Molecular Mapping of Complex Traits - Genetics, Genomics and Breeding of Crop Plants - page 170

In another experiment conducted by Poormohammad Kiani et al. (2008),
QTLs controlling chlorophyll fluorescence parameters, as the functioning
of photosynthesis apparatus were mapped under drought stress ( Table 5-
1 ) . Four chlorophyll fluorescence parameters were studied as: the potential
photochemical efficiency of photosystem II (PSII) electron transport ( P),

the actual efficiency of PSII electron transport ( PSII), non-photochemical

fluorescence quenching (NPQ) and the proportion of closed PSII traps
(1-qP). The number of QTLs varied from 5 to 9, depending on the trait and
water treatments, explaining from 5% to 26% of the phenotypic variance of
the traits; and LOD scores varied from 3.06 to 12.72. Five QTLs were
constitutive and the rests were water treatment-specific (Poormohammad
Kiani et al. 2008). Several QTLs controlling photosynthesis-related traits
were overlapped with the QTLs controlling plant water status traits on LGs
1, 5, 7, 12, 13, 14, 16 and 17 (Poormohammad Kiani et al. 2007a, 2008),
which showed that photosynthesis performance and water status traits are
genetically related and should therefore be considered together when used
as selection criteria for drought tolerance improvement in sunflower.
Identification of QTLs influencing several traits and yield under different
growth conditions, using the same mapping population (PAC2×RHA266)
facilitated (1) the identification of consistent genomic regions from those
expressed under specific growth conditions for each trait of interest specially
for yield and (2) the genetically determination of the trait association by
evaluation of overlapping QTLs ( Fig. 5-1 ) . This would increase the efficiency
of MAS and enhance genetic progress. One of the major goals for sunflower
plant breeders is to develop genotypes with high yield potential and the
ability to be stable across environments. There are three main ways in which
a genotype can achieve yield stability. The first one is the identification of
the non-environment-specific QTLs or QTLs with minor interaction with
environment (as those located on LG 14 for yield), which should be
particularly useful in MAS for yield. The second is the development of widely
adapted genotypes by pyramiding different QTLs each controlling
adaptation to a different environment (as nine environment-specific QTLs
for yield). Finally, the identification of QTLs for yield-related traits which
are co-located with yield itself can provide the information about which
traits and alleles can increase yield in particular growth condition. The
latter helps indirect selection for yield by selecting yield-related traits which
share common QTLs with yield. The whole results obtained by
Poormohammad Kiani et al. (2007a, b, 2008, 2009) showed major genomic
regions controlling plant water status, osmotic adjustment and
photosynthesis performance as well as yield-related traits under drought
stress, which could be used in MAS for drought tolerance in sunflower.