Genomics and Applied Biology 2019, Vol.10, No.2, 10-19
15
2006; Magulama and Sales, 2009) and umc 1066 (Gupta et al., 2009; Gupta et al., 2013; Singh and Ram, 2014)
are worthwhile to trace the
opaque 2
(
o
2
) allele in conversion programme. Distinct polymorphism revealed by
both the primers can discriminate the QPM donors from respective non-QPM recurrent parents and also between
homozygous (
O
2
O
2
) and heterozygous (
O
2
o
2
)
opaque 2
back cross progeny. This paves the way for rejection of
back cross progenies (dominant homozygous) resulting short cutting the breeding cycle (eliminates the need to
grow F
2
) and substantial savings of labour and material resources for amino acid estimation (Tanksley et al., 1989;
Frisch et al., 1999; Gupta et al., 2013). This made it possible to breed a QPM hybrid in less than half the time
required in conventional breeding. Besides, foreground selection for
opaque 2
combined with phenotypic
selection for recipient parent at early back cross generations can bring about rapid recovery of recurrent parent
genotype. The introgression lines developed using marker assisted back cross breeding may serve as important
breeding material for development of QPM hybrids.
The pioneering work initiated by the Breeding Program of the National Maize and Sorghum Research Center
(CNPMS-EMBRAPA) led to release of two Brazian QPM varieties e.g., BR 451 and BR 473 in 1988 and 1994
respectively for commercial cultivation. The former is used as a substitute to wheat due to its white color; while
the later resembling normal maize fetches huge consumers’ acceptance. Mixture of wheat flour with that of BR
451 in a suitable proportion was reported ideal for industrial production of bread, cookies, and pasta (Peixoto et al.,
1989). Besides, a double cross QPM hybrid was released in Brazil during 1997 and a QPM hybrid Zhongdan 9407
and Shakti-1 were released in China and India respectively. In India, Vivek QPM-9: a hybrid product of two QPM
introgression lines was released in 2008 (Gupta et al., 2009; Gupta et al., 2013). For this, the parental normal
maize inbreds, CM 212 and CM 145 were converted to QPM status through marker assisted backcross breeding
using CML 180 and CML 170 respectively as QPM donors. The said QPM hybrid, recorded grain yield at par, but
resulted 41% increase in tryptophan and 30% increase in lysine content over the normal hybrid. Soon after, many
countries participated in QPM network. The Republic of South Africa had earlier released hybrids HL-1, HL-2,
and has recently released HL8 which has hard endosperm, good yield potential, and tolerance to diseases.
Similarly, maize genotypes for reduced anti-nutritional factors has been developed using marker-assisted
backcross breeding (MABB) (Naidoo et al., 2012). Later, Muthusamy et al. (2014) successfully attempted
Marker-Assisted Introgression of ß-carotene hydroxylase Allele to develope ß-Carotene Rich Maize Hybrids.
Chander et al. (2008) identified a major loci (y1) for carotinoid content using gene targeted molecular marker
(Y1ssr).
10 Limitations
QPM seems to be a panacea for salvation of malnutrition, but yet it is not free from limitations. QPM at its present
form (after endosperm modification) look similarly yellow grain, and retain all morphological and agronomic
features of normal maize making them indistinguishable. This poses potential threat for phenotypic selection and
varietal maintenance in seed plot. Besides, cross-pollination would reduce both yield and nutritional value of the
QPM variety. QPM, being nutritionally balanced, is liable to be more susceptible to store grain pests and diseases
than normal maize. Since QPM varieties are few, they may not be suited to variety of ecological variations. In this
regard, QPM hybrid may serve as a good candidate. Hybrids generally yield better and maintain their genetic
qualities more consistently than composites. For this, separate QPM lines must be generated by marker assisted
back crossing and then reassembled to form hybrid combinations, which is a cumbersome job than development
of normal maize hybrid.
11 Conclusion
Maize ranked third important cereal crop in the food chain. Quality protein maize has a far-reaching impact for
nutritional security with the discovery of
opaque 2
mutation. Such a natural recessive mutation led to selective
down-regulation of specific zein genes resulting alteration in amino acid composition and opaque phenotype of
endosperm. Modified Marker assisted back cross breeding made it possible to develop QPM versions of normal
maize inbreds with desirable endosperm characteristics and seed yield. Development of QPM hybrids by
combining elite QPM introgression lines can meet food and nutritional security in developing countries including India.
