An Overview of Omics for Wheat Grain Quality Improvement - Crop Improvement: New Approaches and Modern Techniques - page 327

Wx-B1 null allele in a wheat cultivar is characterized by low amylose level that is
associated with high noodle making quality. Several allele specific markers have
been developed to facilitate marker assisted introgression of desired waxy allele
(Saito et al. 2009 ; Nakamura et al. 2002 ).
The description of puroindoline genes determining the kernel hardness has been
described earlier. Two genes designated as Pina-D1 and Pinb-D1 encoding puroin-
doline a and puroindoline b proteins, respectively, has a profound effect on wheat
milling quality. Molecular markers for identifying alleles at both loci have been
developed by many workers (Giroux and Morris 1997 ; Gazza et al. 2005; Chen et al.
2012 ). The allele specific marker for Pinb-D1b is diagnostic for superior milling and
processing qualities and is in extensive use in wheat breeding (Chen et al. 2012 ).
Polyphenol oxidase (PPO) activity is responsible for brown discoloration of the
wheat products especially Asian noodles, which is an undesirable character. It is
important to screen cultivars for low PPO activity and several markers have been
developed to serve the purpose. The PPO genes are present on chrosomosomes 2A
and 2D (Sun et al. 2005 ; He et al. 2007 ). Low PPO activity encoded by the Ppo-A1
gene is characterized by the presence of 87 and 481 PCR fragments amplified by
PPO18 and PPO33 markers, respectively. Similarly, two other allele specific mark-
ers PPO16 and PPO29 can distinguish alleles Ppo-D1a and Ppo-D1b which are
associated with lower and higher PPO activity, respectively. Practical usage of these
markers in wheat breeding for identification of genotypes with lower PPO activity
is scientifically valid (Liang et al. 2010 ). Nevertheless, PPO gene located on 2B
chromosome had limited polymorphism in Chinese wheat to develop a functional
marker. Lipoxygenase activity is also major determinant of color and processing
quality of wheat products (Geng et al. 2012 ). A lipoxygenase (LOX) gene has been
localized on chromosome 4BS ( TaLox-B1 ) and two allele specific markers LOX16
and LOX18 amplify 48 and 791 bp PCR fragments in cultivars with higher and
lower LOX activities, respectively (Geng et al. 2012 ). The gene, TaLox-B1 was
sequenced and a SNP was identified in the third exon which was helped in develop-
ment of two markers for identifying alleles TaLox-B1a and TaLox-B1b. The color
of wheat derived products is due to the yellow pigment content. Regional prefer-
ence for color does exist, like bright white color is preferred for Chinese white
salted noodles, whereas yellow alkaline noodles with bright yellow color are widely
preferred in southeastern Asia and Japan (Parker et al. 1998 ). Carotenoids are re-
sponsible for yellow pigment (He et al. 2008 ) while phytoene synthase (PSY) and
zeta-carotene desaturase (ZDS) are important enzymes in the biosynthetic pathway
for carotenoid synthesis in wheat (Zhang et al. 2011 ; Dong et al. 2012 ). PSY genes
are present chromosomes 7AL, 7BL and 7DL and several allele specific markers for
PSY genes have been developed (He et al. 2008 , 2009a; Wang et al. 2009a ). Simi-
larly, markers for ZDS genes on chromosomes 2A and 2D can discriminate alleleic
difference in wheat (Zhang et al. 2011 ; Dong et al. 2012 ).