If you've ever savored the silky texture of a banana or crunched through a piece of seedless watermelon, then you have eaten triploid fruit. Triploid plants are produced for numerous reasons, but most fruit trees offer the advantage of having seedless fruit. Triploid trees also require some extra care for that luxury, so use care.
Plants produce sex cells during a process called meiosis, during which one cell separates into two sex cells. As part of this process, the chromosomes also split in half, each half migrating into a separate cell. When fertilization occurs, the two halves merge into one, producing a plant that shares both parents' characteristics. A cell containing the full two sets of chromosomes is called a diploid cell. In contrast, a triploid cell contains three full sets of chromosomes. When meiosis occurs, the chromosomes cannot divide evenly, so offspring cannot result.
Because triploid fruit trees cannot undergo normal meiosis, they cannot produce viable reproductive cells or offspring. In fruit trees, pollen is the most familiar reproductive cell, and the most obvious form of offspring occur as seeds. Therefore, triploid fruit trees do not produce viable pollen, and they produce few--if any--seeds in the fruit.
Several familiar fruits come from triploid fruit trees. Cultivated banana trees are triploid, which is why you don't encounter seeds when eating a banana. Several types of apples come from triploid trees, including Winesap, Jonagold and Mutsu.
Triploid fruit trees are produced by crossing a normal tree with a tetraploid tree, a variety that contains four times the expected number of chromosomes. The resulting offspring has three sets of chromosomes. Other methods generate trees from seed contents that are naturally triploid, although this method has had mixed success, notes North Carolina State University.
For fruit tree growers, the most obvious benefit is the removal or diminishment of seeds in the final fruit. Many people find seedless fruit more enjoyable to eat.
Triploid fruit trees are not without their challenges. Trees produce fruit only when fertilization occurs, which requires viable pollen to land on the tree's flowers. Because triploid trees do not produce viable pollen, they cannot self-pollinate, and you will need to have two normal fruit trees with blossoms open simultaneously for all three to produce fruit. When growing apple trees, the Virginia Cooperative Extension suggests that a crab apple tree within 100 feet of the triploid tree should provide adequate fertilization. According to apple grower Hugh Ermen, triploid trees take longer to produce fruit, sometimes up to 10 years.