Application of the seed-applied fungicides captan, DL-Plus, Evershield, thiram and Metalaxyl reduced nodulation in the field bean cultivar Lancer (Phaseolus vulgaris L.) in the field. Captan, Evershield, B3 and Thiram also lowered the acetylene reducing activity under the same conditions. Captan, DL-Plus, and B3 resulted in significant yield reductions of field bean inoculated with commercial multi-strain rhizobial inoculant. Since captan or captan-containing fungicides were the most potent inhibitors of symbiotic N2 fixation in field bean, spontaneous mutants of Rhizobium phaseoli strains 3644 and 8215 were selected on the basis of ability to grow in microbial medium containing 100 ppm of Captan 50 W. Controlled environment chamber and field evaluations indicated that all mutants were less sensitive to commercial rates of Captan 50 W (2.0 g per kilogram seed) than either parent strain or commercial multi-strain inoculant. Inoculation of captan-treated seed with these mutants 24 h prior to seeding did not affect nitrogenase activity or yield. Assessment of the effect of captan on the N2-fixing symbiosis and the captan tolerance of R. phaseoli strains by the acetylene reduction assay or 15N isotope dilution at levels of 15N natural abundance gave similar results. The existence of mutants of R. phaseoli tolerant to seed-applied captan but unaltered in symbiotic properties makes the combined use of captan as a seed protectant and seed-applied rhizobial inoculation fully compatible. Key words: Phaseolus vulgaris L., Rhizobium phaseoli, captan, N2 fixation, 15N isotope dilution, acetylene reduction
Effects of drought on yield and yield components of two contrasting growth habits of common beans (Phaseolus vulgaris L.)
