Response of Phaseolus vulgaris L. to Molybdenum Under Acid Conditions

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Abstract
Common beans (Phaseolus vulgaris L.) have been found not to respond to molybdenum (Mo) when grown on deficient soils that were also very acid (< pH 5.2).Greenhouse and growth chamber experiments in soil and solution culture were done to (i) test whether soil acidity prevents Mo response in bean by interferring with Mo uptake or translocation to nodules; (ii) establish relationships between Mo concentrations in nodules and in other plant parts; and (iii) assess cultivar differences in Mo uptake.In the six cultivars studied, plant Mo concentrations were little influenced by pH in the range 4.8 to 5.8. In more detailed experiments with the cultivar Venezuela 350, neither pH (4.8 to 6.3) nor temperature (21 to 31°C) affected Mo concentration or distribution over a wide range of Mo supply in soil and solution culture.Nodule Mo concentration varied less than shoot Mo in response to varied external supply. It correlated with Mo in stems better than in leaves or roots. Root Mo related closely to external Mo. Leaves appeared to act as sinks for Mo disposal at high Mo levels.One bean cultivar accumulated more Mo in stem and seed than five other cultivars. It was also noted that Mo was 10 times higher in seeds produced at Davis, Calif., (on an Entisol) than at Goiana, Brazil (on an Oxisol). These data confirm that genetic and environmental controls on seed Mo can be manipulated to help control Mo deficiency.