What is polymorphism with respect to plant breeding ?

In the context of plant breeding, polymorphism refers to the occurrence of genetic variation within a population or species, particularly at the level of DNA sequences or genetic markers. Polymorphisms are manifested as differences in DNA sequences, resulting in the presence of multiple alleles or variants of a gene within a population.

 

Types of polymorphisms commonly studied in plant breeding:

 

Single Nucleotide Polymorphism (SNP): SNPs are the most common type of polymorphism and involve single nucleotide differences at specific positions in the DNA sequence. SNPs are widely used as molecular markers in plant breeding due to their abundance, stability, and amenability to high-throughput genotyping technologies.

 

Insertion-Deletion Polymorphism (Indel): Indels involve the insertion or deletion of nucleotide bases within the DNA sequence, resulting in size variations of DNA fragments. Indels can be detected using molecular techniques such as gel electrophoresis or sequencing and are useful for genetic mapping and diversity analysis in plant breeding.

 

Simple Sequence Repeat (SSR) or Microsatellite Polymorphism: SSRs are short tandem repeats of DNA sequences consisting of 1-6 nucleotide motifs repeated multiple times. Variability in the number of repeats within SSR loci results in allelic diversity, making SSR markers valuable for genetic mapping, diversity analysis, and marker-assisted selection in plant breeding.

 

Restriction Fragment Length Polymorphism (RFLP): RFLPs involve variations in the lengths of DNA fragments generated by restriction enzyme digestion of genomic DNA. Differences in restriction sites or DNA sequence motifs lead to polymorphic DNA fragments that can be visualized using gel electrophoresis. RFLPs have been widely used as molecular markers in plant breeding and genetic mapping studies.

 

Cleaved Amplified Polymorphic Sequences (CAPS): CAPS markers are generated by PCR amplification of DNA regions followed by digestion with restriction enzymes that recognize polymorphic sites within the PCR products. CAPS markers are used for genotyping polymorphic loci and have applications in genetic mapping, diversity analysis, and marker-assisted selection in plant breeding.

 

Polymorphisms are of great interest in plant breeding as they provide the raw material for trait improvement through selection and breeding. By identifying and utilizing polymorphic markers associated with target traits, breeders can accelerate the development of improved crop varieties with desired agronomic characteristics, disease resistance, abiotic stress tolerance, and quality traits. Polymorphism analysis is an essential component of genetic studies aimed at understanding the genetic basis of trait variation and implementing molecular breeding strategies for crop improvement.