Agriculture Reference
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2007). Similarly, genetic factors infl uencing leaf
area duration (e.g., stay-green and leaf disease
resistance) may also aid in extending the period
for assimilation and continued root growth and
nitrogen uptake (Gregory et al., 2005).
Other genetic factors affecting aboveground
growth have been reported to strongly infl uence
shoot-root partitioning and root growth. For
example, selection for greater early growth
(seedling vigor) is associated with greater root
growth early in the season (Palta et al., 2007).
Figure 11.9 shows relatively reduced root-length
density and root number for low-vigor selection
F25 compared to its high-vigor, full-sib F20 and
parent 'Vigour 18'. This difference was maintained
with increasing soil depth. Similarly, Fig. 11.10
illustrates increased seminal root number and
greater root length via selection for greater early
vigor in a recurrent selection program targeting
greater shoot vigor. Genetically vigorous wheats
1,300
RS C4 selections
Controls
1,200
1,100
1,000
900
Vigor 18
Syn 29589
800
Janz
700
3.8 4.0 4.2 4.4 4.6 4.8 5.0 5.2 5.4 5.6 5.8
Seminal root number (n)
Fig. 11.10 Total root length and seminal root number mea-
sured at the one-leaf stage on six high-shoot-vigor cycle 4
recurrent selection lines ( ) and controls ( ): high shoot
vigor, 'Vigour 18', low shoot vigor, 'Janz', and high root vigor,
synthetic selection 29589.
Root length density (cm cm -3 )
Number of roots (roots plant -1 )
0.00
0.05
0.10
0.15
0.20
0.25
0
150
300
450
600
750
900
0
20
0-20
40
20-40
40-60
60
60-80
80
F20
F25
Janz
Vigor 18
80-100
100
F20
F25
Janz
Vigor 18
Fig. 11.9 Root-length density and numbers of roots at commencement of stem elongation (growth stage Z31) for high-vigor
wheat parent 'Vigour 18' and progeny (high- and low-vigor selections F20 and F25, respectively), and low-vigor cultivar Janz.
Leaf areas at Z31 were 267, 224, 179, and 170 cm 2 per plant for Vigour 18, F20, F25, and Janz, respectively. The least
signifi cant difference is given for testing genotypic differences at each root depth (Palta et al., 2007).
 
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