Read the passage and answer the following questions.
Flowering plants employ various mechanisms to discourage self-pollination and promote cross-pollination. These mechanisms include temporal separation of pollen release and stigma receptivity, spatial separation of anther and stigma, self-incompatibility, and the production of unisexual flowers. In some species, the timing of pollen release and stigma receptivity is not synchronised. This prevents self-pollination as either the pollen is released before the stigma becomes receptive or the stigma becomes receptive before the pollen is released. Similarly, in other species, the anther and stigma are positioned in a way that prevents self-pollination by avoiding contact between the pollen and stigma of the same flower. Self-incompatibility is a genetic mechanism that prevents self-pollen, whether from the same flower or other flowers of the same plant, from fertilising the ovules. It achieves this by inhibiting pollen germination or pollen tube growth in the pistil. The production of unisexual flowers is another device to prevent self-pollination. For example, in plants like castor and maize, which are monoecious, having both male and female flowers on the same plant prevents self-pollination (autogamy) but not pollination between flowers on the same plant (geitonogamy). On the other hand, in species like papaya, male and female flowers are present on different plants (dioecy), effectively preventing both autogamy and geitonogamy. During pollination, the pistil may encounter pollen of the wrong type, either from other species or from the same plant if it is self-incompatible. The pistil has the ability to recognise whether the pollen is of the right type (compatible) or the wrong type (incompatible). If the pollen is compatible, the pistil accepts it and promotes post-pollination events leading to fertilisation. However, if the pollen is incompatible, the pistil rejects it by preventing pollen germination on the stigma or pollen tube growth in the style. The recognition and acceptance or rejection of pollen by the pistil involve a continuous dialogue between the pollen grain and the pistil. This dialogue is facilitated by chemical components present in both the pollen and pistil. In recent years, scientists have made progress in identifying some of these components and understanding the interactions that lead to the recognition, acceptance, or rejection of pollen by the pistil.
In an artificial hybridisation programme, which step is NOT needed when the female parent bears unisexual flowers?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Emasculation
In artificial hybridisation, a breeder crosses two chosen parents to combine their useful characters. Only the desired pollen must reach the stigma of the female parent, and the stigma must be kept safe from unwanted pollen. Two techniques do this: emasculation and bagging.
Option (1) Emasculation — Not needed when the flowers are unisexual. Emasculation is the removal of the anthers from a flower bud before they shed pollen. It is needed only in a bisexual flower, to stop its own pollen from reaching its stigma. A unisexual female flower has no anthers, so there is nothing to remove.
Option (2) Bagging of the female flower buds — Still needed when the flowers are unisexual. Bagging is still needed. The female flower buds are covered with a bag before they open, so that no unwanted pollen reaches the stigma.
Option (3) Dusting the desired pollen on the receptive stigma — Still needed when the flowers are unisexual. This is the cross itself. When the stigma becomes receptive, pollen from the chosen male parent is dusted on it, whether the flower is bisexual or unisexual.
Option (4) Rebagging the flower after pollination — Still needed when the flowers are unisexual. After pollination the flower is bagged again, to keep out other pollen while the fruit develops. This step is also kept for unisexual flowers.
NCERT Extract:
Pollen-pistil Interaction – “… If the female parent bears bisexual flowers, removal of anthers from the flower bud before the anther dehisces using a pair of forceps is necessary. This step is referred to as emasculation. Emasculated flowers have to be covered with a bag of suitable size, generally made up of butter paper, to prevent contamination of its stigma with unwanted pollen. This process is called bagging. … If the female parent produces unisexual flowers, there is no need for emasculation. The female flower buds are bagged before the flowers open. When the stigma becomes receptive, pollination is carried out using the desired pollen and the flower rebagged.”