Plant breeding: Induced mutation technology for crop improvement
←
→
Page content transcription
If your browser does not render page correctly, please read the page content below
FEATURES
Plant breeding: Induced mutation
technology for crop improvement
Scientists at the IAEA's Seibersdorf Laboratories are helping
breeders to develop crops having more desirable traits
present forms of life are the product of found suitable for domestication; humans have by F.J. Novak
three factors: used about 3000 of these for food, fibre, spices, and
• mutation, the fundamental source of heritable etc., with 200 ultimately domesticated as crops. H. Brunner
variation, Today, only 15-20 of these are food crops of
• environmental factors, which influence the major importance.
selection of those mutations that survive and The means of developing new plant varieties
reproduce, and for cultivation and use by humans has come to be
• time, during which the genotype and environ- called plant breeding. Early on, it primarily in-
ment constantly interact and evolutionary volved selection, the choice between good and
change is realized. bad plants. People learned not to eat all the "best
Genetic variation found in nature does not fruit" but to plant the seed from some of them.
represent the original spectrum of spontaneous Genetics became a fundamental science of
mutations. Rather, this is the result of genotypes plant breeding after the Moravian monk J.G.
recombining in populations and continuously in- Mendel discovered the laws of heredity in the
teracting with environmental forces. mid-19th century. Plant breeding further ad-
Green plants are the ultimate source of vanced when the methodology of hybridization
resources required for human life, food, clothing, was developed. Its aim was to combine various
and energy requirements. Prehistoric people, desirable properties of many plants in one plant,
who depended on their skills as hunters, drew instead of just choosing between good and bad
upon abundant natural vegetation to collect plants. This method, often supplemented by
nutritious and nonpoisonous fruits, seeds, tubers, germplasm derived from induced mutation, has
and other foods. As human populations in- become the most common one for breeding
creased, greater and safer supplies of food had to plants through sexual reproduction.
be found, and gradually production systems However, some crops—including bananas,
based on plant domestication were developed. apples, cassava, and sugar cane—reproduce
The domestication of crops historically has vegetatively, especially those that are fully
been influenced by ecological and agricultural sterile without seeds. For this important group,
conditions, as well as by food gathering alternative approaches had to be developed,
preferences. Genotypes that have adapted to a namely techniques of manipulation with somatic
wide range of climatic and edaphic conditions tissue: mutation breeding and biotechnology.
typically have been selected for cultivation. The
achievement of higher yielding crops facilitated
population growth, sedentary settlements, and Mutation breeding
further development. Which crops were domes-
ticated depended not only on the number of Plant breeding requires genetic variation of
seeds or the size of fruits, but also on taste, useful traits for crop improvement. Often, how-
palatability, and other factors. ever, desired variation is lacking. Mutagenic
Only a small fraction of the world's ap- agents, such as radiation and certain chemicals,
proximately 200 000 plant species have been then can be used to induce mutations and
generate genetic variations from which desired
Dr Novak is Head of the Plant Breeding Unit at the IAEA's
mutants may be selected.
Seibersdorf Laboratories, and Dr Brunner is a senior scientist Mutation induction has become a proven
in the Unit. way of creating variation within a crop variety.
IAEA BULLETIN, 4/1992 25
FEATURES
One natural evolutionary
product of genetic
variation: a mutant of
dwarf coconut palm.
It offers the possibility of inducing desired at- Major efforts were devoted during this initial
tributes that either cannot be found in nature or phase of mutation induction to define optimal
have been lost during evolution. When no gene, treatment conditions for reproducibility. Re-
or genes, for resistance to a particular disease, or search focused on changing "random" mutation
for tolerance to stress, can be found in the avail- induction into a more directed mutagenesis to
able gene pool, plant breeders have no obvious obtain more desirable and economically useful
alternative but to attempt mutation induction. mutations. However, it did not lead to the desired
Treatment with mutagens alters genes or alterations in the mutant spectrum. Limitations
breaks chromosomes. Gene mutations occur were the concomitant increase of plant injury
naturally as errors in deoxyribonucleic acid with increasing radiation dose and the low fre-
(DNA) replication. Most of these errors are quency of economically useful mutations. This
repaired, but some may pass the next cell led scientists to search for potentially better
division to become established in the plant off- mutagens. As a result, new methods of radiation
spring as spontaneous mutations. treatment, as well as chemical agents with
Although mutations observed in a particular mutagenic properties, were found.
gene are rare, there are probably 100 000 genes
in a cell of a higher plant. This means that every
plant may carry one or more spontaneous muta- Plant biotechnology
tions into the next generation. Gene mutations
without phenotypic (visible) expressions are Breeding for improved plant cultivars is
usually not recognized. Consequently, genetic based on two principles: genetic variation and
variation appears rather limited, and scientists selection. The process is extremely labourious
have to resort to mutation induction. There are and time consuming with high inputs of intellec-
no other economic ways of altering genes, ex- tual and manual work. (See box.) However, the
cept to wait a long time for spontaneous muta- development of plant cell and tissue culture over
tions to occur. the last 20 years has made it possible to transfer
Artificial induction of mutations by ionizing part of the breeding work from field to laboratory-
radiation dates back to the beginning of the 20th conditions.
century. But it took about 30 years to prove that Extensive research has resulted in new areas
such changes could be used in plant breeding. of plant breeding, namely "plant biotechnology"
Initial attempts to induce mutations in plants and "genetic engineering". They are based on
mostly used X-rays: later, at the dawn of the cellular totipotency. or the ability to regenerate
"Atomic Age", gamma and neutron radiation whole, flowering plants from isolated organs
were employed as these types of ionizing radia- (meristems). pieces of tissue, individual cells.
tions became readily available from newly estab- and protoplasts. The isolated plant parts are
lished nuclear research centres. aseptically grown in test tubes on artificial media
26 IAEA BULLETIN, 4/1992
FEATURES
Some tools and products of plant breeding
(clockwise from top left): a mutant of paddy rice
induced by ionizing radiation; yams and other root
and tuber crops can be genetically improved by
mutation breeding; tissue culture and in vitro
mutagenesis are basic methods of biotechnology
for improving crops; "Golden Maidegg", an apple
mutant with improved market value, was induced
at the Seibersdorf Laboratories by irradiation of
cuttings from "Golden Delicious" apples;
mutation breeding has improved the tolerance to
environmental stress of Azolla, a water fern used
as biofertilizer in rice paddies.
IAEA BULLETIN. 4/1992 27
FEATURES
General scheme of
mutation breeding Breeding a new variety of crop takes anywhere from 12 to 15 years of intensive effort The steps in-
clude:
Generation Characterization
Seeds, pollen, vegetative parts, or tissue cultures
treated by physical (radiation) or chemical mutagens.
Mi(MiVi) Plants grown from treated seeds (Mi) or vegetative
propagula (MiVi).
M2(MiV2) Population of plants grown from seeds (M2) or vegetative
parts (MiV2> harvested from Mi or MiVi respectively.
Selection of desired mutants may start in this generation
or later.
MS - MS Continuing selection, genetic confirmation, mulitphcation
(MiV3 - MiV8) and stabilization of field performance of mutant lines.
Next 2 - 3 generations Comparative analyses of mutant lines during different
years and in different locations.
Next 2 - 3 generations Official testing before release as a new variety.
Applications of
nuclear techniques
in plant breeding
Cross Breeding
Mutation Induction
(using mutants)
Genetic Engineering
| | Mutation breeding
Tracer techniques
Both
Biochemical-and
DNA Markers
Crop improvement is
based on two basic
principles: genetic
variation and selection. Disease and Pest
Serving as invaluable Resistance
tools are mutagenic
irradiation and isotope
tracer techniques, which
are incorporated into the Yield (Photo-
various breeding synthesis Studies)
methods.
28 IAEA BULLETIN, 4/1992'Nll3TinS
JIGS qjoq SuiApAui qoresssj psjBjSsjui -sjusujnu -ui suoijBoijddB jBoi§opuqD3j sji PUB aSpgjMoiDi
szijijn oj ssijpBdBD jsjjsq qjiM sjuBp1 puB Dijpusps 'ssaoojd sqj u\ -ssujunoo iBiijsnpui
UOIJBXIJ usSojjiu psAOjduii joj sjuBjd Suipssjq XUBUI JO JOJD3S JBPJ3UJUIOD 3qj OJUI S3DJHOS3J
oj sjBpj A"ijBoijpsds Xsqj^ 'ss§us[[Eqo JO(BUI UBiunq psijijBnb A"iq3iq jo UOIJBJJUSDUOO B
smos SSOBJ A"Bpoj Suipsaiq juBjd siqBurejsns ui puB SJU3UIJS3AUI iBjidBD snouuous ui psjjnssj
•SBSJB [Boidojjqns PUB [Boidojj JBJSASS ui Bireireq uo 3ABq XSoiouqo3joiq juBjd ui sjuauidopASp
SSBSSIp BUIBUBJ pUB 'BUBqQ UI BODOD UO OlUISplds JU303^ 'JI OJ S3UJUHOD §UldopA3p JO SS3DOB
ssEssip sruiA jooqs-usjpMS sqj spnpui ssaqj, 3qj puB 'A"SopuqD3j siqj jo UOIJBZIIBIOJSUIIUOO
•sdojo uoijBjuBjd ui uoijBnjis ottuspids sqj PIOAB aqj SUJ3DUOD paSjguig SBq jBqj snssi jsqjouy
oj dpq /(BUI Suipssjq SDUBJSISS^ "S^B ssujunoD •JU3UJUOJIAU3 3qj OJ SJUBjd DIU3§SUBJJ guiSBSpJ
SuidopASp pus psziiBujsnpui ui jusiudopASp jo spJBZBq jBijusjod sqj jo uoissnosip SUIMOJ§
IBjnjjnouSB si.qBUU3jsns SUIJOSJJB SJIUBSJ sqj Kq psjsdtusj Supq si uisBisnqjus ApB3 'JSAS
DISBq B SI qOiqM 'SIBOllUSqO-OJ§B UO SOUSpUSdsp -MOH "ssiysdoad Suiusdu asjjsq PUB 'SOUBJSISSJ
SSBSJOSP SSIJSUBA qDtig -juBid jBuiSuo sqj UBqj 3SB3SIp SIUIA '30UBJSIS3J JD3SUI SB qOHS 'SJIBJJ
SJS9d OJ SDUBJSpJ pUB 9DUBJSIS9J 9SB9SIp J9JB9J§ sjqBJissp A\3u qjiM sjuBjd jo uoijonpojd sqj
jiqiqxg jBqj sjBAijjno juBjd M9U §uidoj9A9p UI pSJ]nS3J SBq XpBSJJB §UU33UI§US DIJ3US9
SPJBMOJ p9jD9Jip 9JB sjogfojd Suip99jq jsojM •SIUSIUB§JO JU3ldlOSJ UI [BUSJBIU DIJ3U3§
•UOIJD3J9S pUB 'UOlJBUiqUIOD9J 'UOIJ MSU josjsp oj puB tsipo jusidpsj ojui ssusS sonp
-onpui uoijBjnui Xq saainosgj oijauaS jo juaiuao -OJJUI OJ SUISJSXS AJSAIJSp SB U3JSUBJJ JOJ S3US§
-uBqu9 aqj JQJ paXoiduia SJB Xaqx -sjuauodiuoD sp,Bjms 3jB]osi puB Xjijuspi oj 'SuussuiSus
jBaionu apnpui uajjo A\i3A guipaajq uoijBjnui DijsusS ui psXojduis SJB 'ssdojosi Xq psipqBj
OJJ1A UJ pUB 'OAM III '§UIp33jq SSOJ3 SB qDHS sssBq ppB Dppnu uo pssBq 'ssnfaiuqosj JBSpnfvj
spoqjaui Suipgajq JUBIJ -sapads pjiM pgjBpj puB •jps oiusSsuBJj sqj uiojj psjBJSusSsj sdXjousqd
SJBAIJjnD JO SISXJBUB OIJ3U3§ pUB UOIJBDIJISSBp juB{d sqj ui jpsji sssssjdxs (susS) VNQ M9U 3llL
aqj aoj pai^ddB SJB sanbiuqogj JS^JBUI JBinoapjAj •JUBjd DIUSSSUBJJ B UUOJ OJ [pD JUB]d B JO SlUOUSg
'IBU3JBIU JBUOp JO 3§UBqOX3 JBUOIJBUJ3JUI sqj ojui psjBjSsjui sq XBUJ |jso jBusjoBq B uiojj
sqj joj puB uoijBAJ3S3Jd uisBjduusS joj poqj3iu VMQ J° 333jd B 'sjduiBxs joj -uisiuBgjo psjBpj
psjjsjsjd sqj Suiiuoo3q si 'sjduiBxg joj 'jnuoooo -un A"HBOIJSUS§ JsqjouB jo jBqj oj sspsds suo jo
PUB 'OJBJod J33MS 'UIB^ 'OJBJod 'UIBJUB|d pUB [po sqj uiojj (VNQ) IBIJSJBUI oijsusS jo JSJSUBJJ
BUBUBq 'BABSSBO ui XSojouqosj sjnjjno snssij^ sqj MOIJB ssjnpsoojd SuussuiSus DIJSUSQ
•S3pads juBjd jo AjisasAipoiq jo sso) sqj dojs 'SDUBJSUI JOJ 'SSiqBJS§SA
OJ p3dopA3p U33q 9ABq S3I§O]OUqD3J M3f\J puB '/topBq 'sou jo SSIJSUBA MSU jo Suipssjq sqj
•JU3lU3AOjdlUI dOJO JOJ JOOd 3U3§ 3AISU3q3jd dn pssds XjjuBDijiuSis oj usAOjd SABq spoqjsui
-IUOD B jo ju3iuqsitqBjs3 aqj si juiod JBDOJ piojdBH "uoijonpui Jisqj JSJJB XpjBipsuiuii
'3jnjjnOIJ§B XjpUSUJ Xj{BJU3UIUOJIAU3 OJ SUOIJBjnui JO UOIJDSJSp SMO|JB JI SOUIS SnOS§BJUBA
sjnqujuoo XSoiouqoajoiq puB Suipssjq JUBJJ -pB si Suipssjq uoijBjnui ui spio]dBq jo ssn
sqj '(sppjdip) JUSJUOD jBiuosoiuojqD ipj qJ!-^
aiqeuieisns jo^ Bwpaejq )ueid sjuBjd oj psjBduio3 "SppidBq—ssiuosoiuojqo
jo jsquinu sqj jjBq qjiM SSJSUIB§ SJBUI UJGJJ
sjuBjd SJBJSUSSSJ oj sjqissod ji S>[BUI 'sjnjjno
siqj ui psusqjSusjjs Supq usjpd jo 'JsqjuB SB UMOU>{ 'spoqjsui JsqjQ
3JB JU3UldopA3p pUB qDJB3S3J UI SSIJIJiqBdBD (-xoq 33§) -suiij
P^UOIJBU *XBA\ siqj uj 'ssujunoo Suidoj3A3p Suipssjq SUIJBJSPDDB Xq PUB 'XSopuqosj uoij
ui 'puuosjad UIBJJ oj puB 'S3i3oiouqo9joiq -osps SuiAOjduii Xq 'UOIJBUBA oijsusS Supnpui
ajBudojddB JSJSUBJJ puB Xjijuapi oj gjs suiaouoo joj ssnbiuqosj MSU psonpojjui SABq Xsqx '8ui
UIBUI 3SOqM 33Bjd UI J3S U99q 3ABq -pssjq juBid oj uoijnqujuoD juBDijiugis B spBiu
•3JOJ JUBJJOdlUI UB §UI/FEATURES
proved soil and water practice, and composting
—is a desirable support of sustainable agricul-
I Africa Asia & Pacific ture in developing countries. The mixed planting
Middle East & Europe I Latin America of a main crop with specific cover crops (e.g.
forage legumes or grasses) minimizes the use of
herbicides.
28.3° 26.4%
22.6 24.5
Role of the Seibersorf Laboratories
The Plant Breeding U n i t of the IAEA
Laboratories at Seibersdorf was set up in the
mid-1960s to support the Joint FAO/IAEA
15.1% 23.6% Division's programme of genetic crop improve-
34.0% 25.5% ment. Nuclear techniques in plant breeding are
developed and transferred to countries by re-
Fellows Trainees
search and development in mutation breeding
Total: 53 from 26 countries Total: 212 from 73 countries and related biotechnological techniques, training
scientists from developing countries, and provid-
ing irradiation services and technical advice.
Training activities scientists and plant breeders already has iden- Initial research in the Plant Breeding Unit
in the Plant tified desirable genotypes in grain legumes focused on the development of mutation induc-
Breeding Unit of (soybean, garden bean) and other plant species, tion methods with ionizing radiation and chemi-
the Seibersdorf including trees. cal mutagens. The aim was to achieve high
Laboratories, For many developing countries, breeding mutagenic efficiency, i.e., a high frequency of
1982-92 crops for tolerance to salinity and acidity in soils desirable mutations at minimal plant injury and
is of high priority. Current breeding strategies the highest possible reproducibility. This re-
(including mutation induction and in vitro selec- quired a definition of radiation source charac-
tion) have clearly been successful in incorporat- teristics in terms of dose homogeneity and
ing degrees of tolerance in different species. The precise assessment of absorbed dose in biologi-
use of genetic engineering for creating environ- cal targets by appropriate dosimetry. Irradiation
mental stress-resistant plants will depend on the of seeds with gamma rays and neutrons was
identification of specific genes which contribute commonly done, given the ease of handling, the
to the adaptation to specific stress environments. simple standardization of factors which modify
In tropical countries, agriculture practices radiation sensitivity, and good reproducibility.
have maintained the yield level of different crops The establishment of methods for controlling
through "intercropping" instead of by increased oxygen-dependent effects in the radiobiological
monocrop cultivation. Breeding crops for multi- response to electromagnetic radiation was a
ple functions—such as biomass production, im- major achievement. The Laboratory actively
contributed to standardizing neutron irradiation
Radiation service of seeds in nuclear reactors by developing spe-
statistics, 1967-92 cial facilities for this purpose. These were known
Treated samples 20329 as SNIP, for Standard Neutron Irradiation
Treated species 217 Facility for swimming-pool-type reactors; and as
Treated cultivars 1 134 USIF, for Uranium Shielded Irradiation Facility
Recipient Member States 108 for Triga-type reactors.
Seed samples 17872 This research was the basis for the IAEA
Vegetatively propagated plants 1 046 Laboratories' worldwide seed irradiation service
Cobalt-60 gamma treatments 14382 using fast and thermal neutrons at a high-dose
Fast neutron treatments 5416 precision and reproducibility of induced effects.
Other mutagen treatments 531 Moreover, efficient and accurate treatments of
seeds with chemical mutagens, mostly alkylating
Note: Examples of major plant species treated include: cereals
(rice, wheat, barley, Iridíale, millet, tef); legumes (soybean,
agents and azides, were developed with the aid
peanut, common bean, cowpea. mungbean); root and tuber of isotope-labelled compounds and compared
crops (cassava, yam, cocoyam, potato); fruits (citrus, apple, with mutation induction by ionizing radiation.
apricot, peach, grape vine): ornamentals (chrysanthemum, an- The Unit has undertaken supportive research on
tirrhinum, achimenes, tulip): and others (rape, sesame,
amaranth, quinoa, niger).
mutation breeding in cereals, pulse crops, in-
dustrial crops, and vegetatively propagated
crops.
30 IAEA BULLETIN, 4/1992FEATURES
As each crop species has a variable reproduc- ture and in vitro plant regeneration are being
tive capacity (number of progenies per plant) and investigated for use in mutation induction and
a specific system of reproduction (self- or cross- mutant selection. Somatic embryogenesis and
pollinated sexual reproduction or asexual plant regeneration from cell suspensions of
propagation), a universal breeding approach Musa are used to develop somatic cell manipula-
cannot be developed and species-specific proce- tion procedures for banana and plantain breed-
dures have to be applied. Most vegetatively or ing. Methods of screening such plants for resis-
asexually propagated species are difficult to im- tance to Panama disease are studied in tissue
prove genetically by conventional cross- and culture, and biochemical markers (peroxidase)
mutation breeding methods. These breeding are applied for the identification of tolerant
problems can be more easily resolved by using genotypes. DNA markers are used for identify-
biotechnology in combination with mutation in- ing mutants and characterizing cultivars and
duction, and the Unit initiated in vitro mutation species of Musa. Mutant clones identified at the
breeding activities during the mid-1980s. Seibersdorf Laboratories are tested in the field in
Several tropical food crops of great importance tropical countries.
to the food security of developing countries were • Mutation breeding to improve the
chosen as the main focus of R&D and training tolerance to environmental stress of Azolla.
activities in biotechnological plant breeding at Azolla is a small aquatic fern that lives in sym-
the IAEA Laboratories. biotic relationship with the nitrogen-fixing
cyanobacterium Anabaena. Under suitable field
conditions Azolla can double its weight every
Research and development activities 3-5 days. The Azolla-Anabaena symbiotic sys-
tem provides green manure for flooded crops,
The Unit provides focused support to the particularly rice. Induced mutagenesis has
FAO/IAEA's co-ordinated research and techni- produced Azolla variants tolerant to high
cal co-operation programmes. Assistance is salinity, toxic aluminium levels, and/or to her-
provided to numerous projects in terms of exper- bicides. Tolerant plants are being investigated
tise for building facilities for plant tissue culture under field conditions to confirm that heritable
and mutagenic treatment, for quality control of changes cause the increased tolerance to en-
dosimetry of mutagenic irradiation, and for the vironmental stress.
development and transfer of nuclear tech- • Methods of mutation induction and
nologies for plant improvement. breeding of tropical root and tuber crops (cas-
Ongoing R&D includes the application of sava and yam). Cassava and yam are among the
nuclear methods and associated advanced tech- most important staple food crops of the lowland
niques, such as in vitro culture and molecular tropics. Mutation breeding technology is being
genetics, to improve the production of a wide developed to increase variation in plant stature,
range of crops through mutation breeding. The cyanide content, disease, and pest resistance. In
development of biotechnological methods for vitro techniques are used for the propagation of
breeding vegetatively propagated crop plants of healthy plants and improved clones. Somatic
major importance in developing countries has a embryogenesis is being developed for cassava
high priority. and yam improvement through in vitro
Currently, the following R&D areas are mutagenesis and later on by somatic cell
being pursued: manipulation. Mutant and polyploid clones are
• Somaclonal and mutagen induced varia- prepared for field testing in Member States.
tion. Systematic studies are being conducted to • Tissue culture in cocoa as a system for
compare the genetic variation caused by tissue more efficient mutation breeding. Attempts to
culture (somaclonal) variation with that induced breed cocoa for disease resistance have yielded
by irradiation and chemical agents. Genetic very limited success. A major constraint is that
variation is being studied among maize plants little variation exists in currently available cul-
derived from in vitro cultured material via tivars. Somatic embryogenesis is being
somatic embryogenesis. This is being done to developed for propagation of desirable
assess the nature of somaclonal and induced genotypes and, through in vitro mutagenesis and
variation and its potential for use in practical pollen mutagenesis, is being applied for induc-
breeding. tion of virus-resistant cocoa trees in Ghana.
• Mutation induction and breeding tech- Plant breeding research at the Seibersdorf
nology for banana and plantain. Low genetic Laboratories is directly problem- and client-
variation and sterility handicap genetic improve- oriented. Many positive results of scientific work
ment of banana and plantains (Musa spp.) by have been achieved by junior scientists from
conventional breeding techniques. Shoot-tip cul- developing countries during their assignments
IAEA BULLETIN, 4/1992 31FEATURES
under the IAEA's fellowship training discuss and evaluate the potential role of induced
programme. Local cultivars and genetic material mutations and advanced biotechnologies in their
from tropical countries are brought to the national breeding programmes for specific crop
Seibersdorf Laboratories, transferred to tissue improvement of cereals, legumes, oil crops,
culture conditions and used for experimental forages, vegetables, fruits, root and tuber crops,
work. Protocols and techniques that are specifi- palms, rubber, and other plants.
cally developed for a crop and a particular
genotype are then directly used in national
programmes. Additionally, breeding material
originating from mutant lines and clones which Support for national programmes
are ready for field testing are dispatched from
Seibersdorf to developing Member States in sup- A radiation treatment service is provided at
port of their breeding programmes. no cost to FAO and IAEA Member States to
foster the application of nuclear techniques in
crop improvement programmes and to render
Training of plant breeders direct support to plant breeders in developing
countries. Mutagenic treatment is applied to
Training in plant breeding represents the seeds, corms, tubers, scions, cuttings, and tissue
most active component of technology transfer at cultures ("in vitro materials") with precise doses
the Seibersdorf Laboratories. For 20 years the of gamma and fast neutron radiation. The doses
Plant Breeding Unit has supported the Agency's are carefully calibrated to assure reproducible
fellowship programme and organized inter- effects. Users of the service are requested to
regional training courses. Training activities are report on the objectives of the applied mutation
closely connected with R&D efforts on crop breeding project and to provide an adequate
plant improvement and the application of material (population size) to ensure a high prob-
nuclear techniques in breeding. (See graphs.) ability for mutation induction of desired charac-
During a period of three to twelve months, fel- ters. Moreover, a prior radiosensitivity test in a
lows usually work with radiation or chemical greenhouse is frequently performed to assess
induced mutagenesis in plant species cultivated useful radiation doses for the great variety of
in their home countries. Whenever possible, biological samples in mutation breeding. The
training of small groups of two-to-five fellows is treated materials are dispatched with a detailed
organized for solving common problems. The irradiation protocol and with the request to report
experiments are individually designed to assure on the induced radiation effects in the first and
that laboratory techniques and results will be second mutation generation. This feedback is
directly applicable upon return to the home in- required to improve radiosensitivity estimates of
stitute. species and cultivars from different environ-
As a result of their work, fellows have ments.
produced numerous scientific publications in in- Over the last 25 years, the Unit has provided
ternationally recognized journals and symposia radiation services on more than 20 000 samples
proceedings. Very often, as continuation of a from the majority of Member States from the
fellowship in Seibersdorf, fellows participate in FAO and IAEA. (See table.) Most of these were
co-ordinated research and technical co-operation seed samples which were irradiated with cobalt-
projects of the IAEA. 60 gamma rays.
The FAO/IAEA Interregional Training Recently, however, requests for mutagen
Course on "Induction and Use of Mutations in treatment of in vitro materials and for fast
Plant Breeding" has been held at the Seibersdorf neutrons have become more frequent. This
Laboratories since 1982. Twenty participants reflects the increasing importance of biotechnol-
from different Member States of FAO and IAEA ogy and molecular genetics in plant improve-
are admitted annually to this intensive training ment programmes.
course that usually lasts 6 to 8 weeks. Through Less than 80 mutant varieties were officially
lectures, laboratory exercises, field experiment released before the start of irradiation services.
evaluations, seminars, and excursions, par- Over the past quarter century, more than 1500
ticipants are made aware of the latest advanced cultivars of crop plants and ornamentals with
mutation techniques and biotechnological and significantly improved attributes — increased
molecular biology methods for crop improve- yield, improved quality, higher market value,
ment. Special training is given in the safe han- disease resistance, and/or stress tolerance —
dling of radiation sources, radioisotopes, and have been released. Some of these mutant
particularly hazardous mutagenic chemicals. At varieties were derived from radiation services
the end of each course, participants are able to provided by the Seibersdorf Laboratory. O
32 IAEA BULLETIN, 4/1992FEATURES
A banana plant
developed by mutation
breeding using ionizing
radiation. At left The
schematic represents a
banana mutation
breeding system.
Propagation of shoot Mutagenic
tips in test tubes irradiation
An initial
plant
DNA 'fingerprinting' for Selection and plant
genetic characterizatioin regeneration in
test tubes
Acclimatization of
plants in soil
Plant selection in the field
Rapid propagation
of a selected plant
in test tubes A mutant clone in the
farmer's field
Breeding
Bananas, plaintains, and cooking bananas are varieties are entirely sterile and therefore impossible hardier bananas
different cultivars and species belonging to the to improve by conventional breeding techniques.
botanical genus Musa. Banana "trees" are actually Research on the induction of mutations in
big herbs which produce fruit that are one of the most bananas by exposing them to radiation and support-
important foods for hundreds of millions of people in ing tissue culture techniques was initiated at the
developing countries. The world's production is Seibersdorf Laboratories in 1985. Shoot tips were
more than 70 million tonnes per year and about 90% isolated from several economically important
of the total harvest is used as food for domestic banana and plantain cultivars and micropropagated
consumption. The banana industry generates an on artificial media in test tubes. Several types of
income of about US $1.7 billion annually for export- mutagenic irradiation (gamma rays and fast
ing developing countries. neutrons) were applied on actively growing cells of
The cultivation of bananas and plantains is apical shoot tips which were regenerated into plants.
seriously threatened by several diseases caused by This research resulted in the development of mutant
pathogenic fungi, bacteria, viruses, and nematodes. clones of the most important cultivar of the dessert
Some of them may be controlled by pesticides; banana. "Grand Nain". These varieties are now
however, the most epidemic pathogen. Fusarium, is being tested in several countries for agronomic per-
a soil borne fungus which causes Panama disease. formance such as yield, quality of fruit, and earlier
There is no effective chemical control against the harvest.
spread of this fungus in infested soil. Panama dis- The Seibersdorf Laboratory supports a co-or-
ease has devastated several hundred thousand dinated research programme on breeding for im-
hectares of banana plantations in Central America provement of Musa crops and assists several tech-
and created serious problems in Africa where many nical co-operation projects in establishing national
people are dependent on plantains and cooking breeding programmes in Colombia, Panama. Costa
bananas as part of their staple diet. The only way to Rica, Cuba. Ghana, Malaysia, and Thailand.
resolve this problem is to breed varieties having Recent developments in molecular biology have
disease resistance. made it possible to characterize plant genomes and
The world's production of bananas is based on to identify markers for practical use in plant breeding.
a very limited number of genetically unimproved Genetic "fingerprinting" of banana cultivars and
clones that were selected and domesticated from mutants opens new perspectives for breeding these
nature. Although cross breeding has contributed a genetically "recalcitrant" crops which are of such vital
little to banana breeding, the most important importance to people in developing countries.
IAEA BULLETIN, 4/1992 33You can also read
