Genomewide Association for Sugar Yield in Sweet Sorghum

Sweet sorghum [Sorghum bicolor (L.) Moench] is characterized by juicy stems with high concentrations of fermentable sugars. The genetic basis of these phenotypes is not understood. A sweet sorghum diversity panel (n = 252), consisting of sweet sorghum cultivars (n = 80) and diverse landraces selected for matching plant height and maturity (n = 172), was genotyped and phenotyped in three environments over 2 yr for sugar-yield-related traits. Sugar yield is the product of juice volume and sugar concentration (Brix). Juice volume but not Brix was significantly higher in sweet sorghum cultivars than in diverse landraces. Most diverse landraces had white midribs, whereas most sweet cultivars had green midribs. The presence of green midribs was strongly correlated with increased sugar yield, juice volume, and moisture but was not significantly correlated with dry biomass. Genomewide association identified a major quantitative trait locus for midrib color, sugar yield, juice volume, and moisture at ~51.8 Mb on chromosome 6, a genomic region previously reported to contain the Dry midrib (D) locus. Midrib color itself was more highly predictive of sugar yield than any significant single nucleotide polymorphism (SNP) in this region, suggesting that either the causal mutation at the D locus is not in high linkage disequilibrium with any SNP in the dataset or that multiple mutations affect midrib color in sorghum. Significant negative correlations between Brix and grain harvest index indicate the existence of tradeoffs between grain and sugar yields. P.S. Burks, C.M. Kaiser, E.M. Hawkins, P.J. Brown, Dep. of Crop Sciences, Univ. of Illinois, Urbana, IL 61801; P.S. Burks, current address: Chromatin Inc., 8509 Venita Ave., Lubbock, Texas 79424-4919; and E.M. Hawkins, current address: Dep. of Agricultural and Biological Engineering, Purdue Univ., West Lafayette, IN 47907. Received 27 Jan. 2015. Accepted 30 Mar. 2015. *Corresponding author ([email protected]). Abbreviations: AG, all genotypes; BLUP; best linear unbiased prediction; D, Dry midrib; DS, Dixon Springs; EF, Energy Farm; GM, green midrib; HAI, harvest–anthesis interval; HI, harvest index; PI, photoperiod insensitive; PS, photoperiod sensitive; QTL, quantitative trait locus; SNP, single nucleotide polymorphism. Published in Crop Sci. 55:2138–2148 (2015). doi: 10.2135/cropsci2015.01.0057 Freely available online through the author-supported open-access option. © 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. Published August 17, 2015