MOLYBDENUM RESERVES OF SEED, AND GROWTH AND N(2) FIXATION BY PHASEOLUS-VULGARIS L

Plants grown from seed with high (1.5-7.3-mu-g Mo seed-1) and low (0.0 7-1.4-mu-g Mo seed-1) Mo contents were grown in the presence and absen ce of Mo in growth media (perlite) or in a flowing-solution culture, i n a controlled environment. Neither the high (1.5-mu-g Mo seed-1) nor the low (0.1-mu-g Mo seed-1) Mo content in seed from a small-seeded ge notype (BAT 1297) was able to prevent Mo deficiency (reduced shoot, ro ot and nodule dry weight, N2 fixation and seed production) in growth m edia without an external supply of Mo, whereas both the high (7.3-mu-g Mo seed-1) and the low (0.07-mu-g Mo seed-1) contents in seed were ab le to prevent Mo deficiency in a large-seeded genotype (Canadian Wonde r). Responses to Mo treatment by the two genotypes were inconsistent b etween the growth media and solution culture experiments. Seed with a large Mo content (3.5-mu-g Mo seed-1) from the Canadian Wonder genotyp e was unable to prevent Mo deficiency (reduced shoot and nodule dry we ight and N2-fixation) in a solution culture without an external source of Mo, whereas both the large (1.7-mu-g Mo seed-1) and the small (0.1 3-mu-g Mo seed-1) contents in seed prevented a deficiency in BAT 1297. Growing plants from seed with a small Mo content, without additional Mo, reduced the seed Mo content by 83-85% and seed production by up to 38% in both genotypes. Changes in seed size and increases in shoot, r oot and nodule dry weight occurred, but varied with the genotype and g rowth conditions. These effects were also observed in some cases where plants were grown with additional Mo, demonstrating that the amount o f Mo in the seed sown can influence plant nutrition irrespective of th e external Mo supply. Nodule dry weight, total N content of shoots and seed production were improved by using seed with a small Mo content ( 1.64-3.57-mu-g Mo seed-1) on acid tropical soils in Northern Zambia. P lants of both the large- and small-seeded genotypes grown from seed wi th a small Mo content (< 1.41-mu-g Mo seed-1) had a smaller nodule wei ght, accumulated less N and produced less seed. The viability of seed with a small Mo content was lower (germination up to 50% less) than th at of seed with a large Mo content.