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

Abstract

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 columns of soil and transient water deficits were induced at pod set on the mainstem and first-order apical branches by withholding water for a 5-day period. Soil water content, leaf water potential, turgor pressure, and leaf conductance declined similarly during each period of transient water deficit. Differences in these parameters were apparent 2 days after water was withheld, 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 matter per plant was reduced by the transient water deficit treatments. The reduction resulted from less accumulation of dry matter on the first, second, and third order apical branches. Leaf area on these branches was also reduced by abscission of the leaves after the water deficit was released. Seed yield per plant after each period of transient water deficit was reduced by 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 fewer pods and seeds per pod. Seed dry weight and harvest index were not significantly 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 number and seeds per pod. Low dry matter accumulation and reduction in leaf area on the first- and second-order apical branches under the transient water deficit were associated with the differences. Whereas the differences in pod number generated differences in the size of the reproductive sink, the differences in leaf area generated differences in the source capacity for assimilates for pod set and pod-filling.