Many people expect an apple tree grown from seed to bear fruit identical to the parent apple. However, after years of waiting, the apples produced by the new tree often look, taste, and feel entirely different. This common experience raises a fundamental question: why do apple seeds grow different apples?
The Genetic Science of Apple Seeds
Apple seeds produce diverse offspring due to their complex genetic makeup. Unlike many plants that can grow true-to-type from seed, apples are highly heterozygous, meaning they possess a vast array of genetic variations within their DNA. This genetic diversity ensures that each seed carries a unique combination of traits, similar to how siblings from the same parents are different.
Apple trees reproduce sexually, requiring pollen from one tree to fertilize the ovules of another. This process, known as cross-pollination, means that an apple seed is the result of genetic contributions from two different parent trees. The genes from both the “mother” tree (where the fruit develops) and the “father” tree (which provides the pollen) combine in a new and unpredictable way.
This genetic recombination is akin to shuffling a deck of cards; while the same cards are present, their arrangement in each new hand is unique. Every apple seed contains a distinct genetic blueprint, a novel combination of characteristics from its two parents. Consequently, the resulting seedling will express traits that may not be apparent in either parent apple.
Most apple varieties require cross-pollination with a compatible, different apple variety to produce viable seeds. This necessity further enhances the genetic diversity of the progeny, contributing to the wide range of outcomes observed in seed-grown apples.
The Diverse Characteristics of Seed-Grown Apples
The genetic variability inherited by an apple seedling manifests in a wide array of characteristics in the resulting fruit and tree. The fruit itself can display significant differences in taste, ranging from intensely sweet to extremely tart, or even bland. Its texture might vary from crisp and juicy to soft and mealy, while its size, color, and shape can also deviate considerably from the parent apple.
Beyond the fruit, the apple tree grown from a seed will also exhibit unique attributes. Its growth habit could be columnar, spreading, or weeping, and its vigor, or growth rate, will be distinctive. The seedling tree will possess its own level of resistance to various diseases and pests, which might be better or worse than the parent trees.
The chilling requirements, bloom time, and ripening time of the seed-grown apple tree will be specific to that individual plant. These factors are crucial for successful fruit production in different climates. Most seed-grown apples are not commercially viable or desirable, often producing smaller, less flavorful fruit, or being more susceptible to common apple diseases than established varieties.
Only a tiny fraction of these unique genetic combinations results in an apple with desirable qualities for human consumption or commercial cultivation. The vast majority of these “new” apples are either unpalatable or lack the characteristics needed for widespread appeal.
How New Apple Varieties Are Developed and Propagated
Given the unpredictable nature of growing apples from seed, commercial apple production relies on a horticultural technique called grafting to ensure consistency. Grafting involves taking a scion, which is a small cutting from a desired apple variety, and joining it to a rootstock, which is the root system and lower stem of another apple tree. The scion then grows to become the upper part of the new tree, producing genetically identical fruit to the tree from which it was taken.
This method effectively creates a clone of the original apple variety, ensuring that every ‘Honeycrisp’ apple, for example, shares the exact same genetic makeup. Commercial orchards depend on grafting to maintain the specific qualities—such as taste, texture, and appearance—that consumers expect from named apple varieties. Grafting allows growers to bypass the genetic lottery of seeds, guaranteeing consistent fruit production.
While grafting maintains existing varieties, new apple varieties are developed through selective breeding. Horticulturists intentionally cross-pollinate two parent apple trees, chosen for their desirable traits, in the hope of creating a new seed with an even better combination of characteristics. These seeds are then planted, and the resulting seedlings are grown out, a process that can take several years before the tree even begins to bear fruit.
The evaluation process for a new apple variety often requiring many more years to assess fruit quality, tree health, and disease resistance. Only a minuscule percentage of these intentionally bred seedlings, perhaps one in many thousands, will yield a commercially viable apple with superior traits. If a promising new variety is identified, it is then propagated through grafting to create an entire orchard of genetically identical trees, bringing the new apple to market.