Influence of photosynthetic restriction due to defoliation at flowering on seed abortion in lucerne (Medicago sativa L.)

The seed yield of lucerne is poor, in contrast to its good vegetativegrowth. This is partly due to a lack of pollination under naturalconditions, pod abortion and the production of only a few seedsper pod. In this study, lucerne plants were grown in controlledconditions and about 30% of the inflorescences were pollinatedmanually. There were about 10 ovules per flower, which remainedconstant throughout the flowering period. There were 4.5 seedsper pod, indicating over 50% seed abortion. One group of plantswas defoliated and the lack of recent assimilates at floweringcaused a small but significant decrease in the number of seedsper pod (4.1). The effect of defoliation varied with seed age;the youngest fertile inflorescences were the most affected andthere was no effect at around 400C d^–1 . This stage markedthe end of the lag phase, which was determined separately incontrol plants. Thus, it is assumed that this date is the abortionlimiting stage (ALS) for this species. The long lag phase forlucerne could be a key influence on seed yield. The longer theALS, the greater the risk of vegetative competition, thus reducingreproductive development. Key words: Lucerne, flowering, pollination, abortion limiting stage (ALS), seed production