Agronomy Journal  Volume 103, Issue 6  2011 1843 Soil Fertility & Crop Nutrition Common Bean Seed Complements Molybdenum Uptake by Plants from Soil R. F. Vieira,* T. J. Paula Jr., A. A. Pires, J. E. S. Carneiro, and G. S. da Rocha Published in Agron. J. 103:1843–1848 (2011) Posted online 4 Oct 2011 doi:10.2134/agronj2011.0115 Copyright © 2011 by the American Society of Agronomy, 5585 Guilford Road, Madison, WI 53711. 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. T he transition element molybdenum (Mo) is essential for biological systems, as it is required by enzymes catalyzing diverse, key reactions in the global C, S, and N metabolism. Te metal is biologically inactive unless it is complexed by a special cofactor. With the exception of bacte- rial nitrogenase (EC 1.18.6.1), where Mo is a constituent of the FeMo-cofactor, Mo is bound to a pterin, thus forming the molybdenum cofactor (Moco), which is the active compound at the catalytic site of all other Mo-enzymes. In eukaryotes, the most prominent Mo-enzymes are nitrate reductase (EC 1.6.6.1), sulfte oxidase (EC 1.8.3.1), xanthine dehydrogenase (EC 1.17.1.4), and aldehyde oxidase (EC 1.2.3.1) (Mendel and Bittner, 2006). Loss of Mo-dependent enzyme activity impacts plant development, in particular those processes involving N metabolism and the synthesis of phytohormones. Molybdenum fertilization through foliar sprays can efectively supplement internal Mo defciencies and rescue the activity of moybdoen- zymes (Kaiser et al., 2005). In Brazil, irrigated common bean (Phaseolus vulgaris L.) under conventional tillage system is usually fertilized with 20 to 30 kg N ha − 1 applied at sowing and 50 to 120 kg N ha − 1 as topdressing before fowering (personal observations). At Zona da Mata, a region in the State of Minas Gerais, Brazil, foliar spraying of Mo has been successfully used on common bean in soil with native strains of Rhizobium instead of N topdressing (Vieira et al., 1992; Amane et al., 1999; Vieira et al., 2005). Common bean yields attained from plants fertilized with N (20–25 kg ha − 1 ), K, and P at sowing, plus foliar spraying of Mo, can be 200% higher in comparison with yields obtained from plants not fertilized with topdressing N nor with Mo (Vieira et al., 1992; Berger et al., 1995, 1996; Amane et al., 1999; Pessoa et al., 2000). In this region, when 24 kg N ha − 1 is applied at sowing, the best time for Mo application to common bean is between 14 and 28 d afer emergence, with the highest yields being obtained with 80 to 90 g Mo ha − 1 (Berger et al., 1996). Despite the advantages of using foliar application of Mo on common bean, many Minas Gerais farmers have no access to this technology, either because they are not familiar with it or because there is no Mo fertilizer available locally, or for both reasons. One strategy to solve this problem would be to provide farmers with Mo-rich seeds. Field researcher studies on com- mon bean (Brodrick et al., 1992; Vieira et al., 2005; Leite et al., 2009) and soybean (Harris et al., 1965; Gurley and Giddens, 1968; Milani et al., 2008; Campo et al., 2009) showed that this strategy works, but the amount of Mo in common bean seed necessary to complement Mo uptake by plants from soil is still unknown. A practical way to produce Mo-rich common bean seeds is spraying plants from which they will be harvested with high rates of Mo, as demonstrated by Vieira et al. (2005) in Zona da Mata. Tese authors showed that foliar applica- tion of Mo at 1440 g ha − 1 increased seed Mo content 13-fold, compared with seeds harvested from unsprayed plants (0.096 vs. 1.272 μg Mo seed − 1 ). In a Mo- and N-poor soil and without topdressing N fertilization, irrigated plants from Mo-rich ABSTRACT Molybdenum (Mo) reserve in large seeds can complement Mo uptake by plants from soil, but the content of Mo in common bean (Phaseolus vulgaris L.) seed for this purpose is unknown. We hypothesized that 3.639 ± 0.751 μg Mo seed –1 would be sufcient to complement Mo uptake by irrigated common bean plants from a Mo-poor soil. Tree feld experiments were performed in a clayey Ultisol naturally infested by native strains of Rhizobium in Zona da Mata, Minas Gerais, Brazil. Treatments were arranged as 4 × 2 factorial combination of Mo contents in seeds [small (0.007 ± 0.007 or 0.248 ± 0.057 μg Mo seed –1 ) or large (3.639 ± 0.751 or 6.961 ± 1.844 μg Mo seed –1 )] and Mo spraying treatments (90 g ha –1 or unsprayed) with six replications. Phosphorus, N (25 kg ha –1 ), and K were applied together in the furrow during planting time. No topdressing N was applied. Final plant popula- tion and seed yield were evaluated in two experiments. Molybdenum contents in the seeds did not afect plant population. On average, unsprayed plants from seeds with small Mo contents yielded 1785 kg ha –1 , while those from seeds with large Mo content yielded 2109 kg ha –1 . Foliar application of Mo increased plant N status, plant growth, and yield in plants originated from seeds with small Mo content, but not in plants grown from seeds with large Mo content. We conclude that 3.639 ± 0.751 μg Mo seed –1 sufciently complement the Mo uptake by common bean plants from soil. R.F. Vieira and T.J. Paula Jr., Empresa de Pesquisa Agropecuária de Minas Gerais, Vila Gianetti, 47, Viçosa, MG 36570-000, Brazil; A.A. Pires, Departamento de Desenvolvimento Educacional, Instituto Federal de Educação Ciência e Tecnologia do Espírito Santo, Colatina, ES 29709-910, Brazil; J.E.S. Carneiro and G.S. da Rocha, Departamento de Fitotecnia, Universidade Federal de Viçosa, Viçosa, MG 36570-000, Brazil. Received 12 Apr. 2011. *Corresponding author (rfvieira@epamig.br). Published November, 2011