Growth rate and competitive ability of susceptible and multiple-resistant late watergrass (Echinochloa phyllopogon) biotypes to rice

Abstract Late watergrass [ Echinochloa phyllopogon (Stapf) Koss.] has evolved multiple-resistance (MR) to herbicides in many areas worldwide and scientists wonder if this resistance imposed fitness cost or advantage on the resistant biotypes. As of weed also been recorded Greece, one susceptible (S), with ALS (penoxsulam, bispyribac, imazamox nicosulfuron + rimsulfuron) ACCase-cyhalofop (MRAC) two synthetic auxin-quinclorac (MRAQ1, MRAQ2) late biotypes collected from rice fields (northern Greece) were studied for their growth rate competitive ability (regarding stem number fresh weight) absence presence rice. Also, competition indices relative yield (RY), ratio (CR) aggressiveness (AI) evaluated. The S three MR grown (one plant/pot) showed different shoot but similar weight rates. In contrast, under intra-specific (one, two, four six plants/pot), biotype produced that MRAQ1 lower than MRAC MRAQ2 However, inter-specific plants watergrass/pot more other at all densities, reduction not followed opposite trend (based both intra- completion data) found most cases biotype. These findings strongly suggest there is no clear association between herbicide resistance.