Abstract:
In common bean (Phaseolus vulgaris L), limited information is available if potential
of nodulation and symbiotic nitrogen fixation is associated with the expression of
traits that confer better adaptation to drought conditions. Adaptive traits were therefore
measured in N‐fixing bean lines BAT 477, DOR 364, and PAN 185 and in nonnodulating
lines BAT 477‐NN and DOR 364‐NN. Drought affected growth in all bean
lines and decreased chlorophyll content but more in DOR 364‐NN and BAT 477‐NN,
and also reduced nodule size with highest reduction in DOR 364 (21.6%). Loss of nitrogen
fixation under drought conditions was further associated with lower water use
efficiency, measured as carbon isotope ratio of 13C/12C, and lower %N in shoots when
compared to capability to fix nitrogen. Loss of symbiotic nitrogen fixation in mutant
bean lines DOR 364‐NN and BAT 477‐NN negatively affected root architectural traits
under drought. Under drought conditions, line BAT 477‐NN had about 50% lower
values for all root architectural traits, such as root angle, strongly emphasizing an association
of capability to fix nitrogen with root development. An association between
capability to fix nitrogen and maintaining a better harvest index and seed yield was
also found in the study. Under well‐watered conditions, all N‐fixing lines had a higher
harvest index and seed yield (2.6–2.8 t of seed yield/ha) in comparison with the two
nonfixing bean lines (1.4 t/ha). Although the harvest index and seed yield declined due
to drought in all tested lines, this decline was only significant for line DOR 364‐NN (harvest index) and lines DOR 364‐NN and BAT 477‐NN (seed yield). Our study has
overall demonstrated an important association between the capability of maintaining
atmospheric N‐fixation and expression of traits conferring better adaptation to drought
conditions with any change in nitrogen fixation affecting these traits.
