QTLs were mapped in F2 progeny derived from a cross between the head-bug resistant sorghum cultivar Malisor 84-7 and susceptible S 34. The phenotypic evaluation was conducted in Mali. The mapped population consisted of 217 F2 plants, with 345 homologous and heterologous RFLP probes and 49 microsatellite markers tested. Eighty-one RFLP markers revealed polymorphism between the two parents, and 14 microsatellite markers gave usable amplification products. A genetic map including 92 loci distributed over 13 linkage groups, and covering a total distance of 1160 cM was built. Three significant and seven putative QTLs were detected and placed on the map

A Ratnadass

J Chantereau

J L Noyer

M A Hamada

M Deu

M Diabate

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African Journal of Biotechnology Vol. 4 (3), pp. 247-250, March 2005     
Available online at http://www.academicjournals.org/AJB 
ISSN 1684–5315 © 2005 Academic Journals    
 
 
 
 
 
Short Communication 
 
Quantitative trait loci for head-bug resistance in 
sorghum 
 
M. Deu1, A. Ratnadass2*, M. A. Hamada2, J.L. Noyer3, M. Diabate2† & J. Chantereau4 
 
1CIRAD-CA, UMR 1096/PIA, TA 40/03, F-34398 Montpellier, France 
2ICRISAT-CIRAD, BP 320 Bamako, Mali 
3CIRAD-AMIS, UMR 1096/PIA, TA 40/03, F-34398 Montpellier, France 
4CIRAD-CA, Programme CALIM, TA 73/09, F-34398 Montpellier, France 
 
Accepted 23 December, 2004 
 
QTLs were mapped in F2 progeny derived from a cross between the head-bug resistant sorghum 
cultivar Malisor 84-7 and susceptible S 34. The phenotypic evaluation was conducted in Mali. The 
mapped population consisted of 217 F2 plants, with 345 homologous and heterologous RFLP probes 
and 49 microsatellite markers tested. Eighty-one RFLP markers revealed polymorphism between the 
two parents, and 14 microsatellite markers gave usable amplification products. A genetic map including 
92 loci distributed over 13 linkage groups, and covering a total distance of 1160 cM was built. Three 
significant and seven putative QTLs were detected and placed on the map.  
 
Key words: Head-bug, Eurystylus oldi, sorghum, resistance, RFLP, microsatellite, QTL. 
 
 
INTRODUCTION 
 
Sorghum [Sorghum bicolor (L.) Moench] is the most 
important food crop in savanna areas of West and 
Central Africa (WCA). Mirid panicle-feeding bugs (= 
head-bugs), particularly Eurystylus oldi Poppius, have 
recently become major pests of sorghum (Ajayi et al., 
2001) in the region. This is seriously threatening 
sorghum production because of the recent adoption of 
improved compact-headed cultivars of the caudatum 
race, which are better yielding but more susceptible to 
head-bug feeding and oviposition punctures than local 
loose-headed guinea landraces. These punctures result 
in severe quantitative and qualitative losses, including a 
higher incidence of grain mold (Ratnadass et al., 2003; 
Showemimo, 2003). 
The use of resistant cultivars is often the most cost-
effective means of controlling crop pests, particularly for 
small-scale farmers with limited access to inputs, so 
sorghum  improvement  programs  in   WCA   have   thus  
 
 
 
*Corresponding author.  E-mail: ratnadass@cirad.fr; Tel: +261 
20 44 49236.  
focused on the resistance breeding option. Earlier efforts 
by ICRISAT, CIRAD and NARS in the region led to the 
development of reliable screening techniques, which 
confirmed the high and stable resistance in compact-
panicled sorghum cultivar Malisor 84-7. Diallel analyses 
revealed that additive gene effects could be very 
important in the inheritance of resistance to this pest, and 
suggested high heritability (Ratnadass et al., 2002). A 
QTL mapping project was undertaken by CIRAD in Mali 
and France from 1997-2000 to complement these earlier 
inheritance studies, particularly by identifying useful 
molecular markers linked to resistance genes. 
 
 
MATERIALS AND METHODS 
 
F2 progeny derived from a cross between the head-bug resistant 
sorghum cultivar Malisor 84-7 and head-bug susceptible S 34 was 
selected for mapping studies. The mapped population consisted of 
217 plants. An F2 phenotypic evaluation trial was planted during 
the 1997 rainy season at the Samanko research station within the 
framework of the ICRISAT-CIRAD Joint Sorghum Program, Mali 
(Lat.8°25'N; Long.12°32'W) in a plot consisting of ten 6 m-rows 
with  0.75 m    inter-row   spacing.   The   sorghum   was   sown   in  
 
248       Afr. J. Biotechnol. 
 
 
 
continuous lines in order to avoid selection, and thinned 2 weeks 
after planting to achieve 0.20  inter-plant spacing, with one plant 
per hill. The F2 plot was bordered with a row of parent plants, i.e. a 
row of resistant plants on one side and a row of susceptible plants 
on the other side. 
The head-cage technique used in earlier inheritance studies 
(Sharma et al., 1992; Ratnadass et al., 2002) was slightly modified 
to allow artificial infestation of the upper part of the panicle by 10 
head-bug pairs, with the protected bottom part serving as a control 
for parameters measured at grain maturity, namely thousand kernel 
weight (TKW) and germination rate (GER); head-bug damage was 
assessed visually on a 1-9 scale (where 1=all grains fully 
developed with only a few head-bug feeding punctures, and 
9=most grains undeveloped and barely visible outside the glumes 
due to head-bug feeding and oviposition: Ratnadass et al., 2002) 
on the infested part of the panicle (NOTF2). The following criteria 
were used to account for head-bug damage: 
 
%TKW: relative difference in TKW between the protected and 
infested parts of the panicle [100(TKWP - TKWI / TKWP)] calculated 
for plants in which the parameter could be measured via several 
replications with 1000 grains, namely 136 plants out of 217. 
DGER: difference in germination rate between the protected and 
infested parts of the panicle [GERP  - GERI] 
 
Seeds of the protected (and self-pollinated) bottom part of each 
of the 217 plants were planted in the glasshouse and DNA was 
extracted from a bulk of five F3 seedlings, representing each F2 
plant. 
During the 1999 cropping season, seeds of F4 plants derived 
from remnant seeds of the protected (and self-pollinated) bottom 
part of 110 F2 panicles from the 1997 trial representing the F3 
families were planted in a randomized complete block design with 
two replications and one 5 m-row per plot, with one row of each of 
the two parents every 10 rows. At grain maturity, panicles of the F5 
plants representing F3 families were scored for head-bug damage 
under natural infestation using the 1-9 scale (NOTF3). 
To build the sorghum genetic map, 345 RFLP probes, selected 
according to their localization on our reference map (Dufour et al., 
1997; Boivin et al., 1999; Ventelon et al., 2001), were screened in 
combination with six restriction enzymes (BamHI, DraI, EcoRI, 
EcoRV, HindIII and  SstI) for their ability to reveal polymorphism. 
Probes were obtained from various sources: rice (RZ prefix), oat 
(CDO prefix) and barley probes (BCD prefix) from Cornell 
University; rice probes (R and C prefixes) from the Rice Genomic 
Project; maize probes (UMC prefix from the University of Missouri, 
BNL prefix from the Brookhaven National Laboratory,  CSU from 
California State University); pearl millet probes (Xpsm prefix) from 
the John Innes Centre; sugarcane probes (SSCIR prefix) from 
CIRAD and sorghum probes (SbRPG prefix) produced in 
collaboration with RUSTICA PROGRAIN GENETIQUE and CIRAD. 
Forty-nine microsatellite markers developed by Brown et al. (1996) 
and Taramino et al. (1997) were also screened (m prefix on the 
map). The Mapmaker 3.0 software package (Lander et al. 1987) 
was used for map construction.  An LOD threshold of 5.0 and a 
maximum distance of 50 centiMorgans (cM) were used to establish 
linkage groups. Markers were ordered by multipoint analyses. 
Genetic distances were estimated with the Haldane mapping 
function. Linkage groups (LGs) were named on the basis of their 
homology with the LGs of our reference map. 
QTLs were detected using the PlabQTL software package (Utz 
and Melchinger, 1995). The analysis was performed using 
composite interval mapping (CIM) (Zeng, 1994; Jansen and Stam, 
1994) with an LOD value of 2.0, and the marker closest to the QTL 
was used as a co-factor. A QTL was considered significant when 
the LOD value was above 3.0. This threshold was determined by 
the permutation method implemented in the QTL Cartographer 
software program  with  a  global  type-I  error  of  5%.  A QTL  was  
 
 
 
 
considered putative when the LOD value was between 2.0 and 3.0.  
 
 
RESULTS AND DISCUSSION 
 
Among the 345 RFLP probes tested, 81 revealed 
polymorphism between the two parents. In addition, 14 
microsatellite markers gave usable amplification 
products. The genetic map based on the Malisor 84-7 X 
S 34 cross includes 92 markers distributed over 13 LGs, 
covering a total distance of 1160 cM. Three markers 
remained independent. The composition and order of 
markers in this map are generally consistent with those 
of the most recent composite map (which includes 416 
RFLP loci distributed over 11 linkage groups, covering a 
genetic distance of 1495 cM: Ventelon et al., 2001; and 
unpublished data). However, the genome coverage is 
low in some regions, particularly for LGs A, B and J 
(Figure 1). 
Three significant and seven putative QTLs were 
detected (Table 1). The significant QTLs, which 
explained an important part of the phenotypic variation 
(R²), were placed on the genetic map (Figure 1). 
Concerning the reduction in TKW, one QTL which 
accounted for 13% of the phenotypic variation was 
detected in the interval between markers SbRPG943 and 
RZ630 on LG C2. For this QTL, resistance is determined 
by the Malisor 84-7 allele and is dominant. Interestingly, 
a QTL for TKW was also found in the same region of LG 
C by Rami et al. (1998). 
Two QTLs were detected for NOTF3. These were on 
LG D, in the interval between markers RZ476 and 
SbRPG872, and on LG E, between markers SbRPG667 
and CDO580. They explained 16 and 26% of the 
phenotypic variation for this trait, respectively. 
Resistance from the QTL on LG D is determined by the S 
34 allele, whereas resistance from the QTL on LG E is 
provided by the Malisor 84-7 allele; in both cases, 
resistance is recessive. No significant QTLs were 
detected for NOTF2 and DGER but two putative QTLs 
for these traits were co-localized in the interval between 
markers BNL 5.37 and SbRPG749 on LG G2 and 
resistance is determined by the S34 allele in both cases. 
These results are partly in line with the recessive nature 
of head-bug resistance suggested by earlier studies 
(Ratnadass et al., 2002; Aladele and Ezeaku, 2003), and 
by the existence of resistance genes in the susceptible 
parent, as indicated by transgressive segregations. Since 
there was no correlation between NOTF2 and NOTF3, 
the results also suggest the possible existence of 
different mechanisms of resistance under natural or 
artificial infestation conditions, as discussed elsewhere 
(Ratnadass et al., 2002). 
However, much remains to be done before an 
application with respect to marker-assisted selection for 
head-bug resistance can be envisaged. As a first step, 
new phenotyping of families derived from this cross 
should be considered, with multilocational  testing.  Other  
 
Deu et al        249 
 
 
 
 
                     
Figure 1. Genetic map and localization of significant QTLs for head-bug resistance in sorghum. Each QTL detected at LOD score >3.0 is 
represented by a circle located on its LOD peak. The colour of the circle indicates the origin of the parental allele contributing to the 
resistance for this QTL (white circle: resistance determined by the allele of the susceptible parent S34; grey circle: resistance determined 
by the allele of the resistant parent Malisor 84-7). 
 
 
Table 1.  Genetic characteristics of significant and putative QTLs detected for the parameters measured under natural and artificial 
infestation. 
    
Parameters Cofactors N LG Markers interval Position LOD  R2 a D Direction 
F2 ( natural infestation) 
NOT BNL5.37 1 G2 BNL5.37-SbRPG749 16,5 2,9 6,5 -0,44 0,64 PB 
%TKW RZ630, BNL5.37 1 C2 SbRPG943-RZ630 132 4,19 13,2 10,31 -7,31 PA 
DGER BNL5.37, RZ123, UMC29 2 G2 BNL5.37-SbRPG749 18,5 2,15 4,9 -6,62 6,28 PB 
   I UMC29-SbRPG931 14 2,45 5,4 7,13 6,02 PA 
 
         250       Afr. J. Biotechnol. 
 
 
        
         Table 1.contd. 
         
F3 (artificial infestation) 
NOT SbRPG826, RZ476, CDO580, 6 C2 CDO20-C223 16 2,08 10,4 -0,09 0,19 PB 
  UMC139  C2 RZ630-SbRPG826 144 2,5 11,9 -0,19 0,15 PB 
   D RZ476-SbRPG872 36 3,65 16,2 -0,09 0,30 PB 
   E SbRPG667-CDO580 5,9 5,91 26,1 0,24 0,20 PA 
   E RZ244b-SbRPG852 55,9 2,49 11,5 -0,19 0,13 PB 
   F mAGB03-UMC139 76 2,44 11,2 0,13 0,18 PA 
 
Italic lines indicate that the QTL was detected at a non-significant level (LOD<3)    
N: number of QTLs detected for each trait       
LG: linkage group             
Position:  cumulative distance in cM from the first marker of the LG to the position of the LOD peak   
R2: percentage of the phenotypic variation explained by the QTL      
a and d: additive and dominance effects as estimated by the programme      
Direction: origin of the allele contributing to the resistance: Parent A (Malisor 84-7) or Parent B (S34).   
 
 
 
parameters usually highly correlated with damage score 
and considered as translating sorghum grain reaction to 
head-bug attacks, could also be evaluated (e.g. per cent 
flottation in a sodium nitrate solution). 
 
 
ACKNOWLEDGEMENTS 
 
This research was supported by a grant from the 
European Commission-INCO-DC Program (Contract 
#18-CT96-0106).  We thank Ms S. Togola-Fane and  Mr 
C.A.T. Thiero for their help in conducting the field 
experiments. 
 
 
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Quantitative trait loci for head-bug resistance in sorghum

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Quantitative trait loci for head-bug resistance in sorghum

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