Results

1

QTL for Root and Shoot Seedling Traits of Maize
at Low Temperature
Hund A.(1), Fracheboud Y.(1), Soldati A.(1),
Frascaroli E.(2), Salvi S.(2), Stamp P.(1) 1)
Institute of Plant Sciences (IPW), Agronomy and
Plant Breeding, ETH Zurich, Switzerland 2) Dip.
Scienze e Tecnologie Agroambientali (DiSTA),
Università di Bologna, Italy
Introduction Improvement of early vigour is
crucial for the adaptation of maize (Zea mays L.)
to spring conditions of central European and
northern Mediterranean climate, where early
sowing becomes an important strategy to avoid
summer drought. Apart from uniform germination
and seedling establishment, at least two factors
are considered to be of major importance for a
vigorous early seedling development under
long-term mild chilling stress (i) a functional
photosynthetic apparatus, and (ii) a well
differentiated root system. The scope of the
present study is to elucidate the phenotypic and
genetic relationship among morpho-physiological
traits related to chilling stress.
a)
b)
c)
SeLat
SeAx
PrLat
PrAx
SeAx
PrAx
Figure 1. Root system of Lo964 (left) and Lo1016
(right) at germination at 25C (a) and at the
1-leaf stage at 15/13 C day/night (b).
Transgressive segregation of F23 families for
photosynthesis at 15/13 C (c). Extreme families
are displayed.
Material and Methods Two parents 1 were chosen,
which were different for root structure 2 (Fig.
1a,b) and germination in the cold 3. The F24
families of the Lo164 x Lo1016 cross were grown
in a sand-vermiculite substrate at 15/13 C
day/night until the 1-leaf stage (Fig. 2). QTL
analyses were performed with the program
described by Zeng 4. A hierarchical cluster
analysis (Fig. 3) was performed on the
correlation distance matrix using the ward
method in R 1.6.2 5. A linkage map (Fig. 4)
based on the allelic segregation of 161 loci in
171 F23 families was available 2.
Figure 2. The test system sowing (a) emergence
(b), FPSII measurement at 15C in the growth
chamber (c) and harvest of the roots (d).
Measurements Roots digitally measured (Root
Detector, ETH) primary (Pr) and seminal (Se)
root lengths each subdivided into axile (Ax)
and lateral roots (Lat). FPSII quantum yield of
electron transfer at photosystem II (Pam2000,
Walz) SPAD greenness (Chlorophyll Meter,
Minolta) Germ. germination after 7 days ,
GI time to 50 germination
Clustering height
Results On the phenotypic level (Fig. 3) SPAD and
?PSII clustered separately from all other
traits, but with the exception of leaf area,
?PSII was closest correlated (r 0.46) to plant
dry weight (DW). Interestingly, the primary
lateral root length (PrLat) clustered together
with germination traits while seminal root
traits were closer related to plant dry weight
and leaf area . On the genetic level (Fig. 4)
between two and eight QTL (for germination and
SPAD, respectively) were detected. QTL accounted
for 14 to 41 (for SeAx and SPAD, respectively)
of the phenotypic variability. An association
between PrLat and the GI (i.e. positive
association with germination speed) was observed
on chromosome 5 . The plant DW was positively
associated on several key loci Germination speed
on chromosome 5 and ?PSII at two loci on
chromosome 10.
Figure 3. Dendrogram obtained following
hierarchical cluster analysis (HCA) on seed,
root, and shoot traits of the F23 families. See
text for further information.

• Conclusions
• The examined population harbours a large amount
  of independent loci for the improvement of vigour
  at low temperatures.
• FPSII and SPAD were clearly the most promising
  candidates for the improvement of the plant dry
  weight, but were not associated with root traits.
• Interestingly, the ability to build a high
  primary root structure was positively associated
  with the germination speed.

Acknowledgements We would like to thank P.
Landi for the supply of the families, and Anna
and Lilly Stamp for the scanning of the root
samples. This project was supported by EU COST
Action 828.
References 1 Parental lines have been selected
at the Istituto Sperimentale per la
Cerealicoltura, BG. 2 R. Tuberosa, M. C.
Sanguineti, P. Landi, M. M. Giuliani, S. Salvi,
S. Conti, Plant Moleculare Biology 48, 697
(2002). 3 E. Frascaroli, unpublished. 4 Zeng,
Z. B., Genetics 136, 1457 (1994). 5 R 1.6.2
mva package (The R Development Core Team, 2003).
Figure 4. Linkage map of 5 chromosomes of the
Lo964 x Lo1016 cross. Frames combine QTL (LOD gt
3) peaking within 10 cM (Joint analyses of two
experiments). Traits in bold indicate an increase
of trait values due to alleles of Lo1016. See
text for further information.
Websites DiSTA (E. Frascaroli)
http//www.agrsci.unibo.it/frascaro/eli.html
ETH, Agronomy and Plant Breeding (A. Hund)
http//www.ipw.agrl.ethz.ch/hundan