ALLELOCHEMICAL REGULATION OF REPRODUCTION AND SEED-GERMINATION OF 2 BRAZILIAN BACCHARIS SPECIES BY PHYTOTOXIC TRICHOTHECENES

The potent phytotoxic trichothecene roridins and baccharinoids occur naturally in the Brazilian plants, Baccharis coridifolia and B. megapotomica. Biosynthesis of roridins in B. coridifolia appears to be linked to pollination, and the phytotoxins then accumulate in the seed. The roles of the phytotoxins in pollination, seed maturation, and germination of the Baccharis species were investigated. The high production of roridins occurred only in seeds resulting from intraspecific pollination, and the concentration of the toxins in the seeds generally increased with seed maturity. Removal of seed coats from trichothecene-producing Brazilian Baccharis species (B. coridifolia and B. megapotamica) and non-trichothecene-producing American Baccharis species (B. halimifolia and B. glutinosa) resulted in improved seed germination of B. halimifolia and B. glutinosa but complete inhibition of seed germination of B. coridifolia and B. megapotamica. Addition of seed coat extracts of the Brazilian Baccharis species of dilute solutions (10(-6)-mu-g/ml) of roridins or baccharinoids to the decoated seeds of B. coridifolia and B. megapotamica resulted in germination, while seeds of B. halimifolia and B. glutinosa were killed by the phytotoxins. Roridins interacted with gibberellic acid, a germination promoter, but not with abscisic acid, a germination inhibitor. The results from this study suggest that macrocyclic trichothecenes have a regulatory role(s) on reproduction and germination of Brazilian Baccharis species in their natural habitat.