Triploids

The crossing of a tetraploid and a diploid gives rise to a triploid. Triploids, having an odd number of chromosomes which are unable to pair up during meiosis, are often infertile in nature. But there are a few important examples in horticulture, notably ‘ Bramley’s Seedling ’ apple cultivar. Pollen from such cultivars is sterile, being derived from an irregular meiosis division in the anthers. The presence nearby of suitable pollinator cultivars such as ‘James Grieve’ and ‘Grenadier’ provide suitable viable pollen at the same flowering time as ‘ Bramley’s Seedling ’ . Thus two pollinators are required, i.e. one to pollinate the Bramley’s Seedling and a second to pollinate the pollinator. An alternative strategy for a private gardener is the inclusion of a pollinator onto the triploid tree by means of a suitable graft, the result is sometimes called a ‘family tree’. Polyploidy only becomes significant in the plant when the mutated cell is part of a meristem.