MSc

The present study ‘In vitro mutagenesis and evaluation of somatic
embryo derived plantlets in cassava (Manihot esculenta Crantz.)’ was conducted
in the Department of Plant Breeding and Genetics, College of Horticulture during
2014-15. They study attempted to assess the variability existing among the in
vitro derived plantlets of cassava genotypes Sree Jaya and CC1 as well as to
generate further variability through in vitro mutagenesis.
With the aim to induce variability, in vitro mutagenesis of callus derived
from cassava genotypes Sree Jaya and CC1 was attempted earlier in the
department. This had resulted in 10 somatic embryo derived plantlets in primary
hardening stage and 58 plantlets yet to be transferred for hardening.
The above plantlets formed the basic material for field evaluation
undertaken in the present study. Sree Jaya and CC1 genotypes were planted as
control. Out of the 58 plantlets transferred from the in vitro cultures to hardening,
only 34 plantlets survived i.e., the survival was found to be 58.62 per cent. All the
ten plants that were already in the primary hardening stage survived.
Observations were recorded during field evaluation of the in vitro
mutagen treated plants at three, six and nine months after planting as per the
descriptor of cassava (Fukuda et al., 2015). The plants varied with respect to
qualitative characters like colour of apical leaves, leaf retention, shape of leaf
lobe, petiole colour, leaf orientation, colour of stem exterior, extend of root
peduncle, shape of tuber, root colour, colour of root pulp and colour of root
cortex. Variability was also observed for quantitative characters like length and
width of leaf lobe, length to width ratio of leaf lobe, petiole length, distance
between leaf scars, height of plant, tuber weight per plant, tuber girth, stem girth,
extend of root peduncle, starch content and dry matter content. Among the
mutagen treated plants of Sree Jaya none of in vitro mutagen treated plants were
found to be superior with respect to tuber yield while in CC1 genotype, six plants
yielded better than the control.
Sensory evaluation of the tubers produced by in vitro mutagen treated
plants as well as control plants was done by twelve panelists to assess consumer
perception. The tubers from plant 32 (Sree Jaya; 1.2 % EMS), followed by plant
31 (Sree Jaya; 1.2 % EMS) and plant 42 (CC1; 0.9 % EMS) were most preferred
for various sensory attributes evaluated.
In vitro mutation being a potential method to induce variability, mutation
of callus derived from genotypes was as attempted to create more variants. The
callus cultures of Sree Jaya and CC1 genotypes were established as per the
protocol standardised by Magaia, (2015). Friable embryogenic calli production
was higher in the media MS + 8 mg L-1 2,4-D + 1 mg L-1 NAA + 0.5 mg L-1 BAP
using leaf explants. Calli were subjected to physical (γ irradiation at 30- 60 Gy at
an interval of 10Gy) and chemical (EMS 0.1 - 0.9 % at an interval of 0.1%)
mutagens as advocated by Magaia, (2015). However, regeneration of mutagen
treated friable calli was not obtained in both genotypes.
Quantum of variability expressed in the in vitro mutated plants of cassava
with respect quantitative traits shows the efficiency of in vitro mutagenesis in
creating variability in cassava. In vitro mutagenesis is a potential tool in the hands
of plant breeder to create variability especially in vegetative propagated crops.
The evaluation of in vitro mutagen treated plants in the field showed wide
variation with respect to most morphological as well as biometrical traits. All the
plants evaluated can hence, be advanced to next generation of evaluation (M1V1)
with replication to identify the mutants. From the results obtained on induction of
in vitro mutation to create more variants in cassava, it is concluded that the friable
callus in both the genotypes need to be cultured in alternate regeneration medium
for successful regeneration of somatic embryos.