**1. Introduction**

206 Gamma Radiation

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Induced mutation is one of the best alternatives for the improvement of horsegram as it can help to regenerate and restore the variability, which is generally lost in the process of adaptation to various stresses. Genetic variability is the most essential prerequisite for any successful crop improvement programme as it provides spectrum of variants for the effective selection, which can be achieved through the processes of hybridization, recombination, mutation and selection.

Genetic variability has been exhausted in horsegram due to natural selection and hence conventional breeding methods are not fruitful (Wani and Anis, 2001). Legumes generally loose different alleles for high productivity, seed quality, pest and disease resistance during the processes of adaptation to environmental stress.

Gamma sources are used to irradiate a wide range of plant materials, like seeds, whole plants, plant parts, flowers, anthers, pollen grains and single cell cultures or protoplasts. Radiations have been used successfully to induce useful mutations for plant breeding. The lower doses/ concentrations of the mutagenic treatments could enhance the biochemical components, which are used for improved economic characters (Muthusamy *et al*., 2003). Gamma radiation can induce useful as well as harmful effects on crops so there is need to predict the most beneficial dose for improvement of specific traits of crop plants (Jamil and Khan, 2002).

Improvement in yield and productivity of pulses is the need of the hour, but for this marginal land, aberrant rainfall, non availability of improved seeds, less or no input and poor crop management are the main constraints. Amongst pulses horsegram (*Macrotyloma uniflorum* (Lam.) Verdc) is highly neglected in India and hence require more emphasis on its improvement as it has nutritional, medicinal and fodder value. In Maharashtra, during the year 2008-2009, horsegram was cultivated on 0.466 lakh ha with annual production of 0.3232 lakh tones. The average yield per hactar was 693.56 Kg.

Horsegram is drought tolerant and having good nitrogen fixing ability, but receives a low priority in cropping system, soil types etc. It is grown in *kharif* and *rabbi* seasons, as main

Induction of Genetic Variability

(1.72%) was noted in 100Gy + 0.3%EMS.

the development and expression of chlorophyll pigments.

viable mutations in M2 generation is illustrated in Table-1.

**2.3 Frequency and spectrum of viable mutations** 

combination treatment (1.81%).

**2.4 Plant habit mutations** 

1.47%.

mutagens.

**2.2 Viable mutations** 

with Gamma Radiation and Its Applications in Improvement of Horsegram 209

(0.64 and 0.58%). The percentage of xantha and viridis was 0.41 and 0.28 respectively. The average number of chlorophyll mutations was 24.25, while the average frequency was

The combination treatments showed wide range of total percentage of chlorophyll mutations. The range varied from 0.74% to 1.72%. Highest chlorophyll mutation frequency

Reddy and Annadurai (1992) claimed that chlorophyll mutation can be used as an index for evaluating the mutagenic action of different mutagens. It is also important for assessing the potency of mutagen and also can be used as an indicator of factor mutations. Chlorophyll mutations are used as a dependable index for evaluating the genetic effects of

Albina, xantha, chlorina and viridis were found to be the most abundant type of chlorophyll mutants induced by GR and combination treatments in horsegram Bolbhat and Dhumal (2009). Manjaya *et al*., (2007) and Tambe *et al*., (2010) attributed this genes concerned with

The mutations affecting gross morphological changes in plant habit, leaf and pod morphology, and maturity were scored as viable mutations. These mutants were characterized and named on the basis of specific characters constantly observed in them throughout the course of investigation. Viable mutants and their characteristic features are given in Table-2. Effect of mutagens on the frequency and spectrum of different types of

All the treatments used have induced the widest spectrum of viable mutations. The range of viable mutations in gamma radiation and GR + EMS (Table-1) was 0.61 to 2.16% and 0.21 to 1.81% respectively. The highest percentage of frequency of mutations noted for plant habit, leaf and pod morphology and maturity, due to various treatments of gamma radiation was 0.77%, 0.66%, 0.58% and 0.30% respectively. These results also indicated that the percentage of plant habit mutations was maximum as compared to others. In combination treatments the percentage of frequency for plant habit, leaf, pod and maturity type mutations, was 0.76%, 0.63%, 0.49% and 0.28% respectively. The highest percentage of mutations was obtained in gamma radiation (2.16%) as compared to

The widest spectrum and frequency of viable mutations may be due to differential mode of action of the mutagens on different base sequences in various genes. The results indicated

Tall and gigas mutants obtained in the present investigation showed vigorous growth (Plate-2). According to Weber and Gottschalk (1973) and Blonstein and Gale (1984) the

that the variety used for study was sensitive to mutagenic treatments.

crop, or as a mixed crop. It is cultivated in areas with annual rainfall 300-600 mm, but does not tolerate flooding or water logging. The favourable average temperature is 18 to 27ºC, and adapted to a wide range of well-drained soils.

The use of dry seeds of horsegram as human food is limited due to its poor cooking quality, presence of high level of enzyme inhibitors and heamagglutinin activities (Ray 1969). The seeds are rich in tannins and polyphenols compared to the other legumes (Kadam and Salunkhe 1985). Antinutrients like phytates, tannins and oxalic acid reduce the availability of iron.
