Reduced growth, competitiveness, and photosynthetic efficiency of triazine-resistant Senecio vulgaris from California.
Triazine-susceptible and resistant biotypes of S. vulgaris, collected from the same field in Salinas, California, were compared to determine whether reduced productivity and competitiveness accompany the trait of triazine resistance in biotypes with identical environmental histories. Characteristics of growth, resource allocation, development and photosynthetic efficiency were measured on plants in non-competitive stands. Competitiveness was evaluated using the replacement series design. In both non-competitiveness and competitive stands, susceptible plants produced a greater total DW and reproductive output than did resistant plants. No differences were detected in number of leaves, root:shoot ratio, total leaf area, RGR or NAR. Under non-competitive and competitive conditions, resistant plants produced relatively more leaf and less reproductive tissue than susceptible ones and had a greater leaf area ratio. The initial rise in leaf chlorophyll fluorescence was higher in resistant than susceptible plants, suggesting that PSII is less efficient.