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6.2 Applications of crossing in plant breeding

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Sometimes, crossing is done for specific purposes, within the general framework of generating variability. Hybridization precedes certain methods of selection in plant breeding to generate general variability.

 Gene transferSometimes, only a specific gene (or a few) needs to be incorporated into an adapted cultivar. Crossing is used for the gene transfer process, followed by additional strategic crossing to retrieve the desirable genes of the adapted cultivar (see backcrossing in Chapter 15).

 RecombinationGenetically diverse parents may be crossed in order to recombine their desirable traits. The goal of recombination, which is a key basis of plant breeding, is to forge desirable linkage blocks.

 Break undesirable linkagesWhereas forging desirable linkage blocks is a primary goal of plant breeding, sometimes crossing is applied to provide opportunities for undesirable linkages to be broken.

 For heterosisHybrid vigor (heterosis) is the basis of hybrid seed development. Specially developed parents are crossed in a predetermined fashion to capitalize on the phenomenon of heterosis for cultivar development.

 For maintenance of parental linesIn hybrid seed development programs, crossing is needed to maintain special parents used in the breeding program (e.g. cytoplasmic‐genetic male sterility [CMS] lines, maintainer lines).

 For maintenance of diversity in a gene poolPlant breeders may use a strategy of introgression (crossing and backcrossing selected entries with desired traits into adapted stocks) and incorporation to develop dynamic gene pools from which they can draw materials for crop improvement.

 For evaluation of parental linesInbred lines for hybrid seed development are evaluated by conducting planned crosses to estimate combining abilities, in order to select appropriate parents for used in hybrid seed development.

 For genetic analysisGeneticists make planned crosses to study the inheritance and genetic behavior of traits of interest.

Principles of Plant Genetics and Breeding

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