Question

The reason for vegetatively reproducing crop plants to suit maintaining hybrid vigour is that? 
A) resistant to diseases
B) once the desired hybrid is produced, no chances of losing it 
C) they can be easily propagated
D) they have a longer life span.

Answer 1

Hint: Asexual reproduction results in the multiplication of genetically identical individuals(clones). Asexual reproduction is also called clonal propagation as the products are genetically identical. Asexual reproduction in angiospermic plants occurs through vegetative propagation.

Complete step-by-step answer: Hybrid vigour is also called heterosis it is about being superior to the hybrid than its parents. It is lost due to inbreeding. It is also called inbreeding depression. It is lost in the plants that are self-pollinated in the F2 generation and decreases slowly in the plants which are cross-pollinated. So it is more advantageous in plants that are propagated vegetatively because these plants do not involve sexual reproduction so hybrid vigour is not lost in these crops, for example, sweet potato, sugarcane, strawberry, grapes, etc.
The majority of flowering plants produce hermaphrodite flowers and pollen grains are likely to come in contact with the stigma of the same flower. Continued self-pollination leads to inbreeding depression. Flowers have developed many devices to discourage self-pollination i.e., production of unisexual flowers, self-incompatibility, release to stigma, and pollen not synchronized. 
Hence the correct answer is option B.

Note: The term heterosis was first coined by Shull in 1914. And in some cases, the hybrid may be inferior to the weaker parent and this is also regarded as heterosis.