Mutation Breeding of Chick pea in Pakistan
January 04, 2013
By: Shehzad Ahmad Kang
What is mutation?
A Mutation occurs when a DNA gene is damaged or changed in such a way as to alter the genetic message carried by that gene.
A Mutagen is an agent of substance that can bring about a permanent alteration to the physical composition of a DNA gene such that the genetic message is changed.
Types of Mutation:
There are two types of mutations e.g. Spontaneous mutation and Induced mutation.
- Spontaneous mutation
Spontaneous mutations on the molecular level can be caused by:
Tautomerism – A base is changed by the repositioning of a hydrogen atom, altering the hydrogen bonding pattern of that base resulting in incorrect base pairing during replication.
Depurination – Loss of a purine base (A or G) to form an apurinic site (AP site).
Deamination – Hydrolysis changes a normal base to an atypical base containing a keto group in place of the original amine group. Examples include C → U and A → HX (hypoxanthine), which can be corrected by DNA repair mechanisms; and 5MeC (5-methylcytosine) → T, which is less likely to be detected as a mutation because thymine is a normal DNA base.
Slipped strand mispairing – Denaturation of the new strand from the template during replication, followed by renaturation in a different spot (“slipping”). This can lead to insertions or deletions.
· Induced mutation
Induced mutations on the molecular level can be caused by:-
- Hydroxylamine NH2OH
- Base analogs (e.g. BrdU)
- Alkylating agents (e.g. N-ethyl-N-nitrosourea)
- These agents can mutate both replicating and non-replicating DNA. In contrast, a base analog can only mutate the DNA when the analog is incorporated in replicating the DNA. Each of these classes of chemical mutagens has certain effects that then lead to transitions, transversions, or deletions.
- Agents that form DNA adducts (e.g. ochratoxin A metabolites)
- DNA intercalating agents (e.g. ethidium bromide)
- DNA crosslinkers
- Oxidative damage
- Nitrous acid converts amine groups on A and C to diazo groups, altering their hydrogen bonding patterns which leads to incorrect base pairing during replication.
Ultraviolet radiation (nonionizing radiation). Two nucleotide bases in DNA – cytosine and thymine – are most vulnerable to radiation that can change their properties. UV light can induce adjacent pyrimidine bases in a DNA strand to become covalently joined as a pyrimidine dimer. UV radiation, particularly longer-wave UVA, can also cause oxidative damage to DNA. Mutation rates also vary across species. Evolutionary biologists have theorized that higher mutation rates are beneficial in some situations, because they allow organisms to evolve and therefore adapt more quickly to their environments. For example, repeated exposure of bacteria to antibiotics, and selection of resistant mutants, can result in the selection of bacteria that have a much higher mutation rate than the original population (mutator strains).
Mutation in chick pea
A comparative study for frequency of morphological mutations induced by physical (gamma rays) and chemical (EMS) mutagens in M2 population was conducted in two desi (Pb2000, C44), one each of kabuli (Pb1) and desi x kabuli introgression genotypes (CH 40/91) of chickpea. In M2 population, about 63 different types of morphological mutations in different parts of the plants, such as branching pattern, stem structure, growth habit, foliage type, plant height, pod and seed size, foliage color, flowering behavior and maturity was observed. The highest frequency of morphological mutations was observed in 300 Gy gamma irradiation (4.11%) of CH40/91 followed by 0.4% EMS (2.08%) of desi genotype C44. The overall frequency of mutations in physical mutagen was high in CH40/91 (2.69%) followed by Pb2000 (1.38%), C44 (1.02%) and Pb-1 (0.27%). The overall frequency of morphological mutations in chemical mutagen was very low in Pb2000 (0.45%) followed by Pb-1 (0.78%), C44 (1.53%) and CH40/91 (1.90%) as compared to physical mutagens. Overall frequency of morphological mutations in M2 population also indicated maximum mutability (2.30%) in introgression genotype (CH40/91) followed by desi genotype C44 (1.28%) and Pb2000 (0.91%), whereas kabuli type had lowest mutation rate (0.52%). The significant higher morphological as well as chlorophyll frequency of CH40/91 as compared to other three genotypes could be due to the diverse genetic nature. The gamma rays and EMS treatments differ in their mutation spectra/frequency.
Varieties Developed by NIAB, Pakistan.
CM-72; a high yielding and blight resistant variety (derivative 6153 at 150Gy dose of gamma rays) was released in 1983 for general cultivation.
CM-1918; an Ascochyta blight resistant and high yielding mutant line (derivative of 6153 at 150 Gy dose of gamma rays) developed at NIAB was approved for general cultivation in NWFP as NIFA-88 in 1991.
CM-88; tolerant to both blight and wilt diseases varieties (derivative of c727 at 100 Gy dose of gamma rays) was released for general cultivation in 1994.
CM-98; a bold seeded, high yielding and disease resistant variety (derivative of k850 at 300 Gy dose of gamma rays) was released in 1998.
CM-2000; a kabuli type (beige color seed) variety (derivative of ILC 195 at 150 Gy of gamma rays) was released for general cultivation in 2000.
Chick pea germplasm developed at NIAB has resulted in the reseased of one desi variety (THAL-2006). For general cultivation in thal area in 2006 by arid zone research institute, Bakher. This variety was an outcome of hybridization of NIAB mutant line CM82/87 with desi variety C44.
By: Shehzad Ahmad Kang, Department of Plant Breeding and Genetics,University of Agriculture, Faisalabad, Pakistan- 38040
Corresponding author’s email: firstname.lastname@example.org