PROBLEMS IN USING INDUCED MUTATIONS IN VEGETATIVELY
                                       PROPAGATED PLANTS
                                       K.Mikaelsen*
                                       ABSTRAK - ABSTRACT
                                           PROBLEMS IN USING INDUCED MUTATIONS IN VEGETATIVELY PROPAGATED
                                       PLANTS. Conventional breeding techniques are difficult to apply in most vegetativdy propaga-
                                       ted plant species. The mutation breeding is therefore very important in these plant species, but
                                       practical results have been difficult to obtain due to the problems in recovering the mutated
                                      cells in the plant. The importance of various techniques are discussed and the advantage develop-
                                       ing various tissue culture techniques have been described.
                                           MASALAH DALAM PENGGUNAAN MUTASI BUATAN PADA TANAMAN YANG
                                       DIBIAK SECARA VEGETATIF. Teknik pemuliaan secara konvensional umumnya sukar
                                       diterapkan pada spesies tanaman yang dibiaksecara vegetatif. Oleh karena itu teknik pemuliaan
                                       mutasi sangat penting bagi spesies tanaman yang demikian, tetapi mutan yang dapat digunakan
                                      dalam praktek sukar diperoleh karena masalah kembalinya sd yang termutasi dalam tanaman
                                       ke bentuk normalnya. Dalam makalah ini dibahas keunggulan berbagai teknik mutasi buatan
                                       clankeuntungan pengembangan berbagai teknik kultur jaringan.
                                      INTRODUCTION
                                           A large number of plant species are propagated asexually (or vegetatively) such
                                      as many root and tuber crops, sugarcane, fruits, and other three species and shrubs
                                      and many ornamentals.
                                           Cross-breeding   is often   limited  by specific   problems   in most vegetatively
                                       propagated plants (VPP). Many VPP have a rather long vegetative phase before going
                                      into sexual reproduction.   In addition, these plants are generally highly heterozygous,
                                      which causes complicated     segregations and makes the detection of a useful recom-
                                      binant very difficult.   'This problem is further enhanced by frequently polyploidi
                                      in such plants.    All these factors make cross breeding very difficult         and time
                                      consuming.    Furthermore,   incompatibility   and other cross barriers, apomixis and
                                      sterility exist quite often and hinder the plant breeder in making use of conventional
                                      cross-breeding.
                                      * Expert, UNDP Project INS/78/074
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                                           MUTATION              BREEDING           OF VEGETATIVELY                      PROPAGATED
                                            PLANTS'
                                                 It is, therefore,  quite clear that mutation      breeding techniques are an attractive
                                           alternative   in breeding of VPP. The most promising aspect of mutation induction
                                           in VPP compared to cross-breeding methods is the ability to change only a few
                                           characters   of an otherwise good cultivar without altering significantly the original
                                           well established     genotype.    Mutation     breeding,   therefore,   must be considered as
                                           the obvious means to perfect the leading cultivars and as a possible sh~r_tcut for
                                           inducing desired genetic alterations in outstanding           cultivars. Obviously, mutations
                                           are the only means for producing variability in sterile VPP and in obligate apomicts.
                                            Further,  mutations can be useful to break apomixis, to overcome self-sterility and
                                           cross barriers as well as to uncover rearrange chimeras.
                                                 In spite of these many advantages of mutation breeding techniques in VPP the
                                           results have been rather small in comparing with seed propagated                   plants such as
                                           rice, barley. and many others crops. The main problem has been the recovery of
                                           mutants in VPP. Normally a shoot, or any other multicellular organ are treated for
                                           mutation    induction    and the desired mutations has occured in one cell. The chances
                                           of such a mutated cell growing into a sector or layer and be able to manifest itself
                                           will depend on l!s .position within the apex as well as its growth rate as compared
                                           with the surrounding cells or tissue layers. It is obvious that mutated cells will be
                                           easily hidden and not be visible in such multicelledar             tissues and special methods
                                           are required to unciver such mutated cells.
                                                 The first    requirement      is, therefore,    that  mutagen      treated   (unirradiated)
                                           material   has to be propagated        to permit the formation of periclinallayers          before
                                           selection   can be applied.       Very often repeated         propagations    are necessary     for
                                           obtaining    large sectors     of mutated     tissue  from which a maximum number of
                                           mutants can be recovered. In fruit trees, for example, (Figure 1) the best conditions
                                           are found in the axillary meristems of the basal leaf primordia of the dormant buds.
                                           (The primordia to be used for treatment           should consist of as few cells as possible).
                                           Experience shows that the buds derived from leaves 4 - 8 (approximately)                    of the
                                           primary shoot are those that exhibit the highest frequency of relatively broad
                                           mutated     sectors  in the second vegetative generation.         Measures have to be taken
                                           (by pruning) to force these buds into growth. Several authors have reported better
                                           results after irradiating buds that have just started growth than with buds in deep
                                           dormancy.     If growing plants are irradiated,        decapitation    of the main shoots will
                                           force new buds to develop through regeneration and thereby increase the chance
                                           for recovering a larger number of mutants.
                                                 Many of the complications          described above could be eliminated if chimera
                                           formation could be avoided. One of the methods available is the adventitious bud
                                           techniques which was developped by BROERTJES and collaborators at Wageningen
                                           (1). This technique     is based on the phenomenon          that the apex of the adventitions
                                           buds, such as may be formed the base of the petiole of detached leaves, originates
                                           from only one (epidermal) cell. Consequently,               adventitious    plantlets   either  are
                                           completely     normal    or are complete,       solide   mutants.    In other words, chimera
                                           formation     does not take place. This adventitious            bud technique      offers a great
                                           108
                                         advantage for practical mutation breeding and has given many good results particu'
                                         larly in ornamental    plant (Saintpaulia,    Streptocarpus,    Achimenes, Begonia, Liliwrli
                                         and many others).
                                              Many plant species can be propagated this way. BROERTJES ~~.                        (1) list
                                         other 350 of such species. Many species of economically important                plant families
                                         have not been tested for developing the adventitious           bud techniques and may not
                                         always develop adventitious buds from only one cell. In addition, the condition of
                                         the mother plant, the age of leaves, environmental              conditions    during and after
                                         rooting   and the auxin-cytokinin        balance appear to influence the formation and
                                         differentiation   of adventitious buds.
                                         POTENTIALS OF TISSUE CULTURE TECHNIQUES IN BREEDING
                                         OF VPP
                                              The modern developments of culturing somatic plant cells should also be
                                         investigated   for use in VPP in this respect tissue culture         technology holds much
                                         promise. Recent advances in the field of plant protoplast,             cell, tissue, and organ
                                         culture  (embryo,    anther) have, transferred      this area if fundamental      research into
                                         one that is dynamic and promising also for obtaining further advances in crop
                                         improvements      programmes.     I  believe the potentials      of this technology     can be
                                         powerfull tool also in the VPP.
                                              During the last 30 years, the culture of ovule, ovary, and embryo has been
                                         employed     to  overcome sterility.     incomtability    and dormancy; to induce poly·
                                         embryony; and to succesfully hybridize various crops.
                                              By meristem culture, large numbers of horticulturally             important    plants have
                                         been commercially propagated and freed from pathogens.
                                              These established techniques have played an important               role in wide hybridi-
                                         zation and clonal propagation       programmes and will, no doubt, continue to contri-
                                         bute to future demands. However, some of the recent advances in the area of plant
                                         protoplast,   cell, tissue,  and organ culture      have attracted    international   attention
                                         because   of   their  significance   in and far-reaching       implications    for agricultural
                                         research and crop improvement programmes.
                                              It is expected    that  the following techniques will playa         significant   role, not
                                        only in the improvement         of existing crops but also in synthesizing new plants :
                                         1.  Wide hybridization in crops through in vitro pollination and fertilization.
                                        2.   Production     of haploid and homozygous plant from exised anthers, isolated
                                              pollen and by chromosome elimination.
                                        3.    Somatic hybridization     and genetic engineering through the fusion of protoplasts
                                              and the uptake of DNA (Figure 2).
                                        4.    Induction   of genetic variability in crops (mutants,        and various ploidy levels)
                                              through protoplast and cell culture and selection in these cultures for resistance
                                              to diseases, salinity, water, and temperature        stresses and possibly many other
                                             important characteristics.
                                              I expext    that   the VPP will have great potentials           for benefits   from such
                                        techniques.
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                                            REFERENCES
                                             1.   BROERTJES, C:; HACCIUS, B., and WEIDLICH, S., Adventitions bud for:
                                                       mation    on isolated     leaves and its sigriificance for mutation          breeding,
                                                       Euphytica 17 (1968) 321.
                                            2.   DONINI, B., '1nduction          and isolation of somatic mutations           in vegetatively
                                                       propagated     plants",    Improvement       of   Vegetatively    Propagated      Plant
                                                       Through Induced Mutations (Technical Reports Series No. 173), IAEA,
                                                       Vienna (1975)35.
                                            3.    BAlAl, Y.P.s., Potential of protoplast culture works in agriculture, Euphytica
                                                       23 (1974)633.
                                            4.   CARLSON, P.s., SMITH, H.H.,and FEARING, R.D., "Parasexual interspecific
                                                      plat   hybridization",    Manual on Mutation Breeding, 2nd Ed. (Technical
                                                       Reports Series No. 119), IAEA, Vienna (1977) 206.
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