Molecular Mapping of Complex Traits - Genetics, Genomics and Breeding of Crop Plants - page 151

characters in breeding for yield, but in case of height for example, it may be
related to lodging. The modern varieties show a wide range of heights and,
for a given yield, a shorter plant is preferred (Miller and Fick 1997).
Bert et al. (2003) reported QTLs for plant height in two successive years
and for plant lodging in an one year experiment using the same F 2 :F 3 mapping
population (XRQ×PSC8) as mentioned above (see 5.2.1.1). They identified
four QTLs in each year (1996 and 1997) for plant height, and three QTLs for
plant lodging ( Table 5-1 ). The total phenotypic variance explained for plant
height was 67.5% and 36.4% for the year 1996 and 1997, respectively, and it
was 20.6% for plant lodging. Three QTLs for plant height were detected in
both the years and only one QTL was year-specific. Plant lodging shared
one of its QTLs with plant height in each year, which further confirmed the
genetic relation between these two traits. A large-effect QTL on LG 8 with R 2
of 39.3% (year 1996) and 17.9% (year 1997) was detected in both the years
for plant height with positive alleles from the parent, XRQ.
Rachid Al-Chaarani et al. (2004) identified five QTLs for each of plant
height (PH) and shoot diameter (SD), and four QTLs for head diameter (HD)
on different linkage groups in the RIL population of the cross PAC2×RHA266
( Table 5-1 ). LOD scores for these QTLs ranged from 4.35 to 13.66 and total
phenotypic variances explained by the QTLs were 71% for PH, 50% for SD
and 25% for HD. For one QTL controlling SD (LG 14) and two QTLs
governing HD (LG 18 and LG 19), positive alleles came from PAC2, but for
the remaining QTLs RHA266 contributed to positive alleles.
More recently, Yue et al. (2008a) developed a new genetic linkage map
and detected QTLs controlling four morphological traits on it. They have
used 120 F 2 individuals from the cross Lg1×HA379 and four traits, including
leaf color (chlorophyll content or greenness degree), plant height, leaf shape,
and head shape were investigated in the F 2 and F 3 generations. Their linkage
map was constructed using 202 polymorphic bands/markers generated
from 54 pairs of TRAP primer combinations and 24 polymorphic SSR primers
selected from each of the 17 linkage groups. The SSR markers were used to
align the new linkage map with the published sunflower reference SSR
map developed by Tang et al. (2002). The linkage map had a total length of
1,597.5 cM with an average distance between the adjacent markers of 7.1
cM. A total of six QTLs were detected on LG 2, LG 3, LG 8 (two loci) and LG
17 (two loci) for plant height. Among them, ph3 , a major QTL on LG 8 alone
explained more than 30% of the phenotypic variation in both the generations.
Six QTLs were identified for leaf shape, which explained 7.8-14.5% of the
phenotypic variation. None of them were detected in both the generations.
Only one QTL was detected for head shape in the F 3 generation that
explained 12.2% of the phenotypic variance. Alleles from Lg1 at nine of the
QTLs for these three traits had positive effects that coincided with the
performance of this parent for these traits. For leaf color-related traits two,