Growth and competitiveness of paraquat-resistant and -susceptible biotypes of Hordeum leporinum

Growth, competitiveness and seed characteristics were compared in paraquat-resistant and -susceptible biotypes of Hordeum leporinum Link collected from neighbouring fields. Dry weight and tiller production were greater in the susceptible biotype as compared with the resistant biotype in the absence of competition, however, the reproductive output was the same. Competitiveness in the field was estimated using a replacement series design that showed only slight differences between the two biotypes, There were no differences in seed weight, number of seeds per head, seed viability or seedling establishment between the two biotypes. When grown in pots in monoculture, the production of tillers was the same throughout the growing season, but inflorescences appeared on the resistant biotype earlier and matured earlier than did those of the susceptible biotype. We conclude that under field conditions the resistant biotype does not show a reduction in fitness as compared with the susceptible biotype.