Effects of sorgoleone allelochemical on chlorophyll fluorescence and growth inhibition in weeds

Inhibition of chlorophyll fluorescence and growth by sorgoleone in several weed species was investigated under in-vivo conditions. Sorgoleone applied to 21- day-old weed seedlings significantly reduced the Fv/Fm value in all weed species both in leaf disc test and greenhouse study. Sorgoleone applied to 21-day-old weed seedlings significantly reduced the Fv/Fm value in all test weed species both in leaf disc test and greenhouse study. In leaf disc experiment, Galium spurium , Aeschynomene indica and Rumex japonicus were the most sensitive species to sorgoleone and the sorgoleone at 200 µg ml -1 at 6-h after application drastically reduced their chlorophyll fluorescence and Fv/Fm values by 93, 88 and 84%, respectively. In greenhouse study, A. indica proved the most sensitive specie in terms of changes in Fv/Fm values in both dose response and time series experiments. The sorgoleone at 200 µg ml -1 at 120 h after application, reduced the Fv/Fm values by 93, 90 and 82% in A. indica , G. spurium and R. japonicus , respectively. At 200 µg ml -1 sorgoleone, the growth of most broadleaf weed species was reduced drastically (80%) and the maximum inhibition (100%) was observed in R. japonicus , G. spurium and A. indica . Chlorophyll fluorescence measurement is useful to evaluate mode of sorgoleone action in test weed species.