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 vegetative growth. This is partly due to a lack of pollination under natural cond itions, pod abortion and the production of only a few seeds per pod. I n this study, lucerne plants were grown in controlled conditions and a bout 30% of the inflorescences were pollinated manually, There were ab out 10 ovules per flower, which remained constant throughout the flowe ring period. There were 4.5 seeds per pod, indicating over 50% seed ab ortion. One group of plants was defoliated and the lack of recent assi milates at flowering caused a small but significant decrease in the nu mber of seeds per pod (4.1). The effect of defoliation varied with see d age; the youngest fertile inflorescences were the most affected and there was no effect at around 400 degrees C d(-1). This stage marked t he end of the lag phase, which was determined separately in control pl ants. Thus, it is assumed that this date is the abortion limiting stag e (ALS) for this species. The long lag phase for lucerne could be a ke y influence on seed yield. The longer the ALS, the greater the risk of vegetative competition, thus reducing reproductive development.