GENOTYPIC DIFFERENCE IN MOLYBDENUM ACCUMULATION AFFECTS N2-FIXATION IN TROPICAL PHASEOLUS-VULGARIS L

Differences in uptake, seed storage and distribution of molybdenum within plants of two genotypes of Phaseolus vulgaris L. were observed with and without external sources of molybdenum in a glasshouse experiment. Differences in the amount of total plant Mo translocated into seed appeared to be under genotypic control, with a consistently larger proportion of total plant molybdenum being accumulated in seed by Kabanima compared to Baseka. The uptake efficiency (total amounts accumulated with time) did not differ between the two genotypes, but the allocation of Mo to plant parts did. Kabanima had larger nodule dry weight (30 to 40%), and nodule molybdenum content up to three times greater than Baseka with concurrent higher rates of N2-fixation, particularly when plants were grown in the absence of an external source of Mo. Kabanima was also more efficient in translocating Mo in roots, nodules and pod walls to the seeds, particularly when Mo was deficient (43% of total plant Mo allocated to seeds in Kabanima compared to 31% in Baseka). Large amounts of molybdenum were accumulated in the pod walls of Baseka plants (11-mu-g plant-1) but this was not translocated to the seed.