Timing of exposure to ozone affects reproductive sensitivity and compensatory ability in Brassica campestris

It is well established that exposure to ozone (O3) may impair vegetative growth and reproductive development in plants, although the consequences for yield depend on the effectiveness of the compensatory processes induced. This study examined the effects of exposing the terminal inflorescence of Brassica campestris L. to 100 ppb O3 for 6 h d−1 on four consecutive days during early flowering while the vegetative organs received charcoal-filtered air. The ordered predictability of development in B. campestris is ideal for studies of the impact of abiotic stress factors such as O3 on reproductive development and seed production. Effects on reproductive development and seed yield characteristics were determined for floral sites exposed at different developmental stages. Flower and pod numbers on the terminal raceme were unaffected by exposure, but effects on pod length varied depending on the developmental stage of floral sites during exposure. Increased ovule abortion and precocious seed germination in the pods of O3-treated plants reduced mature seed number pod−1. Although the individual weight of mature seeds was slightly greater in O3-treated plants, seed yield pod−1 and seed yield plant−1 were reduced due to the lower seed number pod−1. Seed from O3-treated plants germinated more rapidly than control seed irrespective of the stage of floral development during exposure. The results show that exposure to realistic O3 episodes during the early stages of flowering significantly reduced seed yield without impairing the vigour of the seeds produced. The physiological origins of these effects are discussed.

► Pod number and seed weight plant−1 unaffected by O3 exposure during early flowering.
► Increased seed abortion and precocious germination reduced mature seed number pod−1.
► 23% reduction in seed yield plant−1 similar to field exposures of wheat and mustard.
► Germination rate increased but final percentage germination unaffected.