Cross-pollinated crop populations are typically characterized by high levels of heterozygosity. Inbreeding in these crops often leads to a significant decrease in fitness, a phenomenon known as inbreeding depression. To mitigate the undesirable effects of inbreeding depression, breeding methods for these crops are designed to minimize inbreeding.
The commonly used breeding methods for cross-pollinated crops can be broadly categorized into two groups:
A. Selection
B. Progeny Testing and Selection
C. Recurrent Selection
D. Hybrids
E. Synthetics and Composites
Mass selection, which is similar to the approach used in self-pollinated crops, involves selecting a group of plants based on their observable characteristics (phenotype). The seeds produced by these selected plants are mixed together in bulk to create the next generation. This selection cycle can be repeated one or more times to increase the frequency of desirable alleles. This method is often referred to as phenotypic recurrent selection.
In unit selection, the field from which plants are to be chosen is divided into smaller units or plots, each containing approximately 40 to 50 plants. An equal number of plants are then selected from each plot, and the seeds from these selected plants are harvested and combined to produce the next generation. Dividing the field into smaller plots helps minimize environmental variations. This method is commonly used to improve maize crops and is also known as the grid method of mass selection.
(a) Half Sib Family Selection
Half-sibling plants share one common parent. In this method, only superior offspring are planted and allowed to open-pollinate.
There are two variations of this method:
1. Ear to Row Method: This is a straightforward approach widely used in maize breeding. It involves several steps:
(b) Full Sib Family Selection
(c) Inbred or Selfed Family Selection
In this method, families are produced by selfing or inbreeding. Two variations of inbred or selfed family selection are:
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