P a n ic le of ca u d a tu m s o rg h u m . Pho to j. C h a n te re a u H o o k e d P a n ic le of d u rr a s o rg h u m . P ho lo J. Chante rea,
of sorghum
Today, c o lle c tio n , conservation and study
o f tra d itio n a lly cropped sorghum varieties
and related w ild form s are o f great im portance.
C ultivated sorghum diversity must be upheld.
Local varieties and their w ild progenitors
represent a critica l sorghum gene pool
for breeding programmes.
M. DEU, P. HAM O N CIRAD-CA, BP 5 0 3 5 ,
3 4 0 3 2 Montpellier Cedex 1, France
A
lth ough trad ition al sorghum varieties are still w id e ly c u lti v a t e d in A f r i c a a n d A s ia , some A f r ic a n c u ltiv a rs are d is a p p e a r i n g b e c a u s e o f i n c r e a s e d d e s e rtific a tio n . C on servatio n of
sorghum germplasm resources is therefore o f param ou nt im p o r
ta n c e and c u rr e n tly overseen b y th e I n t e r n a t i o n a l C ro p s R e s e a rc h I n s t i t u t e f o r th e Semi-Arid Tropics (ICRISAT), w h ic h n ow has a repository o f 30 0 0 0 a c c e s s io n s . Caution and skill are requi
red in the m a in t e n a n c e , e v a lu a tio n and use of t h e s e g e r m p l a s m resources because o f the size o f the c o ll e c tion. Moreover, it is diffi- c u l t to k n o w n o w w h a t c h a r a c t e r s w i l l in t e r e s t
breeders in the future.
At the Centre de coopération internationale en recherche agronomique pour le dévelo p p e m e n t ( C I R A D ) , g e n e t i c d i v e r s i t y in sorghum is thus b eing analysed a c c o rd in g to m o r p h o lo g ic a l traits, b io c h e m ic a l and molecular markers.
Sorghum taxonomy
The Sorghum genus belongs to the Poaceae (ex-Gramineae) fam ily. High m orphological variation has prompted botanists to increase the classification divisions w ith in this genus — 712 cultivated sorghum taxa according to Snowden (1936). A simplified classification, first introduced by De W e t (1978) and slightly m o d ifie d by A c h e a m p o n g et al. (1 984), is n o w in c o m m o n use and recom m ended by th e I n te rn a tio n a l P la n t G e n e tic Resources
Institute (IPGRl). Sorghum is thus classified in
five botanical sections, but only the Sorghum section is presented here (Fig. 1).
The Sorghum section includes many species and tw o are d ip lo id : S. p ro p in q u u m (peren nial) and 5. bicolor (annual). These tw o species c r o s s - p o l I i n a t e b u t are c o m p l e t e l y g e o graphically isolated.
S. b ic o lo r is d iv id e d into three subspecies:
ssp. b i c o l o r ( c u l t i v a t e d s o r g h u m ) , ssp. a r u n d in a c e u m ( th e ir w i l d re la tiv e s ), and ssp. d ru m o n d ii (weedy forms, obtained by hybridation of w ild and cultivated forms).
W ild S. bicolor sorghum
M o r p h o lo g ic a l and e c o lo g ic a l d iv e rs ity is high in w ild sorghum o f ssp. arundinaceum. They have been d iv id e d into fo ur races1 or ecotypes based on their inflorescence struc ture and g e o g ra p h ic d is t rib u tio n (De W et, 1978), i.e. aeth iopicum, arundinaceum, ver- tici 11 iflorum and virgatum, w h ic h o n ly occur
in Africa (Fig. 2a).
The aethiopicum race is w idespread in the
h o tt e s t a nd d r ie s t r e g io n s o f th e A f r i c a n s a v an na , fr o m M a u r i t a n i a to Sudan. The inflorescences are small and rather contracted.
The arundinaceum race is m ainly limited to
rain fo re s t re g io n s o f w e s te rn A f r ic a , b ut p o p u l a t i o n s h a v e b e e n f o u n d as f a r as southern Africa. The inflorescences are large and pendulous at maturity.
The verticilliflorum race is the most w id e s
pread and is c o m m o n l y fo u n d in A f ric a n savanna regions. The inflorescences are cha racteristically large and opened.
The virgatum race is present in northeastern
A f ric a , a lo n g irr ig a tio n d itc h e s and rivers (particularly the N ile Valley). It is quite close to the verticilliflorum race, but its inflorescence ramifications are more erect.
A ll o f these w ild sorghum races can readily cross even w it h c u lt iv a t e d fo rm s . F e rtile hybrids are c o m m o n ly encountered in areas where tw o races occur together.
Fam ily: poacea
Su bfam ily: panicoidae
Tribe: andropogonae
Genus: Sorghum 5 sections
3 subspecies
drumondii, bicolor, arundinaceum,
weed cultivated w ild
5 main races --- bicolor --- caudatum --- durra --- guinea --- kafir
and 10 intermediate races (e.g.: durra-caudatum, guinea-kafir) 4 races --- aethiopicum — arundinaceum — verticilliflorum — virgatum
Figure 1. Taxonom y o f the Sorghum genus.
was proposed by Harlan and De W e t (1972) according to morphological criteria (spikelet structure, panicle shape, since spikelet traits are considered to be h ig hly stable and thus r e l a t i v e l y u n a f f e c t e d b y e n v i r o n m e n t a l stresses). Five basic races and ten intermediate races (representing crosses of the basic forms) have been defined. The ranges o f these races o v e r l a p , a l t h o u g h s o m e races are m o re predominant in certain regions (Fig. 2b).
S. bicolor
cultivated sorghum
C ultivated sorghum forms are m onoecio us, preferentially self-pollinating, w ith great phe n otypic diversity. A sim plified classification
1. A race is defined as a set of varieties w ith com m on morphological traits and ecological adaptations. It forms a biological/genetic unit (Harlan & De Wet, 1971).
The bicolor race, the most primitive, is crop
ped throughout Africa and w id e ly distributed in Asia. The grains are small, long and shea thed in a sticky glume; the panicles are loose ly branched. These traits are close to those that characterize w ild sorghum races.
The caudatum race is limited to central and
eastern Africa. The grains are asymmetrical ( tu rtle shell shaped). T here is a v a rie ty o f panicle shapes.
• aethiopicum
a arundinaceum
a.
verticilliflorumo virgatum * halepense The durra race is the main cultivated sorghum
race in In dia, and is also fo u n d in eastern Africa. It is w e ll adapted to d ro u g h t c o n d i tions. The grains are large and glo bular; the panicles are c o m p a c t and often borne on a hooked stalk.
The kafir race, p ro b a b ly a recent sorghum
race, is m ainly distributed in southern Africa w h e re f a r m in g was in t r o d u c e d later. The grains are s y m m e tric a l; the dense panicles are cylindrical shaped.
The guinea race is c om m on in western Africa
but is also found in southern Africa. This sorg hum race is adapted to w et zones. The grains are s y m m e tr ic a l, w it h a r o ta tio n b etw e e n glumes at ripeness; the panicles are loosely branched. There is high morphological varia b il i t y in this race. D iffe re n t c la s s ific a tio n s have been proposed based on grain size and the glume/grain ratio. Three or four subraces, i n c l u d i n g m a r g a r it if e r u m (sm a ll v itr e o u s grains) have n ow been distinguished.
The econom ic and nutritional
importance of cultivated sorghum
Sorghum is the fifth -ran king cereal in the w o rld , based on grain production and surface area cropped. It is quite far behind the top-ra nking cereal crops (wheat, rice and maize). In Africa, sorghum is in second position, w ith about half the o u tp u t o f m aize (Chantereau & N ic ou, 1991 ). W o rld w id e , the mean yie ld is 1.3 t/ha, but there is a very w id e range (3.5 t/ha in USA and 0.7 t/ha in Africa).
In tem perate regions, sorghum is c u rre n tly cropped fo r anim al feed, since syrup, sugar, alcohol and starch pro du ction is not cost-effective. In semiarid tropical zones, the w h o le plant is used by m illio n s o f people. The protein- rich grains are processed for hum an c o n s u m p tio n ; the stems are used fo r fuel and as b u ild in g materials; c ro p residues (stems and leaves) p ro vide a
livestock fod der supplement.
The genetic
organization
of cultivated sorghum
Figure 2a. Distribution o f the main sorghum w ild types.
Morphological classification
A quantitative study of 135 cultivated varieties in v o l v in g 26 m o r p h o - p h y s i o l o g i c a l traits (Chantereau et a i , 1989) led to a classifica tion into three groups w ith different cropping performances:
- durra, hardy and adapted to dry zones; - guinea and b icolor, hardy and adapted to wet zones;
- c a u d a t u m and kafir, high yielding, adapted to intermediate zones.
Figure 2b. Distribution o f the five main cultivated sorghum races.
O llitra u lt et al. (1989), highlighted a sorghum o rg a n iz a tio n centred around three geogra p h i c a l l y d i s t i n c t a re a s : w e s t e r n A f r i c a , southern A fric a and eastern-central Africa. Three types of classification have highlighted this genetic organization.
This o rg a n iz a tio n is in lin e w it h the racial classification, but it is not as discriminating.
Enzymatic classification
Isoenzymatic markers do not a llo w discrim i n a tio n o f t h e s o rg h u m races d e f i n e d by FHarlan and De W e t (1972).
The five cultivated sorghum races:
their uses and qualities
Culinary uses o f the different sorghum races seem to be dictated by consumers' food habits and particularities of the local varieties. ^
Durra
The b ic o lo r race is h ig h ly v aried (b ro o m c o rn , sweet sorghum and fod der sorghum). Grain sorghum is rarely consumed directly by humans, it is m ainly used in beer brewing.
G o o d q u a lity flou rs can be p ro du ced fro m the cau da tu m , du rra and kafir races, but this q u a lity depends on the cultivars considered. G enerally, w h ite grain sorghum is ve ry h ig h ly a p p re c ia te d by consum ers, w h ile c o lo u re d grain is o n ly used to produce beer (e.g. some kafir and caudatum forms). The guinea race is pa rtic ula rly w e ll adapted to w e t zones and produces high q u a lit y gra in th a t is resistant to m ild e w and lo c a l diseases. T he gu in e a m a r g a r it if e r u m s u b ra c e p r o d u c e s an e x c e lle n t q u a l it y g ra in w h ic h is prepared like rice in western A frica (boiled grain). Some guinea gam bicum form s are con s id e re d tasteless and o n ly used fo r hu m an c o n s u m p tio n at tim es o f sorghum shortages, o th e rw is e th e y are used in beer b re w in g . In M a li, couscous made w ith guinea ga m bic u m is high ly appreciated. W h ite grain forms o f guinea guineense are ground into flour, w h ile red grain forms are m a in ly used in beer b re w in g . F lo u r m ade fro m gu in e a r o x b u rg h ii is consum ed by poor people in India, elsewhere this sorghum is appreciated as pop-sorghum . In southern Africa, form s of this subrace produce high q u ality grain for hum an c onsum ption.
T h e v a r i a t i o n n o te d in A f r i c a n c u lt iv a r s typifies that o f other sorghum cultivars grown throughout the w o rld . This study confirm ed that cultivated sorghum had a m onophyletic origin and was domesticated in northeastern A f r ic a . In d e e d , d o m e s t ic a t io n o f a set o f w ild-types led to the first p rim itive sorghum form s, s im ila r to the c u rre n t b ic o l o r race, then racial differentiation occurred in various geographical areas.
Finally, the results o f an in-depth analysis of e n z y m a t i c d i v e r s i t y in t h e g u i n e a ra c e (Degrem ont, 1992) revealed three separate groups: a western African group, a southern A frican group and a guinea m argaritiferum group.
Molecular classification
The m o le c u la r c las s ific a tion o f sorghum is based on nuclear and cy to p la s m ic genome studies (chloroplastic and mitochondrial). In the first case, D N A diversity was assessed in 100 c u lt iv a t e d s o rg h u m v a rie t ie s b y a
re s tric tio n fra g m e n t length p o ly m o r p h is m (RFLP) technique using heterologous nuclear genome probes. The results revealed racial d i f f e r e n t i a t i o n in c u l t i v a t e d s o r g h u m (Deu et al., 1994).
Cultivated sorghum can be classified in six groups, e x c lu d in g the b ic o l o r race w h i c h does not form a specific group. The guinea race has been subdivided into three subclus te rs ( w e s te rn A f r i c a n , s o u t h e r n A f r i c a n , m argaritiferum ), w h i l e the caud atu m , kafir and durra races constitute three subclusters groups. Guinea margariteferum seems to be the most differen tiated c u ltiv a te d sorghum race. These o v e ra ll results are c o m p a tib le w it h the m o n o p h y le t ic o rig in o f c u ltiv a te d sorghum.
F ina lly , these sorghum varieties and othe r guinea margaritiferum forms were investigated using chloroplastic and m itochondrial geno me probes (Deu, 1993). The results did not reveal any geographic grouping. Most o f the cultivated sorghum races were found to have a c o m m o n m i t o c h o n d r i a l b a c k g r o u n d , except for the guinea m argaritiferum forms.
Guinea
Traditional culinary uses
D is h e s u s in g b o ile d w h o le g ra in (China, India, Africa).
• Dishes requiring p rior h u llin g and m illin g :
- t h ic k u n fe r m e n te d m ash (tô in western Africa, sankati in India) - clear ferm ented mash - couscous (western Africa) - cakes and doughnuts
- leavened bread (injera in Ethiopia)
and fla t bread (roti and chapati in India).
• N o n - a l c o h o l i c a n d a l c o h o l i c beverages (hom ebrew ed beer, such as dolo in Africa), alcohol (sorghum w in e in China).
• P o p p e d g ra in (p o p -so rg h u m in India).
• C h ew ing sweet sorghum stalks.
Cultivated sorghum diversity: four races and intermediate forms.
PhotoJ.-L. Noyer
therefore g e n e tic a lly isolated from the stu d ied w il d types, and from othe r c u ltiv a te d sorghum races.
The results also confirmed the genetic speci fic ity of guinea margaritiferum and demons trated the presence o f t w o g enetic entities w ith in this sorghum subrace.
Relationships between
cultivated sorghum and
wild types
Studies on the m ito c h o n d ria l genome have demonstrated that the genetic diversity observed in cultivated sorghum is encompassed w ith in the related w ild types, except for one of the tw o guinea margaritiferum groups.
O th e rw is e , there does n ot seem to be any particular affinity between w ild and c u ltiv a te d s o rg h u m races: th e t h re e w i l d races, a e th io p ic u m , v irgatum and v e rtic illiflo ru m , have m itochondrial genomes that are similar to those of most of the cultivated races, w ith the exception o f both guinea margaritiferum groups. The guinea margaritiferum forms are
Conclusion: breeding
applications
The traits and markers used have highlighted various structures and p ro v id e d fresh data that w ill help in clarifying the genetic organi zation o f the species S. bicolor.
W h e re as th e c r o p p in g p e rfo rm a n c e is the same for all forms in the guinea race, it was found to be markedly differentiated in analyses using b io c h e m ic a l and m o le c u la r markers (i.e. three or four groups were distinguished b y i s o e n z y m a t i c a n d RFLP t e c h n i q u e s respectively).
It is q u ite l ik e ly th a t these so rg h u m races were domesticated separately in at least tw o parts o f A frica (western and southern). This diversity in the origins o f the different races has p ro m o te d high b e tw e e n -r a c e g e n e tic variability w h ic h has not yet been exploited by breeders.
Studies using molecular markers have revealed very narrow-ranging genetic variability in the kafir race.
Moreover, molecular markers provide an esti mate of parental divergence correlated w ith heterosis (Chantereau, 1993).
Caudatum
The information obtained in these studies can be r e a d i l y used in th e m a n a g e m e n t and c o n s e r v a t i o n o f s o r g h u m g e r m p l a s m resources. A smaller co lle c tio n w ith a w id e range o f v a r i a t i o n s h o u ld be set up and easily accessible to breeders.
The genetic assessment w ill help in choosing progenitors for breeding programmes (creation of lines or hybrids). A n y breeding of the kafir race, for instance, w ill not lead to any signifi cant genetic progress. Conversely, breeding guinea forms, choosing parents from different groups, w il l produce genetically interesting combinations, e.g. a western African guinea c ro s s e d w i t h a g u i n e a m a r g a r i t i f e r u m (Degremont, 1992). In w et regions o f western Africa, attempts to d irec tly introduce exotic n o n -g u in e a m aterial (from USA and India) h ave fa i le d . C a u d a t u m , d u r u m and k a fir sorghum w ith com pact panicles were found t o be s u s c e p t i b l e to m i l d e w a n d lo c a l diseases. These races produced lo w q u a lity grain th at c o nsu m e rs rated p o o rly . In w et re g io n s , h a r d y fo rm s o f g u in e a s o rg h u m s h o u ld th u s be i n t r o d u c e d in b r e e d in g programmes.
References
A C H E A M P O N C E., M U RTY ANISHETTY N., W ILLIAM S J.T., 1984. A w o rld survey of sorghum and millet germplasm. IBPCR, Rome, Italy, 41 pp.
CHANTEREAU J., AR N A U D M „ OLLITRAULT P., NAB AY AO G O P., NOYER J.-L., 1989. Etude de la diversité morphophysiologique et classification des sorghos cultivés. L'Agronomie Tropicale, 44(3): 223-232.
C H A N T E R E A U J., N I C O U R., 1 9 9 1 . Le s o rg h o . Paris, F ra n ce , E d itio n s Maisonneuve et Larose, 159 pp.
CHANTEREAU J., 1993. Etude de l'hétérosis chez le sorgho (Sorghum b ico lo r L. Moench) par l'exploitation d'écotypes et l'analyse de leurs divergences. PhD thesis in science, Paris, France, university o f Paris Sud, 206 pp.
DEGREMONT I., 1992. Evaluation de la diversité génétique et du comportement en croisement des sorghos (Sorghum b ico lo r L. Moench) de race guinea au moyen de marqueurs enzymatiques et m orphophysio lo giq ues. PhD thesis in science, Paris, France, university of Paris XI, 191 pp.
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Abstract... Resumen... Résumé
M . DEU, P. H AM O N - The genetic organization
of sorghum.
Th e collection, c o ns erva tio n a n d study of tra d itio n a l c u l t i v a t e d v a r i e t i e s a n d r e l a t e d w i ld f a r m s is o f c o n s id e r a b l e i m p o r t a n c e t o d a y . M o r p h o l o g i c a l , en zym atic and molecular classifications have been drawn up to p r o v id e u n d e r s ta n d in g o f th e o r g a n iz a t io n o f cultivated varieties o f the species Sorghum bicolor and t h e l in k s w i t h r e l a t e d w i ld f o r m s . T h e y p r o v i d e c o m p l e m e n t a r y i n f o r m a t i o n w h ic h is o f use in th e m a n a g e m e n t and conservation of sorghum ge rm plas m resources and in breeding pro gram m es.
K e y w o r d s : s o r g h u m , S o rghum , g e n e tic v a r i a b i l i t y , classification, morphology, en zym atic analysis, molecular m a rk er.
M . DEU, P. H AM O N - La organización genética de
los sorgos.
La cosecha, la conservación y el estudio de las variedades c u l t i v a d a s t r a d i c i o n a l e s y las f o r m a s s ilv e s t r e s em p are n tad as revisten ho y una gra n im portancia. Para com prender la organización de los sorgos cultivados de la es p e cie S orghum bicolor y las r e la c io n e s con las fo rm a s silvestres em p are n tad as, se han establecido las tres clasificaciones morfológica, enzim ática y molecular, que aportan informaciones com plem entarias que pueden ser utilizadas eficazm ente en la gestión y la conservación de los recursos genéticos de los sorgos, así como en los pro gram as de selección.
Palabras clave : sorgo, Sorghum, variabilidad genética, clasificación, m o rfo lo gía, análisis enzimótico, m arcad or m olecular.
M . DEU, P. H AM O N - Diversité des sorghos :
application à la gestion des ressources génétiques et à la sélection.
La collecte, la conservation et l'étud e des va rié tés culti vées traditionnelles et des form es sauvages ap parentées revêten t a u jourd 'hu i une gra nd e im portance. Pour com p re n d re l'o rg a n is a tio n des sorghos cultivés de l'espèce
Sorghum bicolor et les relations avec les form es sauvages apparentées, les trois classifications m orphologique, e n z y m a tiq u e et m o léculaire ont été établies. Elles a p po rte nt des inform ations complém entaires pouvant être efficace m e n t utilis ées d a n s la g e stio n et la c o n s e r v a tio n des ressources g é n é tiq u e s des sorghos ainsi q u e dans les pro gram m es de sélection.
M o ts -c lé s : s o r g h o , S o rghum , v a r i a b i l i t é g é n é ti q u e , c la s s if ic a t io n , m o r p h o l o g ie , a n a l y s e e n z y m a t i q u e , m a rq u e u r m oléculaire.
