Tryptophan and methionine levels in quality protein maize breeding germplasm

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Scott, M. P.
Bhatnagar, S.
Betran, J.
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Scott, M. Paul
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The Department of Agronomy seeks to teach the study of the farm-field, its crops, and its science and management. It originally consisted of three sub-departments to do this: Soils, Farm-Crops, and Agricultural Engineering (which became its own department in 1907). Today, the department teaches crop sciences and breeding, soil sciences, meteorology, agroecology, and biotechnology.

The Department of Agronomy was formed in 1902. From 1917 to 1935 it was known as the Department of Farm Crops and Soils.

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  • Department of Farm Crops and Soils (1917–1935)

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Because maize (Lea mays L.) is often used either as food for humans or as feed for monogastric animals, essential amino acid levels are important. Maize kernels containing the opaque-2 (o2) mutation have improved amino acid balance and poor agronomic qualities including opaque kernels that are soft and susceptible to mechanical and biological damage. Quality Protein Maize (QPM) developed through plant breeding has improved amino acid balance conferred by the opaque-2 (o2) mutation, but lacks the agronomic deficiencies normally associated with this mutation. To characterize the amino acid balance in QPM breeding germplasm, we determined the levels of nutritionally limiting amino acids tryptophan and methionine. Tryptophan levels were negatively correlated with endosperm translucence, a measure of kernel hardness suggesting the process of selection for hard-kernels reduces tryptophan levels. On average, germplasm containing the o2/ o2 mutation had lower methionine levels than 02/ 02 germ plasm regardless of kernel hardness, suggesting methionine levels could be reduced by the o2/ o2 mutation. A series of inbred lines was test-crossed to the o2/o2 soft endosperm inbred line Tx804. The predictive value of the characteristics of the inbred line for the characteristics of the hybrids was examined. The amino acid levels of the inbred lines were significantly correlated with those of the hybrids, although the predictive value was low (1{2 = 0.13 and 0.27 for methionine and t1yptophan, respectively). The reduction in tryptophan during conversion to the hard-kernel phenotype and the reduction in methionine in o2 germplasm both reduce the nutritional value of QPM. It may be possible to correct these deficiencies by breeding and selection for levels of tryptophan and methionine.


This article is published as Scott, M. P., Sandeep Bhatnagar, and Javier Betran. "Tryptophan and methionine levels in quality protein maize breeding germplasm." Maydica 49 (2004): 303-311.