1714 WWW.CROPS.ORG CROP SCIENCE, VOL. 48, SEPTEMBER– OCTOBER 2008 RESEARCH T he structure and content of the maize ( Zea mays L.) endosperm inluences the expression of traits targeted for genetic improvement such as grain yield (Salamini et al., 1970; Vyn and Tollenaar, 1998), grain quality (Mazur et al., 1999), suit- ability for industrial processing (Paulsen and Hill, 1985; Chan- drashekar and Mazhar, 1999), ruminal digestibility (Corona et al., 2006), and tolerance to mycotoxin accumulation (Bhatnagar et al., 2003). The protein fraction constitutes only 8 to 9% of the endosperm (Lawton and Wilson, 1987), while starch accounts for about 71% of the kernel (Prasanna et al., 2001). In normal maize, 50 to 70% of the endosperm proteins are of the prolamin type (zeins). The zein proteins are particularly deicient in the essential amino acids lysine (Lys) and tryptophan (Trp). The high propor- tion of zeins in the endosperm is the primary reason for the poor protein quality of maize (Vasal, 2000). Phenotypic Characterization of Quality Protein Maize Endosperm Modiication and Amino Acid Contents in a Segregating Recombinant Inbred Population Andres Gutierrez-Rojas, M. Paul Scott, Otto R. Leyva, Monica Menz, and Javier Betrán* ABSTRACT The protein quality of maize (Zea mays L.) can be improved by replacing normal Opaque2 alleles with nonfunctional recessive alleles (o2). Homozygous o2 kernels have increased levels of lysine and tryptophan. Unfortunately, the asso- ciated soft texture of the o2 kernels causes poor yield and susceptibility to diseases and insects. Breeding has resulted in the development of o2 genotypes with improved endosperm hardness; such genotypes are referred to as quality protein maize (QPM). Quality protein maize germplasm is utilized in breeding programs worldwide and has been competitive in yield trials. To under- stand the genetics of endosperm modiication, a population of 146 recombinant inbred lines (S 5 to S 7 ) derived from a cross between the o2 inbred B73o2 and the QPM inbred CML161 was evaluated in two Texas locations from 2004 to 2006. The endosperm traits texture, opacity, and vitreousness were highly affected by inbred line genotype, were highly correlated with each other, and exhibited high broad-sense heritabil- ity. Relative content of the essential amino acids lysine, tryptophan, and methionine were also highly affected by the inbred line genotype, and exhibited high broad-sense heritability. Negative correlation was observed between endosperm texture traits and amino acid contents. Favor- able responses to selection can be expected for both endosperm texture modiication and rela- tive content of the essential amino acids if they are eficiently monitored. A. Gutierrez-Rojas, M. Menz, and J. Betrán, Dep. of Soil and Crop Sci- ences and Institute for Plant Genomics and Biotechnology, Texas A&M Univ., College Station, TX 77843-2123; M.P. Scott, USDA-ARS, Corn Insects and Crop Genetics Research Unit, Ames, IA 50011; O.R. Leyva, Colegio de Postgraduados, Apartado Postal 143. C.P. 94500, Cordoba, Mexico; M. Menz and J. Betrán, current address: Syngenta Seeds S.A.S. 12 Chemin de L’Hobit, 31790 Saint-Saveur, France; A. Gutierrez-Rojas, current address: Syngenta Seeds, Inc., Stanton, MN. Received 3 Aug. 2007. *Corresponding author (javier.betran@syngenta.com). Abbreviations: BLUP, best linear unbiased predictor; CIMMYT, International Maize and Wheat Improvement Center; CS, College Station, TX; GEI, genotype × environment interaction; Lys, lysine; Met, methionine; QPM, quality protein maize; REML, multivariate restricted maximum likelihood; RIL, recombinant inbred line; Trp, tryptophan; WE, Weslaco, TX. Published in Crop Sci. 48:1714–1722 (2008). doi: 10.2135/cropsci2007.08.0429 © Crop Science Society of America 677 S. Segoe Rd., Madison, WI 53711 USA All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher.