Inheritance of Resistance to the New Race of Powdery Mildew in Watermelon

Watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] production in the United States has, in the past few years, incurred significant losses to races 1W and 2WU.S. powdery mildew (Podosphaera xanthii) infection. We report the mode of inheritance, gene action, and heritability of race 2WU.S. resistance in two populations derived from a cross involving the resistant genotype pI 189225 and the susceptible ‘Charleston Gray’ and pI 269677. parents, F1, F2, BC1p1, and BC1p2 plants were inoculated and evaluated for leaf and stem resistance in two replicated greenhouse experiments. Segregation patterns revealed that only leaf resistance rating in Charleston Gray × pI 189225 fit the model for single gene inheritance. Generation mean analysis established only additive gene action for leaf resistance while for stem resistance, additive, dominance, and epistatic effects were important. Narrow-sense heritability estimates were higher for stem (0.81) than for leaf (0.58) resistance. Lack of dominance and epistatic effects combined with high heritability indicated high probability of success in selecting for leaf resistance in early generations. Stem resistance had a higher additive effect, lower dominance, and moderate heritability, but progress toward resistance should be possible. In population pI 269677 × pI 189225, epistatic effects combined with low heritability (0.20) and presence of duplicate epistasis may result in slower progress from selection. A.Y. Tetteh, Dep. of Biochemistry and Biotechnology, Kwame Nkrumah Univ. of Science and Technology, Kumasi, Ghana; T.C. Wehner, Dep. of Horticultural Science, North Carolina State Univ., Raleigh, NC 27695-7609; A.R. Davis, Harris Moran Seed Company, Davis, CA 95618. A.R. Davis previously with USDA-ARS, South Central Agriculture Research Lab., P.O. Box 159, Lane, OK 74555. This work was supported in part by the graduate school assistantship provided by North Carolina State University, by the Ghana Government Scholarship Fund, and by the American Association of University Women. Received 30 July 2012. *Corresponding author ([email protected]). Abbreviations: 2F, 2 France; 2S, 2 Salinas; h2, narrow-sense heritability; R, resistant; S, susceptible. Published in Crop Sci. 53:880–887 (2013). doi: 10.2135/cropsci2012.07.0453 © 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.