Principles of Plant Breeding

Mechanisms favouring cross pollination

• Imperfect flowers (dicliny or unsexuality) Flowers are unisexual i.e., stamens and pistils lie on separate flowers.

  a. Monoecious plants: E.g., Maize, Castor, Jack, Coconut.
  b.Dioecious plants: E.g., Papaya, Hemp, Asparagus, Datepalm, etc.

1. Dichogamy:
• Unequal maturation of stamens and pistils in bisexual flowers (Anther and stigma of bisexual flowers mature at different times). They are of two types: a. Protogyny: Stigma becomes receptive earlier to stamens. E.g. Bajra. b. Protandry: Antherdehisce and release the pollen grains before stigma of the same flower attains receptivity. E.g., Carrot, Marigold.

2. Herkogamy:
• Presence of mechanical barrier between male and female organs of a flower.E.g., Crepes.

3. Male Sterility :
• Seeds are not set due toabsence of functional pollen grains.Male sterility determined by (i) Genetic factors (E.g.Tomato, barley, Brinjal and Rice). (ii) Cytoplasmic factors (e.g., Onion) and (iii) Interaction (E.g.Chilli, etc.)

4. Self incompatibility:
• Male and female gametes are fertile but seeds are not produced when selfed because of some oppositional factors but can set seeds when there is a cross pollination.E.g., Tobacco, Mango, Tomato, Mustard, Radish, Cabbage, etc.