Step 1: Understanding the Question:
The question asks to identify the fruit crop that uses "M-9" as a common rootstock to control its size, specifically to make it a dwarf tree.
Step 2: Key Formula or Approach:
This is a factual question testing knowledge of horticultural propagation techniques, specifically the use of rootstocks. The approach is to recognize the famous "Malling" series of rootstocks and their association with a particular fruit.
Step 3: Detailed Explanation:
A rootstock is the root system and base of a plant onto which a different plant's top portion (scion) is grafted. Dwarfing rootstocks are crucial for creating smaller, more manageable trees for high-density planting.
(B) Apple: The "M" series of rootstocks, also known as the Malling series, were developed at the East Malling Research Station in England specifically for apple trees. M-9 is one of the most important and widely used dwarfing rootstocks for apple in the world. It induces early fruiting and high yields.
The other crops use different series of rootstocks.
Step 4: Final Answer:
M-9 is a famous dwarfing rootstock used for Apple. Therefore, option (B) is the correct answer.