INFLUENCE OF LIGHT ON THE GERMINATION OF RAGWORT (Senecio jacobaea L., Asteraceae) SEEDS PREVIOUSLY STORED IN THE SOIL SEED BANK OF A PASTURE

Abstract

An experiment was carried out to determine the effect of light on the germination of ragwort (Senecio jacobaea L.) seeds found in the soil seed bank of a cultivated perennial pasture of temperate species. Previous studies used seeds drawn from seed heads, which may not represent the actual physiological conditions of seeds found in the soil. Thus, soil containing ragwort seeds was extracted in the dark (150 soil samples, 2.6cm in diameter, 0-2cm deep) from a dairy pasture and left in plastic pots within two growth cabinets kept either in the dark (scotophase) or in constant light (photophase) conditions at 20oC. Seed germination, assessed through seedling emergence, was four times larger in the light than in the dark, totalling 55.6% and 13.9%, respectively. Of particular interest was the germination in the dark, which suggests that the active form of phytochrome is stable in ragwort seeds. These results are discussed on the basis of the knowledge of phytochrome activity. It is concluded that ragwort germination is positively affected by the presence of unfiltered light and it is argued that, in field conditions, germination would not take place in the dark.