Everything you need to know about molecular plant breeding !
Q. 1. What is molecular plant breeding?
Ans. Molecular breeding is an important branch of plant breeding which is gaining increasing significance these days. Molecular breeding is of very recent origin. It developed In the 1980s with the evolution of DNA marker technologies.
Molecular breeding is defined as a branch of plant breeding which utilizes molecular genetic tools and approaches for genetic improvement of crop plants. In other words, genetic improvement of crop plants for various economic traits using molecular marker and transformation technologies is referred to as molecular plant breeding.
Q. 2. Explain main points related to molecular plant breeding.
Ans. Main points related to molecular plant breeding are briefly presented below:
i. Molecular Plant Breeding (MPB) utilizes latest genetic technologies to develop better varieties of crop plants. Two molecular technologies, viz. molecular marker technology and transformation technology are used in molecular plant breeding.
ii. Molecular breeding is applicable to both plant breeding and animal breeding. In other words MB can be used for genetic improvement of both plants and animals.
iii. MPB is more precise, rapid and cost effective in comparison to conventional phenotypic selection. MPB reduces the time significantly required for the development of new cultivars. It takes 4-5 years for development of new cultivars against 10-12 years of conventional phenotypic selection method.
iv. It offers possibility of achieving those goals which cannot be achieved by conventional methods.
v. It permits gene transfer between unrelated organisms through transformation technology or genetic engineering.
vi. It helps in identification of new genes of economic importance.
vii. Now-a-days, molecular breeding is a vital part of plant breeding programmes.
viii. MPB sometimes contributes novel traits of agronomic value in crop plants.
Q. 3. What are branches of molecular breeding?
Ans. In agriculture or crop improvement, molecular breeding has two distinct branches, viz.:
(i) Molecular marker technology and
(ii) Transformation technology.
Q. 4. What are advantages of molecular markers?
Ans. A molecular marker is a unique sequence of nucleotide located close to the gene of interest. In other words, molecular markers are special segments of DNA which flag the presence of genes that control particular trait. They are located very close to the gene of interest and are easily identifiable.
The important advantages of molecular markers in plant breeding are presented below:
(i) Molecular markers allow selection of desirable trait at any stage of plant growth. There is no need to wait till maturity of the plants.
(ii) They are not affected by environmental conditions. In other words molecular markers are stable.
(iii) They eliminate the need for phenotypic scoring.
(iv) They provide uniform method for scoring.
(v) A very small sample of plant, leaf or grain is required for scoring of molecular markers.
(vi) Much less numbers of breeding generations are required for evaluation of molecular markers.
(vii) They provide information about the percentage of genome contributed by each parent.
Q. 5. What are applications of molecular markers?
Ans. There are several useful applications of molecular markers.
Some important applications of molecular markers are listed below:
(i) Molecular markers help in better understanding of quantitative trait loci (QTL).
(ii) They are highly reproducible and thus help in accurate selection of desired genotypes.
(iii) They are useful in gene pyramiding i.e. in incorporation of multiple target genes into a single cultivar.
(iv) They are useful in identification of cultivars and parents of hybrid.
Q. 6. What is molecular marker technology?
Ans. A technology that utilizes molecular markers for genetic improvement of crop plants is referred to as molecular marker technology. It is also known as DNA marker technology.
Important points related to this technology are briefly presented below:
i. It does not involve genetic transformation and hence does not require biosafety and bioethics measures.
ii. It utilizes various DNA markers such as restriction fragment length polymorphisms (RFLP), amplified fragment length polymorphisms (AFLP), random amplified polymorphic DNA (RAPD), simple sequence repeats (SSR), single nucleotide polymorphisms (SNP), expressed sequence tags (EST), sequence tagged site (STS), etc.
iii. It makes use of two major technologies, viz. marker assisted selection (MAS) and DNA fingerprinting.
iv. Molecular marker technology helps in early detection of cytoplasmic male sterility. By this technology, the cytoplasm type of unknown plants can be identified.
v. It is highly accurate and rapid method of crop improvement. Marker assisted selection (MAS) is a potential tool of crop improvement which should be deployed along with conventional breeding methods.
vi. It is effective technology in achieving new goals which cannot be easily achieved by traditional breeding such as pyramiding disease resistance genes with indistinguishable phenotypes.
vii. The DNA fingerprinting is useful in identification of cultivars, pure lines and parents of a hybrid.
viii. Molecular marker technology (MMT) is useful in mapping desirable quantitative trait loci (QTL).
Q. 7. What is transformation technology?
Ans. The genetically engineered genes are known as transgenes. The technology that utilizes transgenes in developing new crop cultivars is referred to as transformation technology. It is also known as gene technology or genetic engineering.
Genetic engineering is the process of removing, modifying or adding genes to a strand of DNA for specific purposes. For example rye grass produces a protein in its pollen that causes an allergic reaction in humans. By switching off the gene responsible for producing allergen, we can develop allergy free rye grass.
Main points related to transformation technology are briefly presented below:
i. It involves transgenes and hence biosafety and bioethical measures are essential.
ii. It leads to development of transgenic cultivars which are not permitted for organic farming. Moreover, development of transgenic cultivars is not permitted under organic plant breeding.
iii. Transformation technology is useful in developing crop cultivars resistant to biotic (insects, diseases and parasitic weeds) and abiotic stresses and also in improvement of quality traits.
iv. It is an accurate and rapid method of developing superior crop cultivars.
v. It utilizes mainly two methods of gene transfer, viz. biolistic method and agrobacterium mediated method. These methods are being applied to various field crops for developing transgenic cultivars.
vi. This technology leads to over expression of novel genes conferring novel traits. It leads to inhibit expression of harmful genes.
vii. It is useful in evaluation of gene promoters and also of the function of unknown genes.
Q. 8. Give a comparison of molecular marker technology and transformation technology.
Ans. There are some similarities and some dissimilarities between marker technology and transformation technology which are presented in Table 24.1.
Q. 9. What are practical applications of molecular marker technology?
Ans. Molecular marker technology has four principal applications in crop improvement programmes, viz.:
(i) Molecular selection,
(ii) Molecular backcrossing,
(iii) Molecular mapping, and
(iv) Molecular genotyping.
These are briefly discussed below:
(i) Molecular Selection:
This method is used in the segregating populations (F2 or F3) for selection of plants carrying the gene of Interest. It is used to select those genes which are difficult to select on the basis of phenotypes. It is very useful in selection of genes which are highly influenced by environmental conditions. It allows easy stacking of disease resistant genes. The selection can be practised at an early stage of plant growth.
(ii) Molecular Backcrossing:
This is the most common application of molecular marker technology in crop improvement. It requires less material and less space for conducting DNA marker test. It allows recovery of the highest portion of the recurrent parent, with desired genes, in the shortest number of generations. It is possible to identify between homozygous and heterozygous plants through DNA markers, Thus it helps in rapid transfer of desirable gene.
(iii) Molecular Mapping:
DNA marker technology plays important role in gene mapping. It is useful in mapping of both qualitative and quantitative traits. It identifies molecular markers linked to chromosomal regions affecting the desirable trait and thus helps in gene mapping. The gene mapping is possible even during early stages of plant growth. Various breeding populations, viz., recombinant inbred lines (RILs), near isogenic lines (NILs), bulk segregant populations, introgressed lines etc., are used for gene mapping,
(iv) Molecular Genotyping:
It refers to molecular characterization of breeding material. It fulfills DNA fingerprinting needs. It is useful to identifying differences between varieties and hybrids. It is used for varietal verification, varietal purity and hybrid purity and thus is useful for patent protection.
The gene technology or genetic engineering has four principal applications in crop improvement which are listed below:
i. Development of transgenic crop cultivars in different crop plants resistant to biotic and abiotic stresses.
ii. Development of herbicide resistant cultivars in different crop plants.
iii. Improvement in nutritional quality, keeping quality and industrial quality in food, vegetable, fruits and other commercial crops.
iv. Identification of new genes and gene systems. It enables the introduction of novel traits in crop plants such as golden rice and longer blooming flowers in flower plants such as petunia.
Q. 10. What are practical achievements of molecular plant breeding?
Ans. The molecular plant breeding has been used for genetic improvement of various field crops (maize, barley, wheat, rice, sorghum, soybean, chick pea, pea, mungbean), vegetable crops, forage crops and fruit crops for various economic characters.
The notable achievements and briefly presented below:
i. Bacterial blight and blast resistant cultivars have been developed in rice through marker assisted selection.
ii. In soybean, cyst nematode resistant cultivars have been developed through MAS.
iii. In maize, quality protein maize (QPM) lines have been developed through MAS.
iv. In rye, bread making quality has been significantly improved by transferring glutelins gene of wheat through genetic engineering.
v. In wheat and rice, yield has been increased by transferring a gene from maize through gene technology.
vi. In cotton, bollworms and herbicide resistant cultivars have been developed through transgenic technology by using Bt. gene from soil bacterium. Several other examples can be cited from vegetable and forage crops.
Q. 11. What are advantages of molecular marker technology?
Ans. Some of the advantages of molecular marker technology are presented below:
i. It helps in better understanding of quantitative trait loci and as a result in more effective breeding,
ii. Rapid Introgression of simply inherited characters. The number of backcrosses required can be reduced drastically once the marker for the character to be introduced is identified.
iii. Easy or early indirect character selection – It is useful for those genes that cannot be detected at an early stage of plant growth. For example, lysine and tryptophan genes in maize.
iv. It is useful in achieving new goals that cannot be achieved through conventional breeding such as pyramiding of disease resistance genes which cannot be detected by phenotypes. In other words, it offers possibility of achieving unattainable goals.
v. It is accurate, rapid and more reliable method of crop improvement.
vi. The DNA marker test can be conducted at any stage of plant growth even for those traits which express at the maturity.
vii. A very small amount of plant tissue i.e. leaf, stem, flower, seed etc. is required to conduct DNA marker test.
viii. The DNA test is the only available practical technique for ensuring the presence of multiple beneficial genes in a single variety.
ix. DNA based fingerprinting allows the reliable tracking of beneficial traits during varietal selection.
x. DNA based fingerprinting is the best currently available technology to differentiate among varieties for patent protection and plant variety protection Act Certification.
xi. DNA based marker systems are useful in selection of disease or insect resistant material even in the absence of pest incidence.
Q. 12. What are advantages of gene technology?
Ans. Some of the advantages of gene technology are given below:
i. It involves transgenes and leads to development of transgenic cultivars in different self and cross pollinated species.
ii. It permits transfer of desirable gene from unrelated species i.e. from micro-organisms to crop plants and even from animals to plant.
iii. It enhances the expression of novel genes conferring novel traits and switch off the expression of harmful traits such as allergen in rye grass.
iv. It is precised and rapid method of crop improvement. Moreover, it requires less space than conventional breeding methods.
v. It is useful method of improving crop plants for resistance to biotic and abiotic stresses and quality traits.
vi. It helps in evaluating the functionality of unknown genes.
Q. 13. What are disadvantages of molecular plant breeding?
Ans. However, it has some disadvantages which are briefly presented below:
i. The initial cost of both the branches of molecular plant breeding i.e. molecular marker technology and gene technology is very high. Both these technologies require costly equipment, glass wares and chemicals.
ii. Molecular breeding required team of well-trained manpower for handling of costly equipments, chemicals and glassware.
iii. Gene technology involves transgene and thus requires biosafety and bioethical measures,
iv. The scoring of DNA or molecular markers is a laborious and time consuming task.
v. In gene technology, the frequency of desirable transformants is very low which restricts the use of this technology.
Q. 14. What are restriction enzymes?
Ans. A group of endonuclease enzymes, that cuts DNA only at specific sites or base sequences.
Q. 15. What are endonuclease enzymes?
Ans. The enzymes which are able to make Internal cut in the DNA molecule are called endonucleases. Most of the endonucleases cut DNA molecule at random sites, but some cut only at specific sites. Endonucleases are found. In micro-organisms and are also referred to as biochemical scissors. Endonucleases do not cut DNA of their own cell and protect it by methylation process.
Q. 16. What is recognition site?
Ans. The specific base sequence or site recognized by restriction enzyme in DNA molecule to make a cut or cleavage Is called recognition site; also called recognition sequence.
Q. 17. What is DNA Finger Printing?
Ans. A method of genetic engineering in which a DNA probe is hybridized with DNA of plants or animals to determine similarities: and differences between two DNA molecules.
Q. 18. What are DNA probes?
Ans. Small segments of DNA with known base sequences, origin and function are called DNA probes. DNA probes are useful in marker aided selection.
Q. 19. What is DNA library?
Ans. A set of DNA probes is called DNA library.
Q. 20. Define gene amplification.
Ans. An increase in the copy number of a gene/DNA sequence is called gene amplification.
Q. 21. What is restriction fragment?
Ans. A fragment of DNA created by cleavage at specific sites by a restriction endonuclease is called restriction fragment.