Q.Which one of the following selection method takes longer time in bringing about desired variation ?

A group of genetically identical/similar plants produced by breeding (typically via vegetative propagation) is called a clone.

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In plant breeding, a clone refers to a population of plants that are genetically identical (or very nearly so) to one another and to the original 'mother' plant, because they have all been produced through asexual/vegetative propagation (such as cuttings, grafting, layering, or micropropagation) rather than through seed (sexual reproduction), which would introduce genetic recombination. Since asexual propagation does not involve fertilisation, every plant in the clone carries the same genotype, and hence the same desirable traits, as the parent -- making cloning a valuable technique for multiplying elite, high-performing varieties unchanged. Checking the distractors: Autopolyploid refers to an organism carrying more than two chromosome sets, all derived from the same species (a chromosomal condition, not a description of similar plants …

Natural selection is the slowest of the listed selection methods because it is a gradual, undirected evolutionary process.

In plant breeding, methods such as mass selection (bulk selection of superior-looking individuals from a mixed population), pure line selection (isolating and propagating a single genetically uniform line from a self-pollinated population), and clonal selection (selecting and vegetatively propagating superior individual clones) are all consciously directed by the breeder toward a specific desired trait, allowing measurable improvement within just a few generations. Natural selection, in contrast, is not guided by any human intent -- it depends purely on the environment favouring the survival and reproduction of individuals that happen to possess advantageous variations, a process that unfolds over very long evolutionary timescales, often spanning …