Breeding Cycles Expedited by FT-mediated Reduction in Generation Time

Methods for rapid inbreeding are desirable for reducing the time required to complete a breeding cycle and to increase genetic gain per year. Constitutive expression of FLOWERING LOCUS T (FT ) derived from Arabidopsis has previously been shown to reduce generation time in tobacco (Nicotiana tabacum L.) and other crop plants. Here, we used tobacco as a model system to investigate the utility of a modified single-seed descent (SSD) breeding method where transgenic expression of 35S:FT was used to reduce generation time during inbreeding. The transgene was maintained in hemizygous condition during inbreeding, and null segregants were isolated in the F4:5 generation to create nontransgenic F5:6 lines that were produced in nearly half the time that would have been required using conventional SSD. opportunities for selection among 35S:FT plants during inbreeding were demonstrated by selecting for quantitative levels of resistance to the soil-borne pathogen Phytophthora nicotianae. populations of selected lines exhibited significantly higher levels of resistance relative to random lines, greater frequencies of highly resistant genotypes, and lower frequencies of highly susceptible genotypes. The system outlined here could lead to more rapid commercialization of improved cultivars in crop species amenable to manipulation of flowering time via transgenic expression of FT-like genes. Strategies to enhance the frequency of favorable alleles in resulting populations can be incorporated into the method. Dep. of Crop Science, North Carolina State Univ., Raleigh, NC 27695. Received 6 Mar. 2013. *Corresponding author ([email protected]). Abbreviations: AUDPC, area under the disease progress curve; EPS, end percent survival; FT, FLOWERING LOCUS T; SSD, singleseed descent. Published in Crop Sci. 53:2384–2391 (2013). doi: 10.2135/cropsci2013.03.0150 © 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.