Survey of Plant Density Tolerance in U.S. Maize Germplasm

A broad range of U.S. maize (Zea mays L.) germplasm was evaluated for plant density tolerance (PDT) to identify potential sources of favorable alleles and to obtain a better understanding the underlying genetics involved. Thirty-two hybrids created using a set of inbreds representing parentage of key heterotic subgroups were evaluated at plant densities ranging from 47,000 (19,000 plants per acre [ppA]) to 133,000 plants ha-1 (54,000 ppA). Forty-eight phenotypic traits from five categories (photosynthetic capability, plant architecture, growth responses, source– sink relationship, and general stress tolerance) as well as grain yield were evaluated in three environments that differed for levels of soil moisture availability. The relationship between plant density and grain yield was assessed for each hybrid, with a wide range of responses observed. Five hybrids showed substantial tolerance to plant densities ≥116,000 plants ha-1 based on grain yield performance. Phenotypic trait correlations revealed a subset of traits associated with grain yield across plant densities, with all five categories of traits implicated directly; the subset included leaf angle, upper stem diameter, leaf area required to produce a gram of grain, kernel rows per ear, days to canopy closure, barrenness, kernels per plant, kernel length, leaf number, upper leaf area, staygreen, zipper effect, kernels per row, and anthesis–silking interval. Analysis of gene action for grain yield across plant densities emphasized the prominence of additivity, the increasing importance of nonadditivity as plant density and environmental stress levels increased, and genotype by environment interaction. This work paves the way for further characterization of PDT through quantitative trait locus mapping and candidate gene approaches. Department of Crop Sciences and the Illinois Plant Breeding Center, University of Illinois at Urbana-Champaign,1102 S. Goodwin Ave., Urbana, IL 61801; B.D. Mansfield, present address: Northwestern Illinois Agricultural Research and Education Center, 321 210th Ave., Monmouth, IL 61462. This work was funded in part by USDA National Institute of Food and Agriculture, grant award 2010-85117-20532. B.D. Mansfield was supported in part in his graduate studies through the William B. and Nancy L. Ambrose Fellowship in Crop Sciences. Received 17 Apr. 2013. *Corresponding author (ritamumm@illinois.edu). Abbreviations: ASI, anthesis–silking interval; b1, slope; bu/A, bushels per acre; E, environment; Env1, Environment 1; Env2, Environment 2; Env3, Environment 3; GCA, general combining ability; H2, broadsense heritability; h2, narrow-sense heritability; HA, alternate hypothesis; MINN13, Minnesota13; NSS, non-Stiff Stalk Synthetic; QTL, quantitative trait locus; PDT, pant density tolerance; ppA, plants per acre; PVP, Plant Variety Protection; SCA, specific combining ability; SSS, Stiff Stalk Synthetic. Published in Crop Sci. 54:157–173 (2014). doi: 10.2135/cropsci2013.04.0252 © Crop Science Society of America | 5585 Guilford 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.