Role of mutation in plant Breeding Study of mutations commenced in 1927, when Muller showed in Drosophila
that
X-rays
are
able
to
induced
genetic
deiants
indistinguishable from naturally occurring ones! "he notable part of this disc disco oer ery y was was the the ery ery grea greatt incr increa ease se in muta mutati tion on rate rate caus caused ed by irradiation treatment! Shortly afterwards, Stadler, who had been wor#ing on the effect of X-rays in plant, announced that it was possible through this agency to obtain ery high mutation rate in mai$e and barley! "he possibilities inherent in the ability to produce mutations artificially were grasped at once by many plant breeders, and a period followed in which considerable effort was directed toward utili$ing the new discoery in practical breeding! %esults were discouraging, howeer& and e'cept for sustained effort on the part of a group of plant breeders in Sweden, attempts to use induced mutations in practical breeding gradually slowed to irtual standstill! "here were good reasons for the rapid loss of interest on the part of plant breeders! (irst, it soon become clear that induced mutations, li#e spontaneous ones, were almost always deleterious in their effects on the phenotype! Second, many of the genes goerning characteristics in which commercial arieties re)uired improement occurred in one or another
#nown
stoc#,
and
large
numbers
of
other
desirable
charac character terist istics ics were were #nown #nown to occur occur in the rapidl rapidly y e'pand e'panding ing world world
collections of germplasm! *lant breeders had more ariability at their disposal than they could accommodate, and too many obious tas#s to perform in assembling the #nown desirable gene into new commercial ari ariet etie iess to be dire direct cted ed ery ery long long by a proc proced edur uree that that appa appare rent ntly ly produced little constructie ariability! "hus "hus most plant breeders choose to ma#e use of e'isting ariability, rather than depend on hapha$ard mutations produced by radiation!
Mutation Breeding Soon after Muller+s discoery of the mutagenic action of X-rays, erman ilsson-.hle of the Swedish Seed /ssociation at Salof and one of his students, /#e /#e 0ustafsson, began e'periments in mutation breeding that hae been continued to the present! t was soon established that Stadler+s results with barley and mai$e had general alidity with diploid species! hlorophyll, mutation arose in greater number in two-rowed barley following X-ray dosages to seeds! 3hen the dosage approached the lethal point, mutation rates increased to about thousand times the spontaneous rate! Some of the mutant types in barley, particularly the erectoides mutants, seemed to hae useful agricultural properties! 3hen the more promising of these mutants were tested in field trials 40ustafsson and "edin, "edin, 1956& (roier, 1956, they generally produced yield about the same as the mother ariety, ariety, but a few appeared to be significantly superior!
n addition to barely, the Swedish wor#er hae used mutation breeding with many other crops 4wheat, oats, peas, etches, soybeans, lupines, fla' oil turnips, oil rape, white mustard, sugar beets, potatoes, 8entuc#y bluegrass, timothy, red fescue, apples, pears plums, cherries, ornamentals, and forest trees! "hese programs hae resulted in two new ari ariet etie ies s Sal Salof of *rim *rime' e' 3hit 3hitee Must Mustar ard d rele releas ased ed for comm commer erci cial al production in 195:, and %egina Summer oil %ape, released in 195;! *rime' Mustard was selected from a population that was irradiatiated in 1961! t is reported to e'ceed the parent population by 6 percent in yield and 2 percent in oil content! oweer, mustard is highly hetero$ygous cros crosss-po poll llin inat ated ed spec specie ies! s! t is ther theref efor oree not not defi defini nite te wheth hether er the the impr impro oem emen entt in yiel yield d and and oil oil cont conten entt is rela relate ted d to the the irra irradi diat atio ion n treatment, since it could hae been due to effectie selection for genetic ariability that e'isted in the original population! Similar but less e'tensie mutation-breeding programs hae been cond conduc ucte ted d at a numb number er of bree breedi ding ng inst instit itut utes es in .uro .urope pe!! Muta Mutati tion on- breeding wor# on a large scale started in 0ermany about 196: 4barley, 4barley, wheat, oats, oats, lupine, fla', hemp, hemp, tomatoes currants, currants, and fruit trees! "his program has apparently production in 195:! Mutation breeding has also been inestigated in (rance 4wheat, (inland 4barely, wheat, oats, peas, red cloer, .ngland 4barley, wheat, sugar beets,
Unsolved Problems in Mutation Breeding
"her "heree hae hae been been enou enough gh indi indica cati tion onss of posi positi tie e resu result ltss with with mutation breeding to attest to the potential alue of artificially induced mutations in practical plant breeding! oweer, many )uestions remain to be answered before it can be decided whether mutation breeding will assume a place as a ma=or plant-breeding method or whether it will fit in as a minor ad=unct to other methods! "he most important )uestions remaining to be answered are 1!
Do arti artifi fici cial ally ly ind induc uced ed mut mutat atio ions ns dif diffe ferr in any any way way from from nat natura urall mutations, or do mutagenic agents merely reproduce the same spectrum of ariability that occur naturally> nduced mutations are the plant breeder+s one hope for freedom from completed dependence on nature as the only source of the genetic ariants necessary in plant moement! ence the answer to this )uestion is potentially potentially an important important one in the long range future of plant plant
2!
improement! Do mutations with phenotypi ypically constructie e'pressions occur often enough to ma#e the search for them profitable and thei theirr inco incorp rpor orat atio ion n into into comm commer erci cial ally ly acce accept ptab able le ari ariet etie iess competitie with other methods of breeding> f not, can the mutation process be brought under e'perimental control so as increa increase se the propor proportio tion n of constr construct uctie ie change changes> s> "he #ey #ey to thes thesee prob proble lems ms appe appear ar to lie lie in unde unders rsta tand ndin ing g of muta mutati tion on process itself!
Special cial
Meri erits
and
Disadva dvantage age
of
Mut Mutation ion
Breeding Mutation breeding seems to be especially useful in changing single simply simply inheri inherited ted charac character terist istic icss in highly highly deelo deeloped ped genic genic system systems! s! 3hen dealing with highly deeloped ariety, the breeder is reluctant to use standard hybridi$ation method because they may disrupt a superior combination of genes! "his situation is often encountered when some outstanding ariety succumbs to a new race of a disease or is inferior in some some spec specif ific ic morph morphol olog ogic ical al or phys physio iolo logi gica call attr attrib ibut ute! e! 3het 3hethe her r muta mutati tion on bree breedi ding ng or the the stan standa dard rd bac# bac#cr cros osss tech techni ni)u )uee shou should ld use use depend on the two factors 1! "he ease with which which the desired improement improement can be induced, and 2. "he number of deleterious mutants that accompany he specific mutation for which the breeding program is underta#en! "he point is sometimes made that undesirable alterations in order characters are easily handled in mutation-breeding programs because the mutant lines are so similar to the parent ariety that a few bac#crosses will restore the desire bac#ground genotype! oweer, mar#er genes brought in by a genetically dissimilar parent often allow ery effectie sele select ctio ion n towa toward rd the the geno genoty type pe of
the the recu recurr rren entt pare parent nt in stan standa dard rd
bac#cross programs and more rapid return to the type of the recurrent parent than otherwise would be possible! t is therefore doubtful whether the the numb number er of bac# bac#cr cros osse sess re)u re)uir ired ed to guar guaran ante teee reco recoe ery ry of the the
genotype of the outstanding ariety is less in mutation breeding than in standard bac#cross breeding! Muta Mutati tion on bree breedi ding ng appe appear arss to hae hae spec specia iall ada adant ntag agee in addi adding ng specific characteristics to fruit trees and other egetatiely propagated crops! ?a ?arieties in these crops are usually highly hetero$ygous clones not especially suited to improement by the selection of recombinant types in succ succes essi sie e gene genera rati tion onss foll follow owin ing g hybr hybrid idi$ i$at atio ion n or amen amenab able le to improement by bac#cross breeding! "he disadantage of mutation breeding are largely associated with the necessity for testing large second generation populations! "he field wor# re)uired to achiee some particular improement is often substantially grea greate terr with with muta mutati tion on bree breedi ding ng than than that that re)u re)uir ired ed in con conen enti tion onal al methods of breeding! /s a result the practical use of the method is now limited to the improement of a small number of characteristics for which efficient screening methods hae been deeloped 48on$a#, 195@! n a rei reiew ew on the Swe Swedis dish wor# wor# in muta utation tion,, Mac Mac8ey 419 4195@ 5@ concluded Aonsidering the low fraction of progressie mutations and considering at least the present limitation in selectie mutagenesis, it is rath rather er obi obiou ouss that that muta mutati tion on bree breedi ding ng cann cannot ot be cons consid ider ered ed such such a reolutionary tool in crop improement that it will replace old methods! t means a definite contribution to our plant breeding methods, but it should not be oer- or underestimate =ust because it is new!B new!B
ACKNO!"D#"M"N$
am gratefu gratefull to my superi superisor sor Dr. R. N. Singh (or his sincere supp support ort,, crea creati tie e and and prof profou ound nd bles blessi sing ng,, whic which h help helped ed me a lot lot in presenting this seminar! seminar! am than#ful to all those persons, from whose hae gathered a large amount of information, am also e'press my gratitude to all those who hae offered assistance, encouragement and cooperation during the entire manuscript!
Date : ....................... .............................. ....... Vaisali Vaisali Singh M.Sc. IV Sem. (Botany) Udai Prata !"tonomo"s !"tonomo"s #ollage Varanasi
1!
ntroduction
2!
haracteristions of mutation
;!
"ypes of mutation
6!
Mutagens
5!
Mutation at molecular leel
@!
Cse of mutation
7!
*ractical application of mutation
!
onclusion
9!
%eference
