ECOLOGICAL FITNESS OF SENECIO VULGARIS AND AMARANTHUS RETROFLEXUS BIOTYPES SUSCEPTIBLE OR RESISTANT TO ATRAZINE

(1) Biotypes of Senecio vulgaris L. and Amaranthus retroflexus L., which were either resistant or susceptible to atrazine [2-chloro-4(ethylamino)-6(isopropylamino)-s-triazine], were compared. Dry matter production, resource allocation patterns and competitive ability were measured. (2) Dry matter production of susceptible biotypes was greater than that of resistant biotypes, under both competitive and non-competitive conditions. (3) Resource allocation patterns were similar for both biotypes of each species. (4) Susceptible biotypes of Senecio vulgaris and Amaranthus retroflexus were more competitive than resistant biotypes under all treatments tested.