Effect of drought stress on content and composition of seed alkaloids in narrow-leafed lupin, Lupinus angustifolius L.

The effect of drought stress at three growth stages on seed alkaloid content in two sweet (W26 and Polonez) and one bitter variety (Zubr) of spring sown Lupinus angustifolius L. was investigated in a lysimeter experiment on sandy soil in Denmark. Full irrigation resulted in medium alkaloid content. Drought stress during the vegetative phase increased alkaloid content to 0.094, 0.192 and 2.55% of seed dry matter, respectively. At the flowering stage alkaloid content decreased to 0.070, 0.152 and 1.99%, while drought stress during pod-filling increased alkaloid content for the determinate variety W26 to 0.097%, but decreased it to 0.161 and 1.98% for the two indeterminate varieties Polonez and Zubr, respectively. Drought during either flowering or pod-filling resulted in an increased mean seed weight and a reduced number of seed per square metre. Alkaloid content was negatively correlated to seed weight. The alkaloid composition differed for the three genotypes, and was affected by drought treatment. Compared to the bitter variety the sweet varieties were characterized by reduced concentrations of lupanin, 13-hydroxylupanin and angustifolin, whereas spartein, isolupanin and isoangustifolin were little affected.