Yield and components of seed yield of indeterminate narrow-leafed lupin (Lupinus angustifolius L.) subjected to transient water deficit

The effect of transient water deficits on seed yield and components of seed yield of narrow-leafed lupin was measured in plants grown in a controlled environment under simulated field conditions. Lupins were grown in large co lumns of soil and transient water deficits were induced at pod set on the m ainstem and first-order apical branches by withholding water for a 5-day pe riod. Soil water content, leaf water potential, turgor pressure, and leaf c onductance declined similarly during each period of transient water deficit . Differences in these parameters were apparent 2 days after water was with held, and over the 5-day period, leaf water potential declined to -1.3 MPa and leaf conductance fell to 44% of the well-watered controls. Total dry ma tter per plant was reduced by the transient water deficit treatments. The r eduction resulted from less accumulation of dry matter on the first, second , and third order apical branches. Leaf area on these branches was also red uced by abscission of the leaves after the water deficit was released. Seed yield per plant after each period of transient water deficit was reduced b y 30-33%, relative to the well-watered controls. The reduction was largely due to a reduction in seed yield on the branches, mainly because they had f ewer pods and seeds per pod. Seed dry weight and harvest index were not sig nificantly affected by each period of transient water deficit. We conclude that differences in final seed yield between the well-watered controls and the transient water deficit treatments resulted from differences in pod num ber and seeds per pod. Low dry matter accumulation and reduction in leaf ar ea on the first- and second-order apical branches under the transient water deficit were associated with the differences. Whereas the differences in p od number generated differences in the size of the reproductive sink, the d ifferences in leaf area generated differences in the source capacity for as similates for pod set and pod-filling.