Comparative growth of triazine-susceptible and -resistant biotypes of Solanum nigrum at different light levels

Effects of variation in light intensity on growth of plants from five different populations of triazine-susceptible and -resistantSolanum nigrumwere studied in growth chambers at three light levels. Plants were grown without intraspecific competition and with optimal mineral nutrition. After 29 d, the mean biomass of resistant biotypes was about 25% less than that of susceptible biotypes at all light levels. Curve-fitting growth analysis showed that this was the result of a lower initial biomass of the resistant biotype at the start of the experiment, as the relative growth rates (RGR) of the susceptible and resistant biotypes in the early growth phase were equal. Specific leaf area (SLA) was higher for the resistant biotype but this was compensated for by a lower net assimilation rate (NAR). The fraction of dry matter invested in leaves was the same for both biotypes, but the resistant biotype produced more leaf area per unit leaf weight. The equal RGR of the susceptible and resistant biotypes in the early growth phase may have implications for the competitive ability and population dynamics of a population with resistant biotypes