Instability of yield in faba bean is partly caused by drought susceptibility. Four sets with 10‐19 faba bean genotypes each were evaluated in multilocal field trials between 1992 and 1996. Stress occurred as natural drought in one experiment and as artificial terminal drought in three experiments. Artificial drought was induced by rain shelters; the control treatment was irrigated. Tolerance was assessed as the ratio of yield under drought (Yd) to well‐watered yield (Yw). Highly significant variances between genotypes occurred; heritability of tolerance was 0.51 < h2 <0.88. Exotic (North African. Latin American) genotypes were more tolerant than adapted material. Correlations between Yw and Yd were 0.77** < r <0.97**, and variance of Yd was less than one‐third of the variance of Yw. Drought tolerance was negatively correlated with Yd (‐0.41 < r < ‐0.22). Relative reduction of plant height due to drought was a promising trait to improve drought tolerance indirectly in two sets. The prospects of improving Yd are good: heritability was 0.68 < h2 < 0.86. Genetic improvement of drought tolerance also seems feasible. A specific cross was proposed to create improved material.

Twelve parental lines of faba beans and 27 F1 hybrids derived from them were field‐tested under a dry and a well‐watered treatment, at two German locations (Göttingen, Hohenheim) in two years (1995, 1996). Drought was artificially induced using rain shelters from anthesis until maturity. Data were collected on yield under dry (Yd) and well‐watered (Yw) conditions. Drought tolerance was assessed as Yd/Yw. The mid‐parent heterosis was significant for Yd and Yw, but not for Yd/Yw. Relative heterosis for Yd (52.0%) was greater than for Yw (39.3%). Parental heritability was greater for Yw (0.86) than for Yd (0.61). However, it was similar for both traits in F1 hybrids (0.65 and 0.66). Principal component analysis showed that F1 hybrids exhibited the same pattern of adaptation as their parents. The heritability of drought tolerance was 0.48 in F1 hybrids and 0.70 in parents. Attention should be paid to its negative correlation with yield. Several hybrids combined high tolerance, a favourable pattern of adaptation and appropriate performance.

Drought responses of 19 inbred faba bean lines of different origin were studied in the field under rain shelters with and without irrigation. Inbred lines differed significantly in response to drought (P < 0.01): those with a lower drought sensitivity index (SI) (more resistant) originated from the drought‐prone regions characterized by smaller plant size (r = 0.93), and more pods and seeds per plant (r ≥ 0.90) regardless of seed size, while lines with higher SI (more sensitive) were those which mainly exhibited higher yield under favourable conditions accompanied by a greater biomass. In a greenhouse experiment under mild drought (−0.15 MPa soil water potential), comparisons between relatively drought‐sensitive (Adriewaalse) and drought‐resistant (L7) inbred lines showed that Adriewaalse used 38 % more water than L7 and also produced 40 % more biomass. There was a stress‐induced decrease in osmotic potential (ψs) in both lines (by 0.72 and 0.50 MPa for Adriewaalse and L7, respectively) accompanied by decreased turgor in Adriewaalse and increased turgor in L7. The difference in drought‐induced solute accumulation between lines was diminished when solute accumulation due to water loss and growth inhibition was considered, which indicates that solute accumulation was the result of a concentration effect. Similarly, lower SI in the field was not the result of osmotic adjustment, as the relationship between SI and drought‐induced decrease in ψs was negative. The water use efficiency of both inbred lines increased markedly with increasing water deficit, though there was no difference between the lines. It was concluded that differences in drought resistance between these inbred faba bean lines were manifested through plant size‐induced water demand (avoidance) but were not associated with osmotic adjustment (tolerance).

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