1
CHAPTER
1
INTRODUCTION
1 .1 .
MUTATIONS AND IMPORTANCE OF MUTATION BREEDING
M u ta ti o n s
Hugo de Vri es
mutations,
(1901),
a p i o n e e r in
the study of
def ine d mutation as an i n h e r i t a b l e
the c h a r a c t e r s of an org an ism .
has been used to d e s c r ib e
Historically
change in
the word mutation
an i n h e r i t a b l e phenotypic change
r e g a r d l e s s of i t s g en et ic o r i g i n .
The terra m ut a t io n ,
any h e r e d i t a r y change other
se gr e ga t io n
when used in a broad s e n s e ,
means
than that due to Me ndelian
and re co m b in a ti on .
In the
to the change in a gene or i t s v i s i b l e
strict
sense
effect.
It
it refers
refers
to
2
the p ro ces s by which a change occurs i n the gene tic
c o n s t i t u t i o n of an organism as well
ph en ot y p ic change*
change
An i n d i v i d u a l
as to the r e s u l t i n g
expressing
r e s u l t i n g from mutation i s c a l l e d
the phenotypic
a mutant.
gene that has changed i 3 c a l l e d the mutant gene.
The
The genes
are the b a s i s of development of c h a ra ct er s and b r in g
hereditary
It
striking,
about
s t a b i l i t y whi le mutations arejthe b a s i s o f v a r i a t i o n *
uas co n si d er ed e a r l i e r
di s c r e te
that mutations are l a r g e ,
and d r a s t i c i n h e r i t a b l e ch an ge s,
arising
su ddenly
in an otherwise pure b re ed ing v a r i e t y ,
realized
that mutations may also be very small or m i n u t e .
mu t at io ns may not produce v i s i b l e
induce
physiological
but i t
s t r u c t u r a l ch an ge s;
changes which a f f e c t
an organ while others may in f l u e n c e
i s now
All
some
the f u n c t i o n i n g of
the f e r t i l i t y or v i a b i l i t y
o f an or gan ism .
Mutations can occur spontaneously i n nature or they
may be ind uce d e x p e r i m e n t a l l y .
Spontaneous mutations have been
noted both in pl a nt s and a ni m a ls , Mu ta ti o ns can be induc ed
e x p e r i m e n t a l l y with the help of va ri o u s physical
and chemical
agen ts which are c a l l e d mutagens. M uta tio ns may prove to be
harmful
or b e n e f i c i a l
S in c e mut ations b ri ng
to the organism in which they o c c u r .
about v a r i a t i o n ,
they provide
ultimate b a s i s for e v o l u t i o n of new forms,
the
v a r i e t i e s or s p e c i e s .
Importance of mutation breed ing
One of the most urgent problems fo r man today i s the
p r ov is io n of adequate
food supply in view of the r a p i d l y
increa-
s i n g population.*
One of the methods of t a c k l in g
problem i s through
varieties
of
characters
to
as
unfavourable
insect
plant
wheat
yield
environm ental
has
b re e d ing methods
in
exhibiting
higher
p e sts0 This
revolution”
to
such
the evo lut io n of new and b e t t e r
t
plans
food
our
been
country
and
w ith
brought
some
desirable
greater
conditions,
done
which
various
the
diseases
help
about
year
3
ago
resistance
hybridization,
polyploidy,
etc.
t e c h n i q u e s were
hybridization.
i n d u c t io n
The e a r l i e r
various
"green
w ith
reference
of m u t a t io n s ,
with s e l e c t i o n
in d u c ti o n
and
These methods are l i m i t e d in scope because
fo r improving a p a r t i c u l a r crop i s
l i m i t e d by the amount of v a r i a b i l i t y within
a v a i l a b i l i t y to the b r e e d e r .
hybridization
such as
conventional b r e e d i n g
concerned l a r g e l y
application
and i t s
and
cultivation.
selection,
their
of
the
Plant b re e d in g in cl ud es va ri o us aspects
of
this
can
utilize
available
the
Selection
variations
s pec ies
and
and produce
v a r i o u s recombinations out of them but can not create new
variations,
constitute
Mutatio ns produce new v a r i a t i o n s ,
which
the b a s i s for ev o lu ti o n of new s p e c i e s in
na tu re as well as for breeding new v a r i a t i e s e x p e r i m e n t a l l y .
By producing new phenotypic c h a r a c t e r s ,
the
scopB for
artificial
in
mut ations widen
s e l e c t i o n and h y b r i d i z a t i o n .
Therefore,
i n d u c t i o n of mutations can be of
hybridization
work p a r t i c u l a r l y
v a r i a b i l i t y or are
deficient
in
if
special
help
the p a re n ts lack
desirable
characters.
4
Mutation breeding often provides a solution for
some specific plant breeding problems. The direct use
of mutations is often a very valuable supplementary
approach to plant breeding. While
dealing uith a highly
developed variety, the breeder is reluctant to use standard
hybridization methods for
further improvement because
they may disrupt a superior combination of genes that has
already been achieved. In this regard mutation breading
seems to be specially useful when it is desired to improve
one or tuo easily identifiable characters in an otherwise
uell-adapted variety. Here the special advantage is that the
basic genotype of the variety is usually only s l i g h t l y
altered, when the desired character(s) is (are) added. An
additional advantage is that the time required to evolve the
improved variety can be much shorter than uhen hybridization
is used to achieve the same result,
be o b t a i n e d
in a homozygous state in
'h
desired mutation can
or
generation as
compared uith F^ or F^ generation in the case of
hybridization. So the ‘time required for breeding a
particular crop is cut short- considerably,, Elegant examples
of such achievement were provided b y Suaminathan uhen
he
added auns to an aunless w h e a t variety and changed the
grain colour of sonora -64
from red to amber to produce
the variety sharbatl-sonora (Suaminathan et,,. _al. 196*3).
Mutation b r ea di n g has proved of
in
sp ec ia l
advantage
b r i n g i n g about g en eti c improvement in v e g e t a t i v e l y
pr opa gat ed p l a n t s *
These p la n t s can not be h y b r i d i z e d
b e c a u s e they reproduce a se x u a ll y
mutation breed ing i s
and,
therefore,
the only method a v a i l a b l e
for
improving them.
Through induced mutations i t i s p o s s i b l e
s e x u a l i t y in aporaictic species which may l a s t
generations.
Thus i t may be p o s s i b l e
s p e c i e s through normal h y b r i d i z a t i o n
Sigurbjornsson,
in
several
programmes (s ee
1977),
used the
the improvement o f a great v a r i e t y of
crop p la n t s y i e l d i n g
medicines,
for
to breed apomictic
The mutational methods have been widely
wor ld o v e r ,
to induce
food,
or i n d u s t r i a l
fodder,
horticultural
commodities.
products#
As a r e s u l t ,
a
number of important mutant crop v a r i e t i e s has been
commercially r e l e a s e d .
These now i n c l u d e ,
for example
one of the h i g h e s t y i e l d i n g r i c e v a r i e t i e s and improved
v a r i e t i e s of soybean in 3 ap a n,
v a r i e t i e s of wheat in
and b es t adapted
India,
one of
the l e a d i n g
some of the h i g h e s t y i e l d i n g
durum wheat v a r i e t i e s
and Europe and some of the l e a d i n g
in the Middle Cast
barley v a r i e t i e s o f
N o rth er n Europe,
Mutation b re e d in g li k e
any other b re ed in g method,
ha s i t s l i m i t a t i o n s and d i s a d v a n t a g e s . Mutatio ns occur
at random.
control
Their chara ct er oT frequency i s
so f a r beyond
and u n p r e d i c t a b l e . M uta tio ns cannot be produced
a c c or di n g to our d e s i r e .
Us have
to try and take a
c h a n c e . Mutation b re ed ing also i n v o l v e s
large populations.
b r e e d i n g i s of t en
t e s t i n g of
The f i e l d work involved in mutation
substantially
greate r than that
r e q u i r e d in con ventional methods of b r e e d i n g .
vo l v e
all
Mutagens i n ­
se rio us ha za rd for the i n v e s t i g a t o r and,
care anA p r e c a u t i o n s
u s i n g them.
However,
therefore,
should be taken in ha nd li ng
they are p e r f e c t l y
and
safe when used with
p r op e r p r e c a u t i o n s .
The Mutagens
A l arg e number of agents has been found capab le
of
inducing mutations.
or
chemical in n a t u r e .
Ra d i a t i o n s
classified
ionizing
These mutagens may be p h y s i c a l
that are used to induce mut ations are
as no n- io niz in g and i o n i z i n g . Use of non­
radiations
(ultravofllet
th e treatment of c e l l s free
as
swimming s p er ma toz oi ds,
in
devel opin g p o l l e n
rays)
is
from extraneous t i s s u e s
po l l e n
t ub es .
T h is
grains,
Ionizing
beta rays,
The
X-rays
wave
first
(M u ller,
length
energy
content
per
radiation
1927).
than
photon
they
are
pr oto ns ,
X-rays
Gamma r a y s
among
the
most
gamma r a y s ,
inducing
in
Owing
m utations
general
therefore,
than X ~ ra y 3 .
t h e i r low
neutrons and alp ha r a y s .
U3ed f o r
and,
cells
damage caused by
r a d i a t i o n s in clu de X-rays,
electrons,
to
such
g e n e r at i ve
i s because of
p e n e t r a t i o n and n e g l i g i b l e p h y s i o l o g i c a l
them.
restricted
to
have
was
shorter
p o s s e s s more
their
penetrating
high
energy
ra d ia tio n s ,,
7
Radioactive
is o to p e s l i k e Cobalt-60 and Caesium-137 are
mostly
as the sources of gamma rays in r a d i o b i o l o g i c a l
wo r k .
U 3e d
The gamma r a d i a t i o n
sources have the d i s t i n c t
advantage for pr olo nged treatments because they may be placed
in
a green house or f i e l d
so that p l a n t s w i l l
be exposed
as they develop over long pe r io d s of time.
Recently a larg e number of chemicals has been found
to be m ut age nic .
effects
Most of them have been found with general
comparable
to those of r a d i a t i o n s *
Some of
the
chemi ca l mutagens are reported to possess an e f f e c t i v e n e s s
which corresponds to or even su rpas ses
radiations*
of
The a t t r a c t i v e p o t e n t i a l ,
application
have
that of i o n i z i n g
the r e l a t i v e ease
and comparatively low cost of chemicals
made them very popular with mutation b r e e d e r s .
The a l k y l a t i n g agents c o n s t i t u t e
the most important
c l a s s o f chemical mutagens having an a t t r a c t i v e p o t e n t i a l
for
the in d u c ti o n of mutations in
cultivated plants.
Among the most commonly used a l k y l a t i n g
ethyl en ei- min e,
etc.
In a dd it io n
d ie t h y l
s ul p h a t e ,
ethyl m e t h a n e ^ u l p h o n a t e ,
are
to t h e s e , many other chemicals^known to
p o s s e s s mutagenic p r o p e r t i e s .
are
agents are
As more and more i n v e s t i g a t o r s
becoming i n t e r e s t e d in mutation b r e e d in g ,
new chemicals
w i t h mutagenic p r o p e r t i e s are also b ei ng d i s c o v e r e d .
8
1.2.
POLYPLOIDY
An i n d i v i d u a l
is
AND I T S
SIGNIFICANCE
said to be a p o lyp loi d
when i t
p o s s e s s e s more than two sets of homologous chromosomes
or
genomes.
groupsc
They are c l a s s i f i e d
in to
tuo very general
Those pfilyploids whose chromosome number i s not
a whole number m u l t i p l e of the b a s i c number are
called
a n e u o l o i d s whereas those whose chromosome number i s
e x a c t m ul t ip le
an
of the b as ic or ha pl oi d number are c a l l e d
eueloidsc
E-uploids occupy a f a i r l y
important p o s i t i o n
among
c u l t i v a t e d pl a n t s because of f a v o u r a b l e morphological
physiological
by
e f f e c t s which are
the i nc r ea se
in
g e n e r a l l y brought about
the number of
chromosome s e t s 0
A good number of a g r i c u l t u r a l
Autotetraploids
of
may
us ua ll y e x h i b i t
v e g et a ti ve parts,,
They tend
show reduced f e r t i l i t y , .
and
crops i s
atitopfclyploid *
great vigour and gigantism
towards p e r e n n i a l i t y
and
B e s i d e s other f a v o u r a b l e
c h a r a c t e r s they us u a ll y e x h i b i t
g re ate r v a r i a b i l i t y ,
a d a p t a b i l i t y and sometimes d is e a s e
resistance.
A fter ju d g in g the frequency with which the d i f f e r e n t
l e v e l s of au to p o ly p lo id s appear among economically
important p l a n t s ,
a u t o t e t r a p l o id s appear to be more
fr e q u e n t l y encountered in p o p u l a t i o n s of crop p l a n t s which
speaks for th eir
ploids
millet,
importance in pl a nt
have been reported in
m a iz e,
wheat,
chilli,
rice,
improvement.
sorghum,
sesamum,
A u to t e t r a ­
pe a rl
red gram,
bl ac k gram,
green gram, Bengal
etc*
gram,
lablab,
co tto n,
Because of t h e i r co n si de rab le
and breed ing p o s s i b i l i t i e s ,
in d u c e d
plants
artificially
guava,
coffee,
economic importance
a ut o t e t r a p lo id y i s
nou
in d i f f e r e n t economically important
to improve them further*.
Attempts to induce p o l y p l o id y
be en made for a long
tried©
artificially
have
time and va ri o u s methods haue been
The i n t e r e s t in p o ly pl oi d y as a tool of the
p l a n t breeder was given a tremendous boost uhen i t
d is c o v e r e d
at w i l l
that po ly p lo id y can be induced more or l e s s
in p l a n t s
through the aotion of c o l c h i c i n e .
Po ly p lo id y has i t s advantages as well
It
i s capable of
programmes, but
f u r n i s h i n g rau ma ter ial
it
so many important a g r i c u l t u r a l
as l im ita tio ns ,.
for br ee d in g
seldom capable of producing
f o r immediate use'* N e v e r t h e l e s s ,
that
was
s t r a i n s ready
can not be overlooked
p la nt s are polyploids'*
10
1.3.
THE
AIM
OF
THE
PRESENT
INVESTIGATIONS
Keeping in v ie u the role of mutation b r e e d i n g
i n d u c t i o n of p o l y p l o i d y in a changing a g r i c u l t u r e ,
considered
desirable
botany vigorously
of
to pursue
t h i s branch of
in the va ll ey of Kashmir*
Kashmir has some d i s t i n c t i v e
the p o i n t of view of geography,
horticulture,
etc.,
and,
f o r mutation b r e e d i n g
extensive
is
appl ie d
The va ll ey
f e a t u r e s of i t s oun from
climate,
therefore,
so f a r ,
been conducted in Kashmir,
flora,
agriculture,
there i s va st
scops
work of t h i s na ture has not
a pla n of in d uc ti o n of mutations
the ve g eta ble s c u l t i v a t e d
v a l l e y was i n i t i a t e d
it
and i n d u c t io n of po ly pl oi d y on an
scale0 Since,
and po ly p lo id y in
and
in
the Kashmir
a feu ye ars ago uith a view to
e v o l v i n g neu and b e t t e r v a r i e t i e s .
Local v a r i e t i e s of
Ly c o p e r si c o n esculentum
tuo vege tab le
(tomato,
Solanurn melonoena ( b r i n j a l ,
selected
for experimental
species9
Local K ashmiri)
Local
Long Kashmiri)
and
were
work and i n v e s t i g a t i o n s .
S e l e c t i o n of ve g e t a b le s uas based on some important
considerations.
part
of every day food for a l l
constitute
uhile
The ve g eta ble s const itu te
a very e s s e n t i a l
human b ei ng s and
part of a balanced d i e t ;
a good deal of work has been
cereals,
pu ls es
an important
done in our country u it h
and other food p l a n t s ,
comparatively l e s s
a t t e n t i o n has been paid to v e g e t a b l e s .
In Kashmir v a l l e y ,
v e g e t a b l e s are consumed in la rg e
q u a n t i t i e s and many
v e g e t a b l e s are dehydrated by people
uhen they are a v a i l a b l e
li
fresh
to be weed du ri ng the wint er
season when f r e sh
v e g e t a b l e s become s c a r c e .
Local
v a r i e t i e s were p r e f e r r e d
to ex o t ie
varieties.
H a u i n § been c u l t i v a t e d here for a long time they have
become adapted
to the local
however a t t r a t i v e
serious risks.
the l o c a l
conditions.
they may appear to b e ,
Exo tic v a r i e t i e s
i nv ol ve
c e r t a in
Upart from the ques tion of ad a p ta t i on
conditions,
to
they can b ri ng with them new
r
p a t h o ge n s and p e s t s not occ u^i ng in the v a ll e y
then create new problems.
and may