Undesirable effects

1. Reduction in Diversity:

• Plant breeding leads to reduction in diversity.
• The uniform varieties are more prone to the new races of pathogen than land races which have high genetic diversity.

2. Narrow genetic base:

• Uniform varieties have narrow genetic base. Such varieties generally have poor adaptability.

3. Danger of Uniformity:

• Most of the improved varieties have some common parents in the pedigree which may cause danger of uniformity.

4. Undesirable combinations:

• Sometimes, plant breeding leads to undesirable combinations. The examples of man-made crops having undesirable combination of characters are Raphanobrassica and Pomato.

5. Increased susceptibility to minor diseases and pests:

• Due to emphasis on breeding for resistance to major diseases and insect pests often resulted in an increased susceptibility to minor diseases and pests.
• These have gained importance and, in some cases, produced severe epidemics.
• The epidemic caused by Botrytis cinerea (grey mold) in chickpea during 1980-82 Punjab, Haryana.
• The severe infection by Karnal bunt (Tilletia sp.) on some wheat varieties, infestation of mealy bugs in Bt cotton.