Step 1: Understanding the Concept:
Somatic mutations are genetic changes that occur in non-reproductive cells of a plant. In vegetatively propagated crops, these mutations can be preserved and multiplied by grafting or budding.
Step 2: Detailed Explanation:
- A spontaneous somatic mutation occurring in a single bud or branch of a woody plant is known as a "bud sport" (or "sport").
- If the mutant branch produces fruits with improved characteristics (such as better color, early ripening, or seedlessness), it can be propagated vegetatively to establish a new cultivar.
- Many important commercial fruit varieties, such as red mutants of 'Delicious' apples or seedless citrus selections, originated as bud sports.
- A chimera refers to a plant that contains tissues of more than one genotype, which can result from a somatic mutation but is not the term for the mutant branch itself.
Step 3: Final Answer:
Spontaneous somatic mutations in vegetatively propagated materials are called bud sports.