Savidan, Yves

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GENETIC CONTROL OF FACULTATIVE APOMIXIS
AND APPLICATION IN BREEDING PANICUM MAXIMUM
( Communication to the XIVth International Congress
of Genetics, Moscow , 21 - JO /8/1978 )
l'
1
1
y, SAVIOAN
___________________----J' ,
OFFICE DE LA~ RECHERCHE SCIENTIFIQUE ET TECHNIQUE OUTRE - MER
CENTRE D' ADIOPODOUMÉ - CÔTE D'IVOIRE
B.P. Y 51 - ABIDJAN
OFFICE DE LA RECHERCHE SCIENTIFIQUE ET TECHNIQUE OUTP~-MER
CENTRE D'ADIOPODOUME (Côte d'Ivoire)
Department of Genetics
GENETIC CONTROL OF FACULTATIVE APOMIXIS AND
APPLICATION IN BREEDING PANICUM MAXIMUM
by
Yves SAVIDAN
Communication to the XIVth INTERNATIONAL CONGRESS OF GENETICS
MOSCOW, 21 - 30/08/78
1ABSTRACT
SAVIDAN Y., Dept. of Genetics, Office de la Recherche
Scientifique et Technique Outre-Mer, Abidjan, Ivory Coast
GENETIC CONTROL OF FACULTATIVE APOMIXIS AND APPLICATION IN
BREEDING PANICUM MAXIMUM
A diallel cross realized between eight sexual tetraploids
and eight facultative apomicts of Paniaum maximum gave tetra-
ploid hybrids that segregate in a.1 : 1 ratio between sexual and
apomictic plants. Selfed, backrosses and further progenies
led to specify the simple genetic control of apomixis in this
species. Apomictic hybrids are either facultative or obligate,
and this characteristic looks to be under a more complex
genetic determinism. Two, three and four ways hybrids with
good forage productivity emphasize the efficiency of using
facultative apomixis in a breeding programme for this tropical
grass. That probably should also successfully be done with other
plants of the Paniaoideae subfamily.
2The Panicum maximum agamie complex has its center of diver-
sity in East Africa. It includes mostly tetraploid types which
are facultative apomicts. Sorne small natural populations with
diploid number of chromosomes were found in Kenya. They were
shown to be entirely sexual (1).
A lot of theoretical investigations have been conducted on
this biological material during the last decade, in such fields
as numerical taxonomy, quantitative and population genetics,
cytogenetics (2 to 6). They have led to a good knowledge of the
structural organization and evolution of natural variability.
An evolutionary scheme has been proposed (7) that is in agree-
ment with the diploid-tetraploid-haploid cycle previously pre-
sented by DE WET (8) for the BothriochZoa-Dichanthium complex,
after which an improvement programme was built and successfully
tested (9).
Four years aga, crosses were attempted between eight sexual
tetraploids and eight natural apomicts (Table 1). Among these
sexual genitors, five were issued from colchicine treatment of
diploids, while the other three were Fl hybrids from previous
sexual x apomictic crosses. The eight apomicts were choosen to
2n = 16 24 32° 48 64 sum
Fl 1 4 77 32 3 117
Rl 1 0 20S 13 2 221
reproduction sexual S & A apomictic
TABLE 1. Chromosome numbers in Fl (sex x apo) and
Rl (Fl crossed by another apomict) with modes of
reproduction.
o including aneuploids with 30, 31 or 33 chromosomes.
represent - as weIl as it was possible with only eight plants -
the main divisions of our classification of the variability
encountered within the complex (10). Quite distant plants were
crossed in this way, but fertile hybrids were obtained from
3most of these crosses. Genetic distances between genitors
however led to numerous chromosornal abnorrnalities, since 16.6
per cent of the plants produced showed to have a ploidy level
different from 4x.
These results were first reported in a book published by
Dr. PETROVat the beginning of 1978 (11).
Embryological studies were undertaken to specify the mode
of reproduction of each plant produced. Panicum belongs to the
Panicoideae subfamily of the Gramineae. Such material presents
a good opportunity to study inheritance of apomixis and sexua-
litY as these two modes of reproduction are characterized by
two different types of embryo-sacs. While sexual have the
normal Potygonum type whith antipodals and two polar nuclei,
apomicts get only one polar nucleus without antipodals. This
fact, combined with a good and rapid cytological technique
using phase contrast microscopy (12), allows us to analyse a
great number of plants, their mode of reproduction being deter-
mined by the observation of twenty ovules.
Several hybrids coming from our 8 x 8 diallel cross were
recently selfed and backcrossed. Ernbryological studies of Fl,
F2 and F3 products will be analysed in the present cOInlmmication.
Non-tetraploid plants
We observed two dihaploids sprung from the parthenogenetic
development of a reduced egg-cell. They are entirely sexual. Four
triploids were also observed, but their origin is not explained.
They are also entirely sexual. Hexaploids and octoploids, coming
from fertilization of unreduced egg-cells are aIl apomictic.
Thus modes of reproduction would appear to segregate only
at the tetraploid level.
Fl generation
In the Fl generation (Table 2), 134 hybrids were observed
up to the present. One half (72) are apomicts, the other half
(62) being sexual.
4AP0 SEX
T34.T x apo 4 2
T35.T x apo 1 0
T44.T x apo 6 3
K189.T x apo 34 37
51. T x apo 4 5
52. T x apo 23 15
süm 72 62
TABLE 2. Modes of reproduction of F1 hybrids.
F2 generatioIl
Within F2 generation, plants we shall examine result of
selfing, backcrossing and recrossing of F1 by a new apomict
(which we have called Rl hybrids).
§~!!~Q:P!Qg~~!~~
122 plants sprung from self-fertilization were analysed.
Table 3 shows that 121 are sexual, only one being apomictic.
APO SEX
(K189.T x G3)1 0 18
(K189.T x K4) 1 0 29
(K189.T x K26)1 0 46
(K189.T x K26)2 0 21
(S2.T x Cl)l 0 5
(S2.T x C1)2 1 2
sum 1 121
TABLE 3. Modes of reproduction in selfed progenies
of sexual x apomictic Fl hybrids.
Backcrosses
~A s,kew appeard in the backcrosses (Table 4) : while our
natural sexual diploids and the artificial sexual tetraploids
were shown to reproduce mostly by outcrossing, the, rate··.(!lf "
autocompatibility greatly increased in further sexual proge-· .
nies. Combining numbers of seeds producGd comparatively from
5self-fertilization and from backcrosses, with morphological and
cytological observations, it is clearly demonstrated that a
sexual outcrossing Fl hybrid give many more apomictic than
sexual plants in its backcrosses progenies.
APO 5EX sum
(1(189.T x (4)1 1 39 40
(K189.T x K26)1 9 42 51
(52.T x Cl)l 11 10 21
(K189.T x G3)2 12 2 14
(K189.T x G3)3 23 2 25
TABLE 4. Modes of reproduction in backcrosses progenies
of sexual x apomictic Fl hybrids.
g~~!2~~!~g_2!_!1_hYQ!!~§
5exual Fl hybrids were crossed by a new (second) apomict
(Table 5). Among the 279 Rl hybrids obtained, one half is
apomictic - 135 plants - and the other is sexual (144) as it
was observed for Fl hybrids.
APO 5EX
P2 x apo' 56 56
153 x apo' 32 42
154 x apo' 47 46
SUffi 135 144
TABLE 5. Modes of reproduction of Rl hybrids
(sex x apo x apo')
F3 generation
Our F3 material is composed of selfed and backcrossed
progenies of Rl hybrids. From selfing, the 56 plants observed
were aIl sexu~l. In the backcrosses (Table 6), the same obser-
vations as inprevious backcrosses can be made. When autocompati-
bility is low, apomictic and sexual products seem to segregate
in a 3 to 1 ratio.
6APO SEX sum
(IS4 x T25)1 3 38 41
(P2 x Cl)l 12 8 20
(IS4 x T25)2 36 16 52
TABLE 6. Modes of reproduction in backcrosses
progenies of R1 hybrids .
Discussion
Suming thesc results, which come from analysis of S55
hybrids, a simple rnonogenic determinism can be proposed for
inheritance of apomixis. A+ would be the wild allele, while
A- would induce unreduced ernbryo-sac formation. Art ificial
sexual tetraploids would be A+ A+ A+ A+, and natural apomicts
+ - - -A A A A . If backcrosses of sexual Fl hybrids can give a
majority of apomictic plants in such a model, the structure
of these sexual Fl hybrids has to be heterozygote. This does
not agree with data from self-fertilization in which apomixis
is quite absent.
Differences in pollen competitivity, as observed by NOGLER
(13) in RanunauZus, can perhaps be considered. We observed a
significant difference between the fertility of backcrossed and
selfed seeds. So both gametophytic and sporophytic selections
can be argued for the absence of apomixis in selfed progenies.
Several new crosses will he undertaken this year to test these
different hypotheses.
Gametophytic apomixis of Paniaum maximum is facultative.
As it has been often said that this was a barrier to farming
utilization, we also studied the rate of sexuality of natural
and hybrid apomicts. In our collection, which comprises more
than five hundred natural apomictic accessions, a polymorphism
can be observcd for this rate of sexuality. At the cytological
level, natural apomicts showed to have from 1 to 27 per cent of
ovules with a single sexual embryo-sac. In the field, we observe
only 1 to 5 per cent of off-type plants in non-competitive condi-
tions. This difference is due largcly to selection : off-types
are plants with a low vigour because of their selfed origin in
plants that reproduce by outcrossing whon sexuality appears. In
farming conditions, aIl off-types are e~iminated.
771 apomictic hybrids of our 8 x 8 diallcl cross werc exami-
ned for this characteristic. One hundred ovules were observed for
each of them. The large majority of these apomicts seems to be
obligate or nearly obligate. Only two hybrids showed a high
degree of sexuality that really exclude farming utilization.
And in these latter cases, sister plants could be found that
were obligate apomicts.
While apomixis looks likc a presence-absence characteristic
with a simple genetic determinisrn, the rate of sexuality in apo-
micts seems to have a much more complex inheritance. It has
already been showed within several apomictic species that it
can be greatly conditionncd by environmental variations such as
day length (14 to 19). It does not constitute a barrier to
farming utilization of facultative apomicts of Panicum maximum.
In this species, apomictic hybrids which combine informations
from a sexual and one, two or three different apornictic genitors
were successfully tested in farming conditions. Our improvement
programme yielded a great increase of productivity as early as
the first hybrid generation.
The same is to be expected from other apomictic grasses,
i.e. almost aIl tropical forage grasses. Data on biology and
evolution already available in these plants emphasizes a great
homology of function. Even if details are different, a research
programme such as that rcalized within the Panicum agamic
complex could be successfully engaged with each/these Gramineae
(20). ~
REFERENCES
(1) COMBES D. and PERNES J., 1970. Variations dans les nombres chro-
mosomiques du Panicum maximum Jacq. en relation avec
le mode de reproduction.
C.R. Acad. Sei. Paris, 270 : 782-785.
(2) PERNES J., 1971. Etude du mode de reproduction: apom1x1e facul-
tative, du point de vue de la génétique des populations.
Travaux et Documents de l'ORSTOM, 9 : 66 p.
(3) PERNES J., 1975. Organisation évolutive d'un groupe agamique la
section des Maximae du genre Panicum (Graminées).
Mémoires ORSTOM, n° 75 : 106 p.
(Thèse Doct. d'Etat, Univ. Paris XI, déc.72).
(4) COMBES D., 1975. Polymorphisme et modes de reproduction dans la
section des Maximae du genre Panicum (Graminées) en
Afrique.
Mémoires ORSTOM, nO 77 : 112 p.
(Thèse Doct. d'Etat, Univ. Paris XI, déc. 72).
(S) PERNES J., SAVIDAN Y. and RENE-CHAUME R., 1975. Panicum: struc-
tures génétiques du complexe des Maximae et organisation
de ses populations naturelles en relation avec la spé-
ciation.
Boissiera, 24 : 383-402.
(6) PERNES J., COMBES D., RENE-CHAUME R. and SAVIDAN Y., 1975. Biolo-
gie des populations naturelles du Panicum maximum Jacq.
Cah. ORSTOM, sér. Biol., X (2) : 77-89.
(7) SAVIDAN Y., PERNES J. and CHAill4E R., 1978. Diploid-tetraploid-
dihaploid cycles and their role in the organization of
the variability and evolution of Panicum maximum Jacq.
Cano J. Genet. Cytol., in press.
(8) DE WET J.M.T., 1968. Diploid-tetraploid-haploid cycles and the
origin of variability in Dichanthium agamospecies.
Evolution, 22 : 394-397.
(9) PERNES J., RENE-Ct~UME R., RENE J. and SAVIDAN Y., 1975. Schéma
d'amélioration génétique des complexes agamiques du type
Panicum.
Cah. ORSTOM, sér. Biol., X(2) : 67-75.
(10) PERNES J., RENE J., RENE-CHAUME R., LETENNEUR L., ROBERGE G. and
MESSAGER J.-L., 1975. Panicum maximum (Jacq) et l'intensification
fourragère en Côte d'Ivoire.
Rev. Elev. Méd.vét.Pays trop., 28 (2): 239-264.
(11) SAVIDAN Y., 1978. Analyse génétique des descendants de croisements
sexués x apomictiques chez Panicum maximum. II. Nombres
chromosomiques et modes de reproduction.
D.F. PETROV editor, in rus sian.
(12) SAVIDAN Y., 1975. Hérédité de l'apomixie. Contribution à l'étude
de l'hérédité de l'apomixie sur Panicum maximum Jacq.
(analyse des sacs embryonnaires).
Cah. ORSTOM, sér. Biol., X(2) : 91-95.
(13) NOGLER G.A., 1978. Zur Zytogenetik der Apomixis bei Ranunaulus
auriaomus. 56 p. (in press).
(14) GRAZI F. s UMAERUS M. and AKERBERG E., 1901. Observations on the
mode of reproduction and the embyology of Poa pratensis.
Hereditas, 47 : 489-541.
(15) KNOX R.B. and HESLOP-HARRISON J., 1963. Experimental control of
aposporous apomixis in a grass of the Andropogoneae.
Bot. Notisher, 116 : 127-141.
(16) KNOX R.B., 1967. Apomixis : seasonal and population differences
in a grasse
Science, 157 : 325-326.
(17) GUPTA P.K., ROY R.P. and SING A.P., 1970. Aposporous apomixis
seasonal variation in tetraploid Diahanthium annulatum
(Forssk.) Stapf.
Portug. Acta Biol., 11 : 253-260.
(18) SARAN S. and DE WET J.M.J., 1970. The mode of reproduction in
Dichanthium intermedium (Gramineae).
Bull. Torrey ~ot. Club, 97 : 6-13.
(19) SING A.P. and MEHRA K.L., 1971. Methods for induction and utiliza-'
tion of variability in the improvement of an apomictic
grass : Diahanthium annulatum complexe
Theoret. Appl. Genetic~_, 41 : 259-262.
(20) SAVIDAN Y., 1978. L'apomixie gamétophytique chez les Gralninées et
son utilisation en amélioration des plantes.
Ann. Amé l i 0 r. Plantes, 28 (1) : 1 - q •


Genetic control of facultative apomixis and application in breeding Panicum maximum

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