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Journal ArticleDOI

Phenology and reproductive effort of cultivated and wild forms of Pennisetum glaucum under experimental conditions in the Sahel : implications for the maintenance of polymorphism in the species

01 Jun 1996-Botany (NRC Research Press Ottawa, Canada)-Vol. 74, Iss: 6, pp 959-964

TL;DR: The wild and the cultivated forms of pearl millet, Pennisetum glaucum (L.) R.Br.

AbstractIn the Sahel region of Africa, the wild and the cultivated forms of pearl millet, Pennisetum glaucum (L.) R.Br., are sympatric and interfertile and yet have remained distinct for millenia. Reproductive barriers are not sufficient to explain this situation. To elucidate other possible mechanisms, the two forms were compared under experimental conditions in the Sahel for their phenology and reproductive effort. The length of the flowering period of each type was much longer than the average individual flowering period. When the last cultivated plants were finishing flowering, 65% of the wild plants were still flowering and 30% were just starting to flower. Thus, the last group was completely isolated from cultivated pearl millet gene flow (endogamic reproduction). The two forms of pearl millet also differed in the distribution of aboveground biomass among different plant parts, except for the number of seeds per plant. Both phenological behaviour and reproductive effort contribute to the maintenance of dist...

Topics: Pennisetum (52%), Cultivated plant taxonomy (50%), Phenology (50%)

Summary (1 min read)

Materials and methods

  • The seeds uscil liir tlic stiidy saiiiplcs wcrc collcctcd from hundreds of spikes.
  • The first D A E wiis the sanie for wild pearl niillet Lind cultiviited pearl millet, 3 days after sowing.
  • In riich pocket one randomly chosen plant wiis observed until the ciid of its cycle.
  • The llowcring phase for the cultivatctl li)riii hegins with tlic Il~i\vcriiig of the spike of the niain stcni (the lïrsi stciii ciiicrgcd) aiid crids with ;I spike of a priniary tiller.

I'llcnology or ~lowcrillg

  • HOWcvcr, the total Ilowcring tinic ol'thc siirill>lcs WU 45 d:iys l'or cultivated pc¿irl millet and iiiorc thcin 49 days for wild pcarl niillct, sincc the latter population had not finishcd Ilowcring at harvest (Fig. IO ).
  • The distribution over tirrie of thc pcrcentagc of' cultivatcd plants in thc flowering phasc followcd a noriilal curvc.
  • Flowcring bcgan at 42 DAE, whcri thc tillcring pliasc was finished.
  • Thc siinic typc of distribution was obscrvcd for the wild plunts.

Discussion

  • This study shows that undcr cxperinicnlal conditions, thc cultivatcd pcarl millct was always influenced by the wild pearl millet pollcnic cloud, whereas the wild pearl millct population escapcd from the cultivatcd pollenic cloud for a large part of its flowcring period.
  • The pared with those frolli dcviíint foriiis, Iikc sliibra.

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Phenology and reproductive eort of cultivated and wild
forms of Pennisetum glaucum under experimental
conditions in the Sahel : implications for the
maintenance of polymorphism in the species
Jean-François Renno, Thierry Winkel
To cite this version:
Jean-François Renno, Thierry Winkel. Phenology and reproductive eort of cultivated and wild forms
of Pennisetum glaucum under experimental conditions in the Sahel : implications for the maintenance
of polymorphism in the species. Canadian Journal of Botany, National Research Council Canada,
1996, 74 (6), pp.959-964. �10.1139/cjb-74-6-959�. �ird-00142188�

.3
959
Phepslogy and reproductive effort of cultivated
and wild forms of P~NI~~&J~ g/arua=um wnder
experimental conditions in the Sahel: impllieatisns
for the maintenance of polymorphism in the species
J.-F. Renno and T. Winkel
Abstract:
In the Snhel region of Africa. the wild and the cultivated forms of pearl millet, Pe~~~~i.sc~frr~~r g/tr~rc~r~r (L.)
R.Br., are syrnpntric and interfertile and yet have rcmaincd distinct for millenia. Rcproductivc harriers are not sufficient
to explain this situafion. To elucidate other possible mchanisms, the two forms were coniparcd under cxperiniental
conditions in the S:~hcl for their phrnology and rcproductivc effort. The length of the flowering period of each type ~‘3s
much longer than the average individual flowering period. When the last cultivated plants were finishing knvering,
65% of the wild plants were still tlowcring and 30% were just starting to tlowcr. Thus,
tlic last group wils conipletrly
isolated from ctIltiv;lted pearl millet gene now (endog;mic reproduction). The two forms of pearl millet also differed in
tht: distribution of aboveground biomass among different plant pnrts,
except for the number uf seeds per plant. Both
phrnological behaviour and ruproductivr: effort contribute to the maintenance: of distinct forms of wild ;rlld cultivated
pCild
millet.
Introduction
Archi~eologicnl traces of inqxints of both wild and cultivntcd
pcnrl niillct (Pcrrrri.rc~urn gln~rr~r) seeds rind hrisrlcs on pot-
tery, found in southcast Mauritania and dating from around
3000 BP,
arc
evidence of a neolithic agriculture with culti-
valcd and wilcl pcnrl n1illct populations in synipatry (Amblarcl
and
Pcrni3 1989).
The current wild fomm is distributed across
the northern Sahel
and
is phylogenctically close to the anccstol
of the cullivakd pearl niillct (Harlan 1975: Portkrcs 1976).
Van der ZOII (1992) recognized three subspecies in Pcrl-
rrisc~~cm ,yhcm (L.) R.Br. : P. gkzucrtnr ssp.
gk7wrrur. the
cultivated pearl inillct; P. glfrrrc~otl ssp. I.I’~cILY~IIII~ (Lam.)
A. Rich., the \viltl and weedy forms: and P. gk~rcrrrn ssp.
sidcrkrrltr~ (Schlccht.) Slapf C! Hubh., lhc inlcrnlcdiatc
forni bctwccn the wild nncl the
CulliViltNl IlXnls, known 35
shibra in Niger. These three I;CGI hclong to rhc satne gene
pool of the allr)gamic
and polyinorphic annual species.
P. g/(~rr~~ttr (L.) R.Br. (f-iarlan rind de Wet 197 I).
Rcgnrding the cultivated pearl niilicr. die farnicr plays an
csscntial sclcctivc role through agriculrurnl practices: choice
of scccIs from spikes typical fur n local cultivar, batches of
seeds (cnllcd pockets) sown into holes Ihvoring the growth 01
the biggest seeds, hoeing to elin~inole
~ccrls
and pearl millet
plants outside the pockets, thinning out to preserve the most
vigourous plants. and elin~ination of the shibra. Ncverthe-
Icss, in the field. the frequency ol’thc rcnxiining shibra varies
bctwccn 5 and 30% in the :lI’CilS whcrc the wild and cultisxd
fornis
arc
in contact (Rcy-Hcrnx 1983). These wild popu-
lations arc: not hubjcct LU conscious scloctiun prcssurc by
huinaiis. f’or lwo saniplcs of sccrls tukcn from wiid pa-1
millet populations in Scncgul and Niger, the proportion 01
dcsccndants of the hybrid phenolypc (shihrn).
supposcdl~ the:
producl
of fertilization by CllltiVil~Cd
pdlcrl, \Sxi cstimared at
3 I iId I9%, rcbpcclivcly (MnKhiliS anil Tosrain 19911
Fonds Docurngmtaire ORSTOM

9GO
3
I-low
is
the polymorphism
of
I'.
glwcrrtrr
maintained'?
How
is
it
t1i;tt
wild
pearl
niillct
docs not rlis;ippcar
in
contact
with cultiv;itcd
pearl
niillct
under
the
cI'l'clcts
of
gene
flow?
Many
studies
have
addrcsscd
thcsc
questions. Studies
of
gcnclic
dist;ince indicated strong intcrniixing of genes
hctwccn
wild and cultivatcd
pearl
millet
(Tostain
1993).
Pcrnk
(1983,
1985)
underlines
the
fxt
that
the
two forms
interact
but
cai cxchnngc alleles without
a
modification
of
phtilotypcs
because
the
genetic control of clonicstication is
supposed
to
dcpcncl
on
a
few
linked
genes.
Moreover, gene
flow ciin be controllecl by mechanisms
that
act
at
the pre- and
post-zygote
stages
in
I'iivour
of
the niaintennnce
of
differ-
entiation between
the
wild and cultivutecl fornis. Pollen
competition was observed as a prezygotc
barrier,
giving
the
advantage
to
sel(-pollination (Sarr
et
al.
1988; Robert
et
al.
1991),
while
the
reduction
in
viability
of
hybrid grains was
olmrvctl
;is
n
postzygotc brake (Anioukou and Marchais
1993). Genomic
stratcgies
in
wild
pearl
millet
in
contact
with
cultivated pearl
niillet
were mentionccl by Joly-Ichenhauser
(1984)
and Prrnhs
(I
986). who assiiiiic the existence of
two
linkage groups of predomrstication genes that would have
the effect of favouring the maintenance
of
plicnotypes
in
spite
of
hybridization. However,
if
these
reprocluctive barriers
liniit
gene
flow, they
do
not
entirely cliniinutc
it
and are not
sufficient
hy
theiiisclvcs
to
explain
the niainteniince
of
two
distinct
interfertile
forms
in
contact for
riiillcnin.
Isolated
rcprodiiclioii
in
sp;icc
aiid
iilso
in
liille.
LIS
wcll as selective
~~rcsstrres,
cc~rltl
phy
iiii
cssenti:il
role
ill
scriicluring
[tic
poly-
IllllrpllisI11
ol'
pciir1
Illillcl.
WI1cI.L'
wiltl
ill111
cullivirlcll
fc)rllls
01'
p!itl~l
Illillet
yc
ill
~togi~iil)ltic;\l
CtilitiIcI.
wl~itt
is
[IIC
l)I~O1)(iIIiOiI
of
pli\t1ts
ill
cli~(iliic
Ilt)tvcrilig
I)e~iotls?
Wliitt
itre
IIIC
tlil'l'c~t~lccs
in
rc171'0-
c;1c41
limi cst.qirtg
ilic
geite llow ol'lttc
(iflier
liwrii
by
asyn-
tluct
ive
c'1'1i)rt
I)ctwecli wild
niid
otiltivalcd
pc:irI
inillet?
I
Iotv
:I~C
IIIC
cIiI'Ii.l.cllccs
~tl~ti~ltiti~i~d
~~[IVCCII
syliil);itriC
Wild
~11111
c~ll~iv~ttcd ~lo~~~ll;ltiotls
t1tilt
1l;Ivc
I)CCll
cxcll~ulging
genes
lo
r
I
Il
i
I
IC
II
ia?
Ill
;I11
;tllcrtl~ll
to
:ldrlrcss
IlluSc
c~ucstiolls,
wc'
compared,
tilitlcr
SiillcIiaIl
cxl)criIticiititI coiitlitiolis.
tl~c
l~hcnology
of
tillcring
ond
Ilowcrillg
of
¿I
wild
pc:"'I
Illillcl
:Illcl
a
cultivatecl
pearl
riiillct
fixmi
tltc
wiic
gcogrnpliicul region,
;IS
wcll
as
the
distributiwi
nt'
abovcground bionioss proiluction bctwccn
vcgct:itivc
and
rcprocluctivc organs
in
citeli
oftlicse
two forms.
Materials and methods
1
lilt
c'
ria
I
The
seeds
uscil
liir
tlic
stiidy
saiiiplcs
wcrc
collcctcd
from
hundreds
of
spikes
Ihr
each
rnriii,
in
six
sites
hctwccri
Uclhcji
(14"43'N.
X'OS'E)
aiitl
Taiiout
(I4"S7'N. 8"49'E)
iii
Nigcr.
whcrc
wild and
culiivntctf
pearl niillct
(cv. Ankoutcss)
;ire
syiiipatric.
'Ankoutess'
li
adapted
to
a
short
rainy
season
(3
inontlis
~'IUIU
June
to
Septem-
kr)
aiid
thus
cilri
be
considercd
;IS
miniiii;illy
or
riot
at
all
photo-
F+rioJ
sensitive
(Cleiiiciit
1985:
Burtori
niid
I'owcll
1968
in
Skcrnian
and
Riveros
IY9Uj.
Thc
sccds
01'
tvild
pl;lr)t\
were
Iiarvcstcd near
pari
Illillet
t'iclds.
Can.
J.
Bof.
Vol.
74,
1996
hctwccn
FeImiiIry
arid
bliiy
.
The tliiily
iiiciin
tciiipcr;ittire
varicd
lict\vccn
26
and
37"C,
;incl
the
diiily
niciin
incident
riidiiitioii
bctwccn
17
and
27
MJl(m'
.
clay).
Irrigiitioii
\viis
rcgul;itctl
to
simulate
tlic
;ivcr;ige
rainfall
rcginic
during
rlic
rainy
sciison
in
the
region
of
Tanout.
It
was
started
on
Fc1iru;iry
9.
one
d:iy
tierore
sowing,
then
stopped 74 days
after
emergence
(DAE,
date
at
which
SOO/,
of
the
pockets
had
emerged). There
was
one
niituriil
r;iinfiill
at
71
DAE
(7.5
mm).
Weeds
were
controlled
manually. l~crtili~ers
wcrc
supplied
at
30
kg
.
ha-'
N.
P,
;ind
K
1
thy
More
soWiiig
and
IS
kg.
ha-'
N
at
16
DAE.
The
expcrinicnt;il
ficlil
wiis divided
into
five repliciitions
with
two
subplots
each.
The
suhplots
measured
4
x
10
ni,
sown
either
with
cultivated
or
wild
sccds.
;ind
were
randomized
per
replication.
Seeds
were
sown
in
pockets
(1
pockct/m2)
and
the
development
of
eight
pockets
in
the
center
of
c;icIi
subplot
was observed. The
first
DAE wiis the
sanie
for
wild
pearl
niillet
Lind
cultiviited pearl
millet,
3
days
after
sowing.
At
15
DAE,
the
cultivated
plants
were
thinned
out
to
three
planta
per
pocket,
ii
planting
density considercd
to
be
optimal
under
Salieliun
conilitions (Institut
National
de Recherches
Agronomiques du
Niger
1987). In riich
pocket
one
randomly
chosen
plant
wiis observed
until
the
ciid
of
its
cycle.
For
tlie wild
plants,
no standard
density
can
be
represcnt;itivc
ofthc
lack
of
homogeneity
in
density
of
natural
poptil;itions.
For
the
convenience
of
observii-
tions,
taking
into
:recount
the
very
iniportiint
tillcring
of
each
plant,
the wild
plnnts
were thinned
IO
1
pl;tnt/m2.
This
experimental
iippronch
resulted
from
ii
comproiiiisc
between
111c
nerd
to
collect
precise
inforniiltioli
on
e;icli
inilivitlu;il
plant
iinil
the
iiced
to
observe
tlie
phenotypic expressitrii
of
e;ich
pl;int
form
as
it
is found
untler
niituriil
conditions.
l'lier
rolo,q>*
OJ
/i11criirg
ut
rtl
.//(I
i
I
*c*t.ir
rg
Every
2
or
3
d;iys during
the
rlcvclopriiciit
of
tlic
plants,
the
fol-
lowing
obscrv;itioris wcrc
iiwlc.
(i)
The
iiiiiiibcr
of
plants
in
the
primary
tillcring
phase:
ii
plant
WIS
ccwsitlcrcrl
to
I,c
in
the
primary
tillcring
phase
during
the
wliolc
period
hctwccri
the
tlcvcloprncnt
of
the
first
aiid
the
last
priiiiary
tiller
(the
priiiiary
tillers
arc
those
growing
out
of
the
first
stcni
th;it
lias
ciiicrgcd).
Tlic
young
pearl
riiillct
plorits.
particularly
the
wild
plants.
arc
too
fragile
to
be
frc-
clucntly
ninniptilotcd.
so
the
ohscrv;itioris
bcgnn
at
I7
DAE (2 days
:ifter
thinning)
for
the
ciiltiviitcd
torin
xrid
;it
30
DAE
(15
days
artcr
thinning)
for
thc
wild
form.
-1'11~
obscrviitions
were
niade until
harvest.
(ii)
lhe
nuiiihcr
ol'
plorits
in
tlic
Ilowcring
phase:
a
phnt
wiis
corisidcrcd
to
hc
in
tlic
Ilowcriiig
pli;isc
during
the
\\.hole
period
bctwccn
tlic
lint
and
tlic
Iiist
Ilowcr.
The
llowcring
phase
for
the
cultivatctl
li)riii
hegins
with
tlic
Il~i\vcriiig
of
the
spike
of
the
niain
stcni
(the
lïrsi
stciii
ciiicrgcd)
aiid
crids
with
;I
spike
of
a
priniary
tiller.
Siricc
thc
iiumbcr
of
priniary
tillers
\viis
low
and secondary
tillers
were
wry
rare
aiitl
;ilways
stcrilc,
the
Ilmvcring
phase
could
be
f~llowctl c.xliaiIstivcly
for
each
pliiiit.
With
the
wild
forni,
the
Ilowcririg
phax
nlso
begiris
with
tlic
Ilowcririg
of'
the
spike
of
the
but
cnds
with
ttic
Ilowcriiig
01'
tlic
y)ikcs
ol'
the
I~SI
additional
tiller
lïrst
btClll
(Ille
cr~"ivalcllr
ul'
the
II1;lill
StClll
01
Ille
culli\atcd
plant^

Renno
and
Winkel
¡Jig.
1.
Phenology of tillcring
(ti)
;ind flowering
(h)
in
cultiviited
(O)
and
wild
Iffiirl
millet
(O).
1
O0
u)
90
-
(o
80
0
70
-
U
60
Q-
50
40
c
30
u
C
Q
C
.-
L
-
.-
4
O
(o
a,
a,
Q
c
i2
20
10
O
4
15
25 35 45 55
65
75 85
Days
after emergence
ìü
a
80
-
o,
'C
a,
O
O
o,
C
a,
a,
C
70
3
GO
50
a,
40
2
30
IC
2
20
Q
10
O
35
45
55
65 75
85
Days
after emergence
(derived
from
the
rith
rank
of
a
primary
tiller).
For
each wild
plant,
the
flowering
period
of
the
first
stcni.
of
the
first
priniary
tiller.
and
of
the
last
tiller
were
noted carcl'ully. Thus, the whole
of
the
flowering period of each plant was covered.
Aboivgroi~ttcl biottrciss prodirciioti
rit
Iiciriwt
At
harvest, thc
plants
were
scpiiratctl
out
into
stenis,
leaves,
arid
spikcs
iind
dried
;II
gooc,
until
ii
constant weight was reachcd
(72
II).
For
each
plant,
the
nie;isiircniciits
ol'
(tic bioniass and the
following counts
were
carried
out:
(i)
vcgctiitivc organs:
mass
of
96
1
'priiniiry
tillers
(nhTi):
(i;)
rcprotluctivc orgiiiis:
numhcr
of
spikes
(nhSp),
nius
of
spikes
bcforc
tlircshiiig
(niSp),
iintl
;ifter
threshing.
ni;iss
of
seeds
(niSd)
and
nuiiihcr of
seeds
(nhStI).
The
reproductive effort wiis
cstirniitcd
by
(i)
the
reproductive
riitio
(RR),
which
is
the
niiiss
of
the
rcproductivc organs (spikes
including
seeds)
divitlctl by
tlic
total
hioni;iss
and
(i;)
tlic
secd
riitio
(SR).
which
is
the
miss
of
seeds
divided
by
the lotiil
bicm
An
cstiniution
WIS
niailc
of
the potential nuniber of
scctls
per
pliint
(pStllPI),
the
potential
number being
the
niiixinitiiii
nunihcr
of
seeds
produced
ifdl
the ovules (one
per
spikelet
in
pearl
millet) hat1
produced
seeds.
A
sample of spikes
(40
and
63
spikes for
the
culti-
vated and wild forms, respectively) was taken
at
rmlom from the
total nuniber
of
spikes
produced
by each forni of
pearl
millet. The
number of involucres on
the
central portion
of
each spike
was
counted for
a
length of
1.5
to
3
cm depending on the
size
of
the
spike. On each spike, the nuniber
of
spikelets per involucre was
counted
(I
for wild,
1-3
for cultivated pearl
millet).
After
nieiisur-
ing
the
total
length
of
the spikes, the mean potential nuniber
of
seeds
per spike
was
calculated and
niultiplied
by
the
number of spikes
per
plant
to
obtain
the
potentiiil number
of
seeds
per
plant
(pSd/PI).
The differences observed between cultivated and wild forms
were tested by
a
I
test
iis
a
5%#
probability level.
I'llcnology
or
~lowcrillg
'llic
nvcriigc llowcritig
period
ol'
:I
ctiltiv;itcd
pliiiit
w;is
strong
inclividual
vari;ltiolls
l'or
lXllI1
(CV
ol'
39%
l'or
lllC
wild
7.5
~~IYS,
wll~~~iis
tlicit
of
;I
\vild
IJI~IIII
\viis
21
tiiiys
\vitIl
s:liliplc
:IIKI
70%
lor
tl~
cultiv;Itcd
s;iIilplc)
(Tíiblc
I).
HOW-
cvcr, the
total
Ilowcring tinic
ol'thc
siirill>lcs
WU
45
d:iys
l'or
cultivated
pc¿irl
millet
and
iiiorc
thcin
49 days
for
wild
pcarl
niillct, sincc the
latter
population had
not
finishcd Ilowcring
at
harvest (Fig.
IO).
The distribution over
tirrie
of
thc pcrcentagc
of'
cultivatcd
plants
in
thc flowering
phasc
followcd
a
noriilal
curvc. Flow-
cring
bcgan
at
42
DAE,
whcri thc tillcring pliasc
was
finished.
Thc iiiaxiniiiiii level
\vas
attained at
63
DAE. with
50%
of
the
plants flowering. At 77 DAE, about
IO%
of
the
plants
wcrc continuing
to
flowcr. Thcrc werc
no
morc llowcrs
aftcr
84
DAE.
Thc siinic typc
of
distribution
was
obscrvcd
for
the
wild
plunts.
Thcy
began
to
flowcr
at
42
DAE,
well bcl'orc the cnd
ol'
their
tillcring phasc. The tii;1xinium numbcr
of
plants
in
tlic flowcring
phase
(85%)
w;is
at
74 DAE.
when
about
30%
of
thc cultivated plnnts
were
llowcring.
When
the
last
culti-
vatcd
plants
were I'inishing flowering
at
84
IIAE,
65
%)
of
the
thcmsclvcs; thus reproduction
was
cndoganiic.
Wlicn
irriga-
sturting
to
Ilowcr
mcl
iiiorc
than
80%
01'
their
Ilowcriiig
wild
pl~lllrs
saniplc
wcrc
going
to
exchangc
gcncs
only
anlong
tion
wits
sto^@
(74 DAE). 30%
ut'
thc
wild
pliilits

*
~
962
Can.
J.
Rot.
Vol.
74,
1996
Tnblc-
I.
Distribution
of
aboveground
Iioriiiiss
production,
secd
potcnri:il,
rcproductivc
riitio.
seed
riitio,
and
llowering duration
of
cultivated
and
wild
pcnrl
millct
plants
(nieans
pcr
indivitlual).
mSt
mL
niSp
niSd
TAm
nbSp
nbSd
nbTi
pSdlPI
RR
SR
Flowering
Cult
ivnted
Mcan
63.4 43.7 38.2 22.6
146.9 1.6
3194 6.8 8365 0.25 0.14 7.5
N
17
17
17 17 17
17
17 17
17
17
17 32
CV
46
46
64
71 42
71
68 I9 71 52 60 70
SE
7.0
4.9 5.9 3.9
14.8 0.3
525 0.3
1432 0.03 0.02
0.9
Wild
Mean
252.5 94.0
79.9
4.9
426.3
89.9
4158 16.2 32312
0.18
0.01
20.9
N
19
19
19 19
19
19
19
19
19 19 19
40
CV
52 41
67 108 44
75
108
21
75 54 98 39
SE
29.9
8.8
12.3 1.2
42.6 15.4
1026
0.8 5528
0.02
0.003
I
.3
Note:
Abbreviations
are
as
follows:
nisi, niiiss
of
stems;
mL.
nias
of
Ienves;
mSp,
iiiass
of
spikes;
niSd,
niass
of
seeds;
TAni.
total
biomass;
nhSp,
numher
of
spikes;
nhSti,
niimher
of
seeds;
nhTi, nuinber
of
primary tillers;
pSdlPI.
porential
seed
niimhrr
per
plilni;
RR.
reproductive riitio; SR,
seed
riitio;
flowering,
niem
diimtion
per
pliint
(tlaya);
N,
sample
size;
CV,
coefficient of variation
(%);
SE,
standard error.
Misses
are
in
grimis
of
dry matter per
plant.
Fig.
2.
Percentage differences
in
aboveground
hioni;iss
production, seed potential, reproductive
ratio,
srcd
riitio,
and
llowering duration of
wild
pciirl
millet rclíitive
to
cultivated
pciirl
millet.
Set
Titble
I
for
subheadings.
I
5563
208
2lld
U
I
period
took
plocc bctwcctl
this
dntc
itlid
tllc I1arvcsta
At
har-
vest
(90
DAE),
58%
of
thc wild plants wcrc
still
producing
hvcrs. The flowering period
of
thc
cultivutcd pcnrl niillct
thus
took
placc cntircly within
that
of
thc wild
pearl
millet.
Rcprocinctive
ct'fort
Exccpt
for
tlic numbcr
of
sccds per
plant,
all
the rcsults
rclatcrl
to
rcproductivc
effort
wcrc significantly diffcrcnt
(P
<
0.05)
bctwccn
the
two forms
of
pearl
niillct (Table
1;
Fig.
2).
Comp:ircd
with
a
cultivatcd
plant,
a wild plant had
thc following charactcristics:
(i)
the nunibcr
of
spikes was
57
tinics grcatcr, but
it
rcprcsentcd a total niass only twice
;IS
much as thc spikes
of
a
cultivated plant because
of
the
largcr six
of
the
spikes
of
cultivatcd
plants;
(i¡)
thc nunibcr
of
seeds
per plant was not significantly diffcrcnt from that
of
cultivatcd pcarl millct
(4
158
as
oppscd
to
3
194)
but
cor-
rcspt~ndctl
to
ti
niass
4.5
tinics
less
(4.9
g
íis
opposcd
to
27.6
g
for
the
cultivated
pciirl
millct)
bcciiUsc
of
the larger
siic
of
thc scctls
of
thc cultiviitcd plants;
(iii)
thc
investment
in
the
nunibcr
of
seeds
produccd
conipnrcd
with the total
hiotiiass
W;IS
half
(IO
scccls/g
of
dv
tiinttcr
;IS
oppscd to
32
sccdslg
of
dry
ni;ittcr
for
;i
cultivavd
plant).
his
being duc
principally
to
the difference
in
the average number
of
seeds
per
spike
(46
for
a
wild plant,
1996
for
a
cultivated plant).
The average reproductive ratios
(RR)
of
wild
and
cul-
tivnted plants were significantly different
(IS
ancl
2596,
respectively)
but
wcrc
still
quite close conip:ireti with
the
scetl
riitio
(SR),
which was
14
timcs
less
for
íi
wild plant than
for
ii
cttlI¡v;itcll
I>l;l[iI
(1
ti11t1
14%,
respectively),
A
wild
011
LtVeriIgc S-O
S~>I~CS.
A
cliltivi~tctl
pl;lt1I
li;id
[)II
ílvetïigc
1)Iiint
Iii\d
011
iivcri!gc
16.2
Ilritl1i\ry
tillers,
c;irh
Ijrotl\tcitig
0.8
priiwry
tillers
íintl
protlucctl
0.3
spikes
Ibr
ciich
of
tlicm.
'rllcrcrorc,
il
hrgc
proportion
of
its
tillers
did
not ~"'c"l1Icc
any
spikes.
Wie
cttltiviitd
IXXI~I
tilill~t
itttíiitlcd
40%
of
its cstitlli\tctI
potctltiitl
it1
IC~IIIS
of
secd
1)rotItlctiotI
(reiil
autiibcr
of
SCCC~S
Altholtgll tlic
tvild
1>ciirl
tllillct prodttcctl
i\
qit;intity
of
only
13%
of
its potc~itiill, which
W:IS
3,s
titiics
highcl
thiiti
per
plont
(nbSd)
tlivitlctl by
tlic
polcntial number (pSd/l'l))Q
cquivolcnt
to
ltial
of
cultivatcd
pcarl
tiiillct.
il
hacl
uttaincd
that
of
tlic cultivatcd
pearl
millct.
Discussion
This study shows that undcr cxperinicnlal conditions, thc
cultivatcd pcarl millct was always influenced by
the
wild
pearl millet pollcnic cloud, whereas the wild pearl millct
population escapcd
from the
cultivatcd pollenic cloud
for
a
large part
of
its flowcring
period.
If
thcrc had not becn
a
harvest, the Icngth
of
the endogamous reproduction
of
the
sample
of
wild plants would have depcndcd
on
the availability
of
water
in
the soil. According to Marchais
(1994),
undcr
natural conditions
in
Niger,
the observation
of
the flowering
of
a samplc of
tillers
in
a
population
of
wild pearl
millet
rcvcalcd that
40%
of
the
spikes
were still flowering when thc
plants
of
the cultivated and
shibra
phcnotypcs had finished,
The
latter
obscrvation docs
not
provide
any information
on
tlic
fraction
of
individual plants
that
participate
in
the endog-
atiioiis system but supports the
idea
of strong endogamy
in
ii
wild
pearl
millct population.
For
cultivated
iis
for
wild
pearl
millet,
tlic average tlower-
ing pcriod
of
a
single
plant was
much
shortcr
than
the
total

Citations
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Journal ArticleDOI
TL;DR: A significantly lower number of alleles and lower gene diversity in cultivated pearl millet accessions than in wild accessions is shown, which contrasts with a previous study using iso-enzyme markers showing similar genetic diversity between cultivated and wild pearl Millet populations.
Abstract: Genetic diversity of crop species in sub-Sahelian Africa is still poorly documented. Among such crops, pearl millet is one of the most important staple species. In Niger, pearl millet covers more than 65% of the total cultivated area. Analyzing pearl millet genetic diversity, its origin and its dynamics is important for in situ and ex situ germplasm conservation and to increase knowledge useful for breeding programs. We developed new genetic markers and a high-throughput technique for the genetic analysis of pearl millet. Using 25 microsatellite markers, we analyzed genetic diversity in 46 wild and 421 cultivated accessions of pearl millet in Niger. We showed a significantly lower number of alleles and lower gene diversity in cultivated pearl millet accessions than in wild accessions. This result contrasts with a previous study using iso-enzyme markers showing similar genetic diversity between cultivated and wild pearl millet populations. We found a strong differentiation between the cultivated and wild groups in Niger. Analyses of introgressions between cultivated and wild accessions showed modest but statistically supported evidence of introgressions. Wild accessions in the central region of Niger showed introgressions of cultivated alleles. Accessions of cultivated pearl millet showed introgressions of wild alleles in the western, central, and eastern parts of Niger.

128 citations


Cites background from "Phenology and reproductive effort o..."

  • ...Phenology (Renno and Winkel 1996), pollen competition (Sarr et al....

    [...]

  • ...Phenology (Renno and Winkel 1996), pollen competition (Sarr et al. 1988; Robert et al. 1991), and reproductive barriers (Amoukou and Marchais 1993) could explain this result....

    [...]


Journal ArticleDOI
TL;DR: It is found that a monophyletic origin of cultivated pearl millet in West Africa is the most likely scenario supported by the data set and the phylogenetic relationship among accessions not showing introgression is analyzed.
Abstract: During the last 12,000 years, different cultures around the world have domesticated cereal crops. Several studies investigated the evolutionary history and domestication of cereals such as wheat in the Middle East, rice in Asia or maize in America. The domestication process in Africa has led to the emergence of important cereal crops like pearl millet in Sahelian Africa. In this study, we used 27 microsatellite loci to analyze 84 wild accessions and 355 cultivated accessions originating from the whole pearl millet distribution area in Africa and Asia. We found significantly higher diversity in the wild pearl millet group. The cultivated pearl millet sample possessed 81% of the alleles and 83% of the genetic diversity of the wild pearl millet sample. Using Bayesian approaches, we identified intermediate genotypes between the cultivated and wild groups. We then analyzed the phylogenetic relationship among accessions not showing introgression and found that a monophyletic origin of cultivated pearl millet in West Africa is the most likely scenario supported by our data set.

123 citations


Journal ArticleDOI
TL;DR: Key examples of crop/wild sympatry and overlapping flowering phenology, pollen and seed dispersal, the barriers to hybridisation and introgression, the evolution and fate of interspecific hybrids, their fitness, and the potential cost of transgenes are reviewed.
Abstract: Crop-to-wild gene flow has received close attention over the past ten years in connection with the development and cultivation of transgenic crops. In this paper, we review key examples of crop/wild sympatry and overlapping flowering phenology, pollen and seed dispersal, the barriers to hybridisation and introgression, the evolution and fate of interspecific hybrids, their fitness, and the potential cost of transgenes. We pay particular attention to ways in which the evolution and divergence between crops and their wild relatives may interfere with these successive steps. Our review suggests that crop-to-weed gene flow is highly idiosyncratic and that crop gene dispersion will certainly be very difficult to preclude totally. Future directions for research should thus focus on the long-term establishment and effects of transgenes on natural communities.

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Cites background from "Phenology and reproductive effort o..."

  • ...Conversely, overlaps can be limited, so that many wild plants will be isolated from the cultivated pollen source (Renno and Winkel, 1996)....

    [...]

  • ...overlaps can be limited, so that many wild plants will be isolated from the cultivated pollen source (Renno and Winkel, 1996)....

    [...]


01 Jan 1997
Abstract: l~lH~~~~il~~~~~l Abstract Several studies conducted under high input conditions have indicated little susceptibility of pearl millet to water deficit until1 early grain filling, because the Introduction losses in main shoot production were fully compens- ated by increased tiller fertility. The present study assessed the impact of water deficits at three develop- ment stages: prior to flowering (S30), at the beginning of flowering (545), and at the end of flowering (S60) in pearl millet grown in experimental conditions similar to Sahelian farming conditions. It included a control irrigation treatment simulating the natural distribution of rainfall throughout the cropping season. Both bio- mass production and grain yield were severely reduced by S30 and S45, while S60 had no effect. In S30 and S45, the flowering of tillers was delayed or totally inhibited. In both of these treatments, the low number of productive tillers did not compensate for damage The usual effects of drought on the development of a plant are a lowered production of biomass and/or a change in the distribution of this biomass among the different organs. The drought resistance of a cultivated plant reflects its capacity to limit the impact on the economic yield of these changes in biomass production and distribution. This capacity will depend on the devel- opment phase affected by water deficit, as well as on the intensity and the length of the drought. In Sahelian climates, where agrosystems are based essentially on pearl millet (Petznisetum gluucum (L.) R. Br.), the risks of drought can be classed into two types according to their impact on pearl millet cultivation. l i to panicle initiation and flowering of the main shoot. (1) Droughts at the beginning or end of the cropping All treatments maintained green leaves on the main season, frequent and often long, but to which peasant shoot during the grain filling period, and in S30 leaf farmers respond by successive re-sowing (in the case growth recovered from mid-season drought. These of early droughts) or by the choice of short-season results illustrate how pearl millet mostly escapes cultivars tolerant of post-floral water deficits (in the drought by matching its phenology to the mean rainfall case of late droughts); distribution in the Sahel. In the case of mid-season (2) Intermediate droughts, less frequent and often brief drought, some late productive tillers and the mainten- (about 10 d), but very unpredictable and without any ance of green leaf biomass of the main shoots limited, practical remedies. They affect development stages but did not overcome, the yield losses. This study such as initiation of panicles, earing, or flowering stresses the importance of agro-ecological conditions which, in cereals, are generally sensitive to water in control treatments, particularly the water regime deficits. The variability of these droughts in time and and crop density, when assessing crop drought space complicates the characterization of drought- __ .-- - resistant varieties. I l resistance.

72 citations


Journal ArticleDOI
Abstract: Several studies conducted under high input conditions have indicated little susceptibility of pearl millet to water deficit untill early grain filling, because the losses in main shoot production were fully compensated by increased tiller fertility. The present study assessed the impact of water deficits at three development stages: prior to flowering (S30), at the beginning of flowering (S45), and at the end of flowering (S60) in pearl millet grown in experimental conditions similar to Sahelian farming conditions. It included a control irrigation treatment simulating the natural distribution of rainfall throughout the cropping season. Both biomass production and grain yield were severely reduced by S30 and S45, while S60 had no effect. In S30 and S45, the flowering of tillers was delayed or totally inhibited. In both of these treatments, the low number of productive tillers did not compensate for damage to panicle initiation and flowering of the main shoot. All treatments maintained green leaves on the main shoot during the grain filling period, and in S30 leaf growth recovered from mid-season drought. These results illustrate how pearl millet mostly escapes drought by matching its phenology to the mean rainfall distribution in the Sahel. In the case of mid-season drought, some late productive tillers and the maintenance of green leaf biomass of the main shoots limited, but did not overcome, the yield losses. This study stresses the importance of agro-ecological conditions in control treatments, particularly the water regime and crop density, when assessing crop drought resistance.

68 citations


References
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Journal ArticleDOI

1,236 citations


"Phenology and reproductive effort o..." refers background in this paper

  • ...The current wild form is distributed across the northern Sahel and is phylogenetically close to the ancestor of the cultivated pearl millet (Harlan 1975; Portbres 1976)....

    [...]


Book
01 Jan 1975

1,119 citations


Journal ArticleDOI
01 Aug 1971-Taxon
TL;DR: An attempt is made to provide a framework in which both taxonomy and infraspecific classification can operate with a minimum of confusion.
Abstract: The methods of formal taxonomy have not been very satisfactory for the classification of cultivated plants. As a result, the people who deal with cultivated plants the most have developed their own informal and intuitive classifications based on experience as to what constitutes useful groupings. An attempt is made to provide a framework in which both systems can operate with a minimum of confusion. The structure of the total available gene pool is characterized by assigning taxa to primary, secondary and tertiary gene pools. At the infraspecific level, cultivars are grouped into races and subraces in an informal way without rigid rules for the use of terms.

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Abstract: Cope's Rule is the name customarily applied to the widespread tendency of animal groups to evolve toward larger physical size. According to Kurten (1953), this paleontologic rule of evolution "is second in repute only to 'Dollo's Law' of . . .irreversibility." Although the rule was never concisely formulated by Cope, it is generally implicit in his writings (Cope, 1887, 1896). Like many other evolutionary generalizations extracted from the fossil record, Cope's Rule was derived primarily from study of mammalian phylogeny. Writers like Deperet (1909), Newell (1949), and Rensch (1959) have added diverse examples of evolutionary size increase to the mammalian trends discussed by Cope. Because numerous exceptions are known, recognition of the concept as a law has been rejected by most workers. Still, it has been widely upheld as a valid empirical generalization, and of the definitions for "rule" listed by Webster, "a generally prevailing condition," describes it accurately. Most modern interpreters of Cope's Rule have attributed its validity solely to certain fundamental advantages of size increase, at least one of which is alleged to have operated within most evolutionary lineages (Newell, 1949, p. 122-123; Kurten, 1953, p. 105; Simpson, 1953, p. 151; Rensch, 1959, p. 210-211; Gould, 1966b, p. 1138). Most of the proposed advantages of evolutionary size increase have been reviewed by Newell (1949), Kurten (1953), Rensch (1959), and Gould (1966a). Among the more salient are: improved ability to capture prey or ward off predators, greater reproductive success, increased intelligence (with increased brain size), better stamina, expanded size range of acceptable food, decreased annual mortality, extended individual longevity, and increased heat retention per unit volume. Certainly when evolutionary size increase occurs, it is in response to selection pressure resulting from one or more advantages. As Bonner (1968) pointed out, however, a net trend toward increased size within a higher taxon usually produces an increase in mean and maximum animal size, but not necessarily in minimum animal size. Selection pressure favoring size decrease is not rare but only less common than pressure favoring size increase. Reliance solely on inherent advantages of larger size to explain the high incidence of size increase suffers from deficiencies resembling some of those attached to the discarded concept of orthogenesis. The "inherent advantage" idea attempts only to account for directional evolution, without reference to limits. Clearly when size increase occurs in a

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Abstract: First, we shall introduce the materials with which we are dealing, and this requires some understanding of formal names and botanical classification. The taxonomy of cultivated plants has long been in a state of confusion. The same array of variation is treated in radically different ways by different taxonomists (see Jirasek, 1966; Jeffrey, 1968). Classifications are cluttered with Latin names that have little or no biological meaning, and some individual taxa are given ranks ranging from variety to genus depending on who is doing the classifying. Inept classifications have probably caused more difficulty in understanding the origin and evolution of cultivated plants than any other factor. We shall use the gene pool classification suggested by Harlan and de Wet (1971) in order to treat the several cereals on a uniform basis. In this system the total array of variation within maximum genetic reach is partitioned into primary, secondary, and tertiary gene pools. The primary gene pool includes all those races that can be crossed with the crop, yielding reasonably fertile hybrids in which the chromosomes pair well and in whose offspring genetic segregation is reasonably normal. The primary gene pool corresponds to the widely accepted concept of the biological species. The secondary gene pool includes all those species that can be crossed with the crop but with restricted gene flow. Genes can be transferred from the secondary to the primary gene pool, but one must struggle with those barriers that separate biological species such as sterility, poor chromosome pairing, lethal or weak hybrids, or poorly adapted hybrid derivatives and so on. The tertiary gene pool includes all those species that can be crossed with the crop, but the hybrids lead essentially nowhere. The hybrids are lethal, completely sterile, or anomalous. If any gene transfer is possible at all, it must be through radical manipulation of some sort such as embryo culture, tissue culture, use of complex hybrid bridges and so on (see Harlan and de Wet, 1971). Polyploid series in cultivated plants pose some special problems. As a general rule, we have suggested (Harlan and de Wet, 1971) that each level be treated as a separate gene pool. The barriers between ploidy levels are not necessarily strong, however, and morphological differences are sometimes minimal and difficult to describe. Each series is different and appropriate treatments must be worked out crop by crop. Separate gene pools for ploidy levels in potato or sugarcane may not be appropriate at all. In the cereals considered here, the only problem of separation by ploidy level occurs in oats where A vena strigosa and A. barbata races are difficult to distinguish morphologically. Our gene pool classification is not intended to be a formal taxonomic system but rather a simple device to bring a genetic focus to bear on the taxonomies already available. The conventional epithets can be used without undue confusion pro-

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