(a) Define the terms budding and grafting (b) List four materials required for budding (c) Give two reasons why the improvement of crops by selection may no...

(a) Budding and grafting [4 marks]

• Budding is a method of vegetative (asexual) propagation in which a single bud, cut with a piece of bark from a desired parent plant (the scion), is inserted into a slit in the bark of a rootstock so that the two unite and grow as one plant.
• Grafting is a method of vegetative propagation in which a portion of stem bearing several buds (the scion) from a desired plant is joined onto the rootstock of another plant so that their cambium layers unite and continue to grow together.

(b) Four materials required for budding [4 marks]

• A sharp budding knife.
• A healthy rootstock.
• Bud sticks (scion bearing buds) from the desired parent plant.
• Budding tape/raffia (or polythene strip) for wrapping the union, and wax to seal it.

(c) Two reasons why improvement of crops by selection may not give desired results [4 marks]

• The desirable character selected may be controlled by recessive genes, so it fails to show up in the offspring.
• Cross-pollination (out-crossing) with inferior plants nearby, and the influence of environment rather than genes, can mask or lose the selected trait in later generations.

(d) Four disadvantages of asexual and four advantages of sexual reproduction [8 marks]

Disadvantages of asexual reproduction:

• There is no genetic variation, so no improved varieties arise.
• Diseases present in the parent are passed on to the offspring.
• The offspring are all weak in the same way and can be wiped out by the same disease/pest.
• It does not allow the crop to adapt to new/changing environments.

Advantages of sexual reproduction:

• It produces variation, which is the basis for crop improvement and new varieties.
• The seeds produced are easy to store, handle and transport.
• Offspring may be more vigorous (hybrid vigour) and better adapted to the environment.
• It gives a means of surviving unfavourable conditions through resistant/dormant seeds and reduces carry-over of some diseases.