the ovule.
- Pollen viability can be judged crudely by examining the grains under a low powered light microscope.
- Small shrunken grains are not viable.
- Many of these are found in the pollen collected from triploid varieties of apple.
- The self fertile clones of Cox and Queen Cox also produce a significant proportion of pollen that is small, shrunken and not viable.
A more accurate assessment of pollen viability can be carried out using germination tests on artificial media, such as agar or sugar solutions. Sometimes staining procedures are also used to estimate pollen viability (Seilheimer and Stösser, 1982).
- Growers wishing to store pollen for use in hand pollination in the subsequent season can achieve this by placing the pollen in a sealed desiccating jar in a refrigerator.
- Very long-term storage (e.g. 10 years) is possible at -20ºC and reduced pressure.
- Aborted pollen grains are common in the self fertile clones of Cox’s Orange Pippin and Queen Cox but may also occur in other varieties in some seasons (Gagnieu, 1947).
- This is due to faulty reduction division from the diploid to the haploid.
- High temperatures (not common in the UK) can increase the amount of aborted pollen produced.
It should be noted that the anthers of some cider varieties are unable to release their pollen resulting in a form of male sterility.