Diagnostics in Agriculture and Molecular Breeding
The biotechnological tools have advanced our knowledge in understanding the many secretes of the nature. So are the diagnostic tools used in agriculture?
1. Agricultural Diagnostics :
The crop plants suffer from a number of diseases caused by a variety of pathogens such as bacteria, fungi, actinomycetes, nematodes and viruses. Of these, viruses are very dangerous.
So far detection of the pathogens could have been done by isolation of pathogens from plant parts, identification and pathogenicity test (i.e. a microbial procedure to confirm that the specific pathogen causes disease to specific host). The pathological techniques are time consuming.
The diagnostic tests have eased the problem of detecting the pathogen. Basically, it involves two methods, DNA probe technique and immunological techniques like ELISA (enzyme-linked immunosorbent assay), dot-immunobinding assay (DIBA), ELIA, etc.
Using these methods you can find out the presence of pathogen inside the tissues (like vascular bundles, seed cotyledons) of crop plants. Accordingly, farmers can be suggested to control the disease and protect their crops from the attack of pathogens.
i. In DNA probe technique, pathogen-specific DNA probe is prepared. DNA preparation from specific tissue of plant is done. Then the same probe is used to detect the presence of suspected pathogen in specific tissues of plant.
ii. The ELISA technique is very sensitive and can detect viruses in 1-10 nanogram/ml. The diseased part of plant is taken and extract is prepared. The extract contains viral particles.
The cause of viral particles acts as antigen. According to suspected viruses, antibodies linked with enzymes are coated over the well of ELISA plate. When extract is put over the well and substrate is poured, there may or may not develop colour. Development of colour represents the presence of viral particles in plant tissue.
2. Molecular Breeding :
The breeding methodology, in which nucleic acid markers (molecular markers) are used, is called molecular breeding. Various types of molecular markers. Molecular markers can be used to locate the other genes of interest in the genome. These also help in identifying the particular genes and individuals.
In different plants the nucleotide sequence at particular location of DNA differs. These differences called polymorphism arise due to mutation e.g. insertion, deletion, etc. which results in changes in reading frame of DNA.
Using DNA markers polymorphism may be mapped in a genetic linkage group. Based on linkage mapping they can be positioned relative to one another.
During meiosis very far recombination events occur between the two close markers as compared to those markers that are far apart from each other. This shows that the alleles present at closely linked genes are interrelated together.
The objective of constructing molecular marker is to get it linked very tightly to the gene so that the traits can be selected based on marker allele. It would be interesting if the marker is actually the gene. Then it will facilitate the meiotic level separation of two recombinants.