GROWTH AND COMPETITIVENESS OF PARAQUAT-RESISTANT AND PARAQUAT-SUSCEPTIBLE BIOTYPES OF HORDEUM-LEPORINUM

Growth, competitiveness and seed characteristics were compared in para quat-resistant and -susceptible biotypes of Hordeum leporinum Link col lected from neighbouring fields. Dry weight and tiller production were greater in the susceptible biotype as compared with the resistant bio type in the absence of competition, however, the reproductive output w as the same. Competitiveness in the field was estimated using a replac ement series design that showed only slight differences between the tw o biotypes, There were no differences in seed weight, number of seeds per head, seed viability or seedling establishment between the two bio types. When grown in pots in monoculture, the production of tillers wa s 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 wit h the susceptible biotype.