Which one of the following is an auxin-induced phenomenon?

The correct option is Parthenocarpy in tomatoes.

Explanation

Plant growth regulators (PGRs) are organic substances that regulate physiological processes such as growth, differentiation, and development. Different classes of hormones-Auxins, Gibberellins, Cytokinins, Ethylene, and Abscisic Acid-have distinct physiological effects and agricultural applications.

Analysis of Options:

• Parthenocarpy in tomatoes is Correct: Auxins are extensively used in agriculture to induce parthenocarpy, which is the formation of fruit without fertilization. This application is particularly common in tomatoes, resulting in the production of seedless fruits.
• Synchronised fruit-set in pineapples is Incorrect: While auxins can promote flowering in pineapples, the synchronization of flowering and fruit-set is a primary function associated with Ethylene (often applied as Ethephon).
• Bolting in beet is Incorrect: Bolting refers to the sudden elongation of internodes just prior to flowering in rosette plants (e.g., beet, cabbage). This phenomenon is induced by Gibberellins, not auxins.
• Early seed production in conifers is Incorrect: The hastening of the maturity period in juvenile conifers to facilitate early seed production is an application of Gibberellins (specifically GA₃).

Key Takeaway: Auxins are the primary hormones used to induce parthenocarpy in tomatoes. In contrast, Gibberellins are responsible for bolting and early maturity in conifers, while Ethylene regulates fruit ripening and synchronized flowering in pineapples.