Improvement in Grain and Fodder Yields of Early-Maturing Promiscuous Soybean Varieties in the Guinea Savanna of Nigeria

Thirteen early-maturing and promiscuously nodulating soybean [Glycine max (L.) Merr.] varieties that belonged to maturity group I developed at the International Institute of Tropical Agriculture (IITA) from 1980 to 1996 were evaluated at two locations in the Guinea savanna of Nigeria in 2001 and 2002 to determine genetic gain in grain yield and associated agronomic traits. The varieties were grown in a randomized complete block design with four replications. Data on grain yield and seven other traits were recorded. The study showed that grain yield potential of the soybean varieties increased from 1117 to 1710 kg ha–1 during two decades of breeding in IITA. The average rate of increase per year per release period (1980–1996) was 24.2 kg ha–1, which is 2.2%. Fodder yield also showed an annual increase of 22.81 kg ha–1 yr–1. Recent varieties had better lodging resistance scores of 1.25 to 1.37 in a 1 to 5 scoring scale (1 being resistant and 5 susceptible), shattering resistance scores of 1.6 to 2.7, and improved natural nodulation scores of 3.1 to 3.9. Old varieties had 50% or more pod shattering while the corresponding fi gure for new varieties was around 25%. Old varieties produced few and small nodules, while new varieties had many big nodules although size and number of nodules alone may not necessarily indicate nodule effi ciency in N2 fi xation. Grain yield showed a positive and highly signifi cant (P ≤ 0.01) correlation coeffi cient (r = 0.75) with fodder yield, implying that high biomass could serve as an indicator of good yielding ability. H. Tefera, International Institute of Tropical Agriculture (IITA), Chitedze Agricultural Research Station, P.O. Box 30258, Lilongwe, Malawi; A.Y. Kamara, IITA-Kano, PMB 5320, Ibadan, Nigeria; B. Asafo-Adjei, Crop Research Institute, P.O. Box 3785, Kumasi, Ghana; K.E. Dashiell, USDA-ARS, North Central Agricultural Research Laboratory, 2923 Medary Ave, Brookings, SD 57006-9401. Received 15 Feb. 2009. *Corresponding author ([email protected]) Abbreviations: IITA, International Institute of Tropical Agriculture. Published in Crop Sci. 49:2037–2042 (2009). doi: 10.2135/cropsci2009.02.0081 © 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.