An Overview of Omics for Wheat Grain Quality Improvement - Crop Improvement: New Approaches and Modern Techniques - page 317

The genetic control of milling and baking qualities is of paramount interest for
industry. QTL mapping population from a soft x hard wheat was used by Breseghe-
llo et al. ( 2005 ) and about 15 QTL conferred control of milling traits, protein con-
tent and baking assay, were detected on group 1 and group 2 chromosomes with
some QTLs on 3A/B, 4B, 5B, and 6B. In another mapping population from RL4452
x 'AC Domain' hard wheat cross, about 99 QTLs were found on 18 chromosomes
for 41 quality traits (McCartney et al. 2006 ). A major QTL on 4D controlling plant
height (Rht-D1b) flanked about 20 QTLs while a crop maturity controlling locus
adhered about 10 QTLs controlling grain quality characteristics like starch contents,
mixograph, farinograph and baking performance.
Apart from the bi-parental QTL studies, recently few association-mapping stud-
ies have been attempted to detect QTL for quality traits in sets of soft wheat germ-
plasm. Several QTLs conferring control of kernel morphology were detected on
chromosomes 2D, 5A, and 5B. Similarly, several quality-encoding QTLs were de-
tected on 15 different chromosomes in an association mapping population by Reif
et al. ( 2011 ). The majority of QTLs for flour characteristics, retention capacity of
solvent and softness equivalent were found to be located on chromosome 1B and
2B in soft wheat bi-parental mapping population. We have presented an overview of
QTL detection efforts for grain quality traits in wheat in Table 10.1 .
Functional Markers for Wheat Grain Quality Traits
During the past two decades, there are extensive studies on the molecular mapping
of the genes underlying the grain quality traits and a brief overview has been pre-
sented in earlier heading. These QTL analyses identified linked molecular markers
such as SSRs, RAPDs, AFLPs, RFLPs and DArTs with the key quality traits. The
low detection power, distance from the genes and allele specificity to the population
and parents are the key characteristics of the neutral markers which effect on their
predictive value in the diverse populations. Therefore, the diagnostics by the linked
markers (MAS) is questioned in breeding programs and their use is restricted with
some exceptional cases. Due to recent developments in molecular biology, there is
overwhelming response for the use of functional markers as a selection tool due to
their apparent advantage over the linked molecular markers. These are developed
from the nucleotide sequence of the functional gene and it has powerful tendency to
distinguish allelic variation on a single locus, thus are considered perfect markers
for MAB (Varshney et al. 2005 ). Nevertheless, with the progress in gene cloning
during the last years, the development of corresponding functional markers is get-
ting fast track. In quantitative terms, 97 markers have been developed as a result of
cloning of 30 genes. These markers had ability to identify 93 disease resistance al-
leles, agronomic and grain quality traits. In wheat, the grain processing and baking
quality is controlled by high- and low-molecular weight glutenins, grain hardiness,
and starch contents, polyphenol oxidase (PPO) activity, lipoxynase (LOX) activ-
ity and yellow pigment content (YPC). In total, 56 functional markers have been