Quality protein maize biofortification for nutritional security
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Quality Protein Maize- biofortification for nutritional security Dr. Nirupma Singh Scientist Directorate of Maize Research Pusa Campus, New Delhi
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Maize is a versatile crop, used as human food, livestock feed and raw material in industries. Being robust and extremely adaptable in various agro-climatic conditions, it is a favourite crop of farmers throughout the world. For majority of the population, especially rural poor maize constitutes the main bulk of the daily diet. But, the concern lies in the insufficient protein quality and quantity in maize grain leading to malnutrition. Its nutritional value is limited by the low levels of essential amino acids, particularly lysine and tryptophan. In maize endosperm, zein constitutes 50 to 70% of storage protein which is abundant in glutamine, leucine and proline but devoid of the essential amino acids viz., lysine and tryptophan (Prasanna 2001 ; Gibbon and Larkins, 2005; Wu et al., 2010). The discovery of a natural mutation called opaque2 (o2) in 1960’s, caused reduction of zein and increase in non-zein proteins in maize grain doubling the level of lysine (Mertz et al., 1964; Krivanek et al., 2007; Wu et al.,2010). However, the o2 mutation had negative pleiotropic effects that resulted in soft, chalky and dull endosperm, (Babu et al., 2005) leading to decrease in grain den¬sity, increase in susceptibility to attacks by pests and diseases and decrease in productivity. These defects were ameoliarated by the efforts of plant breeders by selecting o2 lines with hard, translucent (vitreous) kernels that retained high lysine content. These modified opaque lines had loci called “modifiers” and such genotypes were called “Quality Protein Maize” (--1,--3,--6, Ortega and Bates, 1983; Villegas et al., 1992; Toro, 2001).
Transcript of Quality protein maize biofortification for nutritional security
Quality Protein Maize- biofortification for nutritional
security
Dr. Nirupma SinghScientistDirectorate of Maize ResearchPusa Campus, New Delhi
Protein composition of maize endosperm
Maize kernel
Pericarp (6%) Endosperm(82%) Embryo (12%)
Albumins(3%) Globulins(3%) Zeins(60%) Glutelins(34%)
Devoid of lysine and tryptophan
opaque2-a gene for improving quality of protein in maize
• A natural spontaneous maize mutant with soft and opaque grain was found in a Connecticut maize field in USA during the 1920s, which was later named as opaque2 (o2)maize by Singleton
• The mutant was passed onto Mertz at Purdue University, USA, who, in turn, reported that the o2 homozygous maize contained substantially higher lysine (+69%) in the grain endosperm compared to normal maize7.
• The reduction of leucine in these mutants is considered desirable since it makes the leucine– isoleucine ratio more balanced and helps in liberating more tryptophan for niacin biosynthesis.
Pleiotropic effects of o2 mutation Soft endosperm Damaged kernels Increased susceptibility to pest and diseases Inferior food processing and generally reduced yields
From opaque-2 to Quality Protein Maize
Genetic systems involved in development of QPM• The simple recessive allele of the opaque-2 gene
• Modifiers / enhancers of the o2o2 containing endosperm
• Genes that modify the opaque-2 induced soft endosperm to hard endosperm
O2O2 x o2o2
O2o2
1/4 O2O2; 1/2 O2o2; 1/4 o2o2
Quality Protein Maize
• o2 gene in homozygous recessive state(o2o2)
• high lysine and tryptophan levels, and
• an endosperm hard enough to ensure acceptable ear characteristics Millennium World Food Prize was jointly awarded in 2000
to Dr. Surinder Vasal and Dr. Evangelina Villegas
QPM cultivars released for commercial cultivation in India
Culture Pedigree Year of release Centre Maturity group
Shakti Composite 1970 AICRP Full seasonRattan Composite 1970 AICRP Full seasonProtina Composite 1970 AICRP Full seasonShakti 1 Composite 1997 DMR Full seasonShaktiman 1 Hybrid 2001 Dholi Full seasonShaktiman 2 Hybrid 2004 Dholi Full seasonHQPM 1 Hybrid 2005 Uchani Full seasonShaktiman 3 Hybrid 2006 Dholi Full seasonShaktiman 4 Hybrid 2006 Dholi Full seasonHQPM 5 Hybrid 2007 Uchani Full seasonHQPM 7 Hybrid 2008 Uchani Full seasonVivek QPM 9 Hybrid 2008 Almora Extra early
Development of QPM genotypes through conventional breedingeding
• Development of QPM donor stocks -modified ear-to-row system
• Conversion of non-QPM into QPM versions -modified backcrossing -cum-recurrent
selection
• Emphasis on QPM germplasm management
• Thrust on QPM hybrid development
Need of Marker Assisted Selection-Why?
The opaque2 gene is recessive and the modifiers are polygenic introgression into elite inbreds is not a straight forward procedure because of three major reasons viz.,
(1) each conventional backcross generation needs to be selfed to identify the opaque2 recessive gene and a minimum of six backcross generations are required to recover satisfactory levels of recurrent parent genome
(2) in addition to maintaining the homozygous opaque2 gene, multiple modifiers must be selected and
(3) rigorous biochemical tests to ensure enhanced lysine and tryptophan levels in the selected materials in each breeding generation require enormous labor, time and material resources.
Development of QPM hybrid using marker assisted selection
Screening kernels of BC2F2 individuals under
transmitted light for kernel modification. a V25, b CML176, c 50% or more opaque kernels, d less than 25% opaque kernels, e completely modified kernels
Vivek QPM 9- an early maturing QPM maize hybrid for the Himalayan states and peninsular India
Vivek QPM 9 - yielded at par with the parent hybrid in the Himalayan states (58 q/ha) as well as in peninsular India (54 q/ha), under the AICRP on Maize during 2005 and 2007.
In addition, it possesses all the good quality of Vivek Hybrid 9 with added advantages of 30% higher lysine and 44% more tryptophan.
Thanks
Hope these small steps bring smile on undernourished small faces
