Genetic and physiologic studies on induced mutants of three kabuli chickpea genotypes viz. ILC 482, ILC 3279, and ILC 6104 were carried out. Physical mutagen (gamma irradiation), and chemical mutagen (ethyl methanesulphonate) were used to create genetic variability, and subsequent selection of mutants. Prior to the mutagenic seed treatment, a laboratory experiment was conducted to obtain useful information about the use of gamma irradiation and EMS in inducing genetic variability, and to estimate the doses of gamma irradiation and EMS effective to reduce the growth (shoot or root) by a given proportion of the growth under control (non treated conditions>. At lower doses of gamma irradiation, stimulating effect on shoot and root length was observed 'in the three genotypes. The shoot and root length decreased at higher doses of gamma irradiation and EMS. The sensitivity to gamma irradiation and EMS appeared to be related with the seed size. The large seeded genotype ILC 6104 seemed to be more sensitive than ILC 3279 and ILC 482. It appeared that shoot and root length reduction can be used with equal reliability for estimating the appropriate mutagen dose. Three gamma irradiation doses (40, 50, and 60 kR ), and two EMS doses (0.1 and 0.2%), which caused reduction in the shoot and root length around 20 - 40% were chosen for large scale mutagenic treatments. After treating the seed with the Selected doses, treated seed along with non-treated control were grown as M1 generation in the field. Based on Ml plant survival in the field, the order of radiosensitivity appeared to be ILC 6104>ILC 3279> ILC 482, which was similar to that of laboratory experiment. All the surviving M1 plants were harvested individually.
The M2 generation was grown on M1 plant to row progeny basis and morphological mutants were isolated. The results indicated that induced mutability is governed by the genetic architecture of the material used; and the gamma irradiation and EMS differ in their mutation spectrum. The appearence of chlorophyll mutants give a good indication that other morphological mutants will occur in a fairly good proportion. The highest frequency of morphological mutants was recorded for the first time. An inverse relationship between radiosensitivity in Ml and mutability in M2 was observed. The genotype ILC 482 was least sensitive to gamma irradiation and EMS, but most mutable genotype, whereas, ILC 6104 was most sensitive to gamma irradiation and EMS, but least mutable.
The mutagenic treatments induced mutations affecting plant height. growth habit. branching and stem structure, stem and foliage colour. leaf type, flowering and maturity, seed and pod type. There were differences in mutation spectrum between the genotypes and between the two mutagens. The most notable mutants were those having large seed size (from ILC 482 and ILC 3279), tall plant type; 80 cm (from ILC 3279; 65 cm). These mutants may be used directly in developing a variety. Other mutants like double flowering, early maturity, long pod, and various leaf type mutations increase the wealth of germplasm for breeding programme according to the need. Mutants like tendril, fasciated, leafless, aphid attracting, are important for phylogenetic and evolutionary point of view.
The mutants were studied for their breeding behaviour and genetic studies. Mutants like miniature, dwarf, semidwarf, compact, tall, erect, spreading, bushy, prostrate, basal branching, umbrella, fasciated, increased branching, large leaf, gigas leaf, tiny leaf, small leaf, narrow leaf, simple leaf, round leaf, leafless, bipinnate compound leaf, long and lax leaf, light green, bluish green and dark green plant colour, cauliflower-head type, male-sterile, early flowering, late flowering, long pod, green seed colour, and round seed shape were found monogenic recessive in nature. Pink flower colour mutation was monogenic dominant. Mutants exhibiting aphid attraction, heat tolerance, leafminer tolerance, long podded, and tendril mutants are reported for the first time in chickpea.
212 true breeding mutants and three parent genotypes were evaluated in M3 generation for favourable or unfavourable characters connected with the mutants by linkage or pleiotropy.
Direct and indirect contribution of various yield components' was worked out to arrive at specific physiological explaination for providing certain parameters that could be used as selection indices in breeding chickpea genotypes with high yield potential.
In mutants, a very wide range of variability existed both in the higher as well as lower direction for most of the characters, which offer immense scope for selecting plants with desired changes in their morphological characteistics. The results have shown that relationships between the traits in the mutant populations changed from that of respective control populations. Increase in correlation among traits suggested that the existing relationships of yield components with yield can be improved further through mutation induction in such a way that yielding ability is not altered.
The changes in the sign of correlations was observed which indicated breakage of relationship between the characters in the mutant populations. These findings lend support to the view that mutagenic treatments could alter the mode of relationship between any two characters, apart from generating variability.
The path coefficient analysis suggested that in the control populations of ILC 482, ILC 3279, and ILC 6104 secondary branches were the most important yield component. However, in the mutants of ILC 482, secondary branches and canopy widthi in ILC 3279, secondary branches, growth habit and hundred seed weight and in ILC 6104, secondary branches, hundred seed weight, and elliptic index of leaf area were the most important yield components among the characters studied.
The results of selection of the most contributing traits to predict yield indicated that yield was highly dependent upon pods per plant, seed per pod, and hundred seed weight in the three genotypes and their mutants. In the absence of these traits. seed yield was found to be highly dependent upon days to maturity, and, secondary branches in ILC 482 control population, and on plant height, canopy width, and secondary branches in mutant population; in ILC 3279 control population, flowering duration and secondary branches were important, while in the mutants, days to maturity, plant height, and growth habit were important; in ILC 6104, for both control and mutant populations, seed yield was highly dependent upon secondary branches and elliptic index of leaf area.
The results of screening of M2 segregating material indicated that mutagenic treatments were effective in inducing variability for Ascochyta blight resistance and cold tolerance. An ILC 482 mutant (no.16119) proved the only source of cold tolerance in the world chickpea germplasm screened at ICARDA during 1989-90. This is the first ever report of induction of cold tolerance in chickpea through induced mutations. The mutant will be of great value as a source of cold tolerance and for studying mechanisms of cold tolerance.