Researchers at East Malling Research studied apple varieties held at the UK National Apple Collection between 2007 - 2010 in order to determine the "ploidy" level. Most apple varieties are "diploid" and have 2 sets of chromomes, just like humans. However it has been known for some time that a number of varieties have 3 sets, and are known as "triploid" - the most well-known being Bramley's Seedling, the popular English cooking apple.
This research is useful for the home orchardist because triploid varieties have complicated pollination requirements, and usually will not pollinate other varieties. However they often produce larger trees with larger fruit, and tend to have naturally good disease resistance. These useful qualities have ensured these varieties remain popular despite the extra care needed in choosing pollination partners.
The research found that more than 10% of the varieties in the UK apple collection were triploid, a higher proportion than expected. One of the surprises is Ashmead's Kernel, a widely-grown traditional English apple. Ashmead's Kernel has always been known to be difficult to pollinate but previously it was assumed this was because it bloomed very late in the blossom season. Other well-known varieties that are now confirmed as triploids include Roxbury Russet and Orleans Reinette.
The research paper can be downloaded here. The Orange Pippin database has been updated with this latest data on triploid varieties. You can check pollination partners for your apple trees on our sister websites - USA here, and UK here.
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