Gamma rays and EMS induced morphological mutation in Indian mustard (Brassica juncea L. Czern and Coss)

Introduction

Mutation is an important breeding method for creating variability in crop species. The utilization of induced mutations for the improvement of crop plants has yield several mutants which have been used directly as new cultivars (Gottschalk and Wolf, 1983) [1] . Induced mutants constitute a valuable resource for research aimed at understanding the process in governing plant development (Cove, 1993) [2] . However, in mutagenic experiments most of the mutations are deleterious and have no direct practical value. Moreover, majority of the agricultural crops exhibit a high percentage of morphological mutations in mutagenesis experiments. The mutagenic effect is being reflected in the form of segregation of morphological mutants and it serves as a good indicator to forecast the spectrum of genetic variability that can arise from the mutated population. The probability of producing desirable mutations and genetic variability by artificial means is theoretically higher in self-pollinated crops (Welsh, 1981) [3] like mustard. The frequency of morphological mutation is being used as a convenient guide for the effectiveness of different mutagen dose. The present paper deals with the frequency and spectrum of morphological mutations in M 2 and M 3 generations of two genotypes of Indian mustard viz. CAULC-2 and NRCHB-101 induced by different doses of gamma rays and EMS. prepared 0.5 per cent EMS solution for 6 hours and thus combined treatment between gamma rays and EMS was prepared. The untreated seeds were used as control. The treated material along with untreated seeds of each variety as control was sown in randomized block design with three replications in the experimental field of Department of Genetics and Plant Breeding, College of Agriculture, Central Agricultural University, Imphal, during rabi 2018-19, 2019-20 and 2020-21. Seeds of M 1 plants were harvested separately and the individually harvested M 1 plants were sown following plant to progeny method during rabi 2019-20 to raise M 2 generation. 252 plants (126 from each genotype) from M 2 population were selected and the progenies of the selected families were again laid out in field following plant to progeny rows during rabi 2020-21 to raise M 3 generation The treated and control material were carefully screened for the frequency of morphological mutation throughout the life period of the plant in M 2 and M 3 generations. All visible changes in comparison to the control were classified for deviation from the normal and the most conspicuous characters taken into consideration were general architecture of the plant, duration, leaf, seed and siliqua characters etc. The spectrum and frequency of viable mutations was calculated using the following formula.

Results and Discussion

Careful screening of control as well as treated populations was undertaken to identify the response of Indian mustard to different mutagenic treatments. Various types of morphological mutations were observed at different stages of growth in the M 2 as well as M 3 generation. The morphological mutations identified were grouped on the basis of the trait affected as listed below.

Mutations affecting plant growth habit

Profuse basal branches ii) High number of branches (Fig 1).

Mutations affecting plant height:

1. Tall: The tall mutants were vigorous and tall, attained the height of 160-175 cm while the parents attained the height of 110-120 cm in CAULC-2 and 100-110 cm in NRCHB-101. (Fig. 3).

Mutations affecting foliage

1. Narrow leaf 2. Broad leaf 3. Round leaf 4. Ovate leaf 5. Purple leaf (Fig. 4).

Mutations affecting seed size and colour 1. Bold seeded 2. Small seeded 3. Orange seeded (Fig. 5). For plant species, these morphological variations may be beneficial or detrimental to cause lethality to the organism. In the present study, the spectrum of mutation was observed to be dependent on the type of mutagen used. Different types of morphological mutants were induced. These include profuse basal branches, high number of branches, tall, dwarf, early flowering, late flowering, white flower, malformed flower, early maturity, narrow leaf, broad leaf, round leaf, ovate leaf, purple leaf, bold seeded, small seeded, orange seeded, long siliqua, short siliqua, sterile siliqua, partially sterile siliqua, appressed siliqua and purple siliqua. The differential spectrum of viable mutants observed in the present investigation was also reported earlier by several workers in Brassica species viz. Verma (1973) [4] , Verma and Rai (1980) [5] , Anand and Mishra (1985) [6] , Chauhan and Kumar (1986a) [7] , Shah et al. (1990) [8] , Rahman and Das (1993) [9] , Roy et al. (1997) [10] , Das et al. (1999) [11] , Singh and Sareen (2004) [12] , Wang et al. (2004) [13] , Patel et al. (2006) [14] , Barve et al. (2009) [15] , Landge et al. (2009) [16] , Hassan and Abl-El-Haleem (2014) [17] , Kumar et al. (2018) [18] , Malek et al. (2014) [19] . The possible cause of these macro-mutations may be chromosomal aberrations, small deficiencies or duplications and most probably gene mutation (Singh et al., 1980) [21] . Several workers have reported that these viable mutations were monogenic and recessive in nature controlled by one or more recessive genes (Singh and Yadav, 1982). Mutation frequency was highest for combination treatments. Similar results were obtained by Yadav (1992) [20] in Brassica juncea. Combined treatment of physical and chemical mutagen may cause greater mutations because of higher frequency of both chromosome and factor mutations.

Mutations affecting

Acknowledgement

AcknowledgementThe authors are thankful to the BCKV, Mohanpur, West Bengal for irradiating the experimental materials, Head of Department of Genetics and Plant Breeding, the Dean and the authorities of College of Agriculture, Central Agricultural University, Imphal for providing all the necessary research facilities throughout the course of investigation.

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