Principles of Plant Breeding (2+1)

Introduction

• The Genetic constitution of plants is determined by mode of pollination.
• Self pollination leads to homozygosity and cross pollination leads to heterozygosity. So we have to exploit homozygisity in self pollinated crops and heterozygosity in cross pollinated crops. Based on genetic constitution plant breading populations are of four types.

Homogenous population:
Genetically similar plant constitutes homogenous populations. Eg: Pure lines, inbred lines, F1between pure lines, progeny of a clone. Pure lines and inbredlines have narrow adaptation.

Heterogeneous population:
Genetically dissimilar plants constitute heterogeneous population E.g: Land races, mass selectedpopulation,synthetics,composites, multiline. Synthetics, Composites, multiline these have wide adaptability stableperformance under different environments.

Homozygous populations:
Individuals with like alleles at the corresponding loci are known as homozygous. Such individuals do not segregate on selfing. E.g.: Pure lines, inbred lines and mass selected population in self pollinated plants. Multiline are homozygous but heterogeneous

Heterozygous population:

Individuals with unlike alleles the corresponding loci are heterozygous. Such individuals segregate into various types on selfing. Eg.F1, composites, Synthetics. Such populations have greater buffering capacity to environmental fluctuation

	Homozygous	Heterozygous
Homogenous	Genetically similar and non segregating population	Genetically similar but segregating on selfing F1, hybrids between inbred lines and progeny of a clone
Heterogenous	Genetically dissimilar but non segregating population Multiline and mass selected varieties of self pollinated crops	Genetically dissimilar but segregating population Eg. composites and synthetics